diff --git a/applypatch/applypatch.cpp b/applypatch/applypatch.cpp
index e52ef99..cf15560 100644
--- a/applypatch/applypatch.cpp
+++ b/applypatch/applypatch.cpp
@@ -408,11 +408,10 @@
 // Search an array of sha1 strings for one matching the given sha1.
 // Return the index of the match on success, or -1 if no match is
 // found.
-int FindMatchingPatch(uint8_t* sha1, char* const * const patch_sha1_str,
-                      int num_patches) {
-    uint8_t patch_sha1[SHA_DIGEST_LENGTH];
-    for (int i = 0; i < num_patches; ++i) {
-        if (ParseSha1(patch_sha1_str[i], patch_sha1) == 0 &&
+int FindMatchingPatch(uint8_t* sha1, const std::vector<std::string>& patch_sha1_str) {
+    for (size_t i = 0; i < patch_sha1_str.size(); ++i) {
+        uint8_t patch_sha1[SHA_DIGEST_LENGTH];
+        if (ParseSha1(patch_sha1_str[i].c_str(), patch_sha1) == 0 &&
             memcmp(patch_sha1, sha1, SHA_DIGEST_LENGTH) == 0) {
             return i;
         }
@@ -423,8 +422,7 @@
 // Returns 0 if the contents of the file (argv[2]) or the cached file
 // match any of the sha1's on the command line (argv[3:]).  Returns
 // nonzero otherwise.
-int applypatch_check(const char* filename, int num_patches,
-                     char** const patch_sha1_str) {
+int applypatch_check(const char* filename, const std::vector<std::string>& patch_sha1_str) {
     FileContents file;
 
     // It's okay to specify no sha1s; the check will pass if the
@@ -432,8 +430,7 @@
     // partitions, where the filename encodes the sha1s; no need to
     // check them twice.)
     if (LoadFileContents(filename, &file) != 0 ||
-        (num_patches > 0 &&
-         FindMatchingPatch(file.sha1, patch_sha1_str, num_patches) < 0)) {
+        FindMatchingPatch(file.sha1, patch_sha1_str) < 0) {
         printf("file \"%s\" doesn't have any of expected "
                "sha1 sums; checking cache\n", filename);
 
@@ -448,7 +445,7 @@
             return 1;
         }
 
-        if (FindMatchingPatch(file.sha1, patch_sha1_str, num_patches) < 0) {
+        if (FindMatchingPatch(file.sha1, patch_sha1_str) < 0) {
             printf("cache bits don't match any sha1 for \"%s\"\n", filename);
             return 1;
         }
@@ -532,8 +529,7 @@
                const char* target_filename,
                const char* target_sha1_str,
                size_t target_size,
-               int num_patches,
-               char** const patch_sha1_str,
+               const std::vector<std::string>& patch_sha1_str,
                Value** patch_data,
                Value* bonus_data) {
     printf("patch %s: ", source_filename);
@@ -573,7 +569,7 @@
     }
 
     if (!source_file.data.empty()) {
-        int to_use = FindMatchingPatch(source_file.sha1, patch_sha1_str, num_patches);
+        int to_use = FindMatchingPatch(source_file.sha1, patch_sha1_str);
         if (to_use >= 0) {
             source_patch_value = patch_data[to_use];
         }
@@ -589,7 +585,7 @@
             return 1;
         }
 
-        int to_use = FindMatchingPatch(copy_file.sha1, patch_sha1_str, num_patches);
+        int to_use = FindMatchingPatch(copy_file.sha1, patch_sha1_str);
         if (to_use >= 0) {
             copy_patch_value = patch_data[to_use];
         }
@@ -701,8 +697,8 @@
         printf("patch is not a blob\n");
         return 1;
     }
-    char* header = patch->data;
-    ssize_t header_bytes_read = patch->size;
+    const char* header = &patch->data[0];
+    size_t header_bytes_read = patch->data.size();
     bool use_bsdiff = false;
     if (header_bytes_read >= 8 && memcmp(header, "BSDIFF40", 8) == 0) {
         use_bsdiff = true;
diff --git a/applypatch/bspatch.cpp b/applypatch/bspatch.cpp
index a4945da..eb45e9c 100644
--- a/applypatch/bspatch.cpp
+++ b/applypatch/bspatch.cpp
@@ -64,7 +64,7 @@
         );
 }
 
-static off_t offtin(u_char *buf)
+static off_t offtin(const u_char *buf)
 {
     off_t y;
 
@@ -130,7 +130,7 @@
     // from oldfile to x bytes from the diff block; copy y bytes from the
     // extra block; seek forwards in oldfile by z bytes".
 
-    unsigned char* header = (unsigned char*) patch->data + patch_offset;
+    const unsigned char* header = reinterpret_cast<const unsigned char*>(&patch->data[patch_offset]);
     if (memcmp(header, "BSDIFF40", 8) != 0) {
         printf("corrupt bsdiff patch file header (magic number)\n");
         return 1;
@@ -149,7 +149,7 @@
     int bzerr;
 
     bz_stream cstream;
-    cstream.next_in = patch->data + patch_offset + 32;
+    cstream.next_in = const_cast<char*>(&patch->data[patch_offset + 32]);
     cstream.avail_in = ctrl_len;
     cstream.bzalloc = NULL;
     cstream.bzfree = NULL;
@@ -159,7 +159,7 @@
     }
 
     bz_stream dstream;
-    dstream.next_in = patch->data + patch_offset + 32 + ctrl_len;
+    dstream.next_in = const_cast<char*>(&patch->data[patch_offset + 32 + ctrl_len]);
     dstream.avail_in = data_len;
     dstream.bzalloc = NULL;
     dstream.bzfree = NULL;
@@ -169,8 +169,8 @@
     }
 
     bz_stream estream;
-    estream.next_in = patch->data + patch_offset + 32 + ctrl_len + data_len;
-    estream.avail_in = patch->size - (patch_offset + 32 + ctrl_len + data_len);
+    estream.next_in = const_cast<char*>(&patch->data[patch_offset + 32 + ctrl_len + data_len]);
+    estream.avail_in = patch->data.size() - (patch_offset + 32 + ctrl_len + data_len);
     estream.bzalloc = NULL;
     estream.bzfree = NULL;
     estream.opaque = NULL;
diff --git a/applypatch/imgpatch.cpp b/applypatch/imgpatch.cpp
index 0c06d6b..1c4409e 100644
--- a/applypatch/imgpatch.cpp
+++ b/applypatch/imgpatch.cpp
@@ -24,6 +24,7 @@
 #include <unistd.h>
 #include <string.h>
 
+#include <string>
 #include <vector>
 
 #include "zlib.h"
@@ -35,10 +36,10 @@
 int ApplyImagePatch(const unsigned char* old_data, ssize_t old_size,
                     const unsigned char* patch_data, ssize_t patch_size,
                     SinkFn sink, void* token) {
-  Value patch = {VAL_BLOB, patch_size,
-      reinterpret_cast<char*>(const_cast<unsigned char*>(patch_data))};
-  return ApplyImagePatch(
-      old_data, old_size, &patch, sink, token, nullptr, nullptr);
+    Value patch(VAL_BLOB, std::string(
+            reinterpret_cast<const char*>(patch_data), patch_size));
+
+    return ApplyImagePatch(old_data, old_size, &patch, sink, token, nullptr, nullptr);
 }
 
 /*
@@ -51,9 +52,7 @@
                     const Value* patch,
                     SinkFn sink, void* token, SHA_CTX* ctx,
                     const Value* bonus_data) {
-    ssize_t pos = 12;
-    char* header = patch->data;
-    if (patch->size < 12) {
+    if (patch->data.size() < 12) {
         printf("patch too short to contain header\n");
         return -1;
     }
@@ -61,6 +60,8 @@
     // IMGDIFF2 uses CHUNK_NORMAL, CHUNK_DEFLATE, and CHUNK_RAW.
     // (IMGDIFF1, which is no longer supported, used CHUNK_NORMAL and
     // CHUNK_GZIP.)
+    size_t pos = 12;
+    const char* header = &patch->data[0];
     if (memcmp(header, "IMGDIFF2", 8) != 0) {
         printf("corrupt patch file header (magic number)\n");
         return -1;
@@ -68,20 +69,19 @@
 
     int num_chunks = Read4(header+8);
 
-    int i;
-    for (i = 0; i < num_chunks; ++i) {
+    for (int i = 0; i < num_chunks; ++i) {
         // each chunk's header record starts with 4 bytes.
-        if (pos + 4 > patch->size) {
+        if (pos + 4 > patch->data.size()) {
             printf("failed to read chunk %d record\n", i);
             return -1;
         }
-        int type = Read4(patch->data + pos);
+        int type = Read4(&patch->data[pos]);
         pos += 4;
 
         if (type == CHUNK_NORMAL) {
-            char* normal_header = patch->data + pos;
+            const char* normal_header = &patch->data[pos];
             pos += 24;
-            if (pos > patch->size) {
+            if (pos > patch->data.size()) {
                 printf("failed to read chunk %d normal header data\n", i);
                 return -1;
             }
@@ -97,21 +97,21 @@
             ApplyBSDiffPatch(old_data + src_start, src_len,
                              patch, patch_offset, sink, token, ctx);
         } else if (type == CHUNK_RAW) {
-            char* raw_header = patch->data + pos;
+            const char* raw_header = &patch->data[pos];
             pos += 4;
-            if (pos > patch->size) {
+            if (pos > patch->data.size()) {
                 printf("failed to read chunk %d raw header data\n", i);
                 return -1;
             }
 
             ssize_t data_len = Read4(raw_header);
 
-            if (pos + data_len > patch->size) {
+            if (pos + data_len > patch->data.size()) {
                 printf("failed to read chunk %d raw data\n", i);
                 return -1;
             }
-            if (ctx) SHA1_Update(ctx, patch->data + pos, data_len);
-            if (sink((unsigned char*)patch->data + pos,
+            if (ctx) SHA1_Update(ctx, &patch->data[pos], data_len);
+            if (sink(reinterpret_cast<const unsigned char*>(&patch->data[pos]),
                      data_len, token) != data_len) {
                 printf("failed to write chunk %d raw data\n", i);
                 return -1;
@@ -119,9 +119,9 @@
             pos += data_len;
         } else if (type == CHUNK_DEFLATE) {
             // deflate chunks have an additional 60 bytes in their chunk header.
-            char* deflate_header = patch->data + pos;
+            const char* deflate_header = &patch->data[pos];
             pos += 60;
-            if (pos > patch->size) {
+            if (pos > patch->data.size()) {
                 printf("failed to read chunk %d deflate header data\n", i);
                 return -1;
             }
@@ -149,7 +149,7 @@
             // the patch was constructed with bonus data.  The
             // deflation will come up 'bonus_size' bytes short; these
             // must be appended from the bonus_data value.
-            size_t bonus_size = (i == 1 && bonus_data != NULL) ? bonus_data->size : 0;
+            size_t bonus_size = (i == 1 && bonus_data != NULL) ? bonus_data->data.size() : 0;
 
             std::vector<unsigned char> expanded_source(expanded_len);
 
@@ -189,7 +189,7 @@
 
                 if (bonus_size) {
                     memcpy(expanded_source.data() + (expanded_len - bonus_size),
-                           bonus_data->data, bonus_size);
+                           &bonus_data->data[0], bonus_size);
                 }
             }
 
diff --git a/applypatch/include/applypatch/applypatch.h b/applypatch/include/applypatch/applypatch.h
index 9ee39d2..80d6816 100644
--- a/applypatch/include/applypatch/applypatch.h
+++ b/applypatch/include/applypatch/applypatch.h
@@ -20,6 +20,7 @@
 #include <stdint.h>
 #include <sys/stat.h>
 
+#include <string>
 #include <vector>
 
 #include "openssl/sha.h"
@@ -52,19 +53,16 @@
                const char* target_filename,
                const char* target_sha1_str,
                size_t target_size,
-               int num_patches,
-               char** const patch_sha1_str,
+               const std::vector<std::string>& patch_sha1_str,
                Value** patch_data,
                Value* bonus_data);
 int applypatch_check(const char* filename,
-                     int num_patches,
-                     char** const patch_sha1_str);
+                     const std::vector<std::string>& patch_sha1_str);
 
 int LoadFileContents(const char* filename, FileContents* file);
 int SaveFileContents(const char* filename, const FileContents* file);
 void FreeFileContents(FileContents* file);
-int FindMatchingPatch(uint8_t* sha1, char* const * const patch_sha1_str,
-                      int num_patches);
+int FindMatchingPatch(uint8_t* sha1, const std::vector<std::string>& patch_sha1_str);
 
 // bsdiff.cpp
 void ShowBSDiffLicense();
diff --git a/applypatch/main.cpp b/applypatch/main.cpp
index 1968ae4..a3a45d0 100644
--- a/applypatch/main.cpp
+++ b/applypatch/main.cpp
@@ -20,6 +20,7 @@
 #include <unistd.h>
 
 #include <memory>
+#include <string>
 #include <vector>
 
 #include "applypatch/applypatch.h"
@@ -30,7 +31,12 @@
     if (argc < 3) {
         return 2;
     }
-    return applypatch_check(argv[2], argc-3, argv+3);
+    std::vector<std::string> sha1;
+    for (int i = 3; i < argc; i++) {
+        sha1.push_back(argv[i]);
+    }
+
+    return applypatch_check(argv[2], sha1);
 }
 
 static int SpaceMode(int argc, char** argv) {
@@ -49,11 +55,13 @@
 // Parse arguments (which should be of the form "<sha1>:<filename>"
 // into the new parallel arrays *sha1s and *files.Returns true on
 // success.
-static bool ParsePatchArgs(int argc, char** argv, std::vector<char*>* sha1s,
+static bool ParsePatchArgs(int argc, char** argv, std::vector<std::string>* sha1s,
                            std::vector<FileContents>* files) {
-    uint8_t digest[SHA_DIGEST_LENGTH];
-
+    if (sha1s == nullptr) {
+        return false;
+    }
     for (int i = 0; i < argc; ++i) {
+        uint8_t digest[SHA_DIGEST_LENGTH];
         char* colon = strchr(argv[i], ':');
         if (colon == nullptr) {
             printf("no ':' in patch argument \"%s\"\n", argv[i]);
@@ -83,18 +91,15 @@
 
 static int PatchMode(int argc, char** argv) {
     FileContents bonusFc;
-    Value bonusValue;
-    Value* bonus = nullptr;
+    Value bonus(VAL_INVALID, "");
 
     if (argc >= 3 && strcmp(argv[1], "-b") == 0) {
         if (LoadFileContents(argv[2], &bonusFc) != 0) {
             printf("failed to load bonus file %s\n", argv[2]);
             return 1;
         }
-        bonus = &bonusValue;
-        bonus->type = VAL_BLOB;
-        bonus->size = bonusFc.data.size();
-        bonus->data = reinterpret_cast<char*>(bonusFc.data.data());
+        bonus.type = VAL_BLOB;
+        bonus.data = reinterpret_cast<const char*>(bonusFc.data.data());
         argc -= 2;
         argv += 2;
     }
@@ -112,29 +117,26 @@
 
     // If no <src-sha1>:<patch> is provided, it is in flash mode.
     if (argc == 5) {
-        if (bonus != nullptr) {
+        if (bonus.type != VAL_INVALID) {
             printf("bonus file not supported in flash mode\n");
             return 1;
         }
         return FlashMode(argv[1], argv[2], argv[3], target_size);
     }
-    std::vector<char*> sha1s;
+    std::vector<std::string> sha1s;
     std::vector<FileContents> files;
     if (!ParsePatchArgs(argc-5, argv+5, &sha1s, &files)) {
         printf("failed to parse patch args\n");
         return 1;
     }
-    std::vector<Value> patches(files.size());
-    std::vector<Value*> patch_ptrs(files.size());
+    std::vector<Value> patches;
+    std::vector<Value*> patch_ptrs;
     for (size_t i = 0; i < files.size(); ++i) {
-        patches[i].type = VAL_BLOB;
-        patches[i].size = files[i].data.size();
-        patches[i].data = reinterpret_cast<char*>(files[i].data.data());
-        patch_ptrs[i] = &patches[i];
+        patches.push_back(Value(VAL_BLOB, reinterpret_cast<const char*>(files[i].data.data())));
+        patch_ptrs.push_back(&patches[i]);
     }
     return applypatch(argv[1], argv[2], argv[3], target_size,
-                      patch_ptrs.size(), sha1s.data(),
-                      patch_ptrs.data(), bonus);
+                      sha1s, patch_ptrs.data(), &bonus);
 }
 
 // This program applies binary patches to files in a way that is safe
diff --git a/applypatch/utils.cpp b/applypatch/utils.cpp
index fef250f..450dc8d 100644
--- a/applypatch/utils.cpp
+++ b/applypatch/utils.cpp
@@ -38,22 +38,22 @@
   fputc((value >> 56) & 0xff, f);
 }
 
-int Read2(void* pv) {
-    unsigned char* p = reinterpret_cast<unsigned char*>(pv);
+int Read2(const void* pv) {
+    const unsigned char* p = reinterpret_cast<const unsigned char*>(pv);
     return (int)(((unsigned int)p[1] << 8) |
                  (unsigned int)p[0]);
 }
 
-int Read4(void* pv) {
-    unsigned char* p = reinterpret_cast<unsigned char*>(pv);
+int Read4(const void* pv) {
+    const unsigned char* p = reinterpret_cast<const unsigned char*>(pv);
     return (int)(((unsigned int)p[3] << 24) |
                  ((unsigned int)p[2] << 16) |
                  ((unsigned int)p[1] << 8) |
                  (unsigned int)p[0]);
 }
 
-int64_t Read8(void* pv) {
-    unsigned char* p = reinterpret_cast<unsigned char*>(pv);
+int64_t Read8(const void* pv) {
+    const unsigned char* p = reinterpret_cast<const unsigned char*>(pv);
     return (int64_t)(((uint64_t)p[7] << 56) |
                        ((uint64_t)p[6] << 48) |
                        ((uint64_t)p[5] << 40) |
diff --git a/applypatch/utils.h b/applypatch/utils.h
index 1c34edd..c7c8e90 100644
--- a/applypatch/utils.h
+++ b/applypatch/utils.h
@@ -24,8 +24,8 @@
 
 void Write4(int value, FILE* f);
 void Write8(int64_t value, FILE* f);
-int Read2(void* p);
-int Read4(void* p);
-int64_t Read8(void* p);
+int Read2(const void* p);
+int Read4(const void* p);
+int64_t Read8(const void* p);
 
 #endif //  _BUILD_TOOLS_APPLYPATCH_UTILS_H
diff --git a/edify/edify_parser.cpp b/edify/edify_parser.cpp
index 1b89cf2..908fcf1 100644
--- a/edify/edify_parser.cpp
+++ b/edify/edify_parser.cpp
@@ -66,12 +66,12 @@
         ExprDump(0, root, buffer);
 
         State state(buffer, nullptr);
-        char* result = Evaluate(&state, root);
-        if (result == NULL) {
+        std::string result;
+        if (!Evaluate(&state, root, &result)) {
             printf("result was NULL, message is: %s\n",
                    (state.errmsg.empty() ? "(NULL)" : state.errmsg.c_str()));
         } else {
-            printf("result is [%s]\n", result);
+            printf("result is [%s]\n", result.c_str());
         }
     }
     return 0;
diff --git a/edify/expr.cpp b/edify/expr.cpp
index 4000bc4..ec24097 100644
--- a/edify/expr.cpp
+++ b/edify/expr.cpp
@@ -22,184 +22,164 @@
 #include <string.h>
 #include <unistd.h>
 
+#include <memory>
 #include <string>
 #include <unordered_map>
+#include <vector>
 
+#include <android-base/parseint.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
 
 // Functions should:
 //
 //    - return a malloc()'d string
-//    - if Evaluate() on any argument returns NULL, return NULL.
+//    - if Evaluate() on any argument returns nullptr, return nullptr.
 
-int BooleanString(const char* s) {
-    return s[0] != '\0';
+static bool BooleanString(const std::string& s) {
+    return !s.empty();
 }
 
-char* Evaluate(State* state, Expr* expr) {
-    Value* v = expr->fn(expr->name, state, expr->argc, expr->argv);
-    if (v == NULL) return NULL;
+bool Evaluate(State* state, Expr* expr, std::string* result) {
+    if (result == nullptr) {
+        return false;
+    }
+
+    std::unique_ptr<Value> v(expr->fn(expr->name, state, expr->argc, expr->argv));
+    if (!v) {
+        return false;
+    }
     if (v->type != VAL_STRING) {
         ErrorAbort(state, kArgsParsingFailure, "expecting string, got value type %d", v->type);
-        FreeValue(v);
-        return NULL;
+        return false;
     }
-    char* result = v->data;
-    free(v);
-    return result;
+
+    *result = v->data;
+    return true;
 }
 
 Value* EvaluateValue(State* state, Expr* expr) {
     return expr->fn(expr->name, state, expr->argc, expr->argv);
 }
 
-Value* StringValue(char* str) {
-    if (str == NULL) return NULL;
-    Value* v = reinterpret_cast<Value*>(malloc(sizeof(Value)));
-    v->type = VAL_STRING;
-    v->size = strlen(str);
-    v->data = str;
-    return v;
+Value* StringValue(const char* str) {
+    if (str == nullptr) {
+        return nullptr;
+    }
+    return new Value(VAL_STRING, str);
 }
 
-void FreeValue(Value* v) {
-    if (v == NULL) return;
-    free(v->data);
-    free(v);
+Value* StringValue(const std::string& str) {
+    return StringValue(str.c_str());
 }
 
 Value* ConcatFn(const char* name, State* state, int argc, Expr* argv[]) {
     if (argc == 0) {
-        return StringValue(strdup(""));
+        return StringValue("");
     }
-    char** strings = reinterpret_cast<char**>(malloc(argc * sizeof(char*)));
-    int i;
-    for (i = 0; i < argc; ++i) {
-        strings[i] = NULL;
-    }
-    char* result = NULL;
-    int length = 0;
-    for (i = 0; i < argc; ++i) {
-        strings[i] = Evaluate(state, argv[i]);
-        if (strings[i] == NULL) {
-            goto done;
+    std::string result;
+    for (int i = 0; i < argc; ++i) {
+        std::string str;
+        if (!Evaluate(state, argv[i], &str)) {
+            return nullptr;
         }
-        length += strlen(strings[i]);
+        result += str;
     }
 
-    result = reinterpret_cast<char*>(malloc(length+1));
-    int p;
-    p = 0;
-    for (i = 0; i < argc; ++i) {
-        strcpy(result+p, strings[i]);
-        p += strlen(strings[i]);
-    }
-    result[p] = '\0';
-
-  done:
-    for (i = 0; i < argc; ++i) {
-        free(strings[i]);
-    }
-    free(strings);
     return StringValue(result);
 }
 
 Value* IfElseFn(const char* name, State* state, int argc, Expr* argv[]) {
     if (argc != 2 && argc != 3) {
         state->errmsg = "ifelse expects 2 or 3 arguments";
-        return NULL;
-    }
-    char* cond = Evaluate(state, argv[0]);
-    if (cond == NULL) {
-        return NULL;
+        return nullptr;
     }
 
-    if (BooleanString(cond) == true) {
-        free(cond);
-        return EvaluateValue(state, argv[1]);
-    } else {
-        if (argc == 3) {
-            free(cond);
-            return EvaluateValue(state, argv[2]);
-        } else {
-            return StringValue(cond);
-        }
+    std::string cond;
+    if (!Evaluate(state, argv[0], &cond)) {
+        return nullptr;
     }
+
+    if (!cond.empty()) {
+        return EvaluateValue(state, argv[1]);
+    } else if (argc == 3) {
+        return EvaluateValue(state, argv[2]);
+    }
+
+    return StringValue("");
 }
 
 Value* AbortFn(const char* name, State* state, int argc, Expr* argv[]) {
-    char* msg = NULL;
-    if (argc > 0) {
-        msg = Evaluate(state, argv[0]);
-    }
-    if (msg) {
+    std::string msg;
+    if (argc > 0 && Evaluate(state, argv[0], &msg)) {
         state->errmsg = msg;
     } else {
         state->errmsg = "called abort()";
     }
-    return NULL;
+    return nullptr;
 }
 
 Value* AssertFn(const char* name, State* state, int argc, Expr* argv[]) {
-    int i;
-    for (i = 0; i < argc; ++i) {
-        char* v = Evaluate(state, argv[i]);
-        if (v == NULL) {
-            return NULL;
+    for (int i = 0; i < argc; ++i) {
+        std::string result;
+        if (!Evaluate(state, argv[i], &result)) {
+            return nullptr;
         }
-        int b = BooleanString(v);
-        free(v);
-        if (!b) {
+        if (result.empty()) {
             int len = argv[i]->end - argv[i]->start;
             state->errmsg = "assert failed: " + state->script.substr(argv[i]->start, len);
-            return NULL;
+            return nullptr;
         }
     }
-    return StringValue(strdup(""));
+    return StringValue("");
 }
 
 Value* SleepFn(const char* name, State* state, int argc, Expr* argv[]) {
-    char* val = Evaluate(state, argv[0]);
-    if (val == NULL) {
-        return NULL;
+    std::string val;
+    if (!Evaluate(state, argv[0], &val)) {
+        return nullptr;
     }
-    int v = strtol(val, NULL, 10);
+
+    int v;
+    if (!android::base::ParseInt(val.c_str(), &v, 0)) {
+        return nullptr;
+    }
     sleep(v);
+
     return StringValue(val);
 }
 
 Value* StdoutFn(const char* name, State* state, int argc, Expr* argv[]) {
-    int i;
-    for (i = 0; i < argc; ++i) {
-        char* v = Evaluate(state, argv[i]);
-        if (v == NULL) {
-            return NULL;
+    for (int i = 0; i < argc; ++i) {
+        std::string v;
+        if (!Evaluate(state, argv[i], &v)) {
+            return nullptr;
         }
-        fputs(v, stdout);
-        free(v);
+        fputs(v.c_str(), stdout);
     }
-    return StringValue(strdup(""));
+    return StringValue("");
 }
 
 Value* LogicalAndFn(const char* name, State* state,
                    int argc, Expr* argv[]) {
-    char* left = Evaluate(state, argv[0]);
-    if (left == NULL) return NULL;
-    if (BooleanString(left) == true) {
-        free(left);
+    std::string left;
+    if (!Evaluate(state, argv[0], &left)) {
+        return nullptr;
+    }
+    if (BooleanString(left)) {
         return EvaluateValue(state, argv[1]);
     } else {
-        return StringValue(left);
+        return StringValue("");
     }
 }
 
 Value* LogicalOrFn(const char* name, State* state,
                    int argc, Expr* argv[]) {
-    char* left = Evaluate(state, argv[0]);
-    if (left == NULL) return NULL;
-    if (BooleanString(left) == false) {
-        free(left);
+    std::string left;
+    if (!Evaluate(state, argv[0], &left)) {
+        return nullptr;
+    }
+    if (!BooleanString(left)) {
         return EvaluateValue(state, argv[1]);
     } else {
         return StringValue(left);
@@ -208,75 +188,75 @@
 
 Value* LogicalNotFn(const char* name, State* state,
                     int argc, Expr* argv[]) {
-    char* val = Evaluate(state, argv[0]);
-    if (val == NULL) return NULL;
-    bool bv = BooleanString(val);
-    free(val);
-    return StringValue(strdup(bv ? "" : "t"));
+    std::string val;
+    if (!Evaluate(state, argv[0], &val)) {
+        return nullptr;
+    }
+
+    return StringValue(BooleanString(val) ? "" : "t");
 }
 
 Value* SubstringFn(const char* name, State* state,
                    int argc, Expr* argv[]) {
-    char* needle = Evaluate(state, argv[0]);
-    if (needle == NULL) return NULL;
-    char* haystack = Evaluate(state, argv[1]);
-    if (haystack == NULL) {
-        free(needle);
-        return NULL;
+    std::string needle;
+    if (!Evaluate(state, argv[0], &needle)) {
+        return nullptr;
     }
 
-    char* result = strdup(strstr(haystack, needle) ? "t" : "");
-    free(needle);
-    free(haystack);
+    std::string haystack;
+    if (!Evaluate(state, argv[1], &haystack)) {
+        return nullptr;
+    }
+
+    std::string result = (haystack.find(needle) != std::string::npos) ? "t" : "";
     return StringValue(result);
 }
 
 Value* EqualityFn(const char* name, State* state, int argc, Expr* argv[]) {
-    char* left = Evaluate(state, argv[0]);
-    if (left == NULL) return NULL;
-    char* right = Evaluate(state, argv[1]);
-    if (right == NULL) {
-        free(left);
-        return NULL;
+    std::string left;
+    if (!Evaluate(state, argv[0], &left)) {
+        return nullptr;
+    }
+    std::string right;
+    if (!Evaluate(state, argv[1], &right)) {
+        return nullptr;
     }
 
-    char* result = strdup(strcmp(left, right) == 0 ? "t" : "");
-    free(left);
-    free(right);
+    const char* result = (left == right) ? "t" : "";
     return StringValue(result);
 }
 
 Value* InequalityFn(const char* name, State* state, int argc, Expr* argv[]) {
-    char* left = Evaluate(state, argv[0]);
-    if (left == NULL) return NULL;
-    char* right = Evaluate(state, argv[1]);
-    if (right == NULL) {
-        free(left);
-        return NULL;
+    std::string left;
+    if (!Evaluate(state, argv[0], &left)) {
+        return nullptr;
+    }
+    std::string right;
+    if (!Evaluate(state, argv[1], &right)) {
+        return nullptr;
     }
 
-    char* result = strdup(strcmp(left, right) != 0 ? "t" : "");
-    free(left);
-    free(right);
+    const char* result = (left != right) ? "t" : "";
     return StringValue(result);
 }
 
 Value* SequenceFn(const char* name, State* state, int argc, Expr* argv[]) {
-    Value* left = EvaluateValue(state, argv[0]);
-    if (left == NULL) return NULL;
-    FreeValue(left);
+    std::unique_ptr<Value> left(EvaluateValue(state, argv[0]));
+    if (!left) {
+        return nullptr;
+    }
     return EvaluateValue(state, argv[1]);
 }
 
 Value* LessThanIntFn(const char* name, State* state, int argc, Expr* argv[]) {
     if (argc != 2) {
         state->errmsg = "less_than_int expects 2 arguments";
-        return NULL;
+        return nullptr;
     }
 
     char* left;
     char* right;
-    if (ReadArgs(state, argv, 2, &left, &right) < 0) return NULL;
+    if (ReadArgs(state, argv, 2, &left, &right) < 0) return nullptr;
 
     bool result = false;
     char* end;
@@ -298,14 +278,14 @@
   done:
     free(left);
     free(right);
-    return StringValue(strdup(result ? "t" : ""));
+    return StringValue(result ? "t" : "");
 }
 
 Value* GreaterThanIntFn(const char* name, State* state,
                         int argc, Expr* argv[]) {
     if (argc != 2) {
         state->errmsg = "greater_than_int expects 2 arguments";
-        return NULL;
+        return nullptr;
     }
 
     Expr* temp[2];
@@ -316,7 +296,7 @@
 }
 
 Value* Literal(const char* name, State* state, int argc, Expr* argv[]) {
-    return StringValue(strdup(name));
+    return StringValue(name);
 }
 
 // -----------------------------------------------------------------
@@ -355,6 +335,43 @@
 //   convenience methods for functions
 // -----------------------------------------------------------------
 
+// Evaluate the expressions in argv, and put the results of strings in
+// args. If any expression evaluates to nullptr, free the rest and return
+// false. Return true on success.
+bool ReadArgs(State* state, int argc, Expr* argv[], std::vector<std::string>* args) {
+    if (args == nullptr) {
+        return false;
+    }
+    for (int i = 0; i < argc; ++i) {
+        std::string var;
+        if (!Evaluate(state, argv[i], &var)) {
+            args->clear();
+            return false;
+        }
+        args->push_back(var);
+    }
+    return true;
+}
+
+// Evaluate the expressions in argv, and put the results of Value* in
+// args. If any expression evaluate to nullptr, free the rest and return
+// false. Return true on success.
+bool ReadValueArgs(State* state, int argc, Expr* argv[],
+                   std::vector<std::unique_ptr<Value>>* args) {
+    if (args == nullptr) {
+        return false;
+    }
+    for (int i = 0; i < argc; ++i) {
+        std::unique_ptr<Value> v(EvaluateValue(state, argv[i]));
+        if (!v) {
+            args->clear();
+            return false;
+        }
+        args->push_back(std::move(v));
+    }
+    return true;
+}
+
 // Evaluate the expressions in argv, giving 'count' char* (the ... is
 // zero or more char** to put them in).  If any expression evaluates
 // to NULL, free the rest and return -1.  Return 0 on success.
@@ -364,8 +381,9 @@
     va_start(v, count);
     int i;
     for (i = 0; i < count; ++i) {
-        args[i] = Evaluate(state, argv[i]);
-        if (args[i] == NULL) {
+        std::string str;
+        if (!Evaluate(state, argv[i], &str) ||
+                (args[i] = strdup(str.c_str())) == nullptr) {
             va_end(v);
             int j;
             for (j = 0; j < i; ++j) {
@@ -385,25 +403,24 @@
 // zero or more Value** to put them in).  If any expression evaluates
 // to NULL, free the rest and return -1.  Return 0 on success.
 int ReadValueArgs(State* state, Expr* argv[], int count, ...) {
-    Value** args = reinterpret_cast<Value**>(malloc(count * sizeof(Value*)));
+    Value** args = new Value*[count];
     va_list v;
     va_start(v, count);
-    int i;
-    for (i = 0; i < count; ++i) {
+    for (int i = 0; i < count; ++i) {
         args[i] = EvaluateValue(state, argv[i]);
         if (args[i] == NULL) {
             va_end(v);
             int j;
             for (j = 0; j < i; ++j) {
-                FreeValue(args[j]);
+                delete args[j];
             }
-            free(args);
+            delete[] args;
             return -1;
         }
         *(va_arg(v, Value**)) = args[i];
     }
     va_end(v);
-    free(args);
+    delete[] args;
     return 0;
 }
 
@@ -413,12 +430,11 @@
 // strings it contains.
 char** ReadVarArgs(State* state, int argc, Expr* argv[]) {
     char** args = (char**)malloc(argc * sizeof(char*));
-    int i = 0;
-    for (i = 0; i < argc; ++i) {
-        args[i] = Evaluate(state, argv[i]);
-        if (args[i] == NULL) {
-            int j;
-            for (j = 0; j < i; ++j) {
+    for (int i = 0; i < argc; ++i) {
+        std::string str;
+        if (!Evaluate(state, argv[i], &str) ||
+                (args[i] = strdup(str.c_str())) == nullptr) {
+            for (int j = 0; j < i; ++j) {
                 free(args[j]);
             }
             free(args);
@@ -433,16 +449,16 @@
 // The caller is responsible for freeing the returned array and the
 // Values it contains.
 Value** ReadValueVarArgs(State* state, int argc, Expr* argv[]) {
-    Value** args = (Value**)malloc(argc * sizeof(Value*));
+    Value** args = new Value*[argc];
     int i = 0;
     for (i = 0; i < argc; ++i) {
         args[i] = EvaluateValue(state, argv[i]);
         if (args[i] == NULL) {
             int j;
             for (j = 0; j < i; ++j) {
-                FreeValue(args[j]);
+                delete args[j];
             }
-            free(args);
+            delete[] args;
             return NULL;
         }
     }
diff --git a/edify/expr.h b/edify/expr.h
index cd6139a..8530654 100644
--- a/edify/expr.h
+++ b/edify/expr.h
@@ -48,13 +48,19 @@
     bool is_retry = false;
 };
 
-#define VAL_STRING  1  // data will be NULL-terminated; size doesn't count null
-#define VAL_BLOB    2
+enum ValueType {
+    VAL_INVALID = -1,
+    VAL_STRING = 1,
+    VAL_BLOB = 2,
+};
 
 struct Value {
-    int type;
-    ssize_t size;
-    char* data;
+    ValueType type;
+    std::string data;
+
+    Value(ValueType type, const std::string& str) :
+        type(type),
+        data(str) {}
 };
 
 struct Expr;
@@ -75,11 +81,11 @@
 Value* EvaluateValue(State* state, Expr* expr);
 
 // Take one of the Expr*s passed to the function as an argument,
-// evaluate it, assert that it is a string, and return the resulting
-// char*.  The caller takes ownership of the returned char*.  This is
-// a convenience function for older functions that want to deal only
-// with strings.
-char* Evaluate(State* state, Expr* expr);
+// evaluate it, assert that it is a string, and update the result
+// parameter. This function returns true if the evaluation succeeds.
+// This is a convenience function for older functions that want to
+// deal only with strings.
+bool Evaluate(State* state, Expr* expr, std::string* result);
 
 // Glue to make an Expr out of a literal.
 Value* Literal(const char* name, State* state, int argc, Expr* argv[]);
@@ -114,6 +120,17 @@
 
 // --- convenience functions for use in functions ---
 
+// Evaluate the expressions in argv, and put the results of strings in
+// args. If any expression evaluates to nullptr, free the rest and return
+// false. Return true on success.
+bool ReadArgs(State* state, int argc, Expr* argv[], std::vector<std::string>* args);
+
+// Evaluate the expressions in argv, and put the results of Value* in
+// args. If any expression evaluate to nullptr, free the rest and return
+// false. Return true on success.
+bool ReadValueArgs(State* state, int argc, Expr* argv[],
+                   std::vector<std::unique_ptr<Value>>* args);
+
 // Evaluate the expressions in argv, giving 'count' char* (the ... is
 // zero or more char** to put them in).  If any expression evaluates
 // to NULL, free the rest and return -1.  Return 0 on success.
@@ -146,11 +163,10 @@
 Value* ErrorAbort(State* state, CauseCode cause_code, const char* format, ...)
     __attribute__((format(printf, 3, 4)));
 
-// Wrap a string into a Value, taking ownership of the string.
-Value* StringValue(char* str);
+// Copying the string into a Value.
+Value* StringValue(const char* str);
 
-// Free a Value object.
-void FreeValue(Value* v);
+Value* StringValue(const std::string& str);
 
 int parse_string(const char* str, Expr** root, int* error_count);
 
diff --git a/tests/component/applypatch_test.cpp b/tests/component/applypatch_test.cpp
index 2f7cb02..75f2e10 100644
--- a/tests/component/applypatch_test.cpp
+++ b/tests/component/applypatch_test.cpp
@@ -153,25 +153,16 @@
             struct FileContents fc;
 
             ASSERT_EQ(0, LoadFileContents(&rand_file[0], &fc));
-            Value* patch1 = new Value();
-            patch1->type = VAL_BLOB;
-            patch1->size = fc.data.size();
-            patch1->data = static_cast<char*>(malloc(fc.data.size()));
-            memcpy(patch1->data, fc.data.data(), fc.data.size());
+            Value* patch1 = new Value(VAL_BLOB, std::string(fc.data.begin(), fc.data.end()));
             patches.push_back(patch1);
 
             ASSERT_EQ(0, LoadFileContents(&patch_file[0], &fc));
-            Value* patch2 = new Value();
-            patch2->type = VAL_BLOB;
-            patch2->size = fc.st.st_size;
-            patch2->data = static_cast<char*>(malloc(fc.data.size()));
-            memcpy(patch2->data, fc.data.data(), fc.data.size());
+            Value* patch2 = new Value(VAL_BLOB, std::string(fc.data.begin(), fc.data.end()));
             patches.push_back(patch2);
         }
         static void TearDownTestCase() {
             delete output_f;
             for (auto it = patches.begin(); it != patches.end(); ++it) {
-                free((*it)->data);
                 delete *it;
             }
             patches.clear();
@@ -210,88 +201,87 @@
 std::string ApplyPatchFullTest::output_loc;
 
 TEST_F(ApplyPatchTest, CheckModeSingle) {
-    char* s = &old_sha1[0];
-    ASSERT_EQ(0, applypatch_check(&old_file[0], 1, &s));
+    std::vector<std::string> sha1s = { old_sha1 };
+    ASSERT_EQ(0, applypatch_check(&old_file[0], sha1s));
 }
 
 TEST_F(ApplyPatchTest, CheckModeMultiple) {
-    char* argv[3] = {
-        &bad_sha1_a[0],
-        &old_sha1[0],
-        &bad_sha1_b[0]
+    std::vector<std::string> sha1s = {
+        bad_sha1_a,
+        old_sha1,
+        bad_sha1_b
     };
-    ASSERT_EQ(0, applypatch_check(&old_file[0], 3, argv));
+    ASSERT_EQ(0, applypatch_check(&old_file[0], sha1s));
 }
 
 TEST_F(ApplyPatchTest, CheckModeFailure) {
-    char* argv[2] = {
-        &bad_sha1_a[0],
-        &bad_sha1_b[0]
+    std::vector<std::string> sha1s = {
+        bad_sha1_a,
+        bad_sha1_b
     };
-    ASSERT_NE(0, applypatch_check(&old_file[0], 2, argv));
+    ASSERT_NE(0, applypatch_check(&old_file[0], sha1s));
 }
 
 TEST_F(ApplyPatchCacheTest, CheckCacheCorruptedSingle) {
     mangle_file(old_file);
-    char* s = &old_sha1[0];
-    ASSERT_EQ(0, applypatch_check(&old_file[0], 1, &s));
+    std::vector<std::string> sha1s = { old_sha1 };
+    ASSERT_EQ(0, applypatch_check(&old_file[0], sha1s));
 }
 
 TEST_F(ApplyPatchCacheTest, CheckCacheCorruptedMultiple) {
     mangle_file(old_file);
-    char* argv[3] = {
-        &bad_sha1_a[0],
-        &old_sha1[0],
-        &bad_sha1_b[0]
+    std::vector<std::string> sha1s = {
+        bad_sha1_a,
+        old_sha1,
+        bad_sha1_b
     };
-    ASSERT_EQ(0, applypatch_check(&old_file[0], 3, argv));
+    ASSERT_EQ(0, applypatch_check(&old_file[0], sha1s));
 }
 
 TEST_F(ApplyPatchCacheTest, CheckCacheCorruptedFailure) {
     mangle_file(old_file);
-    char* argv[2] = {
-        &bad_sha1_a[0],
-        &bad_sha1_b[0]
+    std::vector<std::string> sha1s = {
+        bad_sha1_a,
+        bad_sha1_b
     };
-    ASSERT_NE(0, applypatch_check(&old_file[0], 2, argv));
+    ASSERT_NE(0, applypatch_check(&old_file[0], sha1s));
 }
 
 TEST_F(ApplyPatchCacheTest, CheckCacheMissingSingle) {
     unlink(&old_file[0]);
-    char* s = &old_sha1[0];
-    ASSERT_EQ(0, applypatch_check(&old_file[0], 1, &s));
+    std::vector<std::string> sha1s = { old_sha1 };
+    ASSERT_EQ(0, applypatch_check(&old_file[0], sha1s));
 }
 
 TEST_F(ApplyPatchCacheTest, CheckCacheMissingMultiple) {
     unlink(&old_file[0]);
-    char* argv[3] = {
-        &bad_sha1_a[0],
-        &old_sha1[0],
-        &bad_sha1_b[0]
+    std::vector<std::string> sha1s = {
+        bad_sha1_a,
+        old_sha1,
+        bad_sha1_b
     };
-    ASSERT_EQ(0, applypatch_check(&old_file[0], 3, argv));
+    ASSERT_EQ(0, applypatch_check(&old_file[0], sha1s));
 }
 
 TEST_F(ApplyPatchCacheTest, CheckCacheMissingFailure) {
     unlink(&old_file[0]);
-    char* argv[2] = {
-        &bad_sha1_a[0],
-        &bad_sha1_b[0]
+    std::vector<std::string> sha1s = {
+        bad_sha1_a,
+        bad_sha1_b
     };
-    ASSERT_NE(0, applypatch_check(&old_file[0], 2, argv));
+    ASSERT_NE(0, applypatch_check(&old_file[0], sha1s));
 }
 
 TEST_F(ApplyPatchFullTest, ApplyInPlace) {
-    std::vector<char*> sha1s;
-    sha1s.push_back(&bad_sha1_a[0]);
-    sha1s.push_back(&old_sha1[0]);
-
+    std::vector<std::string> sha1s = {
+        bad_sha1_a,
+        old_sha1
+    };
     int ap_result = applypatch(&old_file[0],
             "-",
             &new_sha1[0],
             new_size,
-            2,
-            sha1s.data(),
+            sha1s,
             patches.data(),
             nullptr);
     ASSERT_EQ(0, ap_result);
@@ -301,8 +291,7 @@
             "-",
             &new_sha1[0],
             new_size,
-            2,
-            sha1s.data(),
+            sha1s,
             patches.data(),
             nullptr);
     ASSERT_EQ(0, ap_result);
@@ -310,15 +299,15 @@
 }
 
 TEST_F(ApplyPatchFullTest, ApplyInNewLocation) {
-    std::vector<char*> sha1s;
-    sha1s.push_back(&bad_sha1_a[0]);
-    sha1s.push_back(&old_sha1[0]);
+    std::vector<std::string> sha1s = {
+        bad_sha1_a,
+        old_sha1
+    };
     int ap_result = applypatch(&old_file[0],
             &output_loc[0],
             &new_sha1[0],
             new_size,
-            2,
-            sha1s.data(),
+            sha1s,
             patches.data(),
             nullptr);
     ASSERT_EQ(0, ap_result);
@@ -327,8 +316,7 @@
             &output_loc[0],
             &new_sha1[0],
             new_size,
-            2,
-            sha1s.data(),
+            sha1s,
             patches.data(),
             nullptr);
     ASSERT_EQ(0, ap_result);
@@ -337,15 +325,15 @@
 
 TEST_F(ApplyPatchFullTest, ApplyCorruptedInNewLocation) {
     mangle_file(old_file);
-    std::vector<char*> sha1s;
-    sha1s.push_back(&bad_sha1_a[0]);
-    sha1s.push_back(&old_sha1[0]);
+    std::vector<std::string> sha1s = {
+        bad_sha1_a,
+        old_sha1
+    };
     int ap_result = applypatch(&old_file[0],
             &output_loc[0],
             &new_sha1[0],
             new_size,
-            2,
-            sha1s.data(),
+            sha1s,
             patches.data(),
             nullptr);
     ASSERT_EQ(0, ap_result);
@@ -354,8 +342,7 @@
             &output_loc[0],
             &new_sha1[0],
             new_size,
-            2,
-            sha1s.data(),
+            sha1s,
             patches.data(),
             nullptr);
     ASSERT_EQ(0, ap_result);
@@ -366,15 +353,15 @@
     mangle_file(old_file);
     mangle_file(cache_file);
 
-    std::vector<char*> sha1s;
-    sha1s.push_back(&bad_sha1_a[0]);
-    sha1s.push_back(&old_sha1[0]);
+    std::vector<std::string> sha1s = {
+        bad_sha1_a,
+        old_sha1
+    };
     int ap_result = applypatch(&old_file[0],
             &output_loc[0],
             &new_sha1[0],
             new_size,
-            2,
-            sha1s.data(),
+            sha1s,
             patches.data(),
             nullptr);
     ASSERT_NE(0, ap_result);
@@ -383,8 +370,7 @@
             &output_loc[0],
             &new_sha1[0],
             new_size,
-            2,
-            sha1s.data(),
+            sha1s,
             patches.data(),
             nullptr);
     ASSERT_NE(0, ap_result);
diff --git a/tests/component/edify_test.cpp b/tests/component/edify_test.cpp
index a4dbb9f..287e40c 100644
--- a/tests/component/edify_test.cpp
+++ b/tests/component/edify_test.cpp
@@ -28,15 +28,15 @@
 
     State state(expr_str, nullptr);
 
-    char* result = Evaluate(&state, e);
+    std::string result;
+    bool status = Evaluate(&state, e, &result);
 
     if (expected == nullptr) {
-        EXPECT_EQ(nullptr, result);
+        EXPECT_FALSE(status);
     } else {
-        EXPECT_STREQ(expected, result);
+        EXPECT_STREQ(expected, result.c_str());
     }
 
-    free(result);
 }
 
 class EdifyTest : public ::testing::Test {
diff --git a/tests/component/updater_test.cpp b/tests/component/updater_test.cpp
index 64a6b37..a859f11 100644
--- a/tests/component/updater_test.cpp
+++ b/tests/component/updater_test.cpp
@@ -32,12 +32,13 @@
 
     State state(expr_str, nullptr);
 
-    char* result = Evaluate(&state, e);
+    std::string result;
+    bool status = Evaluate(&state, e, &result);
 
     if (expected == nullptr) {
-        EXPECT_EQ(nullptr, result);
+        EXPECT_FALSE(status);
     } else {
-        EXPECT_STREQ(expected, result);
+        EXPECT_STREQ(expected, result.c_str());
     }
 
     // Error code is set in updater/updater.cpp only, by parsing State.errmsg.
@@ -46,7 +47,6 @@
     // Cause code should always be available.
     EXPECT_EQ(cause_code, state.cause_code);
 
-    free(result);
 }
 
 class UpdaterTest : public ::testing::Test {
diff --git a/updater/blockimg.cpp b/updater/blockimg.cpp
index 433d980..5f9b437 100644
--- a/updater/blockimg.cpp
+++ b/updater/blockimg.cpp
@@ -1216,7 +1216,7 @@
 
     size_t len;
     if (!android::base::ParseUint(params.tokens[params.cpos++].c_str(), &len)) {
-        fprintf(stderr, "invalid patch offset\n");
+        fprintf(stderr, "invalid patch len\n");
         return -1;
     }
 
@@ -1248,10 +1248,8 @@
         if (status == 0) {
             fprintf(stderr, "patching %zu blocks to %zu\n", blocks, tgt.size);
 
-            Value patch_value;
-            patch_value.type = VAL_BLOB;
-            patch_value.size = len;
-            patch_value.data = (char*) (params.patch_start + offset);
+            Value patch_value(VAL_BLOB,
+                    std::string(reinterpret_cast<const char*>(params.patch_start + offset), len));
 
             RangeSinkState rss(tgt);
             rss.fd = params.fd;
@@ -1398,64 +1396,62 @@
     Value* patch_data_fn = nullptr;
     if (ReadValueArgs(state, argv, 4, &blockdev_filename, &transfer_list_value,
             &new_data_fn, &patch_data_fn) < 0) {
-        return StringValue(strdup(""));
+        return StringValue("");
     }
-    std::unique_ptr<Value, decltype(&FreeValue)> blockdev_filename_holder(blockdev_filename,
-            FreeValue);
-    std::unique_ptr<Value, decltype(&FreeValue)> transfer_list_value_holder(transfer_list_value,
-            FreeValue);
-    std::unique_ptr<Value, decltype(&FreeValue)> new_data_fn_holder(new_data_fn, FreeValue);
-    std::unique_ptr<Value, decltype(&FreeValue)> patch_data_fn_holder(patch_data_fn, FreeValue);
+    std::unique_ptr<Value> blockdev_filename_holder(blockdev_filename);
+    std::unique_ptr<Value> transfer_list_value_holder(transfer_list_value);
+    std::unique_ptr<Value> new_data_fn_holder(new_data_fn);
+    std::unique_ptr<Value> patch_data_fn_holder(patch_data_fn);
 
     if (blockdev_filename->type != VAL_STRING) {
         ErrorAbort(state, kArgsParsingFailure, "blockdev_filename argument to %s must be string",
                    name);
-        return StringValue(strdup(""));
+        return StringValue("");
     }
     if (transfer_list_value->type != VAL_BLOB) {
         ErrorAbort(state, kArgsParsingFailure, "transfer_list argument to %s must be blob", name);
-        return StringValue(strdup(""));
+        return StringValue("");
     }
     if (new_data_fn->type != VAL_STRING) {
         ErrorAbort(state, kArgsParsingFailure, "new_data_fn argument to %s must be string", name);
-        return StringValue(strdup(""));
+        return StringValue("");
     }
     if (patch_data_fn->type != VAL_STRING) {
         ErrorAbort(state, kArgsParsingFailure, "patch_data_fn argument to %s must be string",
                    name);
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     UpdaterInfo* ui = reinterpret_cast<UpdaterInfo*>(state->cookie);
 
     if (ui == nullptr) {
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     FILE* cmd_pipe = ui->cmd_pipe;
     ZipArchive* za = ui->package_zip;
 
     if (cmd_pipe == nullptr || za == nullptr) {
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
-    const ZipEntry* patch_entry = mzFindZipEntry(za, patch_data_fn->data);
+    const ZipEntry* patch_entry = mzFindZipEntry(za, patch_data_fn->data.c_str());
     if (patch_entry == nullptr) {
-        fprintf(stderr, "%s(): no file \"%s\" in package", name, patch_data_fn->data);
-        return StringValue(strdup(""));
+        fprintf(stderr, "%s(): no file \"%s\" in package", name, patch_data_fn->data.c_str());
+        return StringValue("");
     }
 
     params.patch_start = ui->package_zip_addr + mzGetZipEntryOffset(patch_entry);
-    const ZipEntry* new_entry = mzFindZipEntry(za, new_data_fn->data);
+    const ZipEntry* new_entry = mzFindZipEntry(za, new_data_fn->data.c_str());
     if (new_entry == nullptr) {
-        fprintf(stderr, "%s(): no file \"%s\" in package", name, new_data_fn->data);
-        return StringValue(strdup(""));
+        fprintf(stderr, "%s(): no file \"%s\" in package", name, new_data_fn->data.c_str());
+        return StringValue("");
     }
 
-    params.fd.reset(TEMP_FAILURE_RETRY(ota_open(blockdev_filename->data, O_RDWR)));
+    params.fd.reset(TEMP_FAILURE_RETRY(ota_open(blockdev_filename->data.c_str(), O_RDWR)));
     if (params.fd == -1) {
-        fprintf(stderr, "open \"%s\" failed: %s\n", blockdev_filename->data, strerror(errno));
-        return StringValue(strdup(""));
+        fprintf(stderr, "open \"%s\" failed: %s\n", blockdev_filename->data.c_str(), strerror(errno));
+        return StringValue("");
     }
 
     if (params.canwrite) {
@@ -1471,24 +1467,21 @@
         int error = pthread_create(&params.thread, &attr, unzip_new_data, &params.nti);
         if (error != 0) {
             fprintf(stderr, "pthread_create failed: %s\n", strerror(error));
-            return StringValue(strdup(""));
+            return StringValue("");
         }
     }
 
-    // Copy all the lines in transfer_list_value into std::string for
-    // processing.
-    const std::string transfer_list(transfer_list_value->data, transfer_list_value->size);
-    std::vector<std::string> lines = android::base::Split(transfer_list, "\n");
+    std::vector<std::string> lines = android::base::Split(transfer_list_value->data, "\n");
     if (lines.size() < 2) {
         ErrorAbort(state, kArgsParsingFailure, "too few lines in the transfer list [%zd]\n",
                    lines.size());
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     // First line in transfer list is the version number
     if (!android::base::ParseInt(lines[0].c_str(), &params.version, 1, 4)) {
         fprintf(stderr, "unexpected transfer list version [%s]\n", lines[0].c_str());
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     fprintf(stderr, "blockimg version is %d\n", params.version);
@@ -1497,11 +1490,11 @@
     int total_blocks;
     if (!android::base::ParseInt(lines[1].c_str(), &total_blocks, 0)) {
         ErrorAbort(state, kArgsParsingFailure, "unexpected block count [%s]\n", lines[1].c_str());
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     if (total_blocks == 0) {
-        return StringValue(strdup("t"));
+        return StringValue("t");
     }
 
     size_t start = 2;
@@ -1509,7 +1502,7 @@
         if (lines.size() < 4) {
             ErrorAbort(state, kArgsParsingFailure, "too few lines in the transfer list [%zu]\n",
                        lines.size());
-            return StringValue(strdup(""));
+            return StringValue("");
         }
 
         // Third line is how many stash entries are needed simultaneously
@@ -1520,12 +1513,12 @@
         if (!android::base::ParseInt(lines[3].c_str(), &stash_max_blocks, 0)) {
             ErrorAbort(state, kArgsParsingFailure, "unexpected maximum stash blocks [%s]\n",
                        lines[3].c_str());
-            return StringValue(strdup(""));
+            return StringValue("");
         }
 
-        int res = CreateStash(state, stash_max_blocks, blockdev_filename->data, params.stashbase);
+        int res = CreateStash(state, stash_max_blocks, blockdev_filename->data.c_str(), params.stashbase);
         if (res == -1) {
-            return StringValue(strdup(""));
+            return StringValue("");
         }
 
         params.createdstash = res;
@@ -1589,7 +1582,7 @@
         fprintf(stderr, "stashed %zu blocks\n", params.stashed);
         fprintf(stderr, "max alloc needed was %zu\n", params.buffer.size());
 
-        const char* partition = strrchr(blockdev_filename->data, '/');
+        const char* partition = strrchr(blockdev_filename->data.c_str(), '/');
         if (partition != nullptr && *(partition+1) != 0) {
             fprintf(cmd_pipe, "log bytes_written_%s: %zu\n", partition + 1,
                     params.written * BLOCKSIZE);
@@ -1623,7 +1616,7 @@
         state->cause_code = failure_type;
     }
 
-    return StringValue(rc == 0 ? strdup("t") : strdup(""));
+    return StringValue(rc == 0 ? "t" : "");
 }
 
 // The transfer list is a text file containing commands to
@@ -1721,27 +1714,26 @@
     Value* ranges;
 
     if (ReadValueArgs(state, argv, 2, &blockdev_filename, &ranges) < 0) {
-        return StringValue(strdup(""));
+        return StringValue("");
     }
-    std::unique_ptr<Value, decltype(&FreeValue)> ranges_holder(ranges, FreeValue);
-    std::unique_ptr<Value, decltype(&FreeValue)> blockdev_filename_holder(blockdev_filename,
-            FreeValue);
+    std::unique_ptr<Value> ranges_holder(ranges);
+    std::unique_ptr<Value> blockdev_filename_holder(blockdev_filename);
 
     if (blockdev_filename->type != VAL_STRING) {
         ErrorAbort(state, kArgsParsingFailure, "blockdev_filename argument to %s must be string",
                    name);
-        return StringValue(strdup(""));
+        return StringValue("");
     }
     if (ranges->type != VAL_STRING) {
         ErrorAbort(state, kArgsParsingFailure, "ranges argument to %s must be string", name);
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
-    android::base::unique_fd fd(ota_open(blockdev_filename->data, O_RDWR));
+    android::base::unique_fd fd(ota_open(blockdev_filename->data.c_str(), O_RDWR));
     if (fd == -1) {
-        ErrorAbort(state, kFileOpenFailure, "open \"%s\" failed: %s", blockdev_filename->data,
-                   strerror(errno));
-        return StringValue(strdup(""));
+        ErrorAbort(state, kFileOpenFailure, "open \"%s\" failed: %s",
+                   blockdev_filename->data.c_str(), strerror(errno));
+        return StringValue("");
     }
 
     RangeSet rs;
@@ -1753,16 +1745,16 @@
     std::vector<uint8_t> buffer(BLOCKSIZE);
     for (size_t i = 0; i < rs.count; ++i) {
         if (!check_lseek(fd, (off64_t)rs.pos[i*2] * BLOCKSIZE, SEEK_SET)) {
-            ErrorAbort(state, kLseekFailure, "failed to seek %s: %s", blockdev_filename->data,
-                       strerror(errno));
-            return StringValue(strdup(""));
+            ErrorAbort(state, kLseekFailure, "failed to seek %s: %s",
+                       blockdev_filename->data.c_str(), strerror(errno));
+            return StringValue("");
         }
 
         for (size_t j = rs.pos[i*2]; j < rs.pos[i*2+1]; ++j) {
             if (read_all(fd, buffer, BLOCKSIZE) == -1) {
-                ErrorAbort(state, kFreadFailure, "failed to read %s: %s", blockdev_filename->data,
-                        strerror(errno));
-                return StringValue(strdup(""));
+                ErrorAbort(state, kFreadFailure, "failed to read %s: %s",
+                           blockdev_filename->data.c_str(), strerror(errno));
+                return StringValue("");
             }
 
             SHA1_Update(&ctx, buffer.data(), BLOCKSIZE);
@@ -1771,7 +1763,7 @@
     uint8_t digest[SHA_DIGEST_LENGTH];
     SHA1_Final(digest, &ctx);
 
-    return StringValue(strdup(print_sha1(digest).c_str()));
+    return StringValue(print_sha1(digest));
 }
 
 // This function checks if a device has been remounted R/W prior to an incremental
@@ -1785,27 +1777,27 @@
     if (ReadValueArgs(state, argv, 1, &arg_filename) < 0) {
         return nullptr;
     }
-    std::unique_ptr<Value, decltype(&FreeValue)> filename(arg_filename, FreeValue);
+    std::unique_ptr<Value> filename(arg_filename);
 
     if (filename->type != VAL_STRING) {
         ErrorAbort(state, kArgsParsingFailure, "filename argument to %s must be string", name);
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
-    android::base::unique_fd fd(ota_open(arg_filename->data, O_RDONLY));
+    android::base::unique_fd fd(ota_open(arg_filename->data.c_str(), O_RDONLY));
     if (fd == -1) {
-        ErrorAbort(state, kFileOpenFailure, "open \"%s\" failed: %s", arg_filename->data,
+        ErrorAbort(state, kFileOpenFailure, "open \"%s\" failed: %s", arg_filename->data.c_str(),
                    strerror(errno));
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     RangeSet blk0 {1 /*count*/, 1/*size*/, std::vector<size_t> {0, 1}/*position*/};
     std::vector<uint8_t> block0_buffer(BLOCKSIZE);
 
     if (ReadBlocks(blk0, block0_buffer, fd) == -1) {
-        ErrorAbort(state, kFreadFailure, "failed to read %s: %s", arg_filename->data,
+        ErrorAbort(state, kFreadFailure, "failed to read %s: %s", arg_filename->data.c_str(),
                 strerror(errno));
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     // https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout
@@ -1823,7 +1815,7 @@
         uiPrintf(state, "Last remount happened on %s", ctime(&mount_time));
     }
 
-    return StringValue(strdup("t"));
+    return StringValue("t");
 }
 
 
@@ -1835,40 +1827,40 @@
         return NULL;
     }
 
-    std::unique_ptr<Value, decltype(&FreeValue)> filename(arg_filename, FreeValue);
-    std::unique_ptr<Value, decltype(&FreeValue)> ranges(arg_ranges, FreeValue);
+    std::unique_ptr<Value> filename(arg_filename);
+    std::unique_ptr<Value> ranges(arg_ranges);
 
     if (filename->type != VAL_STRING) {
         ErrorAbort(state, kArgsParsingFailure, "filename argument to %s must be string", name);
-        return StringValue(strdup(""));
+        return StringValue("");
     }
     if (ranges->type != VAL_STRING) {
         ErrorAbort(state, kArgsParsingFailure, "ranges argument to %s must be string", name);
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     // Output notice to log when recover is attempted
-    fprintf(stderr, "%s image corrupted, attempting to recover...\n", filename->data);
+    fprintf(stderr, "%s image corrupted, attempting to recover...\n", filename->data.c_str());
 
     // When opened with O_RDWR, libfec rewrites corrupted blocks when they are read
-    fec::io fh(filename->data, O_RDWR);
+    fec::io fh(filename->data.c_str(), O_RDWR);
 
     if (!fh) {
-        ErrorAbort(state, kLibfecFailure, "fec_open \"%s\" failed: %s", filename->data,
+        ErrorAbort(state, kLibfecFailure, "fec_open \"%s\" failed: %s", filename->data.c_str(),
                    strerror(errno));
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     if (!fh.has_ecc() || !fh.has_verity()) {
         ErrorAbort(state, kLibfecFailure, "unable to use metadata to correct errors");
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     fec_status status;
 
     if (!fh.get_status(status)) {
         ErrorAbort(state, kLibfecFailure, "failed to read FEC status");
-        return StringValue(strdup(""));
+        return StringValue("");
     }
 
     RangeSet rs;
@@ -1885,8 +1877,8 @@
 
             if (fh.pread(buffer, BLOCKSIZE, (off64_t)j * BLOCKSIZE) != BLOCKSIZE) {
                 ErrorAbort(state, kLibfecFailure, "failed to recover %s (block %zu): %s",
-                           filename->data, j, strerror(errno));
-                return StringValue(strdup(""));
+                           filename->data.c_str(), j, strerror(errno));
+                return StringValue("");
             }
 
             // If we want to be able to recover from a situation where rewriting a corrected
@@ -1901,8 +1893,8 @@
             //     read and check if the errors field value has increased.
         }
     }
-    fprintf(stderr, "...%s image recovered successfully.\n", filename->data);
-    return StringValue(strdup("t"));
+    fprintf(stderr, "...%s image recovered successfully.\n", filename->data.c_str());
+    return StringValue("t");
 }
 
 void RegisterBlockImageFunctions() {
diff --git a/updater/install.cpp b/updater/install.cpp
index 3546968..d723b38 100644
--- a/updater/install.cpp
+++ b/updater/install.cpp
@@ -116,7 +116,7 @@
 //
 //    fs_type="ext4"   partition_type="EMMC"    location=device
 Value* MountFn(const char* name, State* state, int argc, Expr* argv[]) {
-    char* result = NULL;
+    char* result = nullptr;
     if (argc != 4 && argc != 5) {
         return ErrorAbort(state, kArgsParsingFailure, "%s() expects 4-5 args, got %d", name, argc);
     }
@@ -197,7 +197,7 @@
 
 // is_mounted(mount_point)
 Value* IsMountedFn(const char* name, State* state, int argc, Expr* argv[]) {
-    char* result = NULL;
+    char* result = nullptr;
     if (argc != 1) {
         return ErrorAbort(state, kArgsParsingFailure, "%s() expects 1 arg, got %d", name, argc);
     }
@@ -227,7 +227,7 @@
 
 
 Value* UnmountFn(const char* name, State* state, int argc, Expr* argv[]) {
-    char* result = NULL;
+    char* result = nullptr;
     if (argc != 1) {
         return ErrorAbort(state, kArgsParsingFailure, "%s() expects 1 arg, got %d", name, argc);
     }
@@ -284,7 +284,7 @@
 //    if fs_size > 0, that is the size to use
 //    if fs_size < 0, then reserve that many bytes at the end of the partition (not for "f2fs")
 Value* FormatFn(const char* name, State* state, int argc, Expr* argv[]) {
-    char* result = NULL;
+    char* result = nullptr;
     if (argc != 5) {
         return ErrorAbort(state, kArgsParsingFailure, "%s() expects 5 args, got %d", name, argc);
     }
@@ -358,7 +358,7 @@
 }
 
 Value* RenameFn(const char* name, State* state, int argc, Expr* argv[]) {
-    char* result = NULL;
+    char* result = nullptr;
     if (argc != 2) {
         return ErrorAbort(state, kArgsParsingFailure, "%s() expects 2 args, got %d", name, argc);
     }
@@ -397,15 +397,10 @@
 }
 
 Value* DeleteFn(const char* name, State* state, int argc, Expr* argv[]) {
-    char** paths = reinterpret_cast<char**>(malloc(argc * sizeof(char*)));
+    std::vector<std::string> paths;
     for (int i = 0; i < argc; ++i) {
-        paths[i] = Evaluate(state, argv[i]);
-        if (paths[i] == NULL) {
-            for (int j = 0; j < i; ++j) {
-                free(paths[j]);
-            }
-            free(paths);
-            return NULL;
+        if (!Evaluate(state, argv[i], &paths[i])) {
+            return nullptr;
         }
     }
 
@@ -413,15 +408,12 @@
 
     int success = 0;
     for (int i = 0; i < argc; ++i) {
-        if ((recursive ? dirUnlinkHierarchy(paths[i]) : unlink(paths[i])) == 0)
+        if ((recursive ? dirUnlinkHierarchy(paths[i].c_str()) : unlink(paths[i].c_str())) == 0) {
             ++success;
-        free(paths[i]);
+        }
     }
-    free(paths);
 
-    char buffer[10];
-    sprintf(buffer, "%d", success);
-    return StringValue(strdup(buffer));
+    return StringValue(android::base::StringPrintf("%d", success));
 }
 
 
@@ -483,7 +475,7 @@
                                       NULL, NULL, sehandle);
     free(zip_path);
     free(dest_path);
-    return StringValue(strdup(success ? "t" : ""));
+    return StringValue(success ? "t" : "");
 }
 
 
@@ -536,7 +528,7 @@
       done2:
         free(zip_path);
         free(dest_path);
-        return StringValue(strdup(success ? "t" : ""));
+        return StringValue(success ? "t" : "");
     } else {
         // The one-argument version returns the contents of the file
         // as the result.
@@ -544,10 +536,7 @@
         char* zip_path;
         if (ReadArgs(state, argv, 1, &zip_path) < 0) return NULL;
 
-        Value* v = reinterpret_cast<Value*>(malloc(sizeof(Value)));
-        v->type = VAL_BLOB;
-        v->size = -1;
-        v->data = NULL;
+        Value* v = new Value(VAL_INVALID, "");
 
         ZipArchive* za = ((UpdaterInfo*)(state->cookie))->package_zip;
         const ZipEntry* entry = mzFindZipEntry(za, zip_path);
@@ -556,23 +545,16 @@
             goto done1;
         }
 
-        v->size = mzGetZipEntryUncompLen(entry);
-        v->data = reinterpret_cast<char*>(malloc(v->size));
-        if (v->data == NULL) {
-            printf("%s: failed to allocate %zd bytes for %s\n",
-                    name, v->size, zip_path);
-            goto done1;
-        }
-
+        v->data.resize(mzGetZipEntryUncompLen(entry));
         success = mzExtractZipEntryToBuffer(za, entry,
-                                            (unsigned char *)v->data);
+                reinterpret_cast<unsigned char *>(&v->data[0]));
 
       done1:
         free(zip_path);
         if (!success) {
-            free(v->data);
-            v->data = NULL;
-            v->size = -1;
+            v->data.clear();
+        } else {
+            v->type = VAL_BLOB;
         }
         return v;
     }
@@ -584,13 +566,13 @@
     if (argc == 0) {
         return ErrorAbort(state, kArgsParsingFailure, "%s() expects 1+ args, got %d", name, argc);
     }
-    char* target;
-    target = Evaluate(state, argv[0]);
-    if (target == NULL) return NULL;
+    std::string target;
+    if (!Evaluate(state, argv[0], &target)) {
+        return nullptr;
+    }
 
     char** srcs = ReadVarArgs(state, argc-1, argv+1);
     if (srcs == NULL) {
-        free(target);
         return NULL;
     }
 
@@ -606,12 +588,12 @@
         }
         if (make_parents(srcs[i])) {
             printf("%s: failed to symlink %s to %s: making parents failed\n",
-                    name, srcs[i], target);
+                    name, srcs[i], target.c_str());
             ++bad;
         }
-        if (symlink(target, srcs[i]) < 0) {
+        if (symlink(target.c_str(), srcs[i]) < 0) {
             printf("%s: failed to symlink %s to %s: %s\n",
-                    name, srcs[i], target, strerror(errno));
+                    name, srcs[i], target.c_str(), strerror(errno));
             ++bad;
         }
         free(srcs[i]);
@@ -620,7 +602,7 @@
     if (bad) {
         return ErrorAbort(state, kSymlinkFailure, "%s: some symlinks failed", name);
     }
-    return StringValue(strdup(""));
+    return StringValue("");
 }
 
 struct perm_parsed_args {
@@ -883,20 +865,20 @@
         return ErrorAbort(state, kSetMetadataFailure, "%s: some changes failed", name);
     }
 
-    return StringValue(strdup(""));
+    return StringValue("");
 }
 
 Value* GetPropFn(const char* name, State* state, int argc, Expr* argv[]) {
     if (argc != 1) {
         return ErrorAbort(state, kArgsParsingFailure, "%s() expects 1 arg, got %d", name, argc);
     }
-    char* key = Evaluate(state, argv[0]);
-    if (key == NULL) return NULL;
-
+    std::string key;
+    if (!Evaluate(state, argv[0], &key)) {
+        return nullptr;
+    }
     std::string value = android::base::GetProperty(key, "");
-    free(key);
 
-    return StringValue(strdup(value.c_str()));
+    return StringValue(value);
 }
 
 
@@ -1015,7 +997,7 @@
         return nullptr;
     }
 
-    return StringValue(strdup(CacheSizeCheck(bytes) ? "" : "t"));
+    return StringValue(CacheSizeCheck(bytes) ? "" : "t");
 }
 
 // apply_patch(file, size, init_sha1, tgt_sha1, patch)
@@ -1047,17 +1029,16 @@
     }
 
     int patchcount = (argc-4) / 2;
-    std::unique_ptr<Value*, decltype(&free)> arg_values(ReadValueVarArgs(state, argc-4, argv+4),
-                                                        free);
+    std::unique_ptr<Value*> arg_values(ReadValueVarArgs(state, argc-4, argv+4));
     if (!arg_values) {
         return nullptr;
     }
-    std::vector<std::unique_ptr<Value, decltype(&FreeValue)>> patch_shas;
-    std::vector<std::unique_ptr<Value, decltype(&FreeValue)>> patches;
+    std::vector<std::unique_ptr<Value>> patch_shas;
+    std::vector<std::unique_ptr<Value>> patches;
     // Protect values by unique_ptrs first to get rid of memory leak.
     for (int i = 0; i < patchcount * 2; i += 2) {
-        patch_shas.emplace_back(arg_values.get()[i], FreeValue);
-        patches.emplace_back(arg_values.get()[i+1], FreeValue);
+        patch_shas.emplace_back(arg_values.get()[i]);
+        patches.emplace_back(arg_values.get()[i+1]);
     }
 
     for (int i = 0; i < patchcount; ++i) {
@@ -1071,7 +1052,7 @@
         }
     }
 
-    std::vector<char*> patch_sha_str;
+    std::vector<std::string> patch_sha_str;
     std::vector<Value*> patch_ptrs;
     for (int i = 0; i < patchcount; ++i) {
         patch_sha_str.push_back(patch_shas[i]->data);
@@ -1080,9 +1061,9 @@
 
     int result = applypatch(source_filename, target_filename,
                             target_sha1, target_size,
-                            patchcount, patch_sha_str.data(), patch_ptrs.data(), NULL);
+                            patch_sha_str, patch_ptrs.data(), NULL);
 
-    return StringValue(strdup(result == 0 ? "t" : ""));
+    return StringValue(result == 0 ? "t" : "");
 }
 
 // apply_patch_check(file, [sha1_1, ...])
@@ -1095,21 +1076,17 @@
 
     char* filename;
     if (ReadArgs(state, argv, 1, &filename) < 0) {
-        return NULL;
+        return nullptr;
     }
 
-    int patchcount = argc-1;
-    char** sha1s = ReadVarArgs(state, argc-1, argv+1);
-
-    int result = applypatch_check(filename, patchcount, sha1s);
-
-    int i;
-    for (i = 0; i < patchcount; ++i) {
-        free(sha1s[i]);
+    std::vector<std::string> sha1s;
+    if (!ReadArgs(state, argc-1, argv+1, &sha1s)) {
+        return nullptr;
     }
-    free(sha1s);
 
-    return StringValue(strdup(result == 0 ? "t" : ""));
+    int result = applypatch_check(filename, sha1s);
+
+    return StringValue(result == 0 ? "t" : "");
 }
 
 // This is the updater side handler for ui_print() in edify script. Contents
@@ -1129,7 +1106,7 @@
 
     buffer += "\n";
     uiPrint(state, buffer);
-    return StringValue(strdup(buffer.c_str()));
+    return StringValue(buffer);
 }
 
 Value* WipeCacheFn(const char* name, State* state, int argc, Expr* argv[]) {
@@ -1137,7 +1114,7 @@
         return ErrorAbort(state, kArgsParsingFailure, "%s() expects no args, got %d", name, argc);
     }
     fprintf(((UpdaterInfo*)(state->cookie))->cmd_pipe, "wipe_cache\n");
-    return StringValue(strdup("t"));
+    return StringValue("t");
 }
 
 Value* RunProgramFn(const char* name, State* state, int argc, Expr* argv[]) {
@@ -1180,10 +1157,7 @@
     free(args);
     free(args2);
 
-    char buffer[20];
-    sprintf(buffer, "%d", status);
-
-    return StringValue(strdup(buffer));
+    return StringValue(android::base::StringPrintf("%d", status));
 }
 
 // sha1_check(data)
@@ -1199,32 +1173,32 @@
         return ErrorAbort(state, kArgsParsingFailure, "%s() expects at least 1 arg", name);
     }
 
-    std::unique_ptr<Value*, decltype(&free)> arg_values(ReadValueVarArgs(state, argc, argv), free);
+    std::unique_ptr<Value*> arg_values(ReadValueVarArgs(state, argc, argv));
     if (arg_values == nullptr) {
         return nullptr;
     }
-    std::vector<std::unique_ptr<Value, decltype(&FreeValue)>> args;
+    std::vector<std::unique_ptr<Value>> args;
     for (int i = 0; i < argc; ++i) {
-        args.emplace_back(arg_values.get()[i], FreeValue);
+        args.emplace_back(arg_values.get()[i]);
     }
 
-    if (args[0]->size < 0) {
-        return StringValue(strdup(""));
+    if (args[0]->type == VAL_INVALID) {
+        return StringValue("");
     }
     uint8_t digest[SHA_DIGEST_LENGTH];
-    SHA1(reinterpret_cast<uint8_t*>(args[0]->data), args[0]->size, digest);
+    SHA1(reinterpret_cast<const uint8_t*>(args[0]->data.c_str()), args[0]->data.size(), digest);
 
     if (argc == 1) {
-        return StringValue(strdup(print_sha1(digest).c_str()));
+        return StringValue(print_sha1(digest));
     }
 
     for (int i = 1; i < argc; ++i) {
         uint8_t arg_digest[SHA_DIGEST_LENGTH];
         if (args[i]->type != VAL_STRING) {
             printf("%s(): arg %d is not a string; skipping", name, i);
-        } else if (ParseSha1(args[i]->data, arg_digest) != 0) {
+        } else if (ParseSha1(args[i]->data.c_str(), arg_digest) != 0) {
             // Warn about bad args and skip them.
-            printf("%s(): error parsing \"%s\" as sha-1; skipping", name, args[i]->data);
+            printf("%s(): error parsing \"%s\" as sha-1; skipping", name, args[i]->data.c_str());
         } else if (memcmp(digest, arg_digest, SHA_DIGEST_LENGTH) == 0) {
             // Found a match.
             return args[i].release();
@@ -1232,7 +1206,7 @@
     }
 
     // Didn't match any of the hex strings; return false.
-    return StringValue(strdup(""));
+    return StringValue("");
 }
 
 // Read a local file and return its contents (the Value* returned
@@ -1244,21 +1218,12 @@
     char* filename;
     if (ReadArgs(state, argv, 1, &filename) < 0) return NULL;
 
-    Value* v = static_cast<Value*>(malloc(sizeof(Value)));
-    if (v == nullptr) {
-        return nullptr;
-    }
-    v->type = VAL_BLOB;
-    v->size = -1;
-    v->data = nullptr;
+    Value* v = new Value(VAL_INVALID, "");
 
     FileContents fc;
     if (LoadFileContents(filename, &fc) == 0) {
-        v->data = static_cast<char*>(malloc(fc.data.size()));
-        if (v->data != nullptr) {
-            memcpy(v->data, fc.data.data(), fc.data.size());
-            v->size = fc.data.size();
-        }
+        v->type = VAL_BLOB;
+        v->data = std::string(fc.data.begin(), fc.data.end());
     }
     free(filename);
     return v;
@@ -1326,16 +1291,19 @@
     // package installation.
     FILE* f = ota_fopen(filename, "r+b");
     fseek(f, offsetof(struct bootloader_message, stage), SEEK_SET);
-    int to_write = strlen(stagestr)+1;
-    int max_size = sizeof(((struct bootloader_message*)0)->stage);
+    size_t to_write = strlen(stagestr) + 1;
+    size_t max_size = sizeof(((struct bootloader_message*)0)->stage);
     if (to_write > max_size) {
         to_write = max_size;
-        stagestr[max_size-1] = 0;
+        stagestr[max_size - 1] = 0;
     }
-    ota_fwrite(stagestr, to_write, 1, f);
+    size_t status = ota_fwrite(stagestr, to_write, 1, f);
     ota_fclose(f);
 
     free(stagestr);
+    if (status != to_write) {
+        return StringValue("");
+    }
     return StringValue(filename);
 }
 
@@ -1352,11 +1320,14 @@
     char buffer[sizeof(((struct bootloader_message*)0)->stage)];
     FILE* f = ota_fopen(filename, "rb");
     fseek(f, offsetof(struct bootloader_message, stage), SEEK_SET);
-    ota_fread(buffer, sizeof(buffer), 1, f);
+    size_t status = ota_fread(buffer, sizeof(buffer), 1, f);
     ota_fclose(f);
-    buffer[sizeof(buffer)-1] = '\0';
+    if (status != sizeof(buffer)) {
+        return StringValue("");
+    }
 
-    return StringValue(strdup(buffer));
+    buffer[sizeof(buffer)-1] = '\0';
+    return StringValue(buffer);
 }
 
 Value* WipeBlockDeviceFn(const char* name, State* state, int argc, Expr* argv[]) {
@@ -1378,7 +1349,7 @@
 
     ota_close(fd);
 
-    return StringValue(strdup(success ? "t" : ""));
+    return StringValue(success ? "t" : "");
 }
 
 Value* EnableRebootFn(const char* name, State* state, int argc, Expr* argv[]) {
@@ -1387,7 +1358,7 @@
     }
     UpdaterInfo* ui = (UpdaterInfo*)(state->cookie);
     fprintf(ui->cmd_pipe, "enable_reboot\n");
-    return StringValue(strdup("t"));
+    return StringValue("t");
 }
 
 Value* Tune2FsFn(const char* name, State* state, int argc, Expr* argv[]) {
@@ -1418,7 +1389,7 @@
         return ErrorAbort(state, kTune2FsFailure, "%s() returned error code %d",
                           name, result);
     }
-    return StringValue(strdup("t"));
+    return StringValue("t");
 }
 
 void RegisterInstallFunctions() {
diff --git a/updater/updater.cpp b/updater/updater.cpp
index c752ebb..47696b8 100644
--- a/updater/updater.cpp
+++ b/updater/updater.cpp
@@ -151,13 +151,14 @@
         }
     }
 
-    char* result = Evaluate(&state, root);
+    std::string result;
+    bool status = Evaluate(&state, root, &result);
 
     if (have_eio_error) {
         fprintf(cmd_pipe, "retry_update\n");
     }
 
-    if (result == NULL) {
+    if (!status) {
         if (state.errmsg.empty()) {
             printf("script aborted (no error message)\n");
             fprintf(cmd_pipe, "ui_print script aborted (no error message)\n");
@@ -188,8 +189,7 @@
 
         return 7;
     } else {
-        fprintf(cmd_pipe, "ui_print script succeeded: result was [%s]\n", result);
-        free(result);
+        fprintf(cmd_pipe, "ui_print script succeeded: result was [%s]\n", result.c_str());
     }
 
     if (updater_info.package_zip) {