Get a basic modification of dex file working

This allows the modification of a single classes methods through
transformation. One must ensure that the provided dex file only
contains one function and does not add or remove any methods or fields
and does not change the inheritance hierarchy in any way. The provided
dex file must verify and there must be no frames of the old code
present on any thread. These constraints are not checked or verified.
Breaking them might cause undefined behavior in all parts of the
runtime. Code that has been inlined in any way might not be replaced.
This feature is extremely experimental.

Bug: 31455788
Test: ./test/run-test --host 902-hello-transformation

Change-Id: I35133d24f6cdafdd2af9dc9863e15ba8493fc50e

1 files changed, 71 insertions, 0 deletions

diff --git a/runtime/utils.cc b/runtime/utils.cc
index 6f10aaacaf..b52e2f2bca 100644
--- a/runtime/utils.cc
+++ b/runtime/utils.cc
@@ -52,6 +52,77 @@
 
 namespace art {
 
+static const uint8_t kBase64Map[256] = {
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255,  62, 255, 255, 255,  63,
+  52,  53,  54,  55,  56,  57,  58,  59,  60,  61, 255, 255,
+  255, 254, 255, 255, 255,   0,   1,   2,   3,   4,   5,   6,
+    7,   8,   9,  10,  11,  12,  13,  14,  15,  16,  17,  18,  // NOLINT
+   19,  20,  21,  22,  23,  24,  25, 255, 255, 255, 255, 255,  // NOLINT
+  255,  26,  27,  28,  29,  30,  31,  32,  33,  34,  35,  36,
+   37,  38,  39,  40,  41,  42,  43,  44,  45,  46,  47,  48,  // NOLINT
+   49,  50,  51, 255, 255, 255, 255, 255, 255, 255, 255, 255,  // NOLINT
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
+  255, 255, 255, 255
+};
+
+uint8_t* DecodeBase64(const char* src, size_t* dst_size) {
+  std::vector<uint8_t> tmp;
+  uint32_t t = 0, y = 0;
+  int g = 3;
+  for (size_t i = 0; src[i] != '\0'; ++i) {
+    uint8_t c = kBase64Map[src[i] & 0xFF];
+    if (c == 255) continue;
+    // the final = symbols are read and used to trim the remaining bytes
+    if (c == 254) {
+      c = 0;
+      // prevent g < 0 which would potentially allow an overflow later
+      if (--g < 0) {
+        *dst_size = 0;
+        return nullptr;
+      }
+    } else if (g != 3) {
+      // we only allow = to be at the end
+      *dst_size = 0;
+      return nullptr;
+    }
+    t = (t << 6) | c;
+    if (++y == 4) {
+      tmp.push_back((t >> 16) & 255);
+      if (g > 1) {
+        tmp.push_back((t >> 8) & 255);
+      }
+      if (g > 2) {
+        tmp.push_back(t & 255);
+      }
+      y = t = 0;
+    }
+  }
+  if (y != 0) {
+    *dst_size = 0;
+    return nullptr;
+  }
+  std::unique_ptr<uint8_t[]> dst(new uint8_t[tmp.size()]);
+  if (dst_size != nullptr) {
+    *dst_size = tmp.size();
+  } else {
+    *dst_size = 0;
+  }
+  std::copy(tmp.begin(), tmp.end(), dst.get());
+  return dst.release();
+}
+
 pid_t GetTid() {
 #if defined(__APPLE__)
   uint64_t owner;