Fix CodePatcher test backing storage

Summary:
Use aligned 8-byte storage for the patchpoint and verify patching preserves surrounding memory.

The free-threaded x86 implementation currently accesses a full aligned 8-byte word, even for shorter patches. I’ll investigate separately whether this restriction causes issues for other callers. This change only updates the test to match the current implementation.

AddressSanitizer: stack-buffer-overflow (/data/users/alperyoney/fbsource3/buck-out/v2/art/fbcode/99380b56af1146f2/cinderx/RuntimeTests/__RuntimeTests_3.14t__/RuntimeTests_3.14t+0x33f081a) (BuildId: 1ff8500db347146bd67e824898b0aca4aff0c28e) in __asan_memcpy
Shadow bytes around the buggy address:
  0x7b0b76b89d80: f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
  0x7b0b76b89e00: f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
  0x7b0b76b89e80: f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
  0x7b0b76b89f00: f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
  0x7b0b76b89f80: f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
=>0x7b0b76b8a000: f1 f1 f1 f1 02 f2[02]f2 02 f2 02 f2 00 00 00 f2
  0x7b0b76b8a080: f2 f2 f2 f2 f8 f8 f2 f2 f8 f2 f8 f2 f2 f2 f8 f2
  0x7b0b76b8a100: f2 f2 00 00 f2 f2 f8 f8 f8 f8 f2 f2 f2 f2 f8 f8
  0x7b0b76b8a180: f2 f2 f8 f2 f8 f2 f2 f2 f8 f2 f2 f2 00 00 f2 f2
  0x7b0b76b8a200: f8 f8 f8 f8 f2 f2 f2 f2 00 00 f2 f2 f8 f8 f2 f2
  0x7b0b76b8a280: f8 f2 f8 f2 f2 f2 f8 f2 f2 f2 00 00 f2 f2 f8 f8
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==1751566==ABORTING
```

Reviewed By: DinoV

Differential Revision: D114631917

fbshipit-source-id: 489c4666fc1140ffd8ef9076a3ce5b44f03d2c34

Author: yoney

cinderx/RuntimeTests/deopt_patcher_test.cpp

@@ -75,35 +75,44 @@ class MyDeoptPatcher : public JumpPatcher {
 };
 
 TEST_F(CodePatcherTest, CodePatch) {
-  // Intentionally leaving these together to catch accidental stack scribbling.
-  uint16_t x = 123;
-  uint16_t y = 456;
-  uint16_t z = 789;
-
+  struct PatchpointMemory {
+    uint64_t before;
+    alignas(8) std::array<uint8_t, 8> patchpoint;
+    uint64_t after;
+  };
+
+  const std::array<uint8_t, 8> unpatched{
+      0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08};
+  const std::array<uint8_t, 8> patched{
+      0xef, 0xbe, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08};
+
+  constexpr uint64_t kBefore = 0x123456789abcdef0;
+  constexpr uint64_t kAfter = 0xfedcba9876543210;
+  PatchpointMemory memory{kBefore, unpatched, kAfter};
   std::array<uint8_t, 2> bytes{0xef, 0xbe};
 
   CodePatcher patcher;
   EXPECT_FALSE(patcher.isLinked());
   EXPECT_FALSE(patcher.isPatched());
 
-  patcher.link(reinterpret_cast<uintptr_t>(&y), bytes);
+  patcher.link(reinterpret_cast<uintptr_t>(memory.patchpoint.data()), bytes);
   EXPECT_TRUE(patcher.isLinked());
   EXPECT_FALSE(patcher.isPatched());
-  EXPECT_EQ(x, 123);
-  EXPECT_EQ(y, 456);
-  EXPECT_EQ(z, 789);
+  EXPECT_EQ(memory.before, kBefore);
+  EXPECT_EQ(memory.patchpoint, unpatched);
+  EXPECT_EQ(memory.after, kAfter);
 
   patcher.patch();
   EXPECT_TRUE(patcher.isPatched());
-  EXPECT_EQ(x, 123);
-  EXPECT_EQ(y, 0xbeef);
-  EXPECT_EQ(z, 789);
+  EXPECT_EQ(memory.before, kBefore);
+  EXPECT_EQ(memory.patchpoint, patched);
+  EXPECT_EQ(memory.after, kAfter);
 
   patcher.unpatch();
   EXPECT_FALSE(patcher.isPatched());
-  EXPECT_EQ(x, 123);
-  EXPECT_EQ(y, 456);
-  EXPECT_EQ(z, 789);
+  EXPECT_EQ(memory.before, kBefore);
+  EXPECT_EQ(memory.patchpoint, unpatched);
+  EXPECT_EQ(memory.after, kAfter);
 }
 
 TEST_F(CodePatcherTest, DeoptPatch) {