[libc] [compiler-rt] [scudo] bus error in `LlvmLibcFileTest.WriteOnly` under release build

[SchrodingerZhu]

In full build mode, https://libc.llvm.org/full_host_build.html:

LlvmLibcFileTest.WriteOnly test ran into a bus error shortly after starting. The GDB screenshot is attached.

Compiled with clang++-17. The CPU is TH1520 (RV64GCV0P7, compiled under generic settings).

[SchrodingerZhu]

With debug info:

[SchrodingerZhu]

I looked into this a bit, I think the problem comes from scudo.

StringFile *new_string_file(char *buffer, size_t buflen, int bufmode,
                            bool owned, const char *mode) {
  LIBC_NAMESPACE::AllocChecker ac;
  // We will just assume the allocation succeeds. We cannot test anything
  // otherwise.
  return new (ac) StringFile(buffer, buflen, bufmode, owned,
                             LIBC_NAMESPACE::File::mode_flags(mode));
}

TEST(LlvmLibcFileTest, WriteOnly) {
  const char data[] = "hello, file";
  constexpr size_t FILE_BUFFER_SIZE = sizeof(data) * 3 / 2;
  char file_buffer[FILE_BUFFER_SIZE];
  StringFile *f =
      new_string_file(file_buffer, FILE_BUFFER_SIZE, _IOFBF, false, "w");

  static_assert(alignof(StringFile) <= alignof(void *), "truth");
  ASSERT_EQ(reinterpret_cast<size_t>(f) % alignof(StringFile), 0ul);     // <= this line is misaligned 
  // .....
}

[SchrodingerZhu]

@llvm/pr-subscribers-compiler-rt-sanitizer PTAL