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Merge "Simplify the malloc_debug unwind."

This commit is contained in:
Treehugger Robot 2022-11-11 22:05:24 +00:00 committed by Gerrit Code Review
parent 5c41b06529 eeaf9edb0b
commit cf74c0c020
1 changed files with 15 additions and 32 deletions
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47
libc/malloc_debug/backtrace.cpp
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@ -83,41 +83,24 @@ static _Unwind_Reason_Code trace_function(__unwind_context* context, void* arg)
uintptr_t ip = _Unwind_GetIP(context);
// The instruction pointer is pointing at the instruction after the return
// call on all architectures.
// Modify the pc to point at the real function.
if (ip != 0) {
#if defined(__arm__)
// If the ip is suspiciously low, do nothing to avoid a segfault trying
// to access this memory.
if (ip >= 4096) {
// Check bits [15:11] of the first halfword assuming the instruction
// is 32 bits long. If the bits are any of these values, then our
// assumption was correct:
// b11101
// b11110
// b11111
// Otherwise, this is a 16 bit instruction.
uint16_t value = (*reinterpret_cast<uint16_t*>(ip - 2)) >> 11;
if (value == 0x1f || value == 0x1e || value == 0x1d) {
ip -= 4;
} else {
ip -= 2;
}
}
#elif defined(__aarch64__)
// All instructions are 4 bytes long, skip back one instruction.
ip -= 4;
// `ip` is the address of the instruction *after* the call site in
// `context`, so we want to back up by one instruction. This is hard for
// every architecture except arm64, so we just make sure we're *inside*
// that instruction, not necessarily at the start of it. (If the value
// is too low to be valid, we just leave it alone.)
if (ip >= 4096) {
#if defined(__aarch64__)
ip -= 4; // Exactly.
#elif defined(__arm__) || defined(__riscv)
ip -= 2; // At least.
#elif defined(__i386__) || defined(__x86_64__)
// It's difficult to decode exactly where the previous instruction is,
// so subtract 1 to estimate where the instruction lives.
ip--;
ip -= 1; // At least.
#endif
}
// Do not record the frames that fall in our own shared library.
if (g_current_code_map && (ip >= g_current_code_map->start) && ip < g_current_code_map->end) {
return _URC_NO_REASON;
}
// Do not record the frames that fall in our own shared library.
if (g_current_code_map && (ip >= g_current_code_map->start) && ip < g_current_code_map->end) {
return _URC_NO_REASON;
}
state->frames[state->cur_frame++] = ip;