[libcxx-commits] [PATCH] D114818: [libunwind] Fix unwind_leaffunction test

[Leonard Chan via Phabricator via libcxx-commits]

leonardchan added a comment.

> Interesting it works on Ubuntu20.04/Aarch64, I compile the code with ToT clang or gcc-10.
> could you share an objdump of main?



  00000000002134ac <_Z18crashing_leaf_funcv>:
  ; _Z18crashing_leaf_funcv():
    2134ac: 20 00 20 d4   brk     #0x1
    2134b0: c0 03 5f d6   ret
  
  00000000002134b4 <main>:
  ; main():
    2134b4: ff c3 00 d1   sub     sp, sp, #48
    2134b8: fd 7b 02 a9   stp     x29, x30, [sp, #32]
    2134bc: fd 83 00 91   add     x29, sp, #32
    2134c0: bf c3 1f b8   stur    wzr, [x29, #-4]
    2134c4: a0 83 1f b8   stur    w0, [x29, #-8]
    2134c8: e1 0b 00 f9   str     x1, [sp, #16]
    2134cc: a0 00 80 52   mov     w0, #5
    2134d0: 01 00 00 90   adrp    x1, 0x213000 <main+0x1c>
    2134d4: 21 80 11 91   add     x1, x1, #1120
    2134d8: e1 07 00 f9   str     x1, [sp, #8]
    2134dc: f9 0f 00 94   bl      0x2174c0 <signal at plt>
    2134e0: e1 07 40 f9   ldr     x1, [sp, #8]
    2134e4: 80 00 80 52   mov     w0, #4
    2134e8: f6 0f 00 94   bl      0x2174c0 <signal at plt>
    2134ec: f0 ff ff 97   bl      0x2134ac <_Z18crashing_leaf_funcv>
    2134f0: 20 00 80 12   mov     w0, #-2
    2134f4: fd 7b 42 a9   ldp     x29, x30, [sp, #32]
    2134f8: ff c3 00 91   add     sp, sp, #48
    2134fc: c0 03 5f d6   ret



>>   void func() {
>>    crashing_leaf_func();
>>   }
>>
>> Then the test passes, but it looks like unwinder skips past func (it jumps from _Z18crashing_leaf_funcv to main). Perhaps all this hints at an underlying issue in libunwind?
>
> here `func` will tail call `crashing_leaf_func` so it is expected to not be visible during the unwind because the return address will point to somewhere in main.

Would this still be expected if I added another layer of function calls? That is:

  void crashing_leaf_func() {
    __builtin_trap();
  }
  
  void func() {
    crashing_leaf_func();
  }
  
  void func2() {
    func();
  }
  
  int main() {
    signal(SIGTRAP, signal_handler);
    signal(SIGILL, signal_handler);
    func2();
    return 2;
  }

In this example, I hit `crashing_leaf_func`, `func2`, and `main`, missing only `func`.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D114818/new/

https://reviews.llvm.org/D114818