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08d30c602b
This fixes unwinding in boundary cases on ARM with SEH. In the case of ARM/Thumb, disp->ControlPc points at the following instruction, with the thumb bit set. Thus by decrementing 1, it still points at the next instruction. To achieve the desired effect of pointing at the previous instruction, one first has to strip out the thumb bit, then do the decrement by 1 to reach the previous instruction. When libcxxabi looks for call site ranges, it already does `_Unwind_GetIP(context) - 1` (in `scan_eh_tab` in libcxxabi/src/cxa_personality.cpp), so we shouldn't do the corresponding `- 1` multiple times. In the case of libcxxabi on Thumb, `funcStart` (still in `scan_eh_tab`) may have the thumb bit set. If the program counter address is decremented both in libunwind (first removing the thumb bit, then decremented), and then libcxxabi decrements it further, and compares with a `funcStart` with the thumb bit set, it could point to one byte before the start of the call site. Thus: This modification makes libunwind with SEH work with libcxxabi on Thumb, in settings where libunwind and libcxxabi worked fine with Dwarf before. For existing cases with libunwind with SEH (on x86_64 and aarch64), this modification doesn't break any of my testcases. Differential Revision: https://reviews.llvm.org/D126869 |
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