GCC introduced `__attribute__((mode(unwind_word)))` to work around
Cell Broadband Engine SPU (which was removed from GCC in 2019-09),
which is irrelevant to hwasan.
_Unwind_GetGR/_Unwind_GetCFA from llvm-project/libunwind don't use unwind_word.
Using _Unwind_Word can lead to build failures if libunwind's unwind.h is
preferred over unwind.h in the Clang resource directory (e.g. built with GCC).
One problem with untagging memory in landing pads is that it only works
correctly if the function that catches the exception is instrumented.
If the function is uninstrumented, we have no opportunity to untag the
memory.
To address this, replace landing pad instrumentation with personality function
wrapping. Each function with an instrumented stack has its personality function
replaced with a wrapper provided by the runtime. Functions that did not have
a personality function to begin with also get wrappers if they may be unwound
past. As the unwinder calls personality functions during stack unwinding,
the original personality function is called and the function's stack frame is
untagged by the wrapper if the personality function instructs the unwinder
to keep unwinding. If unwinding stops at a landing pad, the function is
still responsible for untagging its stack frame if it resumes unwinding.
The old landing pad mechanism is preserved for compatibility with old runtimes.
Differential Revision: https://reviews.llvm.org/D66377
llvm-svn: 369721
Fangrui Song