[PATCH] D83134: [asan] Disable fast unwinder on arm-linux-gnueabi with thumb

[Adhemerval Zanella via Phabricator via llvm-commits]

zatrazz added a comment.

In D83134#2225283 <https://reviews.llvm.org/D83134#2225283>, @vitalybuka wrote:

> Is  this patch still needed?

It is to at least make the unwinder not triggering testcase failures on some arm-linux-gnu distros [1]. The fast-unwinder on ARM does not work correctly when unwinding any thumb code built code by gcc, so it would potentially fail on some scenarios (for instance if system libraries or gcc-build ones call malloc). It should be mitigated by 'fast_unwind_on_check=0' and/or 'fast_unwind_on_malloc=0'.

This issues has come up multiple times and compiler-rt developers either state that Android (which is now built with clang) and clang built objects works and that _Unwind based unwind is too slow to be usable. I think we should at least document this issues with gcc built with thumb support and the possible mitigations and tradeoffs.

[1] http://lab.llvm.org:8011/builders/clang-cmake-armv7-full/builds/11561


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