https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119801
--- Comment #3 from GCC Commits ---
The master branch has been updated by Jakub Jelinek :
https://gcc.gnu.org/g:07565115371ea5cdf9e6d75ea3777540d1d31bda
commit r15-9481-g07565115371ea5cdf9e6d75ea3777540d1d31bda
Author: Jakub Jelinek
Date: Tue Apr 15 14:09:55 2025 +0200
tailc: Fix up musttail calls vs. -fsanitize=thread [PR119801]
Calls with musttail attribute don't really work with -fsanitize=thread in
GCC. The problem is that TSan instrumentation adds
__tsan_func_entry (__builtin_return_address (0));
calls at the start of each instrumented function and
__tsan_func_exit ();
call at the end of those and the latter stands in a way of normal tail
calls
as well as musttail tail calls.
Looking at what LLVM does, for normal calls -fsanitize=thread also prevents
tail calls like in GCC (well, the __tsan_func_exit () call itself can be
tail called in GCC (and from what I see not in clang)).
But for [[clang::musttail]] calls it arranges to move the
__tsan_func_exit () before the musttail call instead of after it.
The following patch handles it similarly. If we for -fsanitize=thread
instrumented function detect __builtin_tsan_func_exit () call, we process
it normally (so that the call can be tail called in function returning
void)
but set a flag that the builtin has been seen (only for cfun->has_musttail
in the diag_musttail phase). And then let tree_optimize_tail_calls_1
call find_tail_calls again in a new mode where the __tsan_func_exit ()
call is ignored and so we are able to find calls before it, but only
accept that if the call before it is actually a musttail. For C++ it needs
to verify that EH cleanup if any also has the __tsan_func_exit () call
and if all goes well, the musttail call is registered for tailcalling with
a flag that it has __tsan_func_exit () after it and when optimizing that
we emit __tsan_func_exit (); call before the musttail tail call (or
musttail
tail recursion).
2025-04-15 Jakub Jelinek
PR sanitizer/119801
* sanitizer.def (BUILT_IN_TSAN_FUNC_EXIT): Use BT_FN_VOID rather
than BT_FN_VOID_PTR.
* tree-tailcall.cc: Include attribs.h and asan.h.
(struct tailcall): Add has_tsan_func_exit member.
(empty_eh_cleanup): Add eh_has_tsan_func_exit argument, set what
it points to to 1 if there is exactly one __tsan_func_exit call
and ignore that call otherwise. Adjust recursive call.
(find_tail_calls): Add RETRY_TSAN_FUNC_EXIT argument, pass it
to recursive calls. When seeing __tsan_func_exit call with
RETRY_TSAN_FUNC_EXIT 0, set it to -1. If RETRY_TSAN_FUNC_EXIT
is 1, initially ignore __tsan_func_exit calls. Adjust
empty_eh_cleanup caller. When looking through stmts after the
call,
ignore exactly one __tsan_func_exit call but remember it in
t->has_tsan_func_exit. Diagnose if EH cleanups didn't have
__tsan_func_exit and normal path did or vice versa.
(optimize_tail_call): Emit __tsan_func_exit before the tail call
or tail recursion.
(tree_optimize_tail_calls_1): Adjust find_tail_calls callers. If
find_tail_calls changes retry_tsan_func_exit to -1, set it to 1
and call it again with otherwise the same arguments.
* c-c++-common/tsan/pr119801.c: New test.
