https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120608
--- Comment #12 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:b9523a935aaa28ffae9118e199a2f43a8a98e27e commit r16-1625-gb9523a935aaa28ffae9118e199a2f43a8a98e27e Author: Jakub Jelinek <ja...@redhat.com> Date: Mon Jun 23 15:58:55 2025 +0200 expand: Allow musttail tail calls with -fsanitize=address [PR120608] The following testcase is rejected by GCC 15 but accepted (with s/gnu/clang/) by clang. The problem is that we want to execute a sequence of instructions to unpoison all automatic variables in the function and mark the var block allocated for use-after-return sanitization poisoned after the call, so we were just disabling tail calls if there are any instructions returned from asan_emit_stack_protection. It is fine and necessary for normal tail calls, but for musttail tail calls we actually document that accessing the automatic vars of the caller is UB as if they end their lifetime right before the tail call, so we also want address sanitizer user-after-return to diagnose that. The following patch will only disable normal tail calls when that sequence is present, for musttail it will arrange to emit a copy of that sequence before the tail call sequence. That sequence only tweaks the shadow memory and nothing in the code emitted by call expansion should touch the shadow memory, so it is ok to emit it already before argument setup. 2025-06-23 Jakub Jelinek <ja...@redhat.com> PR middle-end/120608 * cfgexpand.cc: Include rtl-iter.h. (expand_gimple_tailcall): Add ASAN_EPILOG_SEQ argument, if non-NULL and expand_gimple_stmt emitted a tail call, emit a copy of that insn sequence before the call sequence. (expand_gimple_basic_block): Remove DISABLE_TAIL_CALLS argument, add ASAN_EPILOG_SEQ argument. Disable tail call flag only on non-musttail calls if that flag is set, pass it to expand_gimple_tailcall. (pass_expand::execute): Pass VAR_RET_SEQ directly as last expand_gimple_basic_block argument rather than its comparison with NULL. * g++.dg/asan/pr120608.C: New test.
