https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127322
Bug ID: 127322
Summary: -fzero-call-used-regs suppressed on normal returns
when the function also has __builtin_eh_return
Product: gcc
Version: 17.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: 220255623 at seu dot edu.cn
CC: 220245569 at seu dot edu.cn, jianhao.xu at seu dot edu.cn
Target Milestone: ---
`-fzero-call-used-regs=used-gpr` is silently skipped on an ordinary return
when the same function also contains `__builtin_eh_return`.
Reproducer:
void f(long secret, int normal, void *handler)
{
register long r10 asm("r10") = secret;
asm volatile ("" : "+r"(r10));
if (normal)
return;
__builtin_eh_return(0, handler);
}
Command:
gcc -O2 -fzero-call-used-regs=used-gpr -S trigger.c -o trigger.s
Exit status is 0 with no diagnostics.
Observed normal-return path:
movq %rdi, %r10
xorl %ecx, %ecx
testl %esi, %esi
je .L7
addq $16, %rsp
ret
There is no write of zero to %r10 before this ret. The xorl %ecx, %ecx
is part of the __builtin_eh_return stack adjustment, not the requested
scrub of %r10.
Expected:
The ordinary return should contain `xorl %r10d, %r10d` before ret.
Special handling of the __builtin_eh_return exit does not justify skipping
an independent ordinary return.
Unlike a tail-call exit, this ret is executed by f itself and returns
directly to f's caller. There is no subsequent function return that can
provide the missing cleanup. A control function without __builtin_eh_return
does emit `xorl %r10d, %r10d` with the same flags.
Compiler:
gcc (<build package label redacted>) 17.0.0 20260531 (experimental)
Target: x86_64-pc-linux-gnu
Configured with: <source-tree>/configure --prefix=<build-tree>
--disable-bootstrap --disable-multilib --disable-nls --enable-languages=c,c++
--enable-default-pie --enable-cet --disable-werror --enable-checking=release
--with-system-zlib --with-pkgversion=<redacted>
Thread model: posix
gcc version 17.0.0 20260531 (experimental)
Source snapshot: GCC master revision
f20bc4c2fe00928013c533e241b89ae3a6724ca1.
Also reproduced with GCC 13.3.0, 15.2.0, 16.1.0, and 17.0 snapshots
20260426 and 20260531 on x86_64. Other targets were not tested.
