https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91779
Bug ID: 91779
Summary: [9 regression] Unbalanced stack manipulation
Product: gcc
Version: 9.2.1
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: sch...@linux-m68k.org
Target Milestone: ---
Target: i586-*-*
Created attachment 46887
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46887&action=edit
Preprocessed input
When compiled with -m32 -O2, the first call to _fprintf in main
_fprintf(out,"->{'%c'}\n",Cr.x);
saves the format string on the stack at $fp-100:
pushl %eax
leal .LC164@GOTOFF(%ebx), %eax
pushl %eax
pushl (%esi)
movl %eax, -100(%ebp)
call _fprintf
This is then reused by the second call:
pushl %eax
pushl -100(%ebp)
pushl (%esi)
call _fprintf
but here pushl %eax overwrites the value in $fp-100.
The bug appears to be here (after first call to fflush):
pushl (%esi)
call fflush@PLT
leal -84(%ebp), %eax
popl %edx
popl %ecx
The second popl is causing a stack frame underflow.
