https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83641
Bug ID: 83641
Summary: -fstack-clash-protection generates incorrect CFI on
i386
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: fw at gcc dot gnu.org
Target Milestone: ---
Target: i386
Created attachment 42995
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=42995&action=edit
unwind.i
The attached unwind.i file, when compiled with -O2 -fstack-clash-protection
-m32 -fPIC, produces incorrect CFI information:
__GI___pthread_unwind:
.LFB55:
.cfi_startproc
pushl %esi
.cfi_def_cfa_offset 8
.cfi_offset 6, -8
pushl %ebx
.cfi_def_cfa_offset 12
.cfi_offset 3, -12
pushl %esi
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
popl %esi
.cfi_restore 6
.cfi_def_cfa_offset 12
xorl %edx, %edx
call __x86.get_pc_thunk.bx
addl $_GLOBAL_OFFSET_TABLE_, %ebx
#APP
# 114 "unwind.c" 1
movl %gs:8,%ecx
# 0 "" 2
#NO_APP
subl $8, %esp
.cfi_def_cfa_offset 20
movl %eax, %esi
The “.cfi_restore 6” directive claims that %esi has the same value as in the
caller in the following code, but “movl %eax, %esi” clobbers it.
I believe this is the reason why the libgcc unwinder cannot restore %esi to its
original value when pthread_exit is called and glibc has been compiled with a
GCC that has this bug.
