https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96892
Bug ID: 96892
Summary: wrong __stack_chk_guard for comparison
Product: gcc
Version: 10.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: dongjianqiang2 at huawei dot com
Target Milestone: ---
Simpile testcase:
#include<stdio.h>
int main ()
{
int i;
char buf[20];
for (i = 0; i < 20; i++)
{
buf[i] = 'a';
printf("%c ,%d", buf[i], i);
}
return 0;
}
Compile with following command:
arm-linux-gnueabi-gcc -static -fno-PIE -no-pie main.c -fstack-protector-all -g3
gdb ./a.out
0x000105f8 <+124>: mov r3, #0
0x000105fc <+128>: movw r2, #11800 ; 0x2e18
0x00010600 <+132>: movt r2, #6
0x00010604 <+136>: ldr r1, [r2]
0x00010608 <+140>: ldr r2, [r11, #-8]
=> 0x0001060c <+144>: eors r1, r2, r1
0x00010610 <+148>: beq 0x10618 <main+156>
0x00010614 <+152>: bl 0x3257c <__stack_chk_fail>
0x00010618 <+156>: mov r0, r3
0x0001061c <+160>: sub sp, r11, #4
0x00010620 <+164>: pop {r11, pc}
End of assembler dump.
(gdb) p __stack_chk_guard
$8 = 3363780352 // this is canary value
(gdb) p /x $r1
$9 = 0x8ab20 // Comparing the address of __stack_chk_guard ???
(gdb) p /x $r2
$10 = 0x8ab20
(gdb) p &__stack_chk_guard // address of __stack_chk_guard
$11 = (uintptr_t *) 0x8ab20 <__stack_chk_guard>
Confirmed as a 7.5 regression. The most likely change of those comparison is
pr85434.
