Stack operating code that generated by gcc have an error. In some operating
system that saved the thread's context in stack when schedule, it will be have
critical problem.
Enabling the compiler optimalisation (-O2 option) the error will be occuring,
and don't occur when using option -O1 or -O0.
--- sample ---
array.c:
int find_num(int i)
{
const int arr[5] = {0, 1, 2, 3, 4};
return arr[i];
}
using command:
ppc-eabi-gcc -c -O2 array.c -o array.o
ppc-eabi-objdump -S array.o
the disassemble code is:
00000000 <find_num>:
0: 3d 60 00 00 lis r11,0
4: 94 21 ff d0 stwu r1,-48(r1)
8: 39 2b 00 00 addi r9,r11,0
c: 81 0b 00 00 lwz r8,0(r11)
10: 80 e9 00 10 lwz r7,16(r9)
14: 54 63 10 3a rlwinm r3,r3,2,0,29
18: 80 09 00 04 lwz r0,4(r9)
1c: 81 69 00 08 lwz r11,8(r9)
20: 81 49 00 0c lwz r10,12(r9)
24: 7d 21 1a 14 add r9,r1,r3
28: 91 01 00 10 stw r8,16(r1)
2c: 90 01 00 14 stw r0,20(r1)
30: 91 61 00 18 stw r11,24(r1)
34: 91 41 00 1c stw r10,28(r1)
38: 90 e1 00 20 stw r7,32(r1)
3c: 38 21 00 30 addi r1,r1,48
40: 80 69 00 10 lwz r3,16(r9)
44: 4e 80 00 20 blr
The instruction 3c let stack pointer back, and instruction 40 load data from
the stack, this is error. The true code must be:
lwz r3,16(r9)
addi r1,r1,48
And when you using option -O1, the code generated is true.
Release:
GCC v3.4.6 ppc-eabi cross compiler in cygwin
Environment:
Reading specs from
/cygdrive/d/Compiler/gcc3.4.6-ppc-eabi/bin/../lib/gcc/ppc-eab
i/3.4.6/specs
Configured with: ../configure --target=ppc-eabi
--prefix=/usr/local/gcc3.4.6-ppc
-eabi --enable-languages=c
Thread model: single
gcc version 3.4.6
How-To-Repeat:
Using my sample.
--
Summary: Optimization flag -O2 generate error stack operating
code
Product: gcc
Version: 3.4.6
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: chenkb at ruijie dot com dot cn
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30282
