With above code
------------ code --------------------------------------------
int glob_a = 3;
int main ()
{
volatile int a;
glob_a = 1;
if ( 1 == glob_a ) // Cause problem here
{ } // Empty if
return 0;
}
---------------------------------------------------
When compiled with
gcc -fvolatile-global -S -o main.s
To treat glob_a as "volatile", but as a result, it show following
assembly code
------- test section of assembly code -----------------------
00000000 <main>:
main():
/proj/sve/working/komiyama/cpp_test/volatile_test1/main.cc:5
0: 94 21 ff e0 stwu r1,-32(r1)
4: 7c 08 02 a6 mflr r0
8: 93 e1 00 1c stw r31,28(r1)
c: 90 01 00 24 stw r0,36(r1)
10: 7c 3f 0b 78 mr r31,r1
14: 48 00 00 01 bl 14 <main+0x14>
14: R_PPC_REL24 __eabi
/proj/sve/working/komiyama/cpp_test/volatile_test1/main.cc:8
18: 3d 20 00 00 lis r9,0
1a: R_PPC_ADDR16_HA glob_a
1c: 38 00 00 01 li r0,1
20: 90 09 00 00 stw r0,0(r9)
22: R_PPC_ADDR16_LO glob_a
/proj/sve/working/komiyama/cpp_test/volatile_test1/main.cc:13
24: 38 00 00 00 li r0,0
/proj/sve/working/komiyama/cpp_test/volatile_test1/main.cc:14
28: 7c 03 03 78 mr r3,r0
2c: 81 61 00 00 lwz r11,0(r1)
30: 80 0b 00 04 lwz r0,4(r11)
34: 7c 08 03 a6 mtlr r0
38: 83 eb ff fc lwz r31,-4(r11)
3c: 7d 61 5b 78 mr r1,r11
40: 4e 80 00 20 blr
-------------------------------------------------------------
It seems
if ( 1 == glob_a )
{ }
is gone somewhere, When I set
volatile int glob_a = 3;
gcc compile to
-------- assembly code when set glob_a as volatile ------
00000000 <main>:
main():
/proj/sve/working/komiyama/cpp_test/volatile_test1/main.cc:5
0: 94 21 ff e0 stwu r1,-32(r1)
4: 7c 08 02 a6 mflr r0
8: 93 e1 00 1c stw r31,28(r1)
c: 90 01 00 24 stw r0,36(r1)
10: 7c 3f 0b 78 mr r31,r1
14: 48 00 00 01 bl 14 <main+0x14>
14: R_PPC_REL24 __eabi
/proj/sve/working/komiyama/cpp_test/volatile_test1/main.cc:8
18: 3d 20 00 00 lis r9,0
1a: R_PPC_ADDR16_HA glob_a
1c: 38 00 00 01 li r0,1
20: 90 09 00 00 stw r0,0(r9)
22: R_PPC_ADDR16_LO glob_a
/proj/sve/working/komiyama/cpp_test/volatile_test1/main.cc:10
24: 3d 20 00 00 lis r9,0
26: R_PPC_ADDR16_HA glob_a
28: 80 09 00 00 lwz r0,0(r9)
2a: R_PPC_ADDR16_LO glob_a
/proj/sve/working/komiyama/cpp_test/volatile_test1/main.cc:13
2c: 38 00 00 00 li r0,0
/proj/sve/working/komiyama/cpp_test/volatile_test1/main.cc:14
30: 7c 03 03 78 mr r3,r0
34: 81 61 00 00 lwz r11,0(r1)
38: 80 0b 00 04 lwz r0,4(r11)
3c: 7c 08 03 a6 mtlr r0
40: 83 eb ff fc lwz r31,-4(r11)
44: 7d 61 5b 78 mr r1,r11
48: 4e 80 00 20 blr
------------------------------------------------------------------
Envionment
O.S : Linux ( kernel 2.4.20-30.7.legacy)
Glibc 2.2.5
GCC : 3.3.3 configured with cross compiler
( Host is linux, target is ppc-unkown-eabi)
with
binutils ... 2.14
newlib ... 1.12
--
Summary: option -fvolatile-global will not effect in some case
Product: gcc
Version: 3.3.3
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: takeo dot komiyama at freescale dot com
CC: gcc-bugs at gcc dot gnu dot org,takeo dot komiyama at
freescale dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18735
