http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46762
Summary: gcc crosscompiled for arm optimises away volatile
struct member access when -Os
Product: gcc
Version: 4.5.1
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: c
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: do...@cba.si
$ cat bug.c
struct GPIO
{
volatile unsigned int IDR;
} *GPIO = (struct GPIO *)(0x40010808);
volatile unsigned int *GPIO_PTR = (volatile unsigned int *)(0x40010808);
static inline int gpio_get_value_ok()
{
if (*GPIO_PTR & 1)
return 1;
return 0;
}
void function_with_no_bug(void)
{
int timeout = 0x1000000;
while (gpio_get_value_ok() == 0) {
if (timeout-- == 0) {
return;
}
}
}
static inline int gpio_get_value_wrong()
{
if (GPIO->IDR & 1)
return 1;
return 0;
}
void function_with_bug(void)
{
int timeout = 0x1000000;
while (gpio_get_value_wrong() == 0) {
if (timeout-- == 0) {
return;
}
}
}
$ arm-none-eabi-gcc -Wall -Os -c bug.c -o bug.o && arm-none-eabi-objdump -xd
bug.o
bug.o: file format elf32-littlearm
bug.o
architecture: arm, flags 0x00000011:
HAS_RELOC, HAS_SYMS
start address 0x00000000
private flags = 5000000: [Version5 EABI]
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000030 00000000 00000000 00000034 2**2
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
1 .data 00000008 00000000 00000000 00000064 2**2
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000000 00000000 00000000 0000006c 2**0
ALLOC
3 .comment 0000002b 00000000 00000000 0000006c 2**0
CONTENTS, READONLY
4 .ARM.attributes 00000034 00000000 00000000 00000097 2**0
CONTENTS, READONLY
SYMBOL TABLE:
00000000 l df *ABS* 00000000 bug.c
00000000 l d .text 00000000 .text
00000000 l d .data 00000000 .data
00000000 l d .bss 00000000 .bss
00000000 l d .comment 00000000 .comment
00000000 l d .ARM.attributes 00000000 .ARM.attributes
00000000 g F .text 0000002c function_with_no_bug
0000002c g F .text 00000004 function_with_bug
00000004 g O .data 00000004 GPIO
00000000 g O .data 00000004 GPIO_PTR
Disassembly of section .text:
00000000 <function_with_no_bug>:
0: e59f3020 ldr r3, [pc, #32] ; 28
<function_with_no_bug+0x28>
4: e5932000 ldr r2, [r3]
8: e3a03401 mov r3, #16777216 ; 0x1000000
c: e5921000 ldr r1, [r2]
10: e3110001 tst r1, #1
14: 112fff1e bxne lr
14: R_ARM_V4BX *ABS*
18: e3530000 cmp r3, #0
1c: 012fff1e bxeq lr
1c: R_ARM_V4BX *ABS*
20: e2433001 sub r3, r3, #1
24: eafffff8 b c <function_with_no_bug+0xc>
28: 00000000 .word 0x00000000
28: R_ARM_ABS32 .data
0000002c <function_with_bug>:
2c: e12fff1e bx lr
2c: R_ARM_V4BX *ABS*
$ arm-none-eabi-gcc -v
Using built-in specs.
COLLECT_GCC=arm-none-eabi-gcc
COLLECT_LTO_WRAPPER=/home/domen/toolchains/arm-2010.09/bin/../libexec/gcc/arm-none-eabi/4.5.1/lto-wrapper
Target: arm-none-eabi
Configured with:
/scratch/julian/2010q3-release-eabi-lite/src/gcc-4.5-2010.09/configure
--build=i686-pc-linux-gnu --host=i686-pc-linux-gnu --target=arm-none-eabi
--enable-threads --disable-libmudflap --disable-libssp --disable-libstdcxx-pch
--enable-extra-sgxxlite-multilibs --with-gnu-as --with-gnu-ld
--with-specs='%{save-temps: -fverbose-asm} -D__CS_SOURCERYGXX_MAJ__=2010
-D__CS_SOURCERYGXX_MIN__=9 -D__CS_SOURCERYGXX_REV__=51
%{O2:%{!fno-remove-local-statics: -fremove-local-statics}}
%{O*:%{O|O0|O1|O2|Os:;:%{!fno-remove-local-statics: -fremove-local-statics}}}'
--enable-languages=c,c++ --disable-shared --enable-lto --with-newlib
--with-pkgversion='Sourcery G++ Lite 2010.09-51'
--with-bugurl=https://support.codesourcery.com/GNUToolchain/ --disable-nls
--prefix=/opt/codesourcery --with-headers=yes
--with-sysroot=/opt/codesourcery/arm-none-eabi
--with-build-sysroot=/scratch/julian/2010q3-release-eabi-lite/install/arm-none-eabi
--with-gmp=/scratch/julian/2010q3-release-eabi-lite/obj/host-libs-2010.09-51-arm-none-eabi-i686-pc-linux-gnu/usr
--with-mpfr=/scratch/julian/2010q3-release-eabi-lite/obj/host-libs-2010.09-51-arm-none-eabi-i686-pc-linux-gnu/usr
--with-mpc=/scratch/julian/2010q3-release-eabi-lite/obj/host-libs-2010.09-51-arm-none-eabi-i686-pc-linux-gnu/usr
--with-ppl=/scratch/julian/2010q3-release-eabi-lite/obj/host-libs-2010.09-51-arm-none-eabi-i686-pc-linux-gnu/usr
--with-host-libstdcxx='-static-libgcc -Wl,-Bstatic,-lstdc++,-Bdynamic -lm'
--with-cloog=/scratch/julian/2010q3-release-eabi-lite/obj/host-libs-2010.09-51-arm-none-eabi-i686-pc-linux-gnu/usr
--with-libelf=/scratch/julian/2010q3-release-eabi-lite/obj/host-libs-2010.09-51-arm-none-eabi-i686-pc-linux-gnu/usr
--disable-libgomp --enable-poison-system-directories
--with-build-time-tools=/scratch/julian/2010q3-release-eabi-lite/install/arm-none-eabi/bin
--with-build-time-tools=/scratch/julian/2010q3-release-eabi-lite/install/arm-none-eabi/bin
Thread model: single
gcc version 4.5.1 (Sourcery G++ Lite 2010.09-51)
