http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51643
Bug #: 51643
Summary: Incorrect code produced for tail-call of weak function
with -O2/-O3 option
Classification: Unclassified
Product: gcc
Version: 4.6.2
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: rtl-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: sip...@gmail.com
A tail-call of weak function produces incorrect code, compiled with -O2 or -O3.
Target: arm-eabi
Version: GCC 4.6.2 and 4.6.1
***** Test case: t00x1.c
<<<<<
extern void __attribute__((weak)) wfunc(void);
void main(void)
{
wfunc(); // tail weak call fails!!!
// __asm__ volatile ("nop":::"memory"); // workaround
}
>>>>>
$ /opt/arm/gnuarm-4.6.2/bin/arm-eabi-gcc -c -S -o t00x1.S -O2 t00x1.c
***** Contents of t00x1.S:
.file "t00x1.c"
.section .text.startup,"ax",%progbits
.align 2
.global main
.type main, %function
main:
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
@ link register save eliminated.
b wfunc @@@@ <<< Will be replaced by "NOP" in linker!!
@@@@ so, no return sequence!
.size main, .-main
.weak wfunc
.ident "GCC: (GNU) 4.6.2"
***** Disassembled (objdump) code: t00x1.lst:
00000240 <main>:
240: e1a00000 nop ; (mov r0, r0) @@@@ really, NOP
00000244 <__do_global_dtors_aux>:
244: e92d4010 push {r4, lr}
248: e59f4028 ldr r4, [pc, #40] ; 278
.......
******
Call to function "wfunc" was converted to NOP by linker, as expected.
As a result, no return sequence from main(), falling througt to next code line.
For reference: the same program compiled with -O1
*******
.file "t00x1.c"
.text
.align 2
.global main
.type main, %function
main:
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
stmfd sp!, {r3, lr}
bl wfunc
ldmfd sp!, {r3, pc}
.size main, .-main
.weak wfunc
.ident "GCC: (GNU) 4.6.2"
Code with workaround, compiled with -O2 correct:
$ /opt/arm/gnuarm-4.6.2/bin/arm-eabi-gcc -c -S -o t00x1.S -O2 t00x1.c
*******
.file "t00x1.c"
.section .text.startup,"ax",%progbits
.align 2
.global main
.type main, %function
main:
@ args = 0, pretend = 0, frame = 0
@ frame_needed = 0, uses_anonymous_args = 0
stmfd sp!, {r3, lr}
bl wfunc
@ 5 "t00x1.c" 1
nop
@ 0 "" 2
ldmfd sp!, {r3, pc}
.size main, .-main
.weak wfunc
.ident "GCC: (GNU) 4.6.2"
*******
Compiler options:
$ /opt/arm/gnuarm-4.6.2/bin/arm-eabi-gcc -v
Using built-in specs.
COLLECT_GCC=/opt/arm/gnuarm-4.6.2/bin/arm-eabi-gcc
COLLECT_LTO_WRAPPER=/opt/arm/gnuarm-4.6.2/libexec/gcc/arm-eabi/4.6.2/lto-wrapper
Target: arm-eabi
Configured with: ../../src/gcc-4.6.2/configure --target=arm-eabi
--prefix=/opt/arm/gnuarm-4.6.2 --enable-multilib --enable-interwork
--enable-biendian --enable-fpu --with-newlib --with-gnu-ld --with-gnu-as
--disable-nls --disable-shared --with-arch=armv5te --with-fpu=vfp
--with-float=softfp --with-abi=aapcs-linux --enable-lto
--enable-languages=c,c++ --disable-threads --enable-ppl --enable-cloog
--enable-gmp --enable-mpfr --enable-lto
-with-headers=/opt/arm/gnuarm-4.6.2/arm-eabi/include
Thread model: single
gcc version 4.6.2 (GCC)
