Source file:
file test.c
=======================================================
#define __NR_close 2
#define CLOBBER_LIST "memory", "cc", "r11", "r12", "r13", "r14", "r15", "rbx"
#define MY_SYSCALL_1(ARG)
\
__extension__ ((
\
{
\
register unsigned long result;
\
register unsigned long _arg1 asm("rdi") = (unsigned
long)ARG; \
asm volatile (
\
"call my_syscall\n\t"
\
: "=a" (result)
\
: "0" (__NR_close), "r" (_arg1)
\
: CLOBBER_LIST
\
);
\
result;
\
} ))
\
void func_1(int arg)
{
MY_SYSCALL_1(arg);
}
================================================================================
Compilation command:
gcc -O2 -S -o test.S test.c
Output file (test.S)
=====================================================================
.file "bb.c"
.text
.p2align 4,,15
.globl func_1
.type func_1, @function
func_1:
.LFB2:
movq %rbx, -40(%rsp)
.LCFI0:
movq %r12, -32(%rsp)
.LCFI1:
movslq %edi,%rdi
movq %r13, -24(%rsp)
.LCFI2:
movq %r14, -16(%rsp)
.LCFI3:
movl $2, %eax
movq %r15, -8(%rsp)
.LCFI4:
#APP
call my_syscall
#NO_APP
movq -40(%rsp), %rbx
movq -32(%rsp), %r12
movq -24(%rsp), %r13
movq -16(%rsp), %r14
movq -8(%rsp), %r15
ret
=====================================================================
All registers mentioned in the CLOBERR_LIST (but r11) are moved to the stack.
Stack pointer doesn't adjusted !!!
Than 'call my_syscall' overwrite on the stack saved value of 'r15'.
Than, future instructions in the 'my_syscall' can overwrite other saved
registers.
After return from 'my_syscall' overwritten values copied to registers.
I.e while compiler tried to save CLOBER_LIST registers' content it failed to do
it.
I tried to compile code both with gcc-3.4.2 (FedoraCore 3) and gcc-4.1.2
(Fedora 8) - results are same.
Result are same when compile with any of -O1,-O2 or -O3.
When compile without optimization, stack pointer is adjusted, i.e generated
code is OK.
--
Summary: Registers in on clober list are cloberred when compiled
with optimization (x86_64) ?
Product: gcc
Version: 4.1.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: inline-asm
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: valery_reznic at yahoo dot com
GCC host triplet: file bb.c
=====================================================
GCC target triplet: x86_64-redhat-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39078
