In functions utilising varargs gcc generates the below prologue, which
unfortunately results in movaps operating on a non 16byte aligned memory
address. In this particular case we should either be ensuring alignment on the
stack variable, or using movups. I have reason to believe, from discussion on
#gcc that this bug may be present in mainline.
Thanks, Zwane
/usr/bin/gcc -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/3.4.2/include/
-Wall -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common
-march=nocona -mno-red-zone -mcmodel=kernel -pipe -fno-reorder-blocks
-Wno-sign-compare -fno-asynchronous-unwind-tables -funit-at-a-time -DMODULE -O2
-c -o test.o test.c
int z_printf(int fd, const char * fmt, ...)
{
__asm__ __volatile__("nop");
return 0;
}
0000000000000000 <z_printf>:
0: 48 81 ec b8 00 00 00 sub $0xb8,%rsp
7: 48 89 54 24 10 mov %rdx,0x10(%rsp)
c: 0f b6 d0 movzbl %al,%edx
f: 48 89 4c 24 18 mov %rcx,0x18(%rsp)
14: 48 8d 04 95 00 00 00 lea 0x0(,%rdx,4),%rax
1b: 00
1c: 48 c7 c2 00 00 00 00 mov $0x0,%rdx
23: 4c 89 44 24 20 mov %r8,0x20(%rsp)
28: 48 29 c2 sub %rax,%rdx
2b: 48 8d 84 24 af 00 00 lea 0xaf(%rsp),%rax
32: 00
33: 4c 89 4c 24 28 mov %r9,0x28(%rsp)
38: ff e2 jmpq *%edx
3a: 0f 29 78 f1 movaps %xmm7,0xfffffffffffffff1(%rax)
3e: 0f 29 70 e1 movaps %xmm6,0xffffffffffffffe1(%rax)
42: 0f 29 68 d1 movaps %xmm5,0xffffffffffffffd1(%rax)
46: 0f 29 60 c1 movaps %xmm4,0xffffffffffffffc1(%rax)
4a: 0f 29 58 b1 movaps %xmm3,0xffffffffffffffb1(%rax)
4e: 0f 29 50 a1 movaps %xmm2,0xffffffffffffffa1(%rax)
52: 0f 29 48 91 movaps %xmm1,0xffffffffffffff91(%rax)
56: 0f 29 40 81 movaps %xmm0,0xffffffffffffff81(%rax)
5a: 90 nop
5b: 31 c0 xor %eax,%eax
5d: 48 81 c4 b8 00 00 00 add $0xb8,%rsp
64: c3 retq
Giving us;
> -0xb8 + 0xa5 + -15
-34 [0xffffffde]
--
Summary: gcc generated movaps instruction used on unaligned stack
variable
Product: gcc
Version: 3.4.2
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: zwane at arm dot linux dot org dot uk
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: x86_64-redhat-linux
GCC host triplet: x86_64-redhat-linux
GCC target triplet: x86_64-redhat-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21114
