------- Comment #6 from dominiq at lps dot ens dot fr 2010-03-25 07:45 -------
> So, please find out what the difference actually is. The intended difference
> is just that the whole __i686.get_pc_thunk.* snippet is moved from the end of
> the
> file to before .debug_frame/.debug_info and .LF[BE]NNNN labels added around
> the
> thunk's body (plus in .debug_frame section some differences too).
Could you please use English for dummies. I don't have the faintest idea of
what is the "__i686.get_pc_thunk.* snippet" and where I am supposed to find it.
I have compiled the code in comment #5 with -m32 -O2 -g and the executable
gives a "Segmentation fault". The crash report is:
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x000000002b55429b
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Thread 0 Crashed: Dispatch queue: com.apple.main-thread
0 a.out 0x00001ee9 main + 41 (ctype.h:176)
1 a.out 0x00001e75 start + 53
Thread 0 crashed with X86 Thread State (32-bit):
eax: 0x2b554266 ebx: 0xbfffddf4 ecx: 0xbfffdcf8 edx: 0x00000000
edi: 0x00000000 esi: 0xffffff9f ebp: 0xbfffdcd8 esp: 0xbfffdca0
ss: 0x0000001f efl: 0x00010246 eip: 0x00001ee9 cs: 0x00000017
ds: 0x0000001f es: 0x0000001f fs: 0x00000000 gs: 0x00000037
cr2: 0x2b55429b
The Segmentation fault disappear if I remove -g or -m32 or if I change -O2 to
-O1. The beginning of the diff between the assembly generated with -O1 (-) and
-O2 (+) is:
--- conf_omp_1.s 2010-03-25 08:41:34.000000000 +0100
+++ conf_omp_1_c.s 2010-03-25 08:40:59.000000000 +0100
@@ -28,10 +28,12 @@ Ldebug_info0:
Ldebug_line0:
.text
Ltext0:
+ .align 4,0x90
.globl _main
_main:
LFB29:
LM1:
+LVL0:
pushl %ebp
LCFI0:
movl %esp, %ebp
@@ -40,147 +42,149 @@ LCFI1:
LCFI2:
movl %ebx, -12(%ebp)
LCFI3:
+ call ___i686.get_pc_thunk.bx
+"L00000000001$pb":
movl %esi, -8(%ebp)
LCFI4:
+ movl $-97, %esi
movl %edi, -4(%ebp)
LCFI5:
- call ___i686.get_pc_thunk.bx
-"L00000000001$pb":
-LVL0:
-LM2:
- movl $-97, %esi
LVL1:
L11:
-LM3:
+LM2:
leal 97(%esi), %edi
LVL2:
LBB24:
LBB25:
LBB26:
-LM4:
- movl %edi, %eax
- andl $-128, %eax
- movl %eax, -28(%ebp)
+LM3:
+ movl %edi, %edx
+ andl $-128, %edx
jne L2
-LM5:
- leal 0(,%esi,4), %eax
- addl L__DefaultRuneLocale$non_lazy_ptr-"L00000000001$pb"(%ebx), %eax
-LM6:
- testb $16, 441(%eax)
+ movl L__DefaultRuneLocale$non_lazy_ptr-"L00000000001$pb"(%ebx), %eax
+ testb $16, 441(%eax,%esi,4)
setne %al
movzbl %al, %eax
- jmp L3
-L2:
- movl $4096, 4(%esp)
- movl %edi, (%esp)
- call L___maskrune$stub
- testl %eax, %eax
- setne %al
- movzbl %al, %eax
-L3:
...
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43511
