CONFIG_CC_OPTIMIZE_FOR_SIZE breaking tridentfb
From: Ondrej Zary
Date: Fri Dec 12 2014 - 17:51:30 EST
Hello,
I have a weird problem with CONFIG_CC_OPTIMIZE_FOR_SIZE.
When it's enabled, tridentfb hangs with Blade3D card (ID 0x9880) in
blade_image_blit(). The screen is blank with some artifacts and machine does
not respond to ping or keyboard. However, it can be rebooted by Alt+SysRq+B.
It works fine with other cards (3DImage 9750 and CyberBlade XP) with no blit
implementation. Commenting out contents of blade_image_blit() function makes
the hang go away (nothing useful on the screen, of course).
Compiled kernel without CONFIG_CC_OPTIMIZE_FOR_SIZE: works
Then inserted #pragma GCC optimize ("Os") line into tridentfb.c: hangs (1)
Then added __attribute__((optimize("O2"))) to blade_image_blit(): works (2)
Compiled kernel with CONFIG_CC_OPTIMIZE_FOR_SIZE: hangs.
Then inserted #pragma GCC optimize ("O2") line into tridentfb.c: still hangs!
Then added __attribute__((optimize("O2"))) to blade_image_blit(): still hangs
$ gcc --version
gcc (Debian 4.7.2-5) 4.7.2
WTF is going on here?
objdumps from case (1) and (2):
this one hangs:
00000965 <blade_image_blit>:
965: 55 push %ebp
966: 57 push %edi
967: 56 push %esi
968: 89 d6 mov %edx,%esi
96a: 53 push %ebx
96b: 8b 38 mov (%eax),%edi
96d: 8b 54 24 14 mov 0x14(%esp),%edx
971: 8b 5c 24 18 mov 0x18(%esp),%ebx
975: 8b 6c 24 1c mov 0x1c(%esp),%ebp
979: 8b 44 24 20 mov 0x20(%esp),%eax
97d: 89 87 60 21 00 00 mov %eax,0x2160(%edi)
983: 8b 44 24 24 mov 0x24(%esp),%eax
987: 89 87 64 21 00 00 mov %eax,0x2164(%edi)
98d: b8 00 00 18 a0 mov $0xa0180000,%eax
992: 89 87 44 21 00 00 mov %eax,0x2144(%edi)
998: 89 d0 mov %edx,%eax
99a: c1 e0 10 shl $0x10,%eax
99d: 09 c8 or %ecx,%eax
99f: 89 87 08 21 00 00 mov %eax,0x2108(%edi)
9a5: 8d 44 2a ff lea -0x1(%edx,%ebp,1),%eax
9a9: c1 e0 10 shl $0x10,%eax
9ac: 8d 54 19 ff lea -0x1(%ecx,%ebx,1),%edx
9b0: 09 d0 or %edx,%eax
9b2: 89 87 0c 21 00 00 mov %eax,0x210c(%edi)
9b8: 8d 43 1f lea 0x1f(%ebx),%eax
9bb: 8d 0c ad 00 00 00 00 lea 0x0(,%ebp,4),%ecx
9c2: c1 e8 05 shr $0x5,%eax
9c5: 8d 97 00 00 01 00 lea 0x10000(%edi),%edx
9cb: 0f af c8 imul %eax,%ecx
9ce: 89 d7 mov %edx,%edi
9d0: f3 a4 rep movsb %ds:(%esi),%es:(%edi)
9d2: 5b pop %ebx
9d3: 5e pop %esi
9d4: 5f pop %edi
9d5: 5d pop %ebp
9d6: c3 ret
this one works:
00000965 <writemmr.isra.8>:
965: 01 d0 add %edx,%eax
967: 89 08 mov %ecx,(%eax)
969: c3 ret
96a: 8d b6 00 00 00 00 lea 0x0(%esi),%esi
00000970 <blade_image_blit>:
970: 83 ec 1c sub $0x1c,%esp
973: 89 5c 24 0c mov %ebx,0xc(%esp)
977: 89 c3 mov %eax,%ebx
979: 8b 44 24 28 mov 0x28(%esp),%eax
97d: 89 74 24 10 mov %esi,0x10(%esp)
981: 89 ce mov %ecx,%esi
983: 8b 4c 24 2c mov 0x2c(%esp),%ecx
987: 89 54 24 04 mov %edx,0x4(%esp)
98b: ba 60 21 00 00 mov $0x2160,%edx
990: 89 7c 24 14 mov %edi,0x14(%esp)
994: 8b 7c 24 20 mov 0x20(%esp),%edi
998: 89 04 24 mov %eax,(%esp)
99b: 8b 44 24 30 mov 0x30(%esp),%eax
99f: 89 6c 24 18 mov %ebp,0x18(%esp)
9a3: 8b 6c 24 24 mov 0x24(%esp),%ebp
9a7: 89 44 24 08 mov %eax,0x8(%esp)
9ab: 8b 03 mov (%ebx),%eax
9ad: e8 b3 ff ff ff call 965 <writemmr.isra.8>
9b2: 8b 4c 24 08 mov 0x8(%esp),%ecx
9b6: ba 64 21 00 00 mov $0x2164,%edx
9bb: 8b 03 mov (%ebx),%eax
9bd: e8 a3 ff ff ff call 965 <writemmr.isra.8>
9c2: 8b 03 mov (%ebx),%eax
9c4: b9 00 00 18 a0 mov $0xa0180000,%ecx
9c9: ba 44 21 00 00 mov $0x2144,%edx
9ce: e8 92 ff ff ff call 965 <writemmr.isra.8>
9d3: 8b 03 mov (%ebx),%eax
9d5: 89 f9 mov %edi,%ecx
9d7: c1 e1 10 shl $0x10,%ecx
9da: ba 08 21 00 00 mov $0x2108,%edx
9df: 09 f1 or %esi,%ecx
9e1: e8 7f ff ff ff call 965 <writemmr.isra.8>
9e6: 8b 04 24 mov (%esp),%eax
9e9: ba 0c 21 00 00 mov $0x210c,%edx
9ee: 8d 4c 07 ff lea -0x1(%edi,%eax,1),%ecx
9f2: c1 e1 10 shl $0x10,%ecx
9f5: 8d 44 2e ff lea -0x1(%esi,%ebp,1),%eax
9f9: 09 c1 or %eax,%ecx
9fb: 8b 03 mov (%ebx),%eax
9fd: e8 63 ff ff ff call 965 <writemmr.isra.8>
a02: 8b 0c 24 mov (%esp),%ecx
a05: 8d 55 1f lea 0x1f(%ebp),%edx
a08: 8b 03 mov (%ebx),%eax
a0a: c1 ea 05 shr $0x5,%edx
a0d: 8b 5c 24 0c mov 0xc(%esp),%ebx
a11: 8b 74 24 10 mov 0x10(%esp),%esi
a15: c1 e1 02 shl $0x2,%ecx
a18: 8b 7c 24 14 mov 0x14(%esp),%edi
a1c: 0f af ca imul %edx,%ecx
a1f: 8b 6c 24 18 mov 0x18(%esp),%ebp
a23: 05 00 00 01 00 add $0x10000,%eax
a28: 8b 54 24 04 mov 0x4(%esp),%edx
a2c: 83 c4 1c add $0x1c,%esp
a2f: e9 fc ff ff ff jmp a30 <blade_image_blit+0xc0>
a30: R_386_PC32 memcpy
--
Ondrej Zary
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