* [gcc-4.4] Re: arch/x86/events/intel/uncore_snbep.o: warning: objtool: snbep_uncore_msr_enable_event()+0x2e: function has unreachable instruction
[not found] ` <37D7C6CF3E00A74B8858931C1DB2F07712C1ACAF@SHSMSX103.ccr.corp.intel.com>
@ 2016-07-21 4:45 ` Fengguang Wu
0 siblings, 0 replies; 2+ messages in thread
From: Fengguang Wu @ 2016-07-21 4:45 UTC (permalink / raw)
To: Liang, Kan; +Cc: LKML, Andy Lutomirski, gcc
On Thu, Jul 21, 2016 at 11:06:06AM +0800, Liang, Kan wrote:
>Hi Fengguang,
>
>I located the unreachable instruction which is ud2.
>
>This instruction will raise invalid opcode exception. So I think
>normally it should not be reached. Also ud2 should be generated by
>compiler, not our codes.
It's great to know that!
>I have no idea how to fix it.
>Have you met similar issue before?
>Do you have any suggestions?
The warning shows up when we enabled gcc-4.4 for kernel build tests.
It emits this "function has unreachable instruction" warning for
~10000 kernel functions all over the places.
So it must be a toolchain specific problem.
Let's CC LKML and gcc lists for possible solutions.
>0000000000000e0f <snbep_uncore_msr_enable_event>:
> e0f: 55 push %rbp
> e10: 48 89 e5 mov %rsp,%rbp
> e13: 53 push %rbx
> e14: 83 be 80 01 00 00 ff cmpl $0xffffffff,0x180(%rsi)
> e1b: 48 89 f3 mov %rsi,%rbx
> e1e: 74 2b je e4b <snbep_uncore_msr_enable_event+0x3c>
> e20: 31 f6 xor %esi,%esi
> e22: e8 00 00 00 00 callq e27 <snbep_uncore_msr_enable_event+0x18>
> e27: 48 89 c2 mov %rax,%rdx
> e2a: 8b b3 78 01 00 00 mov 0x178(%rbx),%esi
> e30: 48 c1 ea 20 shr $0x20,%rdx
> e34: 48 83 3d 00 00 00 00 cmpq $0x0,0x0(%rip) # e3c <snbep_uncore_msr_enable_event+0x2d>
> e3b: 00
> e3c: 75 02 jne e40 <snbep_uncore_msr_enable_event+0x31>
> e3e: 0f 0b ud2
> e40: 89 f7 mov %esi,%edi
> e42: 89 c6 mov %eax,%esi
> e44: ff 14 25 00 00 00 00 callq *0x0
>
>Thanks,
>Kan
>
>>
>> tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>> master
>> head: 47ef4ad2684d380dd6d596140fb79395115c3950
>> commit: 3b94a891667c30fb4624221497d77fc65d950345
>> perf/x86/intel/uncore: Remove SBOX support for Broadwell server
>> date: 7 weeks ago
>> config: x86_64-randconfig-s0-07191857 (attached as .config)
>> compiler: gcc-4.4 (Debian 4.4.7-8) 4.4.7
>> reproduce:
>> git checkout 3b94a891667c30fb4624221497d77fc65d950345
>> # save the attached .config to linux build tree
>> make ARCH=x86_64
>>
>> All warnings (new ones prefixed by >>):
>>
>> >> arch/x86/events/intel/uncore_snbep.o: warning: objtool:
>> snbep_uncore_msr_enable_event()+0x2e: function has unreachable
>> instruction
>>
>> ---
>> 0-DAY kernel test infrastructure Open Source Technology Center
>> https://lists.01.org/pipermail/kbuild-all Intel Corporation
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