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
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