On Thu, Mar 07, 2019 at 02:13:12PM +0100, Peter Zijlstra wrote:
> On Thu, Mar 07, 2019 at 01:55:26PM +0100, Peter Zijlstra wrote:
> > On Thu, Mar 07, 2019 at 01:03:17PM +0100, Peter Zijlstra wrote:
>
>
> > > 01be 20d3: 31 c0 xor %eax,%eax
> > > 01c0 20d5: 4c 39 eb cmp %r13,%rbx
> > > 01c3 20d8: 77 08 ja 20e2
> > > <__do_sys_waitid+0x1cd>
>
> randconfig-build/kernel/exit.o: warning: objtool: __do_sys_waitid()+0x1c3:
> (branch)
>
> > > 01cd 20e2: 83 f0 01 xor $0x1,%eax
> > > 01d0 20e5: 48 89 c2 mov %rax,%rdx
> > > 01d3 20e8: 83 e2 01 and $0x1,%edx
> > > 01d6 20eb: 48 83 c2 02 add $0x2,%rdx
> > > 01da 20ef: 48 ff 04 d5 00 00 00 incq 0x0(,%rdx,8)
> > > 01e1 20f6: 00
> > > 01de 20f3: R_X86_64_32S _ftrace_branch+0x148
> > > 01e2 20f7: 84 c0 test %al,%al
> > > 01e4 20f9: 75 2d jne 2128
> > > <__do_sys_waitid+0x213>
> >
> > we do not take this branch and fall-through.
>
> And that is the error, I think. We should've taken it and went to:
>
> return -EFAULT;
>
> because:
>
> +1be xor %eax,%eax eax=0
> +1cd xor $0x1,%eax eax=1
> +1e2 test %al,%al 1&1==1 -> ZF=0
> +1e4 jnz
>
> Is an unconditional code sequence, but there's no way objtool can do
> that without becoming a full blown interpreter :/
>
> > > 0213 2128: 49 c7 c7 f2 ff ff ff mov $0xfffffffffffffff2,%r15
> > > ffffffffffffe0eb }
> > > 021a 212f: 48 8d 65 d8 lea -0x28(%rbp),%rsp
> > > 021e 2133: 4c 89 f8 mov %r15,%rax
> > > 0221 2136: 5b pop %rbx
> > > 0222 2137: 41 5c pop %r12
> > > 0224 2139: 41 5d pop %r13
> > > 0226 213b: 41 5e pop %r14
> > > 0228 213d: 41 5f pop %r15
> > > 022a 213f: 5d pop %rbp
> > > 022b 2140: c3 retq
This "fixes" it, and also seems to help -Os make much code:
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 445348facea9..8de63db58fdd 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -67,7 +67,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int
val,
.line = __LINE__, \
}; \
______r = !!(cond); \
- ______f.miss_hit[______r]++;
\
+ if (______r) ______f.miss_hit[1]++; else ______f.miss_hit[0]++;
\
______r; \
}))
#endif /* CONFIG_PROFILE_ALL_BRANCHES */
