On Thu, Mar 07, 2019 at 09:04:36AM -0800, h...@zytor.com wrote: > On March 7, 2019 8:47:05 AM PST, Josh Poimboeuf <jpoim...@redhat.com> wrote: > >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 */ > > if (cond)? Or is ___r used elsewhere?
______r is also the return value. And it's needed because cond should only be evaluated once. -- Josh
