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SubjectRe: objtool warnings on 4.14-stable/gcc-7.3.0
+Kees

On Wed, Feb 14, 2018 at 04:45:25PM -0600, Josh Poimboeuf wrote:
> On Wed, Feb 14, 2018 at 04:24:12PM -0600, Josh Poimboeuf wrote:
> > On Wed, Feb 14, 2018 at 04:11:15PM +0100, Arnd Bergmann wrote:
> > > Hi Josh,
> > >
> > > I recently did some randconfig testing with a plain 4.14-stable kernel
> > > and gcc-7.3.0, and came across three distinct objtool warnings:
> > >
> > > drivers/misc/lkdtm_bugs.o: warning: objtool:
> > > lkdtm_CORRUPT_LIST_ADD()+0x15: return with modified stack frame
>
> While this is probably an objtool bug, the code is very odd:
>
> 00000000000001a8 <lkdtm_CORRUPT_LIST_ADD>:
> 1a8: e8 00 00 00 00 callq 1ad <lkdtm_CORRUPT_LIST_ADD+0x5>
> 1a9: R_X86_64_PC32 __fentry__-0x4
> 1ad: 55 push %rbp
> 1ae: 48 89 e5 mov %rsp,%rbp
> 1b1: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
> 1b5: 48 83 ec 20 sub $0x20,%rsp
> 1b9: 48 89 ec mov %rbp,%rsp
> 1bc: 5d pop %rbp
> 1bd: c3 retq
>
> The function just allocates/aligns its stack space and then returns. It
> seems like GCC was too smart for its own good here, as the function
> doesn't test what it's supposed to. Can you share the config for this
> one?

lkdtm is a "interesting" module in that it tries to do bad things to
test for various stuff. Kees, does the above look like it is doing the
correct thing?

thanks,

greg k-h

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