Messages in this thread | | | Date | Thu, 11 Jan 2018 10:48:26 -0600 | From | Josh Poimboeuf <> | Subject | Re: [PATCH 2/3] objtool: Ignore retpoline alternatives |
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On Thu, Jan 11, 2018 at 04:39:38PM +0000, David Woodhouse wrote: > On Thu, 2018-01-11 at 10:33 -0600, Josh Poimboeuf wrote: > > On Thu, Jan 11, 2018 at 04:27:38PM +0000, David Woodhouse wrote: > > > > > > On Wed, 2018-01-10 at 19:48 -0600, Josh Poimboeuf wrote: > > > > > > > > > > > > +#define ANNOTATE_NOSPEC_ALTERNATIVE \ > > > > + "999:\n\t" \ > > > > + ".pushsection .discard.nospec\n\t" \ > > > > + ".long 999b - .\n\t" \ > > > > + ".popsection\n\t" > > > > + > > > > > > Ick, numbers. Use .Lfoo_%= instead. > > > > > I seem to recall that not working with inline asm, maybe old versions of > > GCC don't like it or something? I can try it and see if 0-day bot > > complains. > > You just need %= (for inline asm) instead of \@ (for .macro). > > I already fixed it up in > http://git.infradead.org/users/dwmw2/linux-retpoline.git/ and will get > nagmail from 0day shortly if it doesn't work :) > > (I love you Fengguang)
I found a description from an old commit of mine:
3d1e236022cc ("objtool: Prevent GCC from merging annotate_unreachable()")
> A workaround for this issue is to ensure that each instance of the > inline asm statement uses a different label, so that GCC sees the > statements are unique and leaves them alone. The inline asm ‘%=’ token > could be used for that, but unfortunately older versions of GCC don't > support it. So I implemented a poor man's version of it with the > __LINE__ macro.
The above macro is protected by '#ifdef RETPOLINE', and I seriously doubt 0-day is testing with an unreleased version of GCC. So you shouldn't see a 0-day warning.
I think I heard that retpolines won't be ported to anything older than GCC 4.9, so maybe it's safe to use '%='. I don't remember when it was introduced into GCC though.
-- Josh
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