Messages in this thread | | | Subject | Re: [v8,02/12] objtool: Allow alternatives to be ignored | From | Guenter Roeck <> | Date | Sun, 28 Jan 2018 17:26:05 -0800 |
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On 01/28/2018 01:06 PM, Josh Poimboeuf wrote: > On Mon, Jan 22, 2018 at 12:25:22PM -0800, Guenter Roeck wrote: >> Hi David, >> >> On Mon, Jan 22, 2018 at 07:34:04PM +0000, David Woodhouse wrote: >>> On Thu, 2018-01-18 at 11:41 -0800, Guenter Roeck wrote: >>>> >>>>> Not sure, does your gcc have retpolines? Give me your .o file and I can >>>>> diagnose it. >>>>> >>>> Yes, it does, only it is the gcc from the Google toolchain which may >>>> generate different code than the upstream version. >>>> >>>> I attached an affected object file. Please let me know if there is anything else >>>> I can do to help. >>> Disassembly of section .text.__x86.indirect_thunk: >>> >>> 0000000000000000 <__x86.indirect_thunk>: >>> 0: e8 04 00 00 00 callq 9 <__x86.indirect_thunk+0x9> >>> 5: f3 90 pause >>> 7: eb fc jmp 5 <__x86.indirect_thunk+0x5> >>> 9: 48 8d 64 24 08 lea 0x8(%rsp),%rsp >>> e: c3 retq >>> >>> That has the old-style CET-incompatible retpoline in a COMDAT section >>> in the .o file. What compiler options are being used for that? The >>> kernel should only use retpoline if GCC supports both of >>> -mindirect-branch=thunk-extern and -mindirect-branch-register, and this >>> compiler is doing *neither* of those. >> >> It uses "-mindirect-branch=thunk -mindirect-branch-loop=pause >> -fno-jump-tables", though I don't know if that even exists in >> upstream gcc (it is the gcc use for Chrome OS builds). I'll pass >> your feedback to our compiler team. >> >> Either case, I think it is less than optimal that objtool crashes >> with _any_ object code. > > I've got a pending fix for this, so that objtool doesn't seg fault, and > instead prints out a warning: > > quirks.o: warning: objtool: efi_delete_dummy_variable()+0x99: unsupported intra-function call > quirks.o: warning: objtool: If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE. > > The code is here, along with a few more fixes: > > https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/log/?h=TODO-objtool-seg-fault >
Excellent. I'll give it a try tomorrow.
Thanks for looking into this!
Guenter
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