Messages in this thread |  | | Date | Sun, 28 Jan 2018 15:06:42 -0600 | From | Josh Poimboeuf <> | Subject | Re: [v8,02/12] objtool: Allow alternatives to be ignored |
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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
Will post it soon.
-- Josh
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