On Sun, Jan 28, 2018 at 03:06:42PM -0600, 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 >
'objtool: Improve retpoline alternative handling' works for me. Thanks! Guenter
