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. Thanks, Guenter
