Re: [tip:x86/alternatives 14/14] arch/x86/kvm/kvm.o: warning: objtool: .altinstr_replacement+0xc5: call without frame pointer save/setup

Peter Zijlstra
2024-06-18T10:42:59Z

On Fri, Jun 14, 2024 at 05:22:28PM +0200, Borislav Petkov wrote:
> On Fri, Jun 14, 2024 at 04:15:14PM +0800, kernel test robot wrote:
> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/alternatives
> > head: f776e41fdcc4141876ef6f297318ab04c2382eb7
> > commit: f776e41fdcc4141876ef6f297318ab04c2382eb7 [14/14] x86/alternative: Replace the old macros
> > config: x86_64-buildonly-randconfig-r001-20211209 (https://download.01.org/0day-ci/archive/20240614/202406141648.jO9qNGLa-lkp@intel.com/config)
> > compiler: gcc-13 (Ubuntu 13.2.0-4ubuntu3) 13.2.0
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240614/202406141648.jO9qNGLa-lkp@intel.com/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202406141648.jO9qNGLa-lkp@intel.com/
> >
> > All warnings (new ones prefixed by >>):
> >
> > >> arch/x86/kvm/kvm.o: warning: objtool: .altinstr_replacement+0xc5: call without frame pointer save/setup
>
> That thing comes from:
>
> SYM_FUNC_START(vmx_do_interrupt_irqoff)
> VMX_DO_EVENT_IRQOFF CALL_NOSPEC _ASM_ARG1
> SYM_FUNC_END(vmx_do_interrupt_irqoff)
>
> at the end of arch/x86/kvm/vmx/vmenter.S.

You sure? Afaict the thing is:

$ OBJTOOL_ARGS="--verbose" make O=tmp-build/ arch/x86/kvm/
...
arch/x86/kvm/kvm.o: warning: objtool: .altinstr_replacement+0xc5: call without frame pointer save/setup
arch/x86/kvm/kvm.o: warning: objtool: em_loop.part.0+0x29: (alt)
arch/x86/kvm/kvm.o: warning: objtool: em_loop.part.0+0x0: <=== (sym)
0000 0000000000028220 <em_loop.part.0>:
0000 28220: 0f b6 47 61 movzbl 0x61(%rdi),%eax
0004 28224: 3c e2 cmp $0xe2,%al
0006 28226: 74 2c je 28254 <em_loop.part.0+0x34>
0008 28228: 48 8b 57 10 mov 0x10(%rdi),%rdx
000c 2822c: 83 f0 05 xor $0x5,%eax
000f 2822f: 48 c1 e0 04 shl $0x4,%rax
0013 28233: 25 f0 00 00 00 and $0xf0,%eax
0018 28238: 81 e2 d5 08 00 00 and $0x8d5,%edx
001e 2823e: 80 ce 02 or $0x2,%dh
0021 28241: 48 05 00 00 00 00 add $0x0,%rax 28243: R_X86_64_32S em_setcc
0027 28247: 52 push %rdx
0028 28248: 9d popf
0029 28249: ff d0 call *%rax
002b 2824b: 90 nop
002c 2824c: 90 nop
002d 2824d: 90 nop
002e 2824e: 31 d2 xor %edx,%edx
0030 28250: 84 c0 test %al,%al
0032 28252: 74 1d je 28271 <em_loop.part.0+0x51>
0034 28254: 55 push %rbp
0035 28255: 48 63 b7 d0 00 00 00 movslq 0xd0(%rdi),%rsi
003c 2825c: 48 03 b7 90 00 00 00 add 0x90(%rdi),%rsi
0043 28263: 48 89 e5 mov %rsp,%rbp
0046 28266: e8 05 fe ff ff call 28070 <assign_eip>
004b 2826b: 5d pop %rbp
004c 2826c: e9 00 00 00 00 jmp 28271 <em_loop.part.0+0x51> 2826d: R_X86_64_PLT32 __x86_return_thunk-0x4
0051 28271: 89 d0 mov %edx,%eax
0053 28273: e9 00 00 00 00 jmp 28278 <em_loop.part.0+0x58> 28274: R_X86_64_PLT32 __x86_return_thunk-0x4
0058 28278: 0f 1f 84 00 00 00 00 00 nopl 0x0(%rax,%rax,1)

Which is in fact test_cc() from em_loop().

Now, that .config is a FRAME_POINTER build, and the fast-call thing
don't do frames, so it is right to complain. Big question is why it
didn't complain previously I suppose.

Also, notably, this patch:

https://lkml.kernel.org/r/20231204093732.323101886@infradead.org

cures things.

Let me poke a little more...