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

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Date: Tue, 18 Jun 2024 12:42:34 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Borislav Petkov <bp@...en8.de>
Cc: kernel test robot <lkp@...el.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [tip:x86/alternatives 14/14] arch/x86/kvm/kvm.o: warning:
 objtool: .altinstr_replacement+0xc5: call without frame pointer save/setup

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@...el.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...