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 12:47:00 +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 Tue, Jun 18, 2024 at 12:42:35PM +0200, Peter Zijlstra wrote:
> 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.

ha! the below (whitespace damanged because copy/paste sucks), also works.

For some reason GCC thought it was fun to put that CALL outside the callframe, silly thing.


diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 5d4c86133453..c8cc578646d0 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1069,7 +1069,7 @@ static __always_inline u8 test_cc(unsigned int condition, unsigned long flags)
 
        flags = (flags & EFLAGS_MASK) | X86_EFLAGS_IF;
        asm("push %[flags]; popf; " CALL_NOSPEC
-           : "=a"(rc) : [thunk_target]"r"(fop), [flags]"r"(flags));
+           : "=a"(rc), ASM_CALL_CONSTRAINT : [thunk_target]"r"(fop), [flags]"r"(flags));
        return rc;
 }