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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Message-ID: <20240614152228.GAZmxgNPmozj7UzRdV@fat_crate.local>
Date: Fri, 14 Jun 2024 17:22:28 +0200
From: Borislav Petkov <bp@...en8.de>
To: kernel test robot <lkp@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>
Cc: 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 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.

I know Sean had a patchset to cleanup that gunk. Sean?

>From reading objtool docs, those functions (vmx_do_nmi_irqoff() too AFAICT)
should have FRAME_BEGIN/FRAME_END  but if I do that, objtool bitches
differently:

arch/x86/kvm/kvm-intel.o: warning: objtool: vmx_do_interrupt_irqoff+0xc: undefined stack state

Suggestions?

The other file it warns about is:

vmlinux.o: warning: objtool: .altinstr_replacement+0x2eb: call without frame pointer save/setup

That is fixed by

diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 89fa50d27a08..8cff4626478b 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -248,7 +248,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
  */
 #define alternative_call(oldfunc, newfunc, ft_flags, output, input...)	\
 	asm_inline volatile(ALTERNATIVE("call %c[old]", "call %c[new]", ft_flags) \
-		: output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
+		: output, ASM_CALL_CONSTRAINT : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
 
 /*
  * Like alternative_call, but there are two features and respective functions.
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 37596a417094..333b16181357 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -1657,7 +1657,7 @@ static noinline void __init alt_reloc_selftest(void)
 	 */
 	asm_inline volatile (
 		ALTERNATIVE("", "lea %[mem], %%" _ASM_ARG1 "; call __alt_reloc_selftest;", X86_FEATURE_ALWAYS)
-		: /* output */
+		: ASM_CALL_CONSTRAINT
 		: [mem] "m" (__alt_reloc_selftest_addr)
 		: _ASM_ARG1
 	);

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette