linux-kernel - Re: [PATCH 03/11] objtool: Convert ANNOTATE_RETPOLINE

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Date:   Wed, 6 Dec 2023 15:31:58 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 03/11] objtool: Convert ANNOTATE_RETPOLINE_SAFE to ANNOTATE

On Mon, Dec 04, 2023, Peter Zijlstra wrote:
> 
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -193,12 +193,7 @@
>   * objtool the subsequent indirect jump/call is vouched safe for retpoline
>   * builds.
>   */
> -.macro ANNOTATE_RETPOLINE_SAFE
> -.Lhere_\@:
> -	.pushsection .discard.retpoline_safe
> -	.long .Lhere_\@
> -	.popsection
> -.endm
> +#define ANNOTATE_RETPOLINE_SAFE	ANNOTATE type=ANNOTYPE_RETPOLINE_SAFE
>  
>  /*
>   * (ab)use RETPOLINE_SAFE on RET to annotate away 'bare' RET instructions
> @@ -317,11 +312,7 @@
>  
>  #else /* __ASSEMBLY__ */
>  
> -#define ANNOTATE_RETPOLINE_SAFE					\
> -	"999:\n\t"						\
> -	".pushsection .discard.retpoline_safe\n\t"		\
> -	".long 999b\n\t"					\
> -	".popsection\n\t"
> +#define ANNOTATE_RETPOLINE_SAFE ASM_ANNOTATE(ANNOTYPE_RETPOLINE_SAFE)

This fails for some of my builds that end up with CONFIG_OBJTOOl=n.  Adding a
stub for ASM_ANNOTATE() gets me past that:

@@ -156,6 +171,7 @@
 #define STACK_FRAME_NON_STANDARD(func)
 #define STACK_FRAME_NON_STANDARD_FP(func)
 #define ANNOTATE_NOENDBR
+#define ASM_ANNOTATE(x)
 #define ASM_REACHABLE
 #else
 #define ANNOTATE_INTRA_FUNCTION_CALL

but then I run into other issues:

arch/x86/kernel/relocate_kernel_32.S: Assembler messages:
arch/x86/kernel/relocate_kernel_32.S:96: Error: Parameter named `type' does not exist for macro `annotate'
arch/x86/kernel/relocate_kernel_32.S:166: Error: Parameter named `type' does not exist for macro `annotate'
arch/x86/kernel/relocate_kernel_32.S:174: Error: Parameter named `type' does not exist for macro `annotate'
arch/x86/kernel/relocate_kernel_32.S:200: Error: Parameter named `type' does not exist for macro `annotate'
arch/x86/kernel/relocate_kernel_32.S:220: Error: Parameter named `type' does not exist for macro `annotate'
arch/x86/kernel/relocate_kernel_32.S:285: Error: Parameter named `type' does not exist for macro `annotate'