linux-kernel - Re: [PATCH] x86/asm: Make <asm/asm.h> valid on cross-builds as well

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Date:   Thu, 13 May 2021 07:10:11 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Ingo Molnar <mingo@...nel.org>
CC:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: [PATCH] x86/asm: Make <asm/asm.h> valid on cross-builds as well

Makes sense to me.

Reviewed-by: H. Peter Anvin <hpa@...or.com>

On May 13, 2021 4:44:51 AM PDT, Ingo Molnar <mingo@...nel.org> wrote:
>
>* H. Peter Anvin <hpa@...or.com> wrote:
>
>> Needed some head scratching, but then...
>> 
>> It makes sense for the cross-build: it's building for the host, and a
>
>> non-x86 machine isn't doing to have a register named "%rsp".
>
>Oh, indeed, sfr is building on powerpc64 I think?
>
>> So this needs to be protected from non-kernel use either via
>__KERNEL__ 
>> or by factoring the basic macros out into a separate file.
>
>So something like the below?
>
>The exception table stuff is definitely kernel-only. The others could,
>in 
>principle, be used by tooling as well.
>
>Thanks,
>
>	Ingo
>
>=======================>
>From: Ingo Molnar <mingo@...nel.org>
>Date: Thu, 13 May 2021 13:41:41 +0200
>Subject: [PATCH] x86/asm: Make <asm/asm.h> valid on cross-builds as
>well
>
>Stephen Rothwell reported that the objtool cross-build breaks on
>non-x86 hosts:
>
>> tools/arch/x86/include/asm/asm.h:185:24: error: invalid register name
>for 'current_stack_pointer'
>  >   185 | register unsigned long current_stack_pointer asm(_ASM_SP);
>  >       |                        ^~~~~~~~~~~~~~~~~~~~~
>
>The PowerPC host obviously doesn't know much about x86 register names.
>
>Protect the kernel-specific bits of <asm/asm.h>, so that it can be
>included by tooling and cross-built.
>
>Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
>Signed-off-by: Ingo Molnar <mingo@...nel.org>
>---
> arch/x86/include/asm/asm.h       | 4 ++++
> tools/arch/x86/include/asm/asm.h | 4 ++++
> 2 files changed, 8 insertions(+)
>
>diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
>index 507a37a46027..3ad3da9a7d97 100644
>--- a/arch/x86/include/asm/asm.h
>+++ b/arch/x86/include/asm/asm.h
>@@ -120,6 +120,8 @@
> # define CC_OUT(c) [_cc_ ## c] "=qm"
> #endif
> 
>+#ifdef __KERNEL__
>+
> /* Exception table entry */
> #ifdef __ASSEMBLY__
> # define _ASM_EXTABLE_HANDLE(from, to, handler)			\
>@@ -186,4 +188,6 @@ register unsigned long current_stack_pointer
>asm(_ASM_SP);
> #define ASM_CALL_CONSTRAINT "+r" (current_stack_pointer)
> #endif /* __ASSEMBLY__ */
> 
>+#endif /* __KERNEL__ */
>+
> #endif /* _ASM_X86_ASM_H */
>diff --git a/tools/arch/x86/include/asm/asm.h
>b/tools/arch/x86/include/asm/asm.h
>index 507a37a46027..3ad3da9a7d97 100644
>--- a/tools/arch/x86/include/asm/asm.h
>+++ b/tools/arch/x86/include/asm/asm.h
>@@ -120,6 +120,8 @@
> # define CC_OUT(c) [_cc_ ## c] "=qm"
> #endif
> 
>+#ifdef __KERNEL__
>+
> /* Exception table entry */
> #ifdef __ASSEMBLY__
> # define _ASM_EXTABLE_HANDLE(from, to, handler)			\
>@@ -186,4 +188,6 @@ register unsigned long current_stack_pointer
>asm(_ASM_SP);
> #define ASM_CALL_CONSTRAINT "+r" (current_stack_pointer)
> #endif /* __ASSEMBLY__ */
> 
>+#endif /* __KERNEL__ */
>+
> #endif /* _ASM_X86_ASM_H */

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