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

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Message-ID: <YJ0RM2JIfFL8a0X2@gmail.com>
Date:   Thu, 13 May 2021 13:44:51 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "H. Peter Anvin" <hpa@...or.com>
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: [PATCH] x86/asm: Make <asm/asm.h> valid on cross-builds as well


* 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 */