linux-kernel - [PATCH] mn10300: fix build error of missing fpu

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Message-ID: <dc421c4f-4842-4429-1b99-92865c2f24b6@infradead.org>
Date:   Thu, 19 Jan 2017 16:58:58 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Howells <dhowells@...hat.com>, linux-am33-list@...hat.com
Cc:     kbuild test robot <fengguang.wu@...el.com>
Subject: [PATCH] mn10300: fix build error of missing fpu_save()

I have 21 occurrences of kbuild test robot reporting this build failure
over more than one year and zero (0) attempts to fix it.  I have 2 alternate
(untested) fixes for it.  (If either of them causes a build error, it should
be simple to fix and I will do so.)

a. #include <asm/fpu.h> in <asm/switch_to.h> so that empty fpu_save() is
	visible
b. make <asm/switch_to.h> know about CONFIG_FPU not enabled

David, which one do you prefer?

Fengguang, it's allnoconfig => CONFIG_FPU=n that causes this build error.

----- a.-----
From: Randy Dunlap <rdunlap@...radead.org>

When CONFIG_FPU is not enabled on arch/mn10300, <asm/switch_to.h>
causes a build error with a call to fpu_save():

kernel/built-in.o: In function `.L410':
core.c:(.sched.text+0x28a): undefined reference to `fpu_save'

Fix this by including <asm/fpu.h> in <asm/switch_to.h> so that
an empty static inline fpu_save() is defined.

Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
Reported-by: kbuild test robot <fengguang.wu@...el.com>
Cc:	David Howells <dhowells@...hat.com>
---
 arch/mn10300/include/asm/switch_to.h |    1 +
 1 file changed, 1 insertion(+)

--- lnx-410-rc4.orig/arch/mn10300/include/asm/switch_to.h
+++ lnx-410-rc4/arch/mn10300/include/asm/switch_to.h
@@ -12,6 +12,7 @@
 #define _ASM_SWITCH_TO_H
 
 #include <asm/barrier.h>
+#include <asm/fpu.h>
 
 struct task_struct;
 struct thread_struct;

-----or b.-----
From: Randy Dunlap <rdunlap@...radead.org>

When CONFIG_FPU is not enabled on arch/mn10300, <asm/switch_to.h>
causes a build error with a call to fpu_save():

kernel/built-in.o: In function `.L410':
core.c:(.sched.text+0x28a): undefined reference to `fpu_save'

Fix this by defining switch_fpu() in <asm/switch_to.h> only when
CONFIG_FPU is enabled.

Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
Reported-by: kbuild test robot <fengguang.wu@...el.com>
Cc:	David Howells <dhowells@...hat.com>
---
 arch/mn10300/include/asm/switch_to.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- lnx-410-rc4.orig/arch/mn10300/include/asm/switch_to.h
+++ lnx-410-rc4/arch/mn10300/include/asm/switch_to.h
@@ -16,7 +16,7 @@
 struct task_struct;
 struct thread_struct;
 
-#if !defined(CONFIG_LAZY_SAVE_FPU)
+#if defined(CONFIG_FPU) && !defined(CONFIG_LAZY_SAVE_FPU)
 struct fpu_state_struct;
 extern asmlinkage void fpu_save(struct fpu_state_struct *);
 #define switch_fpu(prev, next)						\