linux-kernel - Re: x86_64 has 2 x arch_vma_name()

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Message-ID: <20070725205959.GA29548@uranus.ravnborg.org>
Date:	Wed, 25 Jul 2007 22:59:59 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Andi Kleen <ak@...e.de>, LKML <linux-kernel@...r.kernel.org>
Cc:	Nathan Lynch <ntl@...ox.com>, Andy Whitcroft <apw@...dowen.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>
Subject: Re: x86_64 has 2 x arch_vma_name() - can we drop one?

On Wed, Jul 25, 2007 at 08:31:32PM +0200, Sam Ravnborg wrote:
> In include/linux/mm.h arch_vma_name() is declared __weak.
> This hide the fact that x86_64 has 2 implementations of
> said function.
> 
> In arch/x86_64/mm/init.c:
> const char *arch_vma_name(struct vm_area_struct *vma)
> {
> 	if (vma->vm_mm && vma->vm_start == (long)vma->vm_mm->context.vdso)
> 		return "[vdso]";
> 	if (vma == &gate_vma)
> 		return "[vsyscall]";
> 	return NULL;
> }
> 
> And in arch/x86_64/ia32/syscall32.c:
> const char *arch_vma_name(struct vm_area_struct *vma)
> {
> 	if (vma->vm_start == VSYSCALL32_BASE &&
> 	    vma->vm_mm && vma->vm_mm->task_size == IA32_PAGE_OFFSET)
> 		return "[vdso]";
> 	return NULL;
> }
> 
> As no comment were preceeding the fucntions this seems not to be on
> purpose.
> If I am correct which one should die?
> 
> The reason why this popped up is that the __weak definition in mm.h
> causes problems on at least powerpc (trigger a binutils bug).
> A similar bug is present at ia64 - but I have not confirmed if the
> same fix is needed.

I cooked up following patch - but I do not claim I understand this
code. It was done only by merging the functionality into one function.
I need this patch or a similar one to be added so the weak declaration
of arch_vma_name in mm.h can be made a normal prototype.

	Sam


[PATCH] x86_64: merge two identical named funtion into one

The function arch_vma_name() is declared weak and thus it was
not noticed that x86_64 had two almost identical implementations.

It was introduced in syscall32.c by: c633090e3105e779c97d4978e5e3d7d66b291cfb
It was introduced in mm/init.c by: 2aae950b21e4bc789d1fc6668faf67e8748300b7

Signed-off-by: Sam Ravnborg <sam@...nborg.org>
Cc: Roland McGrath <roland@...hat.com>
---
diff --git a/arch/x86_64/ia32/syscall32.c b/arch/x86_64/ia32/syscall32.c
index fc4419f..15013ba 100644
--- a/arch/x86_64/ia32/syscall32.c
+++ b/arch/x86_64/ia32/syscall32.c
@@ -49,14 +49,6 @@ int syscall32_setup_pages(struct linux_binprm *bprm, int exstack)
 	return ret;
 }
 
-const char *arch_vma_name(struct vm_area_struct *vma)
-{
-	if (vma->vm_start == VSYSCALL32_BASE &&
-	    vma->vm_mm && vma->vm_mm->task_size == IA32_PAGE_OFFSET)
-		return "[vdso]";
-	return NULL;
-}
-
 static int __init init_syscall32(void)
 { 
 	char *syscall32_page = (void *)get_zeroed_page(GFP_KERNEL);
diff --git a/arch/x86_64/mm/init.c b/arch/x86_64/mm/init.c
index 38f5d63..6f608d8 100644
--- a/arch/x86_64/mm/init.c
+++ b/arch/x86_64/mm/init.c
@@ -43,6 +43,7 @@
 #include <asm/proto.h>
 #include <asm/smp.h>
 #include <asm/sections.h>
+#include <asm/vsyscall32.h>
 
 #ifndef Dprintk
 #define Dprintk(x...)
@@ -734,6 +735,9 @@ const char *arch_vma_name(struct vm_area_struct *vma)
 {
 	if (vma->vm_mm && vma->vm_start == (long)vma->vm_mm->context.vdso)
 		return "[vdso]";
+	if (vma->vm_mm && vma->vm_start == VSYSCALL32_BASE &&
+	    vma->vm_mm->task_size == IA32_PAGE_OFFSET)
+		return "[vdso]";
 	if (vma == &gate_vma)
 		return "[vsyscall]";
 	return NULL;
-
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