%fs/%gs cleanup in mmu_context.h

PATCH In review Chris Wright 2 participants 3 messages Aug 12, 2005

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Chris Wright

author

2005-08-12 23:05 UTC #0 lore raw

PATCH 1/1 %fs/%gs cleanup in mmu_context.h

Small change to remove difference between Xen and mainline deactivate_mm. While there, cleanup prepare_arch_switch as well. This generates identical code.

Signed-off-by Chris Wright <[email protected]>

---

linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h +5 -5

diff -r ba46bd7f5cdf linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h
@@ -34,10 +34,10 @@
 	 * are always kernel segments while inside the kernel. Must
 	 * happen before reload of cr3/ldt (i.e., not in __switch_to).
 	 */
-	__asm__ __volatile__ ( "mov %%fs,%0 ; mov %%gs,%1"
-		: "=m" (*(int *)&current->thread.fs),
-		  "=m" (*(int *)&current->thread.gs));
-	__asm__ __volatile__ ( "mov %0,%%fs ; mov %0,%%gs"
+	asm volatile ( "movl %%fs,%0 ; movl %%gs,%1"
+		: "=m" (current->thread.fs),
+		  "=m" (current->thread.gs));
+	asm volatile ( "movl %0,%%fs ; movl %0,%%gs"
 		: : "r" (0) );
 }

@@ -100,7 +100,7 @@
 }
 
 #define deactivate_mm(tsk, mm) \
-	asm("mov %0,%%fs ; mov %0,%%gs": :"r" (0))
+	asm("movl %0,%%fs ; movl %0,%%gs": :"r" (0))
 
 #define activate_mm(prev, next) \
 	switch_mm((prev),(next),NULL)

Vincent Hanquez

2005-08-12 23:23 UTC #1 lore raw

Quoted 9 lines · Chris Wright

diff -r ba46bd7f5cdf linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h
linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h +0 -1
@@ -34,10 +34,10 @@
 	 * are always kernel segments while inside the kernel. Must
 	 * happen before reload of cr3/ldt (i.e., not in __switch_to).
 	 */
-	__asm__ __volatile__ ( "mov %%fs,%0 ; mov %%gs,%1"

linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h line 43

Quoted 10 lines

linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h +4 -3

-		: "=m" (*(int *)&current->thread.fs),
-		  "=m" (*(int *)&current->thread.gs));
-	__asm__ __volatile__ ( "mov %0,%%fs ; mov %0,%%gs"
+	asm volatile ( "movl %%fs,%0 ; movl %%gs,%1"
+		: "=m" (current->thread.fs),
+		  "=m" (current->thread.gs));
+	asm volatile ( "movl %0,%%fs ; movl %0,%%gs"
 		: : "r" (0) );
 }

The first inline asm is wrong.
latest binutils no longer accept instructions for moving between a segment register and a 32bit memory location. you should keep the "mov" instead of "movl".

see:
http://sourceware.org/ml/binutils/2005-03/msg00873.html

linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h line 103

Quoted 6 lines

linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h +1 -1

@@ -100,7 +100,7 @@
 }
 
 #define deactivate_mm(tsk, mm) \
-	asm("mov %0,%%fs ; mov %0,%%gs": :"r" (0))
+	asm("movl %0,%%fs ; movl %0,%%gs": :"r" (0))

This one clearing the segment register is fine.

Signature · 1 line

Vincent Hanquez

Chris Wright

author

2005-08-12 23:55 UTC #2 lore raw

Quoted 17 lines · * Vincent Hanquez ([email protected]) wrote:

Quoted 16 lines · Chris Wright

diff -r ba46bd7f5cdf linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h

linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h +4 -4

@@ -34,10 +34,10 @@
 	 * are always kernel segments while inside the kernel. Must
 	 * happen before reload of cr3/ldt (i.e., not in __switch_to).
 	 */
-	__asm__ __volatile__ ( "mov %%fs,%0 ; mov %%gs,%1"
-		: "=m" (*(int *)&current->thread.fs),
-		  "=m" (*(int *)&current->thread.gs));
-	__asm__ __volatile__ ( "mov %0,%%fs ; mov %0,%%gs"
+	asm volatile ( "movl %%fs,%0 ; movl %%gs,%1"
+		: "=m" (current->thread.fs),
+		  "=m" (current->thread.gs));
+	asm volatile ( "movl %0,%%fs ; movl %0,%%gs"

Quoted 8 lines

linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h line 43
Quoted 3 lines
linux-2.6-xen-sparse/include/asm-xen/asm-i386/mmu_context.h +0 -0
 		: : "r" (0) );
 }
 
The first inline asm is wrong.
latest binutils no longer accept instructions for moving between a segment register and a 32bit memory location. you should keep the "mov" instead of "movl".

Thanks Vincent (I had forgotten about that thread, ISTR Linus agruing vehemently against the change). Heh, the irony, objdump is showing the assembler generating movl in both cases. I have no preference, I'll resubmit.

thanks,
-chris