x86: clean up switch_to()
Make the code more readable and more hackable:
- use symbolic asm parameters
- use readable indentation
- add comments that explains the details
No code changed:
kernel/sched.o:
text data bss dec hex filename
28626 684 2640 31950 7cce sched.o.before
28626 684 2640 31950 7cce sched.o.after
md5:
2823d406c18b781975cdb2e7cfea0059 sched.o.before.asm
2823d406c18b781975cdb2e7cfea0059 sched.o.after.asm
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/asm-x86/system.h b/include/asm-x86/system.h
index 428d947..299ae96 100644
--- a/include/asm-x86/system.h
+++ b/include/asm-x86/system.h
@@ -27,22 +27,38 @@
* Saving eflags is important. It switches not only IOPL between tasks,
* it also protects other tasks from NT leaking through sysenter etc.
*/
-#define switch_to(prev, next, last) do { \
+#define switch_to(prev, next, last) \
+do { \
unsigned long esi, edi; \
- asm volatile("pushfl\n\t" /* Save flags */ \
- "pushl %%ebp\n\t" \
- "movl %%esp,%0\n\t" /* save ESP */ \
- "movl %5,%%esp\n\t" /* restore ESP */ \
- "movl $1f,%1\n\t" /* save EIP */ \
- "pushl %6\n\t" /* restore EIP */ \
- "jmp __switch_to\n" \
- "1:\t" \
- "popl %%ebp\n\t" \
- "popfl" \
- :"=m" (prev->thread.sp), "=m" (prev->thread.ip), \
- "=a" (last), "=S" (esi), "=D" (edi) \
- :"m" (next->thread.sp), "m" (next->thread.ip), \
- "2" (prev), "d" (next)); \
+ \
+ asm volatile( \
+ "pushfl \n\t" /* save flags */ \
+ "pushl %%ebp \n\t" /* save EBP */ \
+ "movl %%esp,%[prev_sp] \n\t" /* save ESP */ \
+ "movl %[next_sp],%%esp \n\t" /* restore ESP */ \
+ "movl $1f,%[prev_ip] \n\t" /* save EIP */ \
+ "pushl %[next_ip] \n\t" /* restore EIP */ \
+ "jmp __switch_to \n" /* regparm call */ \
+ "1: \t" \
+ "popl %%ebp \n\t" /* restore EBP */ \
+ "popfl \n" /* restore flags */ \
+ \
+ /* output parameters */ \
+ : [prev_sp] "=m" (prev->thread.sp), \
+ [prev_ip] "=m" (prev->thread.ip), \
+ "=a" (last), \
+ \
+ /* clobbered output registers: */ \
+ "=S" (esi), "=D" (edi) \
+ \
+ /* input parameters: */ \
+ : [next_sp] "m" (next->thread.sp), \
+ [next_ip] "m" (next->thread.ip), \
+ \
+ /* regparm parameters for __switch_to(): */ \
+ [prev] "a" (prev), \
+ [next] "d" (next) \
+ ); \
} while (0)
/*