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x86: clean up switch_to()

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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>
This commit is contained in:
Ingo Molnar 2008-03-05 10:24:37 +01:00
parent ecd94c0809
commit 23b55bd9f3
1 changed files with 31 additions and 15 deletions
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46
include/asm-x86/system.h
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@ -27,22 +27,38 @@ struct task_struct *__switch_to(struct task_struct *prev,
* 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)
/*