hi,
在 2002-03-01 11:11:00 you wrote：
>hi,
> sorry,it seems this patch bring other problem,please don't use.
>i am investigating it.
With this patch, there may be more than one processes having CP0_CU1 enabled,
thus fp context may be corrupted silently.
The fix is to deprive fpu from last_task_used_math(if not null) in init_fpu
See the modified patch below.
BTW,when debugging for this problem,i found that every process will use fpu
at least once. in a statically linked executable of this program:
main() {}
there are two cfc1, one in __setfpucw,the other in __sigsetjmp_aux
and many fpu ops in __mktime_internal.
the first fpu usage is caused by __setfpucw.
>>>
>>>I think it make sense to clear used_math in do_exec(). It also improvies the
>>> performance slightly by not loading the parent's FPU context when it uses
>>> the
>>>FPU for the first time.
it will need init_fpu then,but anyway register access is faster than memory
access.
>>>
>>>Do you have a patch for this?
>>Yes. Here it is.
>>
>>--- processor.h.ori Thu Feb 28 15:02:20 2002
>>+++ processor.h Thu Feb 28 15:00:10 2002
>>@@ -215,6 +215,7 @@
>> regs->cp0_epc = new_pc; \
>> regs->regs[29] = new_sp; \
>> current->thread.current_ds = USER_DS; \
>>+ current->used_math = 0; \
>> } while (0)
>>
>> unsigned long get_wchan(struct task_struct *p);
>>
>>
>>--- traps.c.ori Thu Feb 28 15:04:48 2002
>>+++ traps.c Thu Feb 28 15:05:23 2002
>>@@ -668,8 +668,12 @@
>> if (current->used_math) { /* Using the FPU again. */
>> lazy_fpu_switch(last_task_used_math);
>> } else { /* First time FPU user. */
>>- if (last_task_used_math != NULL)
>>+ if (last_task_used_math != NULL) {
>>+ int status = read_32bit_cp0_register(CP0_STATUS);
>>+ write_32bit_cp0_register(CP0_STATUS,status|ST0_CU1);
>>+
>> save_fp(last_task_used_math);
>>+ }
This should be changed to:
+ if (last_task_used_math != NULL) {
+ __enable_fpu();
save_fp(last_task_used_math);
+ /* last_task_used_math loose
fpu */
+ ((struct pt_regs *)(__KSTK_TOS(last_task_used_math) -
sizeof(struct pt_regs)))->cp0_status &= ~ST0_CU1;
+ }
>> init_fpu();
>> current->used_math = 1;
>> }
>>
>>
>>>
>>>Jun
>>
>>Regards
>> Zhang Fuxin
>> fxzhang@ict.ac.cn
>
>Regards
> Zhang Fuxin
> fxzhang@ict.ac.cn
Regards
Zhang Fuxin
fxzhang@ict.ac.cn
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