Anton Blanchard wrote:
>Hi,
>
>>No. const == never changes.
>>get_TR changes if a task calls schedule, and return on another cpu.
>>
>
>Yes, I found this exact problem on ppc64 where we would cache the
>processor data area across a schedule(). What was interesting was that
>__attribute__ ((pure)) was not enough to fix this.
>
>static inline struct Paca *get_paca(void) __attribute__ ((pure));
>static inline struct Paca *get_paca(void)
>{
> struct Paca *rval;
> __asm__ ("mfspr %0,0x113" : "=r" (rval));
> return rval;
>}
>
>Alan Modra came to the rescue and found that gcc was optimising too much
>and since the function did not touch any global variables, it would
>upgrade the pure to const. This was on gcc 3.0.X.
>
But the function called schedule - mustn't gcc assume that schedule
writes into global variables?
As far as I can see that sounds like a gcc bug.
Could you try how many get_cpu calls are generated by the attached testapp?
the i386 RH compilers generate correct code:
gcc-2.96-98: 4 calls.
gcc3-3.0.1-3: 2 calls.
--
Manfred
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This archive was generated by hypermail 2b29 : Thu Nov 15 2001 - 21:00:26 EST