Messages in this thread | | | Date | Mon, 17 Mar 2003 12:39:39 -0500 | From | Jakub Jelinek <> | Subject | Re: Why is get_current() not const function? |
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On Mon, Mar 17, 2003 at 06:26:05PM +0100, Andi Kleen wrote: > torvalds@transmeta.com (Linus Torvalds) writes: > > >> and why on x86-64 > >>the movq %%gs:0, %0 inline asm is volatile with "memory" clobber? > > > > Can't help you on that one, but it looks like it uses various helper > > functions for doing the x86-64 per-processor data structures, and I bet > > those helper functions are shared by _other_ users who definitely want > > to have their data properly re-read. Ie "current()" may be constant in > > process context, but that sure isn't true about a lot of other things in > > the per-processor data structures. > > Yes, that's the big issue. const current requires non volatile read_pda() > and making read_pda non volatile breaks lots of code currently and probably > needs an audit over all users.
Well, that's one that is not particularly hard to fix. Either a new set of pda access macros without volatile and memory clobber can be written, or just get_current can use its own asm, ie. static inline struct task_struct *get_current(void) { struct task_struct *t; asm ("movq %%gs:%c1,%0" : "=r" (t) : "i"(pda_offset(pcurrent))); return t; }
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