Messages in this thread | | | Date | Tue, 9 Feb 2021 07:50:53 -0600 | From | Segher Boessenkool <> | Subject | Re: [PATCH v5 20/22] powerpc/syscall: Avoid storing 'current' in another pointer |
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On Tue, Feb 09, 2021 at 12:36:20PM +1000, Nicholas Piggin wrote: > What if you did this?
> +static inline struct task_struct *get_current(void) > +{ > + register struct task_struct *task asm ("r2"); > + > + return task; > +}
Local register asm variables are *only* guaranteed to live in that register as operands to an asm. See https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html#Local-Register-Variables ("The only supported use" etc.)
You can do something like
static inline struct task_struct *get_current(void) { register struct task_struct *task asm ("r2");
asm("" : "+r"(task));
return task; }
which makes sure that "task" actually is in r2 at the point of that asm.
Segher
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