Messages in this thread | | | Date | Thu, 17 Sep 2015 11:33:44 +0100 | From | James Morse <> | Subject | Re: [PATCH v2] arm64: Introduce IRQ stack |
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Hi Will,
On 16/09/15 12:25, Will Deacon wrote: > On Sun, Sep 13, 2015 at 03:42:17PM +0100, Jungseok Lee wrote: >> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h >> index dcd06d1..44839c0 100644 >> --- a/arch/arm64/include/asm/thread_info.h >> +++ b/arch/arm64/include/asm/thread_info.h >> @@ -73,8 +73,11 @@ static inline struct thread_info *current_thread_info(void) __attribute_const__; >> >> static inline struct thread_info *current_thread_info(void) >> { >> - return (struct thread_info *) >> - (current_stack_pointer & ~(THREAD_SIZE - 1)); >> + unsigned long sp_el0; >> + >> + asm volatile("mrs %0, sp_el0" : "=r" (sp_el0)); >> + >> + return (struct thread_info *)(sp_el0 & ~(THREAD_SIZE - 1)); > > This looks like it will generate worse code than our current implementation, > thanks to the asm volatile. Maybe just add something like a global > current_stack_pointer_el0?
Like current_stack_pointer does?: > register unsigned long current_stack_pointer_el0 asm ("sp_el0");
Unfortunately the compiler won't accept this, as it doesn't like the register name, it also won't accept instructions in this asm string.
Dropping the 'volatile' has the desired affect[0]. This would only cause a problem over a call to cpu_switch_to(), which writes to sp_el0, but also save/restores the callee-saved registers, so they will always be consistent.
James
[0] A fictitious example printk: > printk("%p%p%u%p", get_fs(), current_thread_info(), > smp_processor_id(), current);
With this patch compiles to: 5f8: d5384101 mrs x1, sp_el0 5fc: d5384100 mrs x0, sp_el0 600: d5384103 mrs x3, sp_el0 604: d5384104 mrs x4, sp_el0 608: 9272c484 and x4, x4, #0xffffffffffffc000 60c: 9272c463 and x3, x3, #0xffffffffffffc000 610: 9272c421 and x1, x1, #0xffffffffffffc000 614: aa0403e2 mov x2, x4 618: 90000000 adrp x0, 0 <do_bad> 61c: f9400884 ldr x4, [x4,#16] 620: 91000000 add x0, x0, #0x0 624: b9401c63 ldr w3, [x3,#28] 628: f9400421 ldr x1, [x1,#8] 62c: 94000000 bl 0 <printk>
Removing the volatile: 5e4: d5384102 mrs x2, sp_el0 5e8: f9400844 ldr x4, [x2,#16] 5ec: 91000000 add x0, x0, #0x0 5f0: b9401c43 ldr w3, [x2,#28] 5f4: f9400441 ldr x1, [x2,#8] 5f8: 94000000 bl 0 <printk>
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