From 971c67ce37cfeeaf560e792a2c3bc21d8b67163a Mon Sep 17 00:00:00 2001 From: James Morse Date: Tue, 15 Dec 2015 11:21:25 +0000 Subject: [PATCH 1/1] arm64: reduce stack use in irq_handler The code for switching to irq_stack stores three pieces of information on the stack, fp+lr, as a fake stack frame (that lets us walk back onto the interrupted tasks stack frame), and the address of the struct pt_regs that contains the register values from kernel entry. (which dump_backtrace() will print in any stack trace). To reduce this, we store fp, and the pointer to the struct pt_regs. unwind_frame() can recognise this as the irq_stack dummy frame, (as it only appears at the top of the irq_stack), and use the struct pt_regs values to find the missing interrupted link-register. Suggested-by: Will Deacon Signed-off-by: James Morse Signed-off-by: Will Deacon --- arch/arm64/include/asm/irq.h | 11 ++++------- arch/arm64/kernel/entry.S | 12 +++++++----- arch/arm64/kernel/stacktrace.c | 19 ++++++++++++++++--- 3 files changed, 27 insertions(+), 15 deletions(-) diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h index 877c7e358384..3bece4379bd9 100644 --- a/arch/arm64/include/asm/irq.h +++ b/arch/arm64/include/asm/irq.h @@ -25,16 +25,13 @@ DECLARE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack); * ------------ * | | <- irq_stack_ptr * top ------------ - * | elr_el1 | + * | x19 | <- irq_stack_ptr - 0x08 * ------------ * | x29 | <- irq_stack_ptr - 0x10 * ------------ - * | xzr | - * ------------ - * | x19 | <- irq_stack_ptr - 0x20 - * ------------ * - * where x19 holds a copy of the task stack pointer. + * where x19 holds a copy of the task stack pointer where the struct pt_regs + * from kernel_entry can be found. * */ #define IRQ_STACK_PTR(cpu) ((unsigned long)per_cpu(irq_stack, cpu) + IRQ_STACK_START_SP) @@ -43,7 +40,7 @@ DECLARE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack); * The offset from irq_stack_ptr where entry.S will store the original * stack pointer. Used by unwind_frame() and dump_backtrace(). */ -#define IRQ_STACK_TO_TASK_STACK(ptr) *((unsigned long *)(ptr - 0x20)); +#define IRQ_STACK_TO_TASK_STACK(ptr) (*((unsigned long *)((ptr) - 0x08))) extern void set_handle_irq(void (*handle_irq)(struct pt_regs *)); diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 2284c296e3f7..0667fb7d8bb1 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -178,7 +178,7 @@ alternative_endif mrs \rd, sp_el0 .endm - .macro irq_stack_entry, dummy_lr + .macro irq_stack_entry mov x19, sp // preserve the original sp this_cpu_ptr irq_stack, x25, x26 @@ -196,10 +196,12 @@ alternative_endif add x26, x25, x26 mov sp, x26 - /* Add a dummy stack frame */ - stp x29, \dummy_lr, [sp, #-16]! // dummy stack frame + /* + * Add a dummy stack frame, this non-standard format is fixed up + * by unwind_frame() + */ + stp x29, x19, [sp, #-16]! mov x29, sp - stp x19, xzr, [sp, #-16]! 9998: .endm @@ -229,7 +231,7 @@ tsk .req x28 // current thread_info .macro irq_handler ldr_l x1, handle_arch_irq mov x0, sp - irq_stack_entry x22 + irq_stack_entry blr x1 irq_stack_exit .endm diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c index d916d5b6aef6..b9fd3a8abfc1 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -70,17 +70,30 @@ int notrace unwind_frame(struct stackframe *frame) * Check whether we are going to walk through from interrupt stack * to task stack. * If we reach the end of the stack - and its an interrupt stack, - * read the original task stack pointer from the dummy frame. + * unpack the dummy frame to find the original elr. * * Check the frame->fp we read from the bottom of the irq_stack, * and the original task stack pointer are both in current->stack. */ if (frame->sp == irq_stack_ptr) { + struct pt_regs *irq_args; unsigned long orig_sp = IRQ_STACK_TO_TASK_STACK(irq_stack_ptr); - if(object_is_on_stack((void *)orig_sp) && - object_is_on_stack((void *)frame->fp)) + if (object_is_on_stack((void *)orig_sp) && + object_is_on_stack((void *)frame->fp)) { frame->sp = orig_sp; + + /* orig_sp is the saved pt_regs, find the elr */ + irq_args = (struct pt_regs *)orig_sp; + frame->pc = irq_args->pc; + } else { + /* + * This frame has a non-standard format, and we + * didn't fix it, because the data looked wrong. + * Refuse to output this frame. + */ + return -EINVAL; + } } return 0; -- 2.39.2