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Date: Wed, 3 Sep 2008 11:29:30 +0200
From: Haavard Skinnemoen <haavard.skinnemoen@...el.com>
To: "Voss, Nikolaus" <N.Voss@...nmann.de>
Cc: <kernel@...32linux.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Add kernel support for oprofile callgraphs on AVR32
"Voss, Nikolaus" <N.Voss@...nmann.de> wrote:
> From: Nikolaus Voss <n.voss@...nmann.de>
>
> This patch adds backtracing capability to oprofile profiling in kernel
> and user mode on AVR32. This is done by going through the frames on the stack
> and adding oprofile traces for all return addresses. The code being profiled has
> to be compiled with frame pointers to make this work.
>
> Signed-off-by: Nikolaus Voss <n.voss@...nmann.de>
Hmm. This appears to be the third backtracer added to avr32, the first
two being dump_stack() and friends in arch/avr32/kernel/process.c, and
save_stack_trace() in arch/avr32/kernel/stacktrace.c.
Would be nice if some of this could be consolidated.
> ---
> diff --git a/arch/avr32/oprofile/Makefile b/arch/avr32/oprofile/Makefile
> index 1fe81c3..e0eb520 100644
> --- a/arch/avr32/oprofile/Makefile
> +++ b/arch/avr32/oprofile/Makefile
> @@ -5,4 +5,4 @@ oprofile-y := $(addprefix ../../../drivers/oprofile/, \
> event_buffer.o oprofile_files.o \
> oprofilefs.o oprofile_stats.o \
> timer_int.o)
> -oprofile-y += op_model_avr32.o
> +oprofile-y += op_model_avr32.o backtrace.o
> diff --git a/arch/avr32/oprofile/backtrace.c b/arch/avr32/oprofile/backtrace.c
> new file mode 100644
> index 0000000..81c89ec
> --- /dev/null
> +++ b/arch/avr32/oprofile/backtrace.c
> @@ -0,0 +1,81 @@
> +/*
> + * AVR32 specific backtracing code for oprofile
> + *
> + * Copyright 2008 Weinmann GmbH
> + *
> + * Author: Nikolaus Voss <n.voss@...nmann.de>
> + *
> + * Based on i386 oprofile backtrace code by John Levon and David Smith
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + */
> +
> +#include <linux/oprofile.h>
> +#include <linux/sched.h>
> +#include <asm/uaccess.h>
> +
> +/* The first two words of each frame on the stack look like this if we have
> + * frame pointers */
> +struct frame_head {
> + unsigned long lr;
> + struct frame_head *fp;
> +};
> +
> +/* copied from arch/avr32/kernel/process.c */
> +static inline int valid_stack_ptr(struct thread_info *tinfo, unsigned long p)
> +{
> + return (p > (unsigned long)tinfo)
> + && (p < (unsigned long)tinfo + THREAD_SIZE - 3);
> +}
> +
> +/* copied from arch/x86/oprofile/backtrace.c */
> +static struct frame_head * dump_user_backtrace(struct frame_head *head)
...though this is something the other two implementations don't have:
userspace stack tracing.
> +{
> + struct frame_head bufhead[2];
> +
> + /* Also check accessibility of one struct frame_head beyond */
> + if (!access_ok(VERIFY_READ, head, sizeof(bufhead)))
> + return NULL;
> + if (__copy_from_user_inatomic(bufhead, head, sizeof(bufhead)))
> + return NULL;
> +
> + oprofile_add_trace(bufhead[0].lr);
> +
> + /* frame pointers should strictly progress back up the stack
> + * (towards higher addresses) */
> + if (head >= bufhead[0].fp)
Could you swap the two operand so that it matches...
> + return NULL;
> +
> + return bufhead[0].fp;
> +}
> +
> +void avr32_backtrace(struct pt_regs * const regs, unsigned int depth)
> +{
> + /* Get first frame pointer */
> + struct frame_head *head = (struct frame_head *)(regs->r7);
> +
> + if (!user_mode(regs)) {
> +#ifdef CONFIG_FRAME_POINTER
> + /*
> + * Traverse the kernel stack from frame to frame up to
> + * "depth" steps.
> + */
> + while (depth-- && valid_stack_ptr(task_thread_info(current),
> + (unsigned long)head)) {
> + oprofile_add_trace(head->lr);
> + if (head->fp <= head)
...this?
> + break;
> + head = head->fp;
> + }
> +#endif
> + } else {
> + /* Assume we have frame pointers in user mode process */
What happens if we don't? I assume it will stop when it detects that
the frame pointer isn't monotonically increasing or when it gets a
fault?
> + while (depth-- && head)
> + head = dump_user_backtrace(head);
> + }
> +}
> +
> +
> diff --git a/arch/avr32/oprofile/op_model_avr32.c b/arch/avr32/oprofile/op_model_avr32.c
> index df42325..a3e9b3c 100644
> --- a/arch/avr32/oprofile/op_model_avr32.c
> +++ b/arch/avr32/oprofile/op_model_avr32.c
> @@ -22,6 +22,8 @@
> #define AVR32_PERFCTR_IRQ_GROUP 0
> #define AVR32_PERFCTR_IRQ_LINE 1
>
> +void avr32_backtrace(struct pt_regs * const regs, unsigned int depth);
> +
> enum { PCCNT, PCNT0, PCNT1, NR_counter };
>
> struct avr32_perf_counter {
> @@ -223,6 +225,8 @@ int __init oprofile_arch_init(struct oprofile_operations *ops)
> memcpy(ops, &avr32_perf_counter_ops,
> sizeof(struct oprofile_operations));
>
> + ops->backtrace = avr32_backtrace;
> +
> printk(KERN_INFO "oprofile: using AVR32 performance monitoring.\n");
>
> return 0;
Thanks,
Haavard
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