Re: [PATCH v5 5/6] arm64: ftrace: add arch-specific stack tracer

From: Jungseok Lee
Date: Wed Nov 11 2015 - 17:57:12 EST

On Nov 11, 2015, at 2:03 PM, AKASHI Takahiro wrote:
> Jungseok,
>
> On 11/10/2015 11:05 PM, Jungseok Lee wrote:
>> On Nov 6, 2015, at 3:44 PM, AKASHI Takahiro wrote:
>>
>> Hi Akashi,
>>
>>> Stack tracer on arm64, check_stack(), is uniqeue in the following
>>> points:
>>> * analyze a function prologue of a traced function to estimate a more
>>> accurate stack pointer value, replacing naive '<child's fp> + 0x10.'
>>> * use walk_stackframe(), instead of slurping stack contents as orignal
>>> check_stack() does, to identify a stack frame and a stack index (height)
>>> for every callsite.
>>>
>>> Regarding a function prologue analyzer, there is no guarantee that we can
>>> handle all the possible patterns of function prologue as gcc does not use
>>> any fixed templates to generate them. 'Instruction scheduling' is another
>>> issue here.
>>> Nevertheless, the current version will surely cover almost all the cases
>>> in the kernel image and give us useful information on stack pointers.
>>>
>>> So this patch utilizes a function prologue only for stack tracer, and
>>> does not affect the behaviors of existing stacktrace functions.
>>>
>>> Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
>>> ---
>>> arch/arm64/include/asm/stacktrace.h | 4 +
>>> arch/arm64/kernel/ftrace.c | 64 ++++++++++++
>>> arch/arm64/kernel/stacktrace.c | 185 ++++++++++++++++++++++++++++++++++-
>>> 3 files changed, 250 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
>>> index 7318f6d..47b4832 100644
>>> --- a/arch/arm64/include/asm/stacktrace.h
>>> +++ b/arch/arm64/include/asm/stacktrace.h
>>> @@ -25,5 +25,9 @@ struct stackframe {
>>> extern int unwind_frame(struct stackframe *frame);
>>> extern void walk_stackframe(struct stackframe *frame,
>>> int (*fn)(struct stackframe *, void *), void *data);
>>> +#ifdef CONFIG_STACK_TRACER
>>> +struct stack_trace;
>>> +extern void save_stack_trace_sp(struct stack_trace *trace, unsigned long *sp);
>>> +#endif
>>>
>>> #endif /* __ASM_STACKTRACE_H */
>>> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
>>> index 314f82d..46bfe37 100644
>>> --- a/arch/arm64/kernel/ftrace.c
>>> +++ b/arch/arm64/kernel/ftrace.c
>>> @@ -9,6 +9,7 @@
>>> * published by the Free Software Foundation.
>>> */
>>>
>>> +#include <linux/bug.h>
>>> #include <linux/ftrace.h>
>>> #include <linux/swab.h>
>>> #include <linux/uaccess.h>
>>> @@ -16,6 +17,7 @@
>>> #include <asm/cacheflush.h>
>>> #include <asm/ftrace.h>
>>> #include <asm/insn.h>
>>> +#include <asm/stacktrace.h>
>>>
>>> #ifdef CONFIG_DYNAMIC_FTRACE
>>> /*
>>> @@ -173,3 +175,65 @@ int ftrace_disable_ftrace_graph_caller(void)
>>> }
>>> #endif /* CONFIG_DYNAMIC_FTRACE */
>>> #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
>>> +
>>> +#ifdef CONFIG_STACK_TRACER
>>> +static unsigned long stack_trace_sp[STACK_TRACE_ENTRIES];
>>> +static unsigned long raw_stack_trace_max_size;
>>> +
>>> +void check_stack(unsigned long ip, unsigned long *stack)
>>> +{
>>> + unsigned long this_size, flags;
>>> + unsigned long top;
>>> + int i, j;
>>> +
>>> + this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
>>> + this_size = THREAD_SIZE - this_size;
>>> +
>>> + if (this_size <= raw_stack_trace_max_size)
>>> + return;
>>> +
>>> + /* we do not handle an interrupt stack yet */
>>> + if (!object_is_on_stack(stack))
>>> + return;
>>> +
>>> + local_irq_save(flags);
>>> + arch_spin_lock(&max_stack_lock);
>>> +
>>> + /* check again */
>>> + if (this_size <= raw_stack_trace_max_size)
>>> + goto out;
>>> +
>>> + /* find out stack frames */
>>> + stack_trace_max.nr_entries = 0;
>>> + stack_trace_max.skip = 0;
>>> + save_stack_trace_sp(&stack_trace_max, stack_trace_sp);
>>> + stack_trace_max.nr_entries--; /* for the last entry ('-1') */
>>> +
>>> + /* calculate a stack index for each function */
>>> + top = ((unsigned long)stack & ~(THREAD_SIZE-1)) + THREAD_SIZE;
>>> + for (i = 0; i < stack_trace_max.nr_entries; i++)
>>> + stack_trace_index[i] = top - stack_trace_sp[i];
>>> + raw_stack_trace_max_size = this_size;
>>> +
>>> + /* Skip over the overhead of the stack tracer itself */
>>> + for (i = 0; i < stack_trace_max.nr_entries; i++)
>>> + if (stack_trace_max.entries[i] == ip)
>>> + break;
>>> +
>>> + stack_trace_max.nr_entries -= i;
>>> + for (j = 0; j < stack_trace_max.nr_entries; j++) {
>>> + stack_trace_index[j] = stack_trace_index[j + i];
>>> + stack_trace_max.entries[j] = stack_trace_max.entries[j + i];
>>> + }
>>> + stack_trace_max_size = stack_trace_index[0];
>>> +
>>> + if (task_stack_end_corrupted(current)) {
>>> + WARN(1, "task stack is corrupted.\n");
>>> + stack_trace_print();
>>> + }
>>> +
>>> + out:
>>> + arch_spin_unlock(&max_stack_lock);
>>> + local_irq_restore(flags);
>>> +}
>>> +#endif /* CONFIG_STACK_TRACER */
>>> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
>>> index 5fd3477..4ee052a 100644
>>> --- a/arch/arm64/kernel/stacktrace.c
>>> +++ b/arch/arm64/kernel/stacktrace.c
>>> @@ -23,6 +23,144 @@
>>>
>>> #include <asm/stacktrace.h>
>>>
>>> +#ifdef CONFIG_STACK_TRACER
>>> +/*
>>> + * This function parses a function prologue of a traced function and
>>> + * determines its stack size.
>>> + * A return value indicates a location of @pc in a function prologue.
>>> + * @return value:
>>> + * <case 1> <case 1'>
>>> + * 1:
>>> + * sub sp, sp, #XX sub sp, sp, #XX
>>> + * 2:
>>> + * stp x29, x30, [sp, #YY] stp x29, x30, [sp, #--ZZ]!
>>> + * 3:
>>> + * add x29, sp, #YY mov x29, sp
>>> + * 0:
>>> + *
>>> + * <case 2>
>>> + * 1:
>>> + * stp x29, x30, [sp, #-XX]!
>>> + * 3:
>>> + * mov x29, sp
>>> + * 0:
>>> + *
>>> + * @size: sp offset from calller's sp (XX or XX + ZZ)
>>> + * @size2: fp offset from new sp (YY or 0)
>>> + */
>>> +static int analyze_function_prologue(unsigned long pc,
>>> + unsigned long *size, unsigned long *size2)
>>> +{
>>> + unsigned long offset;
>>> + u32 *addr, insn;
>>> + int pos = -1;
>>> + enum aarch64_insn_register src, dst, reg1, reg2, base;
>>> + int imm;
>>> + enum aarch64_insn_variant variant;
>>> + enum aarch64_insn_adsb_type adsb_type;
>>> + enum aarch64_insn_ldst_type ldst_type;
>>> +
>>> + *size = *size2 = 0;
>>> +
>>> + if (!pc)
>>> + goto out;
>>> +
>>> + if (unlikely(!kallsyms_lookup_size_offset(pc, NULL, &offset)))
>>> + goto out;
>>> +
>>> + addr = (u32 *)(pc - offset);
>>> +#ifdef CONFIG_DYNAMIC_FTRACE
>>> + if (addr == (u32 *)ftrace_call)
>>> + addr = (u32 *)ftrace_caller;
>>> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
>>> + else if (addr == (u32 *)ftrace_graph_caller)
>>> +#ifdef CONFIG_DYNAMIC_FTRACE
>>> + addr = (u32 *)ftrace_caller;
>>> +#else
>>> + addr = (u32 *)_mcount;
>>> +#endif
>>> +#endif
>>> +#endif
>>> +
>>> + insn = *addr;
>>> + pos = 1;
>>> +
>>> + /* analyze a function prologue */
>>> + while ((unsigned long)addr < pc) {
>>> + if (aarch64_insn_is_branch_imm(insn) ||
>>> + aarch64_insn_is_br(insn) ||
>>> + aarch64_insn_is_blr(insn) ||
>>> + aarch64_insn_is_ret(insn) ||
>>> + aarch64_insn_is_eret(insn))
>>> + /* exiting a basic block */
>>> + goto out;
>>> +
>>> + if (aarch64_insn_decode_add_sub_imm(insn, &dst, &src,
>>> + &imm, &variant, &adsb_type)) {
>>> + if ((adsb_type == AARCH64_INSN_ADSB_SUB) &&
>>> + (dst == AARCH64_INSN_REG_SP) &&
>>> + (src == AARCH64_INSN_REG_SP)) {
>>> + /*
>>> + * Starting the following sequence:
>>> + * sub sp, sp, #xx
>>> + * stp x29, x30, [sp, #yy]
>>> + * add x29, sp, #yy
>>> + */
>>> + WARN_ON(pos != 1);
>>> + pos = 2;
>>> + *size += imm;
>>> + } else if ((adsb_type == AARCH64_INSN_ADSB_ADD) &&
>>> + (dst == AARCH64_INSN_REG_29) &&
>>> + (src == AARCH64_INSN_REG_SP)) {
>>> + /*
>>> + * add x29, sp, #yy
>>> + * or
>>> + * mov x29, sp
>>> + */
>>> + WARN_ON(pos != 3);
>>> + pos = 0;
>>> + *size2 = imm;
>>> +
>>> + break;
>>> + }
>>> + } else if (aarch64_insn_decode_load_store_pair(insn,
>>> + &reg1, &reg2, &base, &imm,
>>> + &variant, &ldst_type)) {
>>> + if ((ldst_type ==
>>> + AARCH64_INSN_LDST_STORE_PAIR_PRE_INDEX) &&
>>> + (reg1 == AARCH64_INSN_REG_29) &&
>>> + (reg2 == AARCH64_INSN_REG_30) &&
>>> + (base == AARCH64_INSN_REG_SP)) {
>>> + /*
>>> + * Starting the following sequence:
>>> + * stp x29, x30, [sp, #-xx]!
>>> + * mov x29, sp
>>> + */
>>> + WARN_ON(!((pos == 1) || (pos == 2)));
>>> + pos = 3;
>>> + *size += -imm;
>>> + } else if ((ldst_type ==
>>> + AARCH64_INSN_LDST_STORE_PAIR) &&
>>> + (reg1 == AARCH64_INSN_REG_29) &&
>>> + (reg2 == AARCH64_INSN_REG_30) &&
>>> + (base == AARCH64_INSN_REG_SP)) {
>>> + /*
>>> + * stp x29, x30, [sp, #yy]
>>> + */
>>> + WARN_ON(pos != 2);
>>> + pos = 3;
>>> + }
>>> + }
>>> +
>>> + addr++;
>>> + insn = *addr;
>>> + }
>>> +
>>> +out:
>>> + return pos;
>>> +}
>>> +#endif
>>> +
>>
>> A small instruction decoder in software!
>>
>> From a high level point of view, it makes sense to deal with only three main
>> cases. Since it is tough to deal with all function prologues in perspective
>> of computational overhead and implementation complexity, the above change looks
>> like a pretty good tradeoff. This is what I can say now. I'm also interested
>> in feedbacks from other folks.
>
> I really appreciate your reviews and comments on the whole series of my patches
> (#2 to #5).
> May I add Reviewed-by (and Tested-by?) with your name if you like?

Sure. Tested-by is also okay.

Regarding patch6, the option would be useful if this analyzer is accepted. So,
like this patch5, I'm waiting for other folk's response.

How about adding your document [1] to this series? I think it explains all
backgrounds, such as motivation, issue, approach, and TODO, on this series.

[1] http://www.spinics.net/lists/arm-kernel/msg444300.html

Best Regards
Jungseok Lee--
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