Re: [PATCH v4 6/6] arm64: ftrace: add arch-specific stack tracer

yalin wang
2015-11-04T08:42:36Z

> On Oct 30, 2015, at 13:25, AKASHI Takahiro <takahiro.akashi@linaro.org> wrote:
>
> 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@linaro.org>
> ---
> arch/arm64/include/asm/stacktrace.h | 4 +
> arch/arm64/kernel/ftrace.c | 68 +++++++++++++
> arch/arm64/kernel/stacktrace.c | 185 ++++++++++++++++++++++++++++++++++-
> 3 files changed, 254 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..e8afd42 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 +175,69 @@ 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++) {
> + unsigned long addr;
> +
> + addr = stack_trace_max.entries[i] + FTRACE_STACK_FRAME_OFFSET;
> + if (addr == 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 631c49d..1b293fe 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -24,6 +24,144 @@
> #include <asm/insn.h>
> #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;

you should use aarch64_insn_read() or inn = le32_to_cpu(*addr)
here , in case the kernel is build as big endian .

> + 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
> +
> /*
> * AArch64 PCS assigns the frame pointer to x29.
> *
> @@ -82,6 +220,9 @@ struct stack_trace_data {
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> unsigned int ret_stack_index;
> #endif
> +#ifdef CONFIG_STACK_TRACER
> + unsigned long *sp;
> +#endif
> };
>
> static int save_trace(struct stackframe *frame, void *d)
> @@ -111,12 +252,33 @@ static int save_trace(struct stackframe *frame, void *d)
> return 0;
> }
>
> +#ifdef CONFIG_STACK_TRACER
> + if (data->sp) {
> + if (trace->nr_entries) {
> + unsigned long child_pc, sp_off, fp_off;
> + int pos;
> +
> + child_pc = trace->entries[trace->nr_entries - 1];
> + pos = analyze_function_prologue(child_pc,
> + &sp_off, &fp_off);
> + /*
> + * frame->sp - 0x10 is actually a child's fp.
> + * See above.
> + */
> + data->sp[trace->nr_entries] = (pos < 0 ? frame->sp :
> + (frame->sp - 0x10) + sp_off - fp_off);
> + } else {
> + data->sp[0] = frame->sp;
> + }
> + }
> +#endif
> trace->entries[trace->nr_entries++] = addr;
>
> return trace->nr_entries >= trace->max_entries;
> }
>
> -void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> +static void __save_stack_trace_tsk(struct task_struct *tsk,
> + struct stack_trace *trace, unsigned long *stack_dump_sp)
> {
> struct stack_trace_data data;
> struct stackframe frame;
> @@ -126,6 +288,9 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
> data.ret_stack_index = current->curr_ret_stack;
> #endif
> +#ifdef CONFIG_STACK_TRACER
> + data.sp = stack_dump_sp;
> +#endif
>
> if (tsk != current) {
> data.no_sched_functions = 1;
> @@ -136,7 +301,8 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> data.no_sched_functions = 0;
> frame.fp = (unsigned long)__builtin_frame_address(0);
> frame.sp = current_stack_pointer;
> - frame.pc = (unsigned long)save_stack_trace_tsk;
> + asm("1:");
> + asm("ldr %0, =1b" : "=r" (frame.pc));
> }
>
> walk_stackframe(&frame, save_trace, &data);
> @@ -144,9 +310,22 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> trace->entries[trace->nr_entries++] = ULONG_MAX;
> }
>
> +void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> +{
> + __save_stack_trace_tsk(tsk, trace, NULL);
> +}
> +
> void save_stack_trace(struct stack_trace *trace)
> {
> - save_stack_trace_tsk(current, trace);
> + __save_stack_trace_tsk(current, trace, NULL);
> }
> EXPORT_SYMBOL_GPL(save_stack_trace);
> +
> +#ifdef CONFIG_STACK_TRACER
> +void save_stack_trace_sp(struct stack_trace *trace,
> + unsigned long *stack_dump_sp)
> +{
> + __save_stack_trace_tsk(current, trace, stack_dump_sp);
> +}
> +#endif /* CONFIG_STACK_TRACER */
> #endif
> --
> 1.7.9.5
>
> --
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