Re: [PATCH v4 01/18] arm64: stacktrace: Add shared header for common stack unwinding code

[Fuad Tabba <tabba@google.com>]

Hi Kalesh,

On Fri, Jul 15, 2022 at 7:10 AM Kalesh Singh <kaleshsingh@google.com> wrote:
>
> In order to reuse the arm64 stack unwinding logic for the nVHE
> hypervisor stack, move the common code to a shared header
> (arch/arm64/include/asm/stacktrace/common.h).
>
> The nVHE hypervisor cannot safely link against kernel code, so we
> make use of the shared header to avoid duplicated logic later in
> this series.
>
> Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
> ---

Reviewed-by: Fuad Tabba <tabba@google.com>

Thanks,
/fuad


>  arch/arm64/include/asm/stacktrace.h        |  35 +------
>  arch/arm64/include/asm/stacktrace/common.h | 105 +++++++++++++++++++++
>  arch/arm64/kernel/stacktrace.c             |  57 -----------
>  3 files changed, 106 insertions(+), 91 deletions(-)
>  create mode 100644 arch/arm64/include/asm/stacktrace/common.h
>
> diff --git a/arch/arm64/include/asm/stacktrace.h b/arch/arm64/include/asm/stacktrace.h
> index aec9315bf156..79f455b37c84 100644
> --- a/arch/arm64/include/asm/stacktrace.h
> +++ b/arch/arm64/include/asm/stacktrace.h
> @@ -8,52 +8,19 @@
>  #include <linux/percpu.h>
>  #include <linux/sched.h>
>  #include <linux/sched/task_stack.h>
> -#include <linux/types.h>
>  #include <linux/llist.h>
>
>  #include <asm/memory.h>
>  #include <asm/ptrace.h>
>  #include <asm/sdei.h>
>
> -enum stack_type {
> -       STACK_TYPE_UNKNOWN,
> -       STACK_TYPE_TASK,
> -       STACK_TYPE_IRQ,
> -       STACK_TYPE_OVERFLOW,
> -       STACK_TYPE_SDEI_NORMAL,
> -       STACK_TYPE_SDEI_CRITICAL,
> -       __NR_STACK_TYPES
> -};
> -
> -struct stack_info {
> -       unsigned long low;
> -       unsigned long high;
> -       enum stack_type type;
> -};
> +#include <asm/stacktrace/common.h>
>
>  extern void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
>                            const char *loglvl);
>
>  DECLARE_PER_CPU(unsigned long *, irq_stack_ptr);
>
> -static inline bool on_stack(unsigned long sp, unsigned long size,
> -                           unsigned long low, unsigned long high,
> -                           enum stack_type type, struct stack_info *info)
> -{
> -       if (!low)
> -               return false;
> -
> -       if (sp < low || sp + size < sp || sp + size > high)
> -               return false;
> -
> -       if (info) {
> -               info->low = low;
> -               info->high = high;
> -               info->type = type;
> -       }
> -       return true;
> -}
> -
>  static inline bool on_irq_stack(unsigned long sp, unsigned long size,
>                                 struct stack_info *info)
>  {
> diff --git a/arch/arm64/include/asm/stacktrace/common.h b/arch/arm64/include/asm/stacktrace/common.h
> new file mode 100644
> index 000000000000..64ae4f6b06fe
> --- /dev/null
> +++ b/arch/arm64/include/asm/stacktrace/common.h
> @@ -0,0 +1,105 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Common arm64 stack unwinder code.
> + *
> + * Copyright (C) 2012 ARM Ltd.
> + */
> +#ifndef __ASM_STACKTRACE_COMMON_H
> +#define __ASM_STACKTRACE_COMMON_H
> +
> +#include <linux/bitmap.h>
> +#include <linux/bitops.h>
> +#include <linux/types.h>
> +
> +enum stack_type {
> +       STACK_TYPE_UNKNOWN,
> +       STACK_TYPE_TASK,
> +       STACK_TYPE_IRQ,
> +       STACK_TYPE_OVERFLOW,
> +       STACK_TYPE_SDEI_NORMAL,
> +       STACK_TYPE_SDEI_CRITICAL,
> +       __NR_STACK_TYPES
> +};
> +
> +struct stack_info {
> +       unsigned long low;
> +       unsigned long high;
> +       enum stack_type type;
> +};
> +
> +/*
> + * A snapshot of a frame record or fp/lr register values, along with some
> + * accounting information necessary for robust unwinding.
> + *
> + * @fp:          The fp value in the frame record (or the real fp)
> + * @pc:          The lr value in the frame record (or the real lr)
> + *
> + * @stacks_done: Stacks which have been entirely unwound, for which it is no
> + *               longer valid to unwind to.
> + *
> + * @prev_fp:     The fp that pointed to this frame record, or a synthetic value
> + *               of 0. This is used to ensure that within a stack, each
> + *               subsequent frame record is at an increasing address.
> + * @prev_type:   The type of stack this frame record was on, or a synthetic
> + *               value of STACK_TYPE_UNKNOWN. This is used to detect a
> + *               transition from one stack to another.
> + *
> + * @kr_cur:      When KRETPROBES is selected, holds the kretprobe instance
> + *               associated with the most recently encountered replacement lr
> + *               value.
> + *
> + * @task:        The task being unwound.
> + */
> +struct unwind_state {
> +       unsigned long fp;
> +       unsigned long pc;
> +       DECLARE_BITMAP(stacks_done, __NR_STACK_TYPES);
> +       unsigned long prev_fp;
> +       enum stack_type prev_type;
> +#ifdef CONFIG_KRETPROBES
> +       struct llist_node *kr_cur;
> +#endif
> +       struct task_struct *task;
> +};
> +
> +static inline bool on_stack(unsigned long sp, unsigned long size,
> +                           unsigned long low, unsigned long high,
> +                           enum stack_type type, struct stack_info *info)
> +{
> +       if (!low)
> +               return false;
> +
> +       if (sp < low || sp + size < sp || sp + size > high)
> +               return false;
> +
> +       if (info) {
> +               info->low = low;
> +               info->high = high;
> +               info->type = type;
> +       }
> +       return true;
> +}
> +
> +static inline void unwind_init_common(struct unwind_state *state,
> +                                     struct task_struct *task)
> +{
> +       state->task = task;
> +#ifdef CONFIG_KRETPROBES
> +       state->kr_cur = NULL;
> +#endif
> +
> +       /*
> +        * Prime the first unwind.
> +        *
> +        * In unwind_next() we'll check that the FP points to a valid stack,
> +        * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be
> +        * treated as a transition to whichever stack that happens to be. The
> +        * prev_fp value won't be used, but we set it to 0 such that it is
> +        * definitely not an accessible stack address.
> +        */
> +       bitmap_zero(state->stacks_done, __NR_STACK_TYPES);
> +       state->prev_fp = 0;
> +       state->prev_type = STACK_TYPE_UNKNOWN;
> +}
> +
> +#endif /* __ASM_STACKTRACE_COMMON_H */
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index fcaa151b81f1..94a5dd2ab8fd 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -18,63 +18,6 @@
>  #include <asm/stack_pointer.h>
>  #include <asm/stacktrace.h>
>
> -/*
> - * A snapshot of a frame record or fp/lr register values, along with some
> - * accounting information necessary for robust unwinding.
> - *
> - * @fp:          The fp value in the frame record (or the real fp)
> - * @pc:          The lr value in the frame record (or the real lr)
> - *
> - * @stacks_done: Stacks which have been entirely unwound, for which it is no
> - *               longer valid to unwind to.
> - *
> - * @prev_fp:     The fp that pointed to this frame record, or a synthetic value
> - *               of 0. This is used to ensure that within a stack, each
> - *               subsequent frame record is at an increasing address.
> - * @prev_type:   The type of stack this frame record was on, or a synthetic
> - *               value of STACK_TYPE_UNKNOWN. This is used to detect a
> - *               transition from one stack to another.
> - *
> - * @kr_cur:      When KRETPROBES is selected, holds the kretprobe instance
> - *               associated with the most recently encountered replacement lr
> - *               value.
> - *
> - * @task:        The task being unwound.
> - */
> -struct unwind_state {
> -       unsigned long fp;
> -       unsigned long pc;
> -       DECLARE_BITMAP(stacks_done, __NR_STACK_TYPES);
> -       unsigned long prev_fp;
> -       enum stack_type prev_type;
> -#ifdef CONFIG_KRETPROBES
> -       struct llist_node *kr_cur;
> -#endif
> -       struct task_struct *task;
> -};
> -
> -static void unwind_init_common(struct unwind_state *state,
> -                              struct task_struct *task)
> -{
> -       state->task = task;
> -#ifdef CONFIG_KRETPROBES
> -       state->kr_cur = NULL;
> -#endif
> -
> -       /*
> -        * Prime the first unwind.
> -        *
> -        * In unwind_next() we'll check that the FP points to a valid stack,
> -        * which can't be STACK_TYPE_UNKNOWN, and the first unwind will be
> -        * treated as a transition to whichever stack that happens to be. The
> -        * prev_fp value won't be used, but we set it to 0 such that it is
> -        * definitely not an accessible stack address.
> -        */
> -       bitmap_zero(state->stacks_done, __NR_STACK_TYPES);
> -       state->prev_fp = 0;
> -       state->prev_type = STACK_TYPE_UNKNOWN;
> -}
> -
>  /*
>   * Start an unwind from a pt_regs.
>   *
> --
> 2.37.0.170.g444d1eabd0-goog
>

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