Re: [PATCH v4 RESEND 4/7] riscv: stacktrace: introduce stack-bound tracking helpers

[Shuai Xue <xueshuai@linux.alibaba.com>]

On 6/29/26 3:27 PM, Wang Han wrote:
> A reliable unwinder needs to validate that every frame record it reads
> is fully contained in a known kernel stack, and it needs to refuse to
> walk back into a stack it has already left. Add the building blocks
> for that:
> 
>    * struct stack_info / struct unwind_state in a new
>      asm/stacktrace/common.h, modelled on the arm64 reference
>      implementation.
>    * stackinfo_get_irq() / stackinfo_get_task() / stackinfo_get_overflow()
>      plus the corresponding on_*_stack() predicates in asm/stacktrace.h,
>      so callers can ask "is this object on stack X?" by stack kind
>      rather than open-coded address arithmetic.
>    * unwind_init_common(), unwind_find_stack() and
>      unwind_consume_stack() helpers that enforce the
>      forward-progress-only invariant required for reliability.
> 
> No existing user is wired up to these helpers in this commit; the
> unwinder switch comes in a follow-up. The header changes leave
> on_thread_stack() with the same semantics as before, just expressed in
> terms of the new helpers.
> 
> Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
> Signed-off-by: Wang Han <wanghan@linux.alibaba.com>
> ---
>   arch/riscv/include/asm/stacktrace.h        |  65 ++++++++-
>   arch/riscv/include/asm/stacktrace/common.h | 159 +++++++++++++++++++++
>   2 files changed, 222 insertions(+), 2 deletions(-)
>   create mode 100644 arch/riscv/include/asm/stacktrace/common.h
> 
> diff --git a/arch/riscv/include/asm/stacktrace.h b/arch/riscv/include/asm/stacktrace.h
> index b1495a7e06ce..bc87c4940379 100644
> --- a/arch/riscv/include/asm/stacktrace.h
> +++ b/arch/riscv/include/asm/stacktrace.h
> @@ -3,8 +3,13 @@
>   #ifndef _ASM_RISCV_STACKTRACE_H
>   #define _ASM_RISCV_STACKTRACE_H
>   
> +#include <linux/percpu.h>
>   #include <linux/sched.h>
> +#include <linux/sched/task_stack.h>
> +
> +#include <asm/irq_stack.h>
>   #include <asm/ptrace.h>
> +#include <asm/stacktrace/common.h>
>   
>   struct stackframe {
>   	unsigned long fp;
> @@ -16,14 +21,70 @@ extern void notrace walk_stackframe(struct task_struct *task, struct pt_regs *re
>   extern void dump_backtrace(struct pt_regs *regs, struct task_struct *task,
>   			   const char *loglvl);
>   
> -static inline bool on_thread_stack(void)
> +/*
> + * IRQ stack accessors
> + */
> +static inline struct stack_info stackinfo_get_irq(void)
> +{
> +	unsigned long low = (unsigned long)raw_cpu_read(irq_stack_ptr);

 From https://sashiko.dev/#/patchset/20260629072713.3273743-1-wanghan%40linux.alibaba.com

Will this cause a link error when CONFIG_IRQ_STACKS is disabled?
Looking at arch/riscv/kernel/irq.c, irq_stack_ptr is defined inside an
#ifdef CONFIG_IRQ_STACKS block. Since stackinfo_get_irq() unconditionally
references it here, it seems this might result in an undefined reference
to irq_stack_ptr during linking.

Should this accessor be conditionally compiled, or should it provide a
fallback when CONFIG_IRQ_STACKS is not set?

Thanks.
Shuai