[PATCH v4 09/10] lib: expose unwind_stack() and call it from panic()

[Casey Connolly]

On 7/29/25 17:52, Casey Connolly wrote:
> unwind_stack() will walk the callstack and show the symbol names
> if available by using the architecture-specific framepointer
> implementation.
> 
> When available, call unwind_stack() during a panic to give more
> information about what caused the panic and help with debugging.
> 
> Adjust the interrupt handlers to call panic_str() to avoid duplicating
> the backtrace.
> 
> Signed-off-by: Casey Connolly <casey.connolly at linaro.org>
> ---
>   arch/arm/lib/interrupts_64.c | 8 ++++----
>   include/symbols.h            | 9 ++++++++-
>   lib/panic.c                  | 7 +++++++
>   3 files changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/lib/interrupts_64.c b/arch/arm/lib/interrupts_64.c
> index 08d81ca7f654c586521ff97bb5ca37229c9b939d..949ae0f94168fd53036c1dff376b574808ebf9ea 100644
> --- a/arch/arm/lib/interrupts_64.c
> +++ b/arch/arm/lib/interrupts_64.c
> @@ -109,10 +109,10 @@ struct stack_frame {
>   
>   static void print_sym(unsigned long lr)
>   {
>   	/* Print the symbol address and the offset to the LR */
> -	printf("\t<%#016lx> %s+%#lx\n", lr - (gd->flags & GD_FLG_RELOC ? gd->reloc_off : 0),
> -	       symname, offset);
> +	printf("\t<%#016lx> %pS\n", lr - (gd->flags & GD_FLG_RELOC ? gd->reloc_off : 0),
> +	       (void *)lr);

Oops, I fluffed this fixup commit.


>   }
>   
>   /**
>    * show_backtrace - show backtrace using frame pointers
> @@ -228,9 +228,9 @@ static void except_msg(const char *msg, struct pt_regs *pt_regs)
>   	show_regs(pt_regs);
>   	if (CONFIG_IS_ENABLED(FRAMEPOINTER))
>   		show_backtrace(pt_regs->elr, pt_regs->regs[30], pt_regs->regs[29]);
>   	show_efi_loaded_images(pt_regs);
> -	panic("Resetting CPU ...\n");
> +	panic_str("Resetting CPU ...\n");
>   }
>   
>   /*
>    * do_bad_sync handles the impossible case in the Synchronous Abort vector.
> @@ -279,9 +279,9 @@ void do_sync(struct pt_regs *pt_regs)
>   	show_regs(pt_regs);
>   	if (CONFIG_IS_ENABLED(FRAMEPOINTER))
>   		show_backtrace(pt_regs->elr, pt_regs->regs[30], pt_regs->regs[29]);
>   	show_efi_loaded_images(pt_regs);
> -	panic("Resetting CPU ...\n");
> +	panic_str("Resetting CPU ...\n");
>   }
>   
>   /*
>    * do_irq handles the Irq exception.
> diff --git a/include/symbols.h b/include/symbols.h
> index c5267edbe768f304bc0f6235e71a39b6c3835a67..845f993060f042139df46bcc51a0180faadc35bc 100644
> --- a/include/symbols.h
> +++ b/include/symbols.h
> @@ -4,9 +4,9 @@
>   #include <string.h>
>   
>   #define KSYM_NAME_LEN 127
>   
> -#if IS_ENABLED(CONFIG_SYMBOL_LOOKUP)
> +#if CONFIG_IS_ENABLED(SYMBOL_LOOKUP)
>   const char * __attribute__((weak)) symbol_lookup(unsigned long addr, unsigned long *symaddr, unsigned long *offset,
>   			   char *namebuf);
>   #else
>   static inline const char *symbol_lookup(unsigned long addr, unsigned long *symaddr, unsigned long *offset,
> @@ -21,4 +21,11 @@ static inline const char *symbol_lookup(unsigned long addr, unsigned long *symad
>   	namebuf[3] = '\0';
>   	return namebuf;
>   }
>   #endif
> +
> +#if CONFIG_IS_ENABLED(FRAMEPOINTER)
> +/**
> + * unwind_stack - unwind the callstack and print a backtrace.
> + */
> +void unwind_stack(void);
> +#endif
> diff --git a/lib/panic.c b/lib/panic.c
> index 0f578b5b5131589d215f5f4b16b95d9c9f3e8ce3..6f8bd7cc1eef7e5d97ba925bef65cc46924b4418 100644
> --- a/lib/panic.c
> +++ b/lib/panic.c
> @@ -14,8 +14,9 @@
>   #include <command.h>
>   #endif
>   #include <linux/delay.h>
>   #include <stdio.h>
> +#include <symbols.h>
>   
>   static void panic_finish(void) __attribute__ ((noreturn));
>   
>   static void panic_finish(void)
> @@ -44,8 +45,14 @@ void panic(const char *fmt, ...)
>   	va_list args;
>   	va_start(args, fmt);
>   	vprintf(fmt, args);
>   	va_end(args);
> +
> +	if (CONFIG_IS_ENABLED(FRAMEPOINTER)) {
> +		puts("\n");
> +		unwind_stack();
> +	}
> +
>   #endif
>   	panic_finish();
>   }
>   
>