Re: [PATCH v2] kdb: unify CMD_BUFLEN definition into kdb_private.h

[Doug Anderson]

Hi,

On Tue, Jun 16, 2026 at 7:28 PM Naveen Kumar Chaudhary
<naveen.osdev@xxxxxxxxx> wrote:
>
> CMD_BUFLEN was defined separately in kdb_io.c (256) and kdb_main.c
> (200), causing kdb_main.c to use the wrong size when formatting the
> prompt string into kdb_prompt_str (which is 256 bytes).
>
> Move CMD_BUFLEN (256) into kdb_private.h so all users share a single
> consistent definition, and remove the local definitions from both
> files.
>
> Fixes: 5d5314d6795f ("kdb: core for kgdb back end (1 of 2)")
> Signed-off-by: Naveen Kumar Chaudhary <naveen.osdev@xxxxxxxxx>
> ---
>  kernel/debug/kdb/kdb_io.c      | 1 -
>  kernel/debug/kdb/kdb_main.c    | 6 ++----
>  kernel/debug/kdb/kdb_private.h | 3 ++-
>  3 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> index c399f11740ef..f5b1b7d4c9c8 100644
> --- a/kernel/debug/kdb/kdb_io.c
> +++ b/kernel/debug/kdb/kdb_io.c
> @@ -22,7 +22,6 @@
>  #include <linux/kallsyms.h>
>  #include "kdb_private.h"
>
> -#define CMD_BUFLEN 256
>  char kdb_prompt_str[CMD_BUFLEN];
>
>  int kdb_trap_printk;
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index ddce56b47b25..ca0126db9850 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -783,8 +783,6 @@ static int kdb_exec_defcmd(int argc, const char **argv)
>
>  /* Command history */
>  #define KDB_CMD_HISTORY_COUNT  32
> -#define CMD_BUFLEN             200     /* kdb_printf: max printline
> -                                        * size == 256 */

Maybe Daniel will know more; otherwise, I need to spend more time
digging. ...but the comment above (that you're deleting) makes me
believe that 200 was purposely chosen to be a number that was under
256. It sounds as if maybe they're keeping some buffers at 200 so that
there'e enough extra space to print the buffer plus some extra stuff?

Maybe safer to keep the number at 200?


>  static unsigned int cmd_head, cmd_tail;
>  static unsigned int cmdptr;
>  static char cmd_hist[KDB_CMD_HISTORY_COUNT][CMD_BUFLEN];
> @@ -1265,8 +1263,8 @@ static int kdb_local(kdb_reason_t reason, int error, struct pt_regs *regs,
>
>  do_full_getstr:
>                 /* PROMPT can only be set if we have MEM_READ permission. */
> -               snprintf(kdb_prompt_str, CMD_BUFLEN, kdbgetenv("PROMPT"),
> -                        raw_smp_processor_id());
> +               snprintf(kdb_prompt_str, CMD_BUFLEN,
> +                        kdbgetenv("PROMPT"), raw_smp_processor_id());

Unrelated whitespace change. Drop from your patch.


>                 /*
>                  * Fetch command from keyboard
> diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
> index 92a28b8ab604..722e8aa50724 100644
> --- a/kernel/debug/kdb/kdb_private.h
> +++ b/kernel/debug/kdb/kdb_private.h
> @@ -225,7 +225,8 @@ extern void kdb_kbd_cleanup_state(void);
>  #define kdb_kbd_cleanup_state()
>  #endif /* ! CONFIG_KDB_KEYBOARD */
>
> -extern char kdb_prompt_str[];
> +#define CMD_BUFLEN 256
> +extern char kdb_prompt_str[CMD_BUFLEN];

Now that this is in a header file, a slightly less generic name would
be good. Maybe rename to KDB_BUFLEN"