linux-kernel - Re: [PATCH v2 2/7] kdb: Use format-strings rather than '\0' injection in kdb

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Message-ID: <CAD=FV=VXFHqOatn3cvwvYCey53+zuzB7ie4gYdvDVbfGL=Qm1Q@mail.gmail.com>
Date: Mon, 22 Apr 2024 16:52:04 -0700
From: Doug Anderson <dianders@...omium.org>
To: Daniel Thompson <daniel.thompson@...aro.org>
Cc: Jason Wessel <jason.wessel@...driver.com>, kgdb-bugreport@...ts.sourceforge.net, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 2/7] kdb: Use format-strings rather than '\0' injection
 in kdb_read()

Hi,

On Mon, Apr 22, 2024 at 9:37 AM Daniel Thompson
<daniel.thompson@...aro.org> wrote:
>
> Currently when kdb_read() needs to reposition the cursor it uses copy and
> paste code that works by injecting an '\0' at the cursor position before
> delivering a carriage-return and reprinting the line (which stops at the
> '\0').
>
> Tidy up the code by hoisting the copy and paste code into an appropriately
> named function. Additionally let's replace the '\0' injection with a
> proper field width parameter so that the string will be abridged during
> formatting instead.
>
> Cc: stable@...r.kernel.org # Not a bug fix but it is needed for later bug fixes
> Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
> ---
>  kernel/debug/kdb/kdb_io.c | 34 ++++++++++++++--------------------
>  1 file changed, 14 insertions(+), 20 deletions(-)

Looks like a nice fix, but I think this'll create a compile warning on
some compilers. The variable "tmp" is no longer used, I think.

Once the "tmp" variable is deleted, feel free to add my Reviewed-by.

NOTE: patch #7 in your series re-adds a user of "tmp", but since this
one is "Cc: stable" you will need to delete it here and then re-add it
in patch #7.


> diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
> index 06dfbccb10336..a42607e4d1aba 100644
> --- a/kernel/debug/kdb/kdb_io.c
> +++ b/kernel/debug/kdb/kdb_io.c
> @@ -184,6 +184,13 @@ char kdb_getchar(void)
>         unreachable();
>  }
>
> +static void kdb_position_cursor(char *prompt, char *buffer, char *cp)
> +{
> +       kdb_printf("\r%s", kdb_prompt_str);
> +       if (cp > buffer)
> +               kdb_printf("%.*s", (int)(cp - buffer), buffer);

nit: personally, I'd take the "if" statement out. I'm nearly certain
that kdb_printf() can handle zero-length for the width argument and
"buffer" can never be _after_ cp (so you can't get negative).


-Doug