linux-kernel - Re: [PATCH 06/13] kdb: Remove "mdW" and "mdWcN" handling of "W" == 0

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Date: Tue, 18 Jun 2024 12:37:54 +0100
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Douglas Anderson <dianders@...omium.org>
Cc: kgdb-bugreport@...ts.sourceforge.net,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>,
	Jason Wessel <jason.wessel@...driver.com>,
	Thorsten Blum <thorsten.blum@...lux.com>,
	Yuran Pereira <yuran.pereira@...mail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/13] kdb: Remove "mdW" and "mdWcN" handling of "W" == 0

On Mon, Jun 17, 2024 at 05:34:40PM -0700, Douglas Anderson wrote:
> The "mdW" and "mdWcN" generally lets the user control more carefully
> what word size we display memory in and exactly how many words should
> be displayed. Specifically, "md4" says to display memory w/ 4
> bytes-per word and "md4c6" says to display 6 words of memory w/
> 4-bytes-per word.
>
> The kdb "md" implementation has a special rule for when "W" is 0. In
> this case:
> * If you run with "W" == 0 and you've never run a kdb "md" command
>   this reboot then it will pick 4 bytes-per-word, ignoring the normal
>   default from the environment.
> * If you run with "W" == 0 and you've run a kdb "md" command this
>   reboot then it will pick up the bytes per word of the last command.
>
> As an example:
>   [1]kdb> md2 0xffffff80c8e2b280 1
>   0xffffff80c8e2b280 0200 0000 0000 0000 e000 8235 0000 0000   ...
>   [1]kdb> md0 0xffffff80c8e2b280 1
>   0xffffff80c8e2b280 0200 0000 0000 0000 e000 8235 0000 0000   ...
>   [1]kdb> md 0xffffff80c8e2b280 1
>   0xffffff80c8e2b280 0000000000000200 000000008235e000   ...
>   [1]kdb> md0 0xffffff80c8e2b280 1
>   0xffffff80c8e2b280 0000000000000200 000000008235e000   ...
>
> This doesn't seem like particularly useful behavior and adds a bunch
> of complexity to the arg parsing. Remove it.
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
>  kernel/debug/kdb/kdb_main.c | 5 -----
>  1 file changed, 5 deletions(-)
>
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index c013b014a7d3..700b4e355545 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -1611,11 +1611,6 @@ static int kdb_md(int argc, const char **argv)
>
>  	if (isdigit(argv[0][2])) {
>  		bytesperword = (int)(argv[0][2] - '0');
> -		if (bytesperword == 0) {
> -			bytesperword = last_bytesperword;
> -			if (bytesperword == 0)
> -				bytesperword = 4;
> -		}
>  		last_bytesperword = bytesperword;
>  		repeat = mdcount * 16 / bytesperword;

Isn't this now a divide-by-zero?


Daniel.