linux-kernel - Re: [Kgdb-bugreport] [PATCH v3] kdb: Remove the misfeature 'KDBFLAGS'

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Message-ID: <20200521154739.ukfro4uuxpmnrpsx@holly.lan>
Date:   Thu, 21 May 2020 16:47:39 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Wei Li <liwei391@...wei.com>
Cc:     Doug Anderson <dianders@...omium.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [Kgdb-bugreport] [PATCH v3] kdb: Remove the misfeature 'KDBFLAGS'

On Thu, May 21, 2020 at 03:21:25PM +0800, Wei Li wrote:
> Currently, 'KDBFLAGS' is an internal variable of kdb, it is combined
> by 'KDBDEBUG' and state flags. It will be shown only when 'KDBDEBUG'
> is set, and the user can define an environment variable named 'KDBFLAGS'
> too. These are puzzling indeed.
> 
> After communication with Daniel, it seems that 'KDBFLAGS' is a misfeature.
> So let's replace 'KDBFLAGS' with 'KDBDEBUG' to just show the value we
> wrote into. After this modification, we can use `md4c1 kdb_flags` instead,
> to observe the state flags.
> 
> Suggested-by: Daniel Thompson <daniel.thompson@...aro.org>
> Signed-off-by: Wei Li <liwei391@...wei.com>
> ---
> v2 -> v3:
>  - Change to replace the internal env 'KDBFLAGS' with 'KDBDEBUG'.
> v1 -> v2:
>  - Fix lack of braces.
> 
>  kernel/debug/kdb/kdb_main.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
> index 4fc43fb17127..392029287083 100644
> --- a/kernel/debug/kdb/kdb_main.c
> +++ b/kernel/debug/kdb/kdb_main.c
> @@ -418,8 +418,7 @@ int kdb_set(int argc, const char **argv)
>  				    argv[2]);
>  			return 0;
>  		}
> -		kdb_flags = (kdb_flags &
> -			     ~(KDB_DEBUG_FLAG_MASK << KDB_DEBUG_FLAG_SHIFT))
> +		kdb_flags = (kdb_flags & ~KDB_DEBUG(MASK))
>  			| (debugflags << KDB_DEBUG_FLAG_SHIFT);
>  
>  		return 0;
> @@ -2081,7 +2080,8 @@ static int kdb_env(int argc, const char **argv)
>  	}
>  
>  	if (KDB_DEBUG(MASK))
> -		kdb_printf("KDBFLAGS=0x%x\n", kdb_flags);
> +		kdb_printf("KDBDEBUG=0x%x\n",
> +			(kdb_flags & KDB_DEBUG(MASK)) >> KDB_DEBUG_FLAG_SHIFT);

For this expression to work correctly, kdb_flags, need to be unsigned
(otherwise we get an arithmetic right shift and mis-report when
KDBDEBUG == 0xfff).

This is just FYI, I think I can fix this up when applying...


Daniel.