linux-kernel - Re: [PATCH] arm: kgdb: fix NUMREGBYTES so that gdb

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Date:   Fri, 6 Apr 2018 14:25:11 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     David Rivshin <drivshin@...rd.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        kgdb-bugreport@...ts.sourceforge.net,
        Jason Wessel <jason.wessel@...driver.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Rabin Vincent <rabin@....in>
Subject: Re: [PATCH] arm: kgdb: fix NUMREGBYTES so that gdb_regs[] is the
 correct size

On Thu, Apr 05, 2018 at 04:09:16PM -0400, David Rivshin wrote:
> From: David Rivshin <DRivshin@...worx.com>
> 
> NUMREGBYTES (which is used as the size for gdb_regs[]) is incorrectly based
> on DBG_MAX_REG_NUM instead of GDB_MAX_REGS. DBG_MAX_REG_NUM is the number
> of total registers, while GDB_MAX_REGS is the number of 'unsigned longs'
> it takes to serialize those registers. Since FP registers require 3
> 'unsigned longs' each, DBG_MAX_REG_NUM is smaller than GDB_MAX_REGS.
> 
> This causes GDB 8.0 give the following error on connect:
> "Truncated register 19 in remote 'g' packet"
> 
> This also causes the register serialization/deserialization logic to
> overflow gdb_regs[], overwriting whatever follows.
> 
> Fixes: 834b2964b7ab ("kgdb,arm: fix register dump")
> Cc: <stable@...r.kernel.org> # 2.6.37+
> Signed-off-by: David Rivshin <drivshin@...worx.com>

I pointed some trivial autotests at both gdb-7.12 and gdb-8.0. Results
look good to me!

Tested-by: Daniel Thompson <daniel.thompson@...aro.org>

> ---
>  arch/arm/include/asm/kgdb.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/kgdb.h b/arch/arm/include/asm/kgdb.h
> index 3b73fdcf3627a..8de1100d10674 100644
> --- a/arch/arm/include/asm/kgdb.h
> +++ b/arch/arm/include/asm/kgdb.h
> @@ -77,7 +77,7 @@ extern int kgdb_fault_expected;
>  
>  #define KGDB_MAX_NO_CPUS	1
>  #define BUFMAX			400
> -#define NUMREGBYTES		(DBG_MAX_REG_NUM << 2)
> +#define NUMREGBYTES		(GDB_MAX_REGS << 2)
>  #define NUMCRITREGBYTES		(32 << 2)
>  
>  #define _R0			0
> 
> base-commit: 0adb32858b0bddf4ada5f364a84ed60b196dbcda
> -- 
> 2.14.3
>