Re: [PATCH] arm: kgdb: fix NUMREGBYTES so that gdb_regs[] is the correct size

From: Daniel Thompson
Date: Fri Apr 06 2018 - 09:49:48 EST

On 06/04/18 14:25, Daniel Thompson wrote:
On Thu, Apr 05, 2018 at 04:09:16PM -0400, David Rivshin wrote:
From: David Rivshin <DRivshin@xxxxxxxxxxx>

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@xxxxxxxxxxxxxxx> # 2.6.37+
Signed-off-by: David Rivshin <drivshin@xxxxxxxxxxx>

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@xxxxxxxxxx>

BTW I noticed that myself and Jason in the only "real people" in
To: . Most arch specific patches end up making their way upstream via the arch maintainer rather than via the kgdb tree so personally I would choose to the arch maintainers in the To: field as well.

I certainly think you will have to follow up via Russell King's patch tracker once you think its had enough time on the ML for review.


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 NUMCRITREGBYTES (32 << 2)
#define _R0 0

base-commit: 0adb32858b0bddf4ada5f364a84ed60b196dbcda