linux-kernel - [PATCH v2] cris: arch-v10: kgdb: Add volatile for static variable is_dyn

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Message-ID: <BLU436-SMTP239D8DB10AA01D4CB30D6B5B99F0@phx.gbl>
Date:	Sat, 11 Jul 2015 05:50:07 +0800
From:	Chen Gang <xili_gchen_5257@...mail.com>
To:	starvik@...s.com, jesper.nilsson@...s.com
CC:	"linux-cris-kernel@...s.com" <linux-cris-kernel@...s.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hans-Peter Nilsson <hans-peter.nilsson@...s.com>
Subject: [PATCH v2] cris: arch-v10: kgdb: Add volatile for static variable
 is_dyn_brkp

Within one C file, current gcc can optimize the global static variables
according to the C code, but it will skip assembly code -- it will pass
them to gas directly.

if the static variable is used between C code and assembly code in one C
file (e.g. is_dyn_brkp in kgdb.c), it needs volatile to let gcc know it
should not be optimized, or it may cause issue.

The related error in this case:

    LD      init/built-in.o
  arch/cris/arch-v10/kernel/built-in.o: In function `kgdb_handle_breakpoint':
  (.text+0x2aca): undefined reference to `is_dyn_brkp'
  arch/cris/arch-v10/kernel/built-in.o: In function `is_static':
  kgdb.c:(.text+0x2ada): undefined reference to `is_dyn_brkp'


Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
---
 arch/cris/arch-v10/kernel/kgdb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/cris/arch-v10/kernel/kgdb.c b/arch/cris/arch-v10/kernel/kgdb.c
index 5b61335..8faddd3 100644
--- a/arch/cris/arch-v10/kernel/kgdb.c
+++ b/arch/cris/arch-v10/kernel/kgdb.c
@@ -351,7 +351,7 @@ char internal_stack[INTERNAL_STACK_SIZE];
    breakpoint to be handled. A static breakpoint uses the content of register
    BRP as it is whereas a dynamic breakpoint requires subtraction with 2
    in order to execute the instruction. The first breakpoint is static. */
-static unsigned char is_dyn_brkp = 0;
+static volatile unsigned char is_dyn_brkp;
 
 /********************************* String library ****************************/
 /* Single-step over library functions creates trap loops. */
-- 
1.9.3
--
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