linux-kernel - [PATCH 4/7] x86,early dr regs,kgdb: Allow kernel debugger early dr register access

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Message-Id: <1274233202-3734-5-git-send-email-jason.wessel@windriver.com>
Date:	Tue, 18 May 2010 20:39:59 -0500
From:	Jason Wessel <jason.wessel@...driver.com>
To:	torvalds@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
	Jason Wessel <jason.wessel@...driver.com>, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 4/7] x86,early dr regs,kgdb: Allow kernel debugger early dr register access

If the kernel debugger was configured, attached and started with
kgdbwait, the hardware breakpoint registers should get restored by the
kgdb code which is managing the dr registers.

CC: x86@...nel.org
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Ingo Molnar <mingo@...hat.com>
CC: H. Peter Anvin <hpa@...or.com>
Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
---
 arch/x86/kernel/cpu/common.c |   29 +++++++++++++++++------------
 1 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 4868e4a..712c1eb 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1084,6 +1084,20 @@ static void clear_all_debug_regs(void)
 	}
 }
 
+#ifdef CONFIG_KGDB
+/*
+ * Restore debug regs if using kgdbwait and you have a kernel debugger
+ * connection established.
+ */
+static void dbg_restore_debug_regs(void)
+{
+	if (unlikely(kgdb_connected && arch_kgdb_ops.correct_hw_break))
+		arch_kgdb_ops.correct_hw_break();
+}
+#else /* ! CONFIG_KGDB */
+#define dbg_restore_debug_regs()
+#endif /* ! CONFIG_KGDB */
+
 /*
  * cpu_init() initializes state that is per-CPU. Some data is already
  * initialized (naturally) in the bootstrap process, such as the GDT
@@ -1174,18 +1188,8 @@ void __cpuinit cpu_init(void)
 	load_TR_desc();
 	load_LDT(&init_mm.context);
 
-#ifdef CONFIG_KGDB
-	/*
-	 * If the kgdb is connected no debug regs should be altered.  This
-	 * is only applicable when KGDB and a KGDB I/O module are built
-	 * into the kernel and you are using early debugging with
-	 * kgdbwait. KGDB will control the kernel HW breakpoint registers.
-	 */
-	if (kgdb_connected && arch_kgdb_ops.correct_hw_break)
-		arch_kgdb_ops.correct_hw_break();
-	else
-#endif
-		clear_all_debug_regs();
+	clear_all_debug_regs();
+	dbg_restore_debug_regs();
 
 	fpu_init();
 
@@ -1239,6 +1243,7 @@ void __cpuinit cpu_init(void)
 #endif
 
 	clear_all_debug_regs();
+	dbg_restore_debug_regs();
 
 	/*
 	 * Force FPU initialization:
-- 
1.6.3.3

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