linux-kernel - [PATCH] sh/kprobes: respect gdb breakpoints

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Message-ID: <1438963475.4896.7.camel@oc1026406570.ibm.com>
Date:	Fri, 07 Aug 2015 09:04:35 -0700
From:	Jim Keniston <jkenisto@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	Ananth Narayan <ananth@...ibm.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	abab@...ux.vnet.ibm.com, vkumar14@...ovo.com
Subject: [PATCH] sh/kprobes: respect gdb breakpoints

On the sh architecture, kprobes and gdb/gdbserver use different
breakpoint opcodes.  Without this fix, kprobes doesn't recognize
the gdb traps, and the resulting NOTIFY_STOP prevents ptrace and gdb
from being notified.  The result is that if kprobes is configured,
a gdb-traced process hangs when its gdb breakpoint is hit.

Signed-off-by: Jim Keniston <jkenisto@...ux.vnet.ibm.com>
Signed-off-by: Reza Arbab <arbab@...ux.vnet.ibm.com>
Reported-by: Vijay Kumar <vkumar14@...ovo.com>
Tested-by: Vijay Kumar <vkumar14@...ovo.com>
---
 arch/sh/include/asm/kprobes.h |    2 ++
 arch/sh/kernel/kprobes.c      |    5 ++++-
 2 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/arch/sh/include/asm/kprobes.h b/arch/sh/include/asm/kprobes.h
index 134f398..f22a3cb 100644
--- a/arch/sh/include/asm/kprobes.h
+++ b/arch/sh/include/asm/kprobes.h
@@ -8,6 +8,8 @@
 
 typedef insn_size_t kprobe_opcode_t;
 #define BREAKPOINT_INSTRUCTION	0xc33a
+#define GDB_BREAKPOINT_INSTRUCTION	0xc3c3
+#define GDBSERVER_BREAKPOINT_INSTRUCTION	0xc320
 
 #define MAX_INSN_SIZE 16
 #define MAX_STACK_SIZE 64
diff --git a/arch/sh/kernel/kprobes.c b/arch/sh/kernel/kprobes.c
index 83acbf3..bcaa072 100644
--- a/arch/sh/kernel/kprobes.c
+++ b/arch/sh/kernel/kprobes.c
@@ -260,7 +260,10 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
 	p = get_kprobe(addr);
 	if (!p) {
 		/* Not one of ours: let kernel handle it */
-		if (*(kprobe_opcode_t *)addr != BREAKPOINT_INSTRUCTION) {
+		kprobe_opcode_t opcode = *(kprobe_opcode_t *)addr;
+		if (opcode != BREAKPOINT_INSTRUCTION &&
+				opcode != GDB_BREAKPOINT_INSTRUCTION &&
+				opcode != GDBSERVER_BREAKPOINT_INSTRUCTION) {
 			/*
 			 * The breakpoint instruction was removed right
 			 * after we hit it. Another cpu has removed

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