linux-kernel - [RFC PATCH 6/6] uprobes/x86: Emulate rip-relative conditional "near" jmp's

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Date:	Sun, 6 Apr 2014 22:16:36 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <aarapov@...hat.com>,
	David Long <dave.long@...aro.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Jonathan Lebon <jlebon@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH 6/6] uprobes/x86: Emulate rip-relative conditional
	"near" jmp's

It seems that 16bit conditional jmp is just
0x0f + short_jump_opcode_incremented by 0x10.

But I'll try to cleanup this patch...

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 arch/x86/kernel/uprobes.c |   18 +++++++++++++++---
 1 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 797b8a4..8f92cbf 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -564,6 +564,19 @@ static int ttt_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
 	if (WARN_ON_ONCE(!insn_complete(insn)))
 		return -ENOEXEC;
 
+#define CASE(op_y, op_n, cond)	\
+		case 0x ## op_y: case 0x ## op_n:
+
+	if (insn->opcode.nbytes == 2 && opc1 == 0x0f) {
+		opc1 = OPCODE2(insn) - 0x10;
+
+		switch (opc1) {
+		X86_COND_OPCODES
+		default:
+			return -ENOSYS;
+		}
+	}
+
 	switch (opc1) {
 	case 0xeb:	/* jmp 8 */
 	case 0xe9:	/* jmp 32 */
@@ -573,10 +586,7 @@ static int ttt_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
 	case 0xe8:	/* call relative */
 		ttt_clear_displacement(auprobe, insn);
 		/* fall through */
-	#define CASE(op_y, op_n, cond)	\
-			case 0x ## op_y: case 0x ## op_n:
 	X86_COND_OPCODES
-	#undef CASE
 		auprobe->ttt.opc1 = opc1;
 		break;
 
@@ -584,6 +594,8 @@ static int ttt_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
 		return -ENOSYS;
 	}
 
+#undef CASE
+
 	auprobe->ttt.ilen = insn->length;
 	auprobe->ttt.disp = insn->moffset1.value;
 	/* so far we assume that it fits into ->moffset1 */
-- 
1.5.5.1

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