[PATCH 15/18] powerpc/uprobes: Add support for prefixed instructions

[Jordan Niethe <jniethe5@gmail.com>]

Uprobes can execute instructions out of line. Increase the size of the
buffer used  for this so that this works for prefixed instructions. Take
into account the length of prefixed instructions when fixing up the nip.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
---
 arch/powerpc/include/asm/uprobes.h | 18 ++++++++++++++----
 arch/powerpc/kernel/uprobes.c      |  4 ++--
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/include/asm/uprobes.h b/arch/powerpc/include/asm/uprobes.h
index 2bbdf27d09b5..5b5e8a3d2f55 100644
--- a/arch/powerpc/include/asm/uprobes.h
+++ b/arch/powerpc/include/asm/uprobes.h
@@ -14,18 +14,28 @@
 
 typedef ppc_opcode_t uprobe_opcode_t;
 
+/*
+ * We have to ensure we have enought space for prefixed instructions, which
+ * are double the size of a word instruction, i.e. 8 bytes. However,
+ * sometimes it is simpler to treat a prefixed instruction like 2 word
+ * instructions.
+ */
 #define MAX_UINSN_BYTES		4
-#define UPROBE_XOL_SLOT_BYTES	(MAX_UINSN_BYTES)
+#define UPROBE_XOL_SLOT_BYTES	(2 * MAX_UINSN_BYTES)
 
 /* The following alias is needed for reference from arch-agnostic code */
 #define UPROBE_SWBP_INSN	BREAKPOINT_INSTRUCTION
 #define UPROBE_SWBP_INSN_SIZE	4 /* swbp insn size in bytes */
 
 struct arch_uprobe {
+	 /*
+	  * Ensure there is enough space for prefixed instructions. Prefixed
+	  * instructions must not cross 64-byte boundaries.
+	  */
 	union {
-		u32	insn;
-		u32	ixol;
-	};
+		uprobe_opcode_t	insn[2];
+		uprobe_opcode_t	ixol[2];
+	} __aligned(64);
 };
 
 struct arch_uprobe_task {
diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
index ab1077dc6148..cfcea6946f8b 100644
--- a/arch/powerpc/kernel/uprobes.c
+++ b/arch/powerpc/kernel/uprobes.c
@@ -111,7 +111,7 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 	 * support doesn't exist and have to fix-up the next instruction
 	 * to be executed.
 	 */
-	regs->nip = utask->vaddr + MAX_UINSN_BYTES;
+	regs->nip = utask->vaddr + ((IS_PREFIX(auprobe->insn[0])) ? 8 : 4);
 
 	user_disable_single_step(current);
 	return 0;
@@ -173,7 +173,7 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
 	 * emulate_step() returns 1 if the insn was successfully emulated.
 	 * For all other cases, we need to single-step in hardware.
 	 */
-	ret = emulate_step(regs, auprobe->insn, 0);
+	ret = emulate_step(regs, auprobe->insn[0], auprobe->insn[1]);
 	if (ret > 0)
 		return true;
 
-- 
2.20.1