[PATCH 3/4] sparc64: kprobes: Resume after a delay slot at the saved next PC

[Stian Halseth <stian@itx.no>]

After single-stepping an instruction that does not branch, execution
resumes at the saved next PC, followed by the probed address plus 8.
For an instruction in the delay slot of a taken branch the saved next
PC is the branch target, so after the target execution goes back to
the probed address plus 8 instead of continuing at the target plus 4.

Use the saved next PC plus 4, which equals the probed address plus 8
for any other instruction.

Link: https://github.com/sparclinux/issues/issues/110
Signed-off-by: Stian Halseth <stian@itx.no>
---
 arch/sparc/kernel/kprobes.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/sparc/kernel/kprobes.c b/arch/sparc/kernel/kprobes.c
index 38e6d9b51a207..327d83188a978 100644
--- a/arch/sparc/kernel/kprobes.c
+++ b/arch/sparc/kernel/kprobes.c
@@ -211,13 +211,14 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
  * 
  */
 static unsigned long __kprobes relbranch_fixup(u32 insn, struct kprobe *p,
-					       struct pt_regs *regs)
+					       struct pt_regs *regs,
+					       struct kprobe_ctlblk *kcb)
 {
 	unsigned long real_pc = (unsigned long) p->addr;
 
 	/* Branch not taken, no mods necessary.  */
 	if (regs->tnpc == regs->tpc + 0x4UL)
-		return real_pc + 0x8UL;
+		return kcb->kprobe_orig_tnpc + 0x4UL;
 
 	/* The cases are call and the branches BPcc, Bicc, BPr, FBPfcc
 	 * and FBfcc.
@@ -294,7 +295,7 @@ static void __kprobes resume_execution(struct kprobe *p,
 {
 	u32 insn = p->ainsn.insn[0];
 
-	regs->tnpc = relbranch_fixup(insn, p, regs);
+	regs->tnpc = relbranch_fixup(insn, p, regs, kcb);
 
 	/* This assignment must occur after relbranch_fixup() */
 	regs->tpc = kcb->kprobe_orig_tnpc;
-- 
2.43.0