[PATCH v2 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. The probed address plus 8 comes next.
For an instruction in the delay slot of a taken branch the saved next
PC is the branch target. Execution then goes back to the probed
address plus 8. It should continue at the target plus 4.

Use the saved next PC plus 4. For any other instruction that is the
probed address plus 8.

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