powerpc: Add PTRACE_SINGLEBLOCK support

Reworked by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

This adds block-step support on powerpc, including a PTRACE_SINGLEBLOCK
request for ptrace.

The BookE implementation is tweaked to fire a single step after a
block step in order to mimmic the server behaviour.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 30 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 6a5b2b731f43..6f0ae1a9bfae 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1041,7 +1041,34 @@ void SoftwareEmulation(struct pt_regs *regs)
 
 void __kprobes DebugException(struct pt_regs *regs, unsigned long debug_status)
 {
-        if (debug_status & DBSR_IC) {   /* instruction completion */
+        /* Hack alert: On BookE, Branch Taken stops on the branch itself, while
+         * on server, it stops on the target of the branch. In order to simulate
+         * the server behaviour, we thus restart right away with a single step
+         * instead of stopping here when hitting a BT
+         */
+        if (debug_status & DBSR_BT) {
+                regs->msr &= ~MSR_DE;
+
+                /* Disable BT */
+                mtspr(SPRN_DBCR0, mfspr(SPRN_DBCR0) & ~DBCR0_BT);
+                /* Clear the BT event */
+                mtspr(SPRN_DBSR, DBSR_BT);
+
+                /* Do the single step trick only when coming from userspace */
+                if (user_mode(regs)) {
+                        current->thread.dbcr0 &= ~DBCR0_BT;
+                        current->thread.dbcr0 |= DBCR0_IDM | DBCR0_IC;
+                        regs->msr |= MSR_DE;
+                        return;
+                }
+
+                if (notify_die(DIE_SSTEP, "block_step", regs, 5,
+                               5, SIGTRAP) == NOTIFY_STOP) {
+                        return;
+                }
+                if (debugger_sstep(regs))
+                        return;
+        } else if (debug_status & DBSR_IC) {    /* Instruction complete */
                 regs->msr &= ~MSR_DE;
 
                 /* Disable instruction completion */
@@ -1057,9 +1084,8 @@ void __kprobes DebugException(struct pt_regs *regs, unsigned long debug_status)
                 if (debugger_sstep(regs))
                         return;
 
-                if (user_mode(regs)) {
-                        current->thread.dbcr0 &= ~DBCR0_IC;
-                }
+                if (user_mode(regs))
+                        current->thread.dbcr0 &= ~(DBCR0_IC);
 
                 _exception(SIGTRAP, regs, TRAP_TRACE, regs->nip);
         } else if (debug_status & (DBSR_DAC1R | DBSR_DAC1W)) {