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>

arch/powerpc/include/asm/ptrace.h

@@ -135,7 +135,9 @@ do {									      \
  * These are defined as per linux/ptrace.h, which see.
  */
 #define arch_has_single_step()	(1)
+#define arch_has_block_step()	(!cpu_has_feature(CPU_FTR_601))
 extern void user_enable_single_step(struct task_struct *);
+extern void user_enable_block_step(struct task_struct *);
 extern void user_disable_single_step(struct task_struct *);
 
 #endif /* __ASSEMBLY__ */
@@ -288,4 +290,6 @@ extern void user_disable_single_step(struct task_struct *);
 #define PPC_PTRACE_PEEKUSR_3264  0x91
 #define PPC_PTRACE_POKEUSR_3264  0x90
 
+#define PTRACE_SINGLEBLOCK	0x100	/* resume execution until next branch */
+
 #endif /* _ASM_POWERPC_PTRACE_H */

arch/powerpc/kernel/head_booke.h

@@ -256,7 +256,7 @@ label:
 	 * off DE in the DSRR1 value and clearing the debug status.	      \
 	 */								      \
 	mfspr	r10,SPRN_DBSR;		/* check single-step/branch taken */  \
-	andis.	r10,r10,DBSR_IC@h;					      \
+	andis.	r10,r10,(DBSR_IC|DBSR_BT)@h;				      \
 	beq+	2f;							      \
 									      \
 	lis	r10,KERNELBASE@h;	/* check if exception in vectors */   \
@@ -271,7 +271,7 @@ label:
 									      \
 	/* here it looks like we got an inappropriate debug exception. */     \
 1:	rlwinm	r9,r9,0,~MSR_DE;	/* clear DE in the CDRR1 value */     \
-	lis	r10,DBSR_IC@h;		/* clear the IC event */	      \
+	lis	r10,(DBSR_IC|DBSR_BT)@h;	/* clear the IC event */      \
 	mtspr	SPRN_DBSR,r10;						      \
 	/* restore state and get out */					      \
 	lwz	r10,_CCR(r11);						      \
@@ -309,7 +309,7 @@ label:
 	 * off DE in the CSRR1 value and clearing the debug status.	      \
 	 */								      \
 	mfspr	r10,SPRN_DBSR;		/* check single-step/branch taken */  \
-	andis.	r10,r10,DBSR_IC@h;					      \
+	andis.	r10,r10,(DBSR_IC|DBSR_BT)@h;				      \
 	beq+	2f;							      \
 									      \
 	lis	r10,KERNELBASE@h;	/* check if exception in vectors */   \
@@ -324,7 +324,7 @@ label:
 									      \
 	/* here it looks like we got an inappropriate debug exception. */     \
 1:	rlwinm	r9,r9,0,~MSR_DE;	/* clear DE in the CSRR1 value */     \
-	lis	r10,DBSR_IC@h;		/* clear the IC event */	      \
+	lis	r10,(DBSR_IC|DBSR_BT)@h;	/* clear the IC event */      \
 	mtspr	SPRN_DBSR,r10;						      \
 	/* restore state and get out */					      \
 	lwz	r10,_CCR(r11);						      \

arch/powerpc/kernel/ptrace.c

@@ -704,15 +704,34 @@ void user_enable_single_step(struct task_struct *task)
 
 	if (regs != NULL) {
 #if defined(CONFIG_40x) || defined(CONFIG_BOOKE)
+		task->thread.dbcr0 &= ~DBCR0_BT;
 		task->thread.dbcr0 |= DBCR0_IDM | DBCR0_IC;
 		regs->msr |= MSR_DE;
 #else
+		regs->msr &= ~MSR_BE;
 		regs->msr |= MSR_SE;
 #endif
 	}
 	set_tsk_thread_flag(task, TIF_SINGLESTEP);
 }
 
+void user_enable_block_step(struct task_struct *task)
+{
+	struct pt_regs *regs = task->thread.regs;
+
+	if (regs != NULL) {
+#if defined(CONFIG_40x) || defined(CONFIG_BOOKE)
+		task->thread.dbcr0 &= ~DBCR0_IC;
+		task->thread.dbcr0 = DBCR0_IDM | DBCR0_BT;
+		regs->msr |= MSR_DE;
+#else
+		regs->msr &= ~MSR_SE;
+		regs->msr |= MSR_BE;
+#endif
+	}
+	set_tsk_thread_flag(task, TIF_SINGLESTEP);
+}
+
 void user_disable_single_step(struct task_struct *task)
 {
 	struct pt_regs *regs = task->thread.regs;
@@ -726,10 +745,10 @@ void user_disable_single_step(struct task_struct *task)
 
 	if (regs != NULL) {
 #if defined(CONFIG_40x) || defined(CONFIG_BOOKE)
-		task->thread.dbcr0 &= ~(DBCR0_IC | DBCR0_IDM);
+		task->thread.dbcr0 &= ~(DBCR0_IC | DBCR0_BT | DBCR0_IDM);
 		regs->msr &= ~MSR_DE;
 #else
-		regs->msr &= ~MSR_SE;
+		regs->msr &= ~(MSR_SE | MSR_BE);
 #endif
 	}
 	clear_tsk_thread_flag(task, TIF_SINGLESTEP);

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)) {