Subject: [PATCH 1/2] [hw-breakpoint] Use generic hw-breakpoint interfaces for new PPC ptrace flags

From: "K.Prasad" <[email-masked]>
Date: Fri, 19 Aug 2011 13:21:36 +0530

PPC_PTRACE_GETHWDBGINFO, PPC_PTRACE_SETHWDEBUG and PPC_PTRACE_DELHWDEBUG are
PowerPC specific ptrace flags that use the watchpoint register. While they are
targeted primarily towards BookE users, user-space applications such as GDB
have started using them for BookS too.

This patch enables the use of generic hardware breakpoint interfaces for these
new flags. The version number of the associated data structures
"ppc_hw_breakpoint" and "ppc_debug_info" is incremented to denote new semantics.

Apart from the usual benefits of using generic hw-breakpoint interfaces, these
changes allow debuggers (such as GDB) to use a common set of ptrace flags for
their watchpoint needs and allow more precise breakpoint specification (length
of the variable can be specified).

[Edjunior: Identified an issue in the patch with the sanity check for version
numbers]

Tested-by: Edjunior Barbosa Machado <[email-masked]>
Signed-off-by: K.Prasad <[email-masked]>
---
 Documentation/powerpc/ptrace.txt |   16 ++++++
 arch/powerpc/kernel/ptrace.c     |  104 +++++++++++++++++++++++++++++++++++---
 2 files changed, 112 insertions(+), 8 deletions(-)

diff --git a/Documentation/powerpc/ptrace.txt b/Documentation/powerpc/ptrace.txt
index f4a5499..97301ae 100644
--- a/Documentation/powerpc/ptrace.txt
+++ b/Documentation/powerpc/ptrace.txt
@@ -127,6 +127,22 @@ Some examples of using the structure to:
   p.addr2           = (uint64_t) end_range;
   p.condition_value = 0;
 
+- set a watchpoint in server processors (BookS) using version 2
+
+  p.version         = 2;
+  p.trigger_type    = PPC_BREAKPOINT_TRIGGER_RW;
+  p.addr_mode       = PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE;
+  or
+  p.addr_mode       = PPC_BREAKPOINT_MODE_RANGE_EXACT;
+
+  p.condition_mode  = PPC_BREAKPOINT_CONDITION_NONE;
+  p.addr            = (uint64_t) begin_range;
+  /* For PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE addr2 needs to be specified, where
+   * addr2 - addr <= 8 Bytes.
+   */
+  p.addr2           = (uint64_t) end_range;
+  p.condition_value = 0;
+
 3. PTRACE_DELHWDEBUG
 
 Takes an integer which identifies an existing breakpoint or watchpoint
diff --git a/arch/powerpc/kernel/ptrace.c b/arch/powerpc/kernel/ptrace.c
index 05b7dd2..18d28b6 100644
--- a/arch/powerpc/kernel/ptrace.c
+++ b/arch/powerpc/kernel/ptrace.c
@@ -1339,11 +1339,17 @@ static int set_dac_range(struct task_struct *child,
 static long ppc_set_hwdebug(struct task_struct *child,
 		     struct ppc_hw_breakpoint *bp_info)
 {
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	int ret, len = 0;
+	struct thread_struct *thread = &(child->thread);
+	struct perf_event *bp;
+	struct perf_event_attr attr;
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 #ifndef CONFIG_PPC_ADV_DEBUG_REGS
 	unsigned long dabr;
 #endif
 
-	if (bp_info->version != 1)
+	if ((bp_info->version != 1) && (bp_info->version != 2))
 		return -ENOTSUPP;
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
 	/*
@@ -1382,13 +1388,9 @@ static long ppc_set_hwdebug(struct task_struct *child,
 	 */
 	if ((bp_info->trigger_type & PPC_BREAKPOINT_TRIGGER_RW) == 0 ||
 	    (bp_info->trigger_type & ~PPC_BREAKPOINT_TRIGGER_RW) != 0 ||
-	    bp_info->addr_mode != PPC_BREAKPOINT_MODE_EXACT ||
 	    bp_info->condition_mode != PPC_BREAKPOINT_CONDITION_NONE)
 		return -EINVAL;
 
-	if (child->thread.dabr)
-		return -ENOSPC;
-
 	if ((unsigned long)bp_info->addr >= TASK_SIZE)
 		return -EIO;
 
@@ -1398,15 +1400,86 @@ static long ppc_set_hwdebug(struct task_struct *child,
 		dabr |= DABR_DATA_READ;
 	if (bp_info->trigger_type & PPC_BREAKPOINT_TRIGGER_WRITE)
 		dabr |= DABR_DATA_WRITE;
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	if (bp_info->version == 1)
+		goto version_one;
+	if (ptrace_get_breakpoints(child) < 0)
+		return -ESRCH;
 
-	child->thread.dabr = dabr;
+	bp = thread->ptrace_bps[0];
+	if (!bp_info->addr) {
+		if (bp) {
+			unregister_hw_breakpoint(bp);
+			thread->ptrace_bps[0] = NULL;
+		}
+		ptrace_put_breakpoints(child);
+		return 0;
+	}
+	/*
+	 * Check if the request is for 'range' breakpoints. We can
+	 * support it if range < 8 bytes.
+	 */
+	if (bp_info->addr_mode == PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE)
+		len = bp_info->addr2 - bp_info->addr;
+	else if (bp_info->addr_mode != PPC_BREAKPOINT_MODE_EXACT) {
+			ptrace_put_breakpoints(child);
+			return -EINVAL;
+		}
+	if (bp) {
+		attr = bp->attr;
+		attr.bp_addr = (unsigned long)bp_info->addr & ~HW_BREAKPOINT_ALIGN;
+		arch_bp_generic_fields(dabr &
+					(DABR_DATA_WRITE | DABR_DATA_READ),
+							&attr.bp_type);
+		attr.bp_len = len;
+		ret =  modify_user_hw_breakpoint(bp, &attr);
+		if (ret) {
+			ptrace_put_breakpoints(child);
+			return ret;
+		}
+		thread->ptrace_bps[0] = bp;
+		ptrace_put_breakpoints(child);
+		thread->dabr = dabr;
+		return 0;
+	}
 
+	/* Create a new breakpoint request if one doesn't exist already */
+	hw_breakpoint_init(&attr);
+	attr.bp_addr = (unsigned long)bp_info->addr & ~HW_BREAKPOINT_ALIGN;
+	attr.bp_len = len;
+	arch_bp_generic_fields(dabr & (DABR_DATA_WRITE | DABR_DATA_READ),
+								&attr.bp_type);
+
+	thread->ptrace_bps[0] = bp = register_user_hw_breakpoint(&attr,
+					       ptrace_triggered, NULL, child);
+	if (IS_ERR(bp)) {
+		thread->ptrace_bps[0] = NULL;
+		ptrace_put_breakpoints(child);
+		return PTR_ERR(bp);
+	}
+
+	ptrace_put_breakpoints(child);
+	return 1;
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
+
+version_one:
+	if (bp_info->addr_mode != PPC_BREAKPOINT_MODE_EXACT)
+		return -EINVAL;
+
+	if (child->thread.dabr)
+		return -ENOSPC;
+
+	child->thread.dabr = dabr;
 	return 1;
 #endif /* !CONFIG_PPC_ADV_DEBUG_DVCS */
 }
 
 static long ppc_del_hwdebug(struct task_struct *child, long addr, long data)
 {
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	struct thread_struct *thread = &(child->thread);
+	struct perf_event *bp;
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
 	int rc;
 
@@ -1426,10 +1499,24 @@ static long ppc_del_hwdebug(struct task_struct *child, long addr, long data)
 #else
 	if (data != 1)
 		return -EINVAL;
+
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	if (ptrace_get_breakpoints(child) < 0)
+		return -ESRCH;
+
+	bp = thread->ptrace_bps[0];
+	if (bp) {
+		unregister_hw_breakpoint(bp);
+		thread->ptrace_bps[0] = NULL;
+	}
+	ptrace_put_breakpoints(child);
+	return 0;
+#else /* CONFIG_HAVE_HW_BREAKPOINT */
 	if (child->thread.dabr == 0)
 		return -ENOENT;
 
 	child->thread.dabr = 0;
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
 
 	return 0;
 #endif
@@ -1536,7 +1623,8 @@ long arch_ptrace(struct task_struct *child, long request,
 	case PPC_PTRACE_GETHWDBGINFO: {
 		struct ppc_debug_info dbginfo;
 
-		dbginfo.version = 1;
+		/* We return the highest version number supported */
+		dbginfo.version = 2;
 #ifdef CONFIG_PPC_ADV_DEBUG_REGS
 		dbginfo.num_instruction_bps = CONFIG_PPC_ADV_DEBUG_IACS;
 		dbginfo.num_data_bps = CONFIG_PPC_ADV_DEBUG_DACS;
@@ -1560,7 +1648,7 @@ long arch_ptrace(struct task_struct *child, long request,
 		dbginfo.data_bp_alignment = 4;
 #endif
 		dbginfo.sizeof_condition = 0;
-		dbginfo.features = 0;
+		dbginfo.features = PPC_DEBUG_FEATURE_DATA_BP_RANGE;
 #endif /* CONFIG_PPC_ADV_DEBUG_REGS */
 
 		if (!access_ok(VERIFY_WRITE, datavp,
-- 
1.7.4.1