linux-kernel - [PATCH 5/7] powerpc/ftrace: Update ftrace_location() for powerpc -mprofile-kernel

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Date:   Tue, 18 Jun 2019 20:17:04 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH 5/7] powerpc/ftrace: Update ftrace_location() for powerpc -mprofile-kernel

Now that we are patching the preceding 'mflr r0' instruction with
-mprofile-kernel, we need to update ftrace_location[_range]() to
recognise that as being part of ftrace. To do this, we make a small
change to ftrace_location_range() and convert ftrace_cmp_recs() into a
weak function. We implement a custom version of ftrace_cmp_recs() which
looks at the instruction preceding the branch to _mcount() and marks
that instruction as belonging to ftrace if it is a 'nop' or 'mflr r0'.

Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
 arch/powerpc/kernel/trace/ftrace.c | 31 ++++++++++++++++++++++++++++++
 include/linux/ftrace.h             |  1 +
 kernel/trace/ftrace.c              |  4 ++--
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index 5e2b29808af1..b84046e43207 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -951,6 +951,37 @@ void arch_ftrace_update_code(int command)
 }
 
 #ifdef CONFIG_MPROFILE_KERNEL
+/*
+ * We need to check if the previous instruction is a 'nop' or 'mflr r0'.
+ * If so, we will patch those subsequently and that instruction must be
+ * considered as part of ftrace.
+ */
+int ftrace_cmp_recs(const void *a, const void *b)
+{
+	const struct dyn_ftrace *key = a;
+	const struct dyn_ftrace *rec = b;
+	unsigned int op;
+
+	if (key->flags < rec->ip - MCOUNT_INSN_SIZE)
+		return -1;
+	if (key->ip >= rec->ip + MCOUNT_INSN_SIZE)
+		return 1;
+
+	if (key->flags > rec->ip)
+		return 0;
+
+	/* check the previous instruction */
+	if (probe_kernel_read(&op, (void *)rec->ip - MCOUNT_INSN_SIZE,
+				sizeof(op)))
+		/* assume we own it */
+		return 0;
+
+	if (op != PPC_INST_NOP && op != PPC_INST_MFLR)
+		return -1;
+
+	return 0;
+}
+
 /* Returns 1 if we patched in the mflr */
 static int __ftrace_make_call_prep(struct dyn_ftrace *rec)
 {
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index fa653a561da5..9941987bf510 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -435,6 +435,7 @@ struct dyn_ftrace *ftrace_rec_iter_record(struct ftrace_rec_iter *iter);
 int ftrace_update_record(struct dyn_ftrace *rec, int enable);
 int ftrace_test_record(struct dyn_ftrace *rec, int enable);
 void ftrace_run_stop_machine(int command);
+int ftrace_cmp_recs(const void *a, const void *b);
 unsigned long ftrace_location(unsigned long ip);
 unsigned long ftrace_location_range(unsigned long start, unsigned long end);
 unsigned long ftrace_get_addr_new(struct dyn_ftrace *rec);
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 21d8e201ee80..b5c61db0b452 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1517,7 +1517,7 @@ ftrace_ops_test(struct ftrace_ops *ops, unsigned long ip, void *regs)
 	}
 
 
-static int ftrace_cmp_recs(const void *a, const void *b)
+int __weak ftrace_cmp_recs(const void *a, const void *b)
 {
 	const struct dyn_ftrace *key = a;
 	const struct dyn_ftrace *rec = b;
@@ -1551,7 +1551,7 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
 	key.flags = end;	/* overload flags, as it is unsigned long */
 
 	for (pg = ftrace_pages_start; pg; pg = pg->next) {
-		if (end < pg->records[0].ip ||
+		if (end <= pg->records[0].ip ||
 		    start >= (pg->records[pg->index - 1].ip + MCOUNT_INSN_SIZE))
 			continue;
 		rec = bsearch(&key, pg->records, pg->index,
-- 
2.22.0