[PATCH 18/73] sparse: Gate context failure warning on Wcontext and catch underflow

[Bart Van Assche <bvanassche@acm.org>]

Gate "context check failure" diagnostics on Wcontext in
context_increase() and return early as soon as entry + sum drops below
zero so an unexpected unlock followed by a lock in the same basic block
still triggers a context imbalance warning.

Add regression test validation/context-fixes.c.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 sparse.c                   |  5 ++++-
 validation/context-fixes.c | 41 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletion(-)
 create mode 100644 validation/context-fixes.c

diff --git a/sparse.c b/sparse.c
index e7cc6f55e503..883a5edec5b1 100644
--- a/sparse.c
+++ b/sparse.c
@@ -59,10 +59,13 @@ static int context_increase(struct basic_block *bb, int entry)
 					continue;
 			} else if (current >= val)
 				continue;
-			warning(insn->pos, "context check failure");
+			if (Wcontext)
+				warning(insn->pos, "context check failure");
 			continue;
 		}
 		sum += val;
+		if (entry + sum < 0)
+			return sum;
 	} END_FOR_EACH_PTR(insn);
 	return sum;
 }
diff --git a/validation/context-fixes.c b/validation/context-fixes.c
new file mode 100644
index 000000000000..ab6c354cacea
--- /dev/null
+++ b/validation/context-fixes.c
@@ -0,0 +1,41 @@
+static void lock(void) __attribute__((context(0, 1)))
+{
+	__context__(1);
+}
+
+static void unlock(void) __attribute__((context(1, 0)))
+{
+	__context__(-1);
+}
+
+/* 1. Context attribute before pointer return type */
+extern __attribute__((context(0, 1))) void *lock_ret_ptr(void);
+
+static void good_ptr_lock(void)
+{
+	void *p = lock_ret_ptr();
+	(void)p;
+	unlock();
+}
+
+static void warn_ptr_lock(void)
+{
+	lock_ret_ptr();
+}
+
+/* 2. Unlock followed by lock in same basic block must warn */
+static void warn_unlock_then_lock(void)
+{
+	unlock();
+	lock();
+}
+
+/*
+ * check-name: context-fixes
+ * check-command: sparse -Wcontext $file
+ *
+ * check-error-start
+context-fixes.c:21:13: warning: context imbalance in 'warn_ptr_lock' - wrong count at exit
+context-fixes.c:27:13: warning: context imbalance in 'warn_unlock_then_lock' - unexpected unlock
+ * check-error-end
+ */