From 1bf908df57cc43f3bc7296f4e51f5708bd323c6b Mon Sep 17 00:00:00 2001
From: Jordan Rose <jordan_rose@apple.com>
Date: Sat, 16 Jun 2012 00:09:20 +0000
Subject: [PATCH] [analyzer] Buffers passed to CGBitmapContextCreate can
 escape.

Specifically, although the bitmap context does not take ownership of the
buffer (unlike CGBitmapContextCreateWithData), the data buffer can be extracted
out of the created CGContextRef. Thus the buffer is not leaked even if its
original pointer goes out of scope, as long as
- the context escapes, or
- it is retrieved via CGBitmapContextGetData and freed.

Actually implementing that logic is beyond the current scope of MallocChecker,
so for now CGBitmapContextCreate goes on our system function exception list.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158579 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/StaticAnalyzer/Checkers/MallocChecker.cpp | 12 +++++++-----
 test/Analysis/malloc.c                        | 19 +++++++++++++++++++
 test/Analysis/system-header-simulator.h       |  7 +++++++
 3 files changed, 33 insertions(+), 5 deletions(-)

diff --git a/lib/StaticAnalyzer/Checkers/MallocChecker.cpp b/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
index c22c6a2687..1adcca03fd 100644
--- a/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/MallocChecker.cpp
@@ -1334,12 +1334,14 @@ bool MallocChecker::doesNotFreeMemory(const CallOrObjCMessage *Call,
                 return false;
     }
 
-    // A bunch of other functions, which take ownership of a pointer (See retain
-    // release checker). Not all the parameters here are invalidated, but the
-    // Malloc checker cannot differentiate between them. The right way of doing
-    // this would be to implement a pointer escapes callback.
-    if (FName == "CVPixelBufferCreateWithBytes" ||
+    // A bunch of other functions which either take ownership of a pointer or
+    // wrap the result up in a struct or object, meaning it can be freed later.
+    // (See RetainCountChecker.) Not all the parameters here are invalidated,
+    // but the Malloc checker cannot differentiate between them. The right way
+    // of doing this would be to implement a pointer escapes callback.
+    if (FName == "CGBitmapContextCreate" ||
         FName == "CGBitmapContextCreateWithData" ||
+        FName == "CVPixelBufferCreateWithBytes" ||
         FName == "CVPixelBufferCreateWithPlanarBytes" ||
         FName == "OSAtomicEnqueue") {
       return false;
diff --git a/test/Analysis/malloc.c b/test/Analysis/malloc.c
index 7c2196ac9e..c532d6813f 100644
--- a/test/Analysis/malloc.c
+++ b/test/Analysis/malloc.c
@@ -955,3 +955,22 @@ void test_double_assign_ints_positive()
   (void*)(long)(unsigned long)ptr; // expected-warning {{unused}} expected-warning {{leak}}
 }
 
+
+void testCGContextNoLeak()
+{
+  void *ptr = malloc(16);
+  CGContextRef context = CGBitmapContextCreate(ptr);
+
+  // Because you can get the data back out like this, even much later,
+  // CGBitmapContextCreate is one of our "stop-tracking" exceptions.
+  free(CGBitmapContextGetData(context));
+}
+
+void testCGContextLeak()
+{
+  void *ptr = malloc(16);
+  CGContextRef context = CGBitmapContextCreate(ptr);
+  // However, this time we're just leaking the data, because the context
+  // object doesn't escape and it hasn't been freed in this function.
+}
+
diff --git a/test/Analysis/system-header-simulator.h b/test/Analysis/system-header-simulator.h
index a8cba9ce5b..d2fb2e8684 100644
--- a/test/Analysis/system-header-simulator.h
+++ b/test/Analysis/system-header-simulator.h
@@ -46,3 +46,10 @@ typedef struct {
 
 int dealocateMemWhenDoneByVal(void*, StWithCallback);
 int dealocateMemWhenDoneByRef(StWithCallback*, const void*);
+
+typedef struct CGContext *CGContextRef;
+CGContextRef CGBitmapContextCreate(void *data/*, size_t width, size_t height,
+                                   size_t bitsPerComponent, size_t bytesPerRow,
+                                   CGColorSpaceRef space,
+                                   CGBitmapInfo bitmapInfo*/);
+void *CGBitmapContextGetData(CGContextRef context);
-- 
2.40.0