https://bugs.llvm.org/show_bug.cgi?id=48207
Bug ID: 48207
Summary: [ObjC] C structures are not cleaned up correctly when
passed as an argument in a method called on a nil
receiver
Product: clang
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: C
Assignee: unassignedclangb...@nondot.org
Reporter: a...@fb.com
CC: blitzrak...@gmail.com, dgre...@apple.com,
erik.pilking...@gmail.com, llvm-bugs@lists.llvm.org,
richard-l...@metafoo.co.uk
If a C structure is passed as an argument of an objective-c method called on a
nil receiver, this C structure is not cleaned up correctly (ie., weak pointers
in such C structure are not destroyed via objc_destroyWeak and strong pointers
are not released).
The same issue happens in C++ unless destructor is defined for a structure.
It looks like clang expects the callee (receiver) to clean up, but since
receiver is nil the cleanup never happens.
This change may be related: https://reviews.llvm.org/D44908
The following code demonstrates this issue.
$ cat ./main.m
#import <Foundation/Foundation.h>
struct FBStruct {
__weak id<NSObject> weakPtr;
};
@protocol FBProtocol <NSObject>
- (void)doSomething:(struct FBStruct)strct;
@end
static void test(NSObject *obj) {
struct FBStruct strct;
strct.weakPtr = obj;
id<FBProtocol> nilReceiver = nil;
[nilReceiver doSomething:strct]; // Temporary structure never cleaned up
}
int main(int argc, const char * argv[]) {
test([NSObject new]);
return 0;
}
$ clang++ -g -fobjc-arc -fobjc-link-runtime ./main.m
$ ./a.out
objc[28864]: __weak variable at 0x7ffeea0d4850 holds 0x7ffeea0d4870 instead of
0x7faa44409750. This is probably incorrect use of objc_storeWeak() and
objc_loadWeak(). Break on objc_weak_error to debug.
I'm able to reproduce this issue on x86_64 (Mac) and ARM (iPhone 11 Pro)
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