[lldb] Add a test for user-defined objc_copyRealizedClassList_nolock

[teemperor]

Summary

LLDB evaluates some utility expression to update the Objective-C class list that ends up
calling function such as free or objc_copyRealizedClassList_nolock. This adds a test that
just tries to define our own bogus version of objc_copyRealizedClassList_nolock. It just
tests that LLDB doesn't crash as we currently don't have a way to tell LLDB to look for
the function in a specific library.

[JDevlieghere]

lldb/test/API/lang/objc/conflicting-class-list-function-from-user/main.m

22–23

The description says "we currently don't have a way to tell LLDB to look for
the function in a specific library", so what guarantees we call the right one? We check if the symbol exists in libobjc (and fallback to the realized class list struct if not), but there's nothing in the source code that could tell the expression evaluator where the symbol should come from.

[teemperor]

lldb/test/API/lang/objc/conflicting-class-list-function-from-user/main.m

22–23

Everything you're saying is right, that's why the test is XFAIL'd. The test is just testing that LLDB doesn't crash or anything like that. The "we currently don't have a way to tell LLDB to look for the function in a specific library" comment is just there to point out that this is the missing functionality to make this test actually pass.

[JDevlieghere]

LGTM

lldb/test/API/lang/objc/conflicting-class-list-function-from-user/main.m

22–23

Ah, I missed that part, thanks for pointing that out! If we really wanted to, we could look up the symbol (which we already do to make sure it's available) and call it through that instead of relying on the expression parser, but that seems unlikely enough to happen.

lldb/test/API/lang/objc/conflicting-class-list-function-from-user/Makefile

+OBJC_SOURCES := main.m
+LD_EXTRAS := -lobjc -framework Foundation
+
+include Makefile.rules

lldb/test/API/lang/objc/conflicting-class-list-function-from-user/TestObjCClassListFunctionFromUser.py

+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    @skipUnlessDarwin
+    # LLDB ends up calling the user-defined function (but at least doesn't
+    # crash).
+    @expectedFailureDarwin
+    def test(self):
+        """
+        Tests LLDB's behaviour if the user defines their own conflicting
+        objc_copyRealizedClassList_nolock function.
+        """
+
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "// break here", lldb.SBFileSpec("main.m"))
+
+        # Get the (dynamic) type of our 'id' variable so that our Objective-C
+        # runtime information is updated.
+        str_val = self.expect_expr("custom_class")
+        dyn_val = str_val.GetDynamicValue(lldb.eDynamicCanRunTarget)
+
+        # We should have retrieved the proper class list even in presence of
+        # the user-defined function.
+        self.assertEqual(dyn_val.GetTypeName(), "CustomClass *")

lldb/test/API/lang/objc/conflicting-class-list-function-from-user/main.m

+#import <Foundation/Foundation.h>
+#include <stdlib.h>
+
+// A function with this signature will be called by LLDB to retrieve the
+// Objective-C class list. We shouldn't call this function that is defined
+// by the user if possible.
+Class *objc_copyRealizedClassList_nolock(unsigned int *outCount) {
+  // Don't try to implement this properly but just abort.
+  abort();
+}
+
+// Define some custom class that makes LLDB read the Objective-C class list.
+@interface CustomClass : NSObject {
+};
+@end
+@implementation CustomClass
+@end
+
+int main(int argc, char **argv) {
+  id custom_class = [[CustomClass alloc] init];
+  // Make sure our trap function is emitted but never called (the test doesn't
+  // launch the executable with any args).
+  if (argc == 123) {
+    objc_copyRealizedClassList_nolock(0);
+  }
+  return 0; // break here
+}