27869 2009-07-31 00:32:26 -0700 strict-aliasing warnings in JSFunction.h 2009-10-28 13:19:49 -0700 1 1 1 Unclassified WebKit JavaScriptCore 528+ (Nightly build) PC Linux RESOLVED FIXED P2 Normal --- 1 xan.lopez webkit-unassigned eric ggaren mjs mrobinson oliver oldest_to_newest 136116 0 33861 xan.lopez 2009-07-31 00:32:26 -0700 Created attachment 33861 aliasing.patch GCC gives me the following warnings when compiling with JSFunction.h: In file included from ../../JavaScriptCore/runtime/JSFunction.cpp:27, from ../../JavaScriptCore/AllInOneFile.cpp:36: ../../JavaScriptCore/runtime/JSFunction.h: In member function ‘JSC::JSValue (* JSC::JSFunction::nativeFunction())(JSC::ExecState*, JSC::JSObject*, JSC::JSValue, const JSC::ArgList&)’: ../../JavaScriptCore/runtime/JSFunction.h:87: warning: dereferencing type-punned pointer will break strict-aliasing rules ../../JavaScriptCore/runtime/JSFunction.h: In member function ‘JSC::ScopeChain& JSC::JSFunction::scopeChain()’: ../../JavaScriptCore/runtime/JSFunction.h:104: warning: dereferencing type-punned pointer will break strict-aliasing rules ../../JavaScriptCore/runtime/JSFunction.h: In member function ‘void JSC::JSFunction::setScopeChain(const JSC::ScopeChain&)’: ../../JavaScriptCore/runtime/JSFunction.h:119: warning: dereferencing type-punned pointer will break strict-aliasing rules ../../JavaScriptCore/runtime/JSFunction.h: In member function ‘void JSC::JSFunction::setNativeFunction(JSC::JSValue (*)(JSC::ExecState*, JSC::JSObject*, JSC::JSValue, const JSC::ArgList&))’: ../../JavaScriptCore/runtime/JSFunction.h:123: warning: dereferencing type-punned pointer will break strict-aliasing rules The problem is that we are accessing a char array as NativeFunction* and ScopeChain*, which GCC deems to be incompatible pointers. Attached is the usual trick-solution for this, which is to use a union type and do all memory access through there. This was done with the help of Maciej on IRC, and he also suggested that we could do further cleanups here, so I'm attaching my current patch for discussion. 136117 1 xan.lopez 2009-07-31 00:33:49 -0700 Actually, just looking at the patch now, the array member in the union is not needed anymore (it was used in previous iterations of the patch). 136124 2 33861 xan.lopez 2009-07-31 02:47:49 -0700 Comment on attachment 33861 aliasing.patch This seems to introduce a crash in the JSFunction destructor (which calls the ScopeChain destructor). Maciej suggested something like this could happen, so this needs further investigation. Removing from the queue. 157448 3 41781 mrobinson 2009-10-24 08:51:30 -0700 Created attachment 41781 Fix using bitwise_cast Seems that using bitwise_cast fixes these compiler warnings. 157956 4 ggaren 2009-10-26 15:12:43 -0700 Strange to see this warning. char* is supposed to be able to alias to anything, even under -fstrict-aliasing. 157957 5 ggaren 2009-10-26 15:13:11 -0700 Can you run SunSpider before and after this patch and post the results? 158681 6 oliver 2009-10-28 13:19:49 -0700 Committed r50232 33861 2009-07-31 00:32:26 -0700 2009-07-31 02:47:49 -0700 aliasing.patch aliasing.patch text/plain 3219 xan.lopez RnJvbSA4ZjBjMzhkNzJjOWNkYzk4YWZiNDdjOWM4M2FhMThlMWY2ZDlhYWVmIE1vbiBTZXAgMTcg MDA6MDA6MDAgMjAwMQpGcm9tOiBYYW4gTG9wZXogPHhsb3BlekBpZ2FsaWEuY29tPgpEYXRlOiBG cmksIDMxIEp1bCAyMDA5IDEwOjMxOjMyICswMzAwClN1YmplY3Q6IFtQQVRDSF0gMjAwOS0wNy0z MSAgWGFuIExvcGV6ICA8eGxvcGV6QGlnYWxpYS5jb20+CgogICAgICAgIFJldmlld2VkIGJ5IE5P 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