Bogus “variable may be clobbered” warning for Objective-C native exception syntax

When compiling Objective-C code with @try blocks using the -Wextra warning flag, I sometimes get warnings of the form “variable 'foo' might be clobbered by 'longjmp' or 'vfork'”. (Despite the specific nature of the text, this applies to all functions which have the returns_twice attribute, including the exception-handling runtime functions.) The warning pertains to this text in the C specification:

All accessible objects have values, and all other components of the abstract machine have state, as of the time the longjmp function was called, except that the values of objects of automatic storage duration that are local to the function containing the invocation of the corresponding setjmp macro that do not have volatile-qualified type and have been changed between the setjmp invocation and longjmp call are indeterminate.

Generally I can work around this by marking affected variables volatile or putting code in an out-of-line function. However, I’m now seeing it for inline functions in a library. Here’s a condensed test case开发者_StackOverflow中文版:

static inline uint64_t Foo(void)
{
    union
    {
        int32_t a;
        uint64_t b;
    } l;
    l.a = 1; // warning: variable 'l' might be clobbered by 'longjmp' or 'vfork'
    return l.b;
}

void Test(uint64_t *value)
{
    @try
    {
        *value = Foo();
    }
    @catch (...) {}
}

The warning occurs when building for i386 using apple-gcc 4.0 or 4.2 (not llvm-gcc) with -Wextra and optimizations enabled. Note that this isn’t a real problem since the value won’t be used if an exception is caught.

The man page suggests this warning is controlled by -Wuninitialized, but this is not the case. Using -Wuninitialized does not trigger it, but using -Wextra -Wno-uninitialized does.

So the question is, is there any way of suppressing this warning other than disabling -Wextra or switching compiler? (As a warnings masochist, I am of course using -Werror.)

Quoth the gcc manual: "Note that some warning flags are not implied by -Wall. Some of them warn about constructions that users generally do not consider questionable, but which occasionally you might wish to check for; others warn about constructions that are necessary or hard to avoid in some cases, and there is no simple way to modify the code to suppress the warning. Some of them are enabled by -Wextra but many of them must be enabled individually."

Basically, -Wextra -Werror is telling the compiler "please break my build even when I do things that many people don't consider questionable at all". I don't understand why that's desirable (although I should note that I have a deep-seated personal vendetta against -Werror for other reasons, so I may be biased).

In an attempt to be more useful than "don't do that", maybe -Wno-clobber?