On Jan 25, 2012, at 12:28 PM, John McCall wrote: > On Jan 23, 2012, at 3:55 PM, Howard Hinnant wrote: >> Author: hhinnant >> Date: Mon Jan 23 17:55:58 2012 >> New Revision: 148750 >> >> URL: http://llvm.org/viewvc/llvm-project?rev=148750&view=rev >> Log: >> A lot of the code in cxa_exception.cpp depends on __cxa_get_globals_fast() >> returning null if __cxa_get_globals() hasn't been called yet. However it >> doesn't reliably do that, at least on OS X if __cxa_get_globals_fast() is >> called prior to pthread_key_create() running. Our choice is to either limit >> our use of __cxa_get_globals_fast() more than we have, or to have >> __cxa_get_globals_fast() initialize with pthread_key_create() if necessary. >> I chose the latter, and replaced pthread_once with a C++11 local static >> (which should do the same thing).
The use of so many pronouns is making me a little nervous, so I'm going to try to confirm the intended use of each pronoun below. Please let me know if I get it wrong. > Are you certain this function is not used in the implementation of > _cxa_guard_acquire? I am certain that neither __cxa_get_globals_fast() nor __cxa_get_globals() is used in the implementation of __cxa_guard_acquire(). I just checked and cxa_guard.cpp does not currently even include the prototypes for __cxa_get_globals_fast() and __cxa_get_globals(). > If so, please at least document in the guard-variables code that it is no > longer allowed to call this. I'm not certain why the guard-variables code should be prohibited from calling __cxa_get_globals_fast() or __cxa_get_globals(), though I don't currently see the need either. My commit notes could probably have been clearer: This commit made calling __cxa_get_globals_fast() safer, but slower, as opposed to the other way around. You can now call __cxa_get_globals_fast() even if __cxa_get_globals() has not previously been called. And if you do, you are now guaranteed that __cxa_get_globals_fast() will return NULL. Previous to this commit __cxa_get_globals_fast() would return a random non-NULL pointer if called prior to __cxa_get_globals(). The previous state (returning a random non-NULL pointer) was conforming to the Itanium ABI spec, but not consistent with our current use of __cxa_get_globals_fast() (which expects a NULL pointer). If we're talking past each other, just let me know, and I'll try to clarify. Thanks for the review. Howard _______________________________________________ cfe-commits mailing list [email protected] http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
