Date: Tue, 17 Jul 2012 02:46:23 +0200 From: John Spencer <maillist-luajit@...fooze.de> To: luajit@...elists.org, Mike Pall <mike-1207@...jit.org> CC: musl@...ts.openwall.com, Rich Felker <dalias@...ifal.cx> Subject: Re: segfault on x86_64 using musl libc On 07/16/2012 04:05 PM, Mike Pall wrote: > Apparently musl doesn't set up thread-local storage correctly. we had a discussion on the musl mailing list about the TLS issue, and it turned out that I mistakenly built gcc without --disable-tls. (musl currently doesn't support TLS for various reasons.) with gcc fixed, luajit seems to work fine (at least for singlethreaded usage). Rich came up with a clever portable (POSIX) way that could be used instead of the existing non-threadsafe fallback code for OSX/OpenBSD/non-TLS. please see forwarded Mail content below. From: Rich Felker <d...@...ifal.cx> Subject: Re: [musl] thread local storage On Mon, Jul 16, 2012 at 02:57:22PM -0400, Gregor Richards wrote: > On 07/16/2012 03:02 PM, John Spencer wrote: > >2 out of 14 sabotage followers wanted to use a musl-based system > >as a platform for luajit (and then were never seen again). > >so i looked into adding it... > > > >luajit builds without problems on musl, but then crashes due to a > >lack of TLS. > > > >is it planned to add this feature ? iirc it wasn't mentioned on > >the latest roadmap... > > > > > > > With a quick perusal of the LuaJIT source, this is the only instance > of TLS I see: > > #if LJ_UNWIND_EXT > #if LJ_TARGET_OSX || defined(__OpenBSD__) > /* Sorry, no thread safety for OSX. Complain to Apple, not me. */ > static _Unwind_Exception static_uex; > #else > static __thread _Unwind_Exception static_uex; > #endif > > Convince it to use the same exception as OS X and OpenBSD and you > should be in business. This is broken and non-thread-safe. Not a good idea. Instead try: #define static_uex (*(_Unwind_Exception *)pthread_getspecific(static_uex_key)) where static_uex_key is a pthread_key_t initialized earlier with: pthread_key_create(&static_uex_key, 0); And where the thread-specific value of the key is set in thread startup as: _Unwind_Exception static_uex_local; pthread_setspecific(static_uex_key, &static_uex_local); The simplicity and generality of this solution is why __thread was just a stupid idea to begin with... Rich
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