Thanks for your informative response, David! This is what I really wanted to know: > All previous and current releases of GCC do not support > native TLS on AIX. GCC 4.8 will provide TLS on AIX, as listed in the > announcements for the release. Great! I'll look forward to testing with 4.8 when it becomes GA . Thanks for comments on configuration options - points noted - but I was only copying the options used for the IBM freeware GCC distribution.
But why didn't the compiler complain that TLS was not supported ? Shouldn't it be doing so ? It is definitely not OK in my book for gcc to finish compilation and linkage with no errors or warnings, when it has encountered a __thread usage that it must know will have no effect. And isn't there an easier way to determine if TLS is enabled or not than by compiling a test program ? Thanks & Regards, Jason On Mon, Mar 11, 2013 at 10:07 PM, David Edelsohn <dje....@gmail.com> wrote: > On Mon, Mar 11, 2013 at 3:46 PM, Jason Vas Dias > <jason.vas.d...@gmail.com> wrote: >> Hi - I wonder if anyone could please tell me if gcc's thread local >> storage support is meant to be enabled on AIX or not - >> I've built gcc-4.7.2 on AIX 6.1 OK, with "---enable-threads" , >> using the AIX system /usr/ccs/bin ld and as , both of which >> claim to provide TLS support , but now this test program is getting >> the same address for its __thread variable in different threads - >> it is compiled and linked without warnings or error, and prints three >> different addresses at the end on Linux, Solaris x86 & SPARC, and >> HP-UX, >> but not on AIX 6.1 . This also happens with the IBM freeware >> gcc-4.4.6. Yet 4.7.2's libgomp was built OK ... doesn't this depend >> on TLS? >> >> Must I use --enable-tls as well as --enable-threads in configuration >> options and rebuild GCC ? Is this likely to work ? >> >> gcc-4.7.2 is reporting its thread model as 'aix' - shouldn't this be >> 'posix' ( the system /usr/lib/libpthread.a is installed and the >> pthread_* headers look POSIX compatible ). > >> Shouldn't GCC be terminating compilation with an error if it >> encounters use of __thread when TLS is not enabled ? >> Is there an option to enable this / if not , could one be added ? >> Is there an option to make GCC tell the user if TLS is enabled or not >> - again, if not, could there be one ? >> >> I don't think gcc should be allowing programmers to assume TLS is in >> use when it is not - this is dangerous! >> >> If GCC does not support TLS with AIX 'ld' + 'as' (which seems likely), >> could this not be documented somewhere in the installation >> documentation (it does not appear to be) ? Any plans to enable it in >> near future ? > > First, because of the way that AIX supports pthreads, GCC requires > different libraries for pthread and non-pthread code. GCC -pthread > links with the pthread version of the libraries. This is why thread > model is reported as "aix" and not "posix". > > Second, when native TLS is not available, GCC emulates TLS using > pthread keys. All previous and current releases of GCC do not support > native TLS on AIX. GCC 4.8 will provide TLS on AIX, as listed in the > announcements for the release. > > Third, one should not add configuration options like "--enable-tls" or > "--enable-threads". The defaults are correct and will enable the > appropriate features for the system. No one chose to implement a > feature but leave it disabled by default. No one is hiding features > and one should not approach the configuration process by trying to > force override options. > > Compiling your example with GCC 4.8 snapshot from last night produces > the following on AIX 7.1: > > $ ./xgcc -B./ -O2 -pthread code.c > $ ./a.out > main : 200080d0 20112000 20218000 > $ ./xgcc -B./ -O2 -pthread -maix64 code.c > $ ./a.out > main : 11000de20 11011a000 110221000 > > Thanks, David
