otherwise disassemblers treat it as data.
the code being removed used atomics to track whether any threads might be using a locale other than the current global locale, and whether any threads might have abstract 8-bit (non-UTF-8) LC_CTYPE active, a feature which was never committed (still pending). the motivations were to support early execution prior to setup of the thread pointer, to partially support systems (ancient kernels) where thread pointer setup is not possible, and to avoid high performance cost on archs where accessing the thread pointer may be very slow. since commit 19a1fe670acb3ab9ead0fe31859ca7d4fe40dd54, the thread pointer is always available, so these hacks are no longer needed. removing them greatly simplifies the affected code.
commit f630df09b1fd954eda16e2f779da0b5ecc9d80d3 added logic to handle the case where __set_thread_area is called more than once by reusing the GDT slot already in the %gs register, and only setting up a new GDT slot when %gs is zero. this created a hidden assumption that %gs is zero when a new process image starts, which is true in practice on Linux, but does not seem to be documented ABI, and fails to hold under qemu app-level emulation. while it would in theory be possible to zero %gs in the entry point code, this code is shared between static and dynamic binaries, and dynamic binaries must not clobber the value of %gs already setup by the dynamic linker. the alternative solution implemented in this commit simply uses global data to store the GDT index that's selected. __set_thread_area should only be called in the initial thread anyway (subsequent threads get their thread pointer setup by __clone), but even if it were called by another thread, it would simply read and write back the same GDT index that was already assigned to the initial thread, and thus (in the x86 memory model) there is no data race.
i386, x86_64, x32, and powerpc all use TLS for stack protector canary values in the default stack protector ABI, but the location only matched the ABI on i386 and x86_64. on x32, the expected location for the canary contained the tid, thus producing spurious mismatches (resulting in process termination) upon fork. on powerpc, the expected location contained the stdio_locks list head, so returning from a function after calling flockfile produced spurious mismatches. in both cases, the random canary was not present, and a predictable value was used instead, making the stack protector hardening much less effective than it should be. in the current fix, the thread structure has been expanded to have canary fields at all three possible locations, and archs that use a non-default location must define a macro in pthread_arch.h to choose which location is used. for most archs (which lack TLS canary ABI) the choice does not matter.
the kernel does not properly clear the upper bits of the syscall argument, so we have to do it before the syscall.
use CAS instead of swap since it's lighter for most archs, and keep EBUSY in the lock value so that the old value obtained by CAS can be used directly as the return value for pthread_spin_trylock.
the leak was found by static analysis (reported by Alexander Monakov), not tested/observed, but seems to have occured both when failing due to O_EXCL, and in a race condition with O_CREAT but not O_EXCL where a semaphore by the same name was created concurrently.
this fixes truncation of error messages containing long pathnames or symbol names. the dlerror state was previously required by POSIX to be global. the resolution of bug 97 relaxed the requirements to allow thread-safe implementations of dlerror with thread-local state and message buffer.
even hidden functions need @PLT symbol references; otherwise an absolute address is produced instead of a PC-relative one.