path: root/src/ldso/aarch64
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2019-09-29remove remaining traces of __tls_get_newSzabolcs Nagy-5/+1
Some declarations of __tls_get_new were left in the code, even though the definition got removed in commit 9d44b6460ab603487dab4d916342d9ba4467e6b9 install dynamic tls synchronously at dlopen, streamline access this can make the build fail with ld: lib/ hidden symbol `__tls_get_new' isn't defined when is linked without --gc-sections, because a .hidden declaration in asm code creates a reference even if the symbol is not actually used.
2019-05-26optimize aarch64 dynamic tlsdesc function to spill fewer registersRich Felker-10/+7
with the glibc generation counter model for reusing dynamic tls slots after dlclose, it's really not possible to get away with fewer than 4 working registers. for us however it's always been possible, but tricky, and only became apparent after the switch to installing new dynamic tls at dlopen time. by merging the negated thread pointer into the addend early, the register holding the thread pointer can immediately be reused, bringing the working register count down to three. this allows saving/restoring via a single stp/ldp pair, since the return register x0 does not need to be saved. net reduction of 3 instructions, 2 of which were push/pop.
2019-02-18install dynamic tls synchronously at dlopen, streamline accessRich Felker-58/+1
previously, dynamic loading of new libraries with thread-local storage allocated the storage needed for all existing threads at load-time, precluding late failure that can't be handled, but left installation in existing threads to take place lazily on first access. this imposed an additional memory access and branch on every dynamic tls access, and imposed a requirement, which was not actually met, that the dynamic tlsdesc asm functions preserve all call-clobbered registers before calling C code to to install new dynamic tls on first access. the x86[_64] versions of this code wrongly omitted saving and restoring of fpu/vector registers, assuming the compiler would not generate anything using them in the called C code. the arm and aarch64 versions saved known existing registers, but failed to be future-proof against expansion of the register file. now that we track live threads in a list, it's possible to install the new dynamic tls for each thread at dlopen time. for the most part, synchronization is not needed, because if a thread has not synchronized with completion of the dlopen, there is no way it can meaningfully request access to a slot past the end of the old dtv, which remains valid for accessing slots which already existed. however, it is necessary to ensure that, if a thread sees its new dtv pointer, it sees correct pointers in each of the slots that existed prior to the dlopen. my understanding is that, on most real-world coherency architectures including all the ones we presently support, a built-in consume order guarantees this; however, don't rely on that. instead, the SYS_membarrier syscall is used to ensure that all threads see the stores to the slots of their new dtv prior to the installation of the new dtv. if it is not supported, the same is implemented in userspace via signals, using the same mechanism as __synccall. the __tls_get_addr function, variants, and dynamic tlsdesc asm functions are all updated to remove the fallback paths for claiming new dynamic tls, and are now all branch-free.
2018-06-02fix TLS layout of TLS variant I when there is a gap above TPSzabolcs Nagy-3/+2
In TLS variant I the TLS is above TP (or above a fixed offset from TP) but on some targets there is a reserved gap above TP before TLS starts. This matters for the local-exec tls access model when the offsets of TLS variables from the TP are hard coded by the linker into the executable, so the libc must compute these offsets the same way as the linker. The tls offset of the main module has to be alignup(GAP_ABOVE_TP, main_tls_align). If there is no TLS in the main module then the gap can be ignored since musl does not use it and the tls access models of shared libraries are not affected. The previous setup only worked if (tls_align & -GAP_ABOVE_TP) == 0 (i.e. TLS did not require large alignment) because the gap was treated as a fixed offset from TP. Now the TP points at the end of the pthread struct (which is aligned) and there is a gap above it (which may also need alignment). The fix required changing TP_ADJ and __pthread_self on affected targets (aarch64, arm and sh) and in the tlsdesc asm the offset to access the dtv changed too.
2015-04-17apply hidden visibility to tlsdesc accessor functionsRich Felker-0/+2
these functions are never called directly; only their addresses are used, so PLT indirections should never happen unless a broken application tries to redefine them, but it's still best to make them hidden.
2015-04-17comment fixes in aarch64 tlsdesc asmSzabolcs Nagy-4/+4
2015-04-14use hidden __tls_get_new for tls/tlsdesc lookup fallback casesRich Felker-2/+4
previously, the dynamic tlsdesc lookup functions and the i386 special-ABI ___tls_get_addr (3 underscores) function called __tls_get_addr when the slot they wanted was not already setup; __tls_get_addr would then in turn also see that it's not setup and call __tls_get_new. calling __tls_get_new directly is both more efficient and avoids the issue of calling a non-hidden (public API/ABI) function from asm. for the special i386 function, a weak reference to __tls_get_new is used since this function is not defined when static linking (the code path that needs it is unreachable in static-linked programs).
2015-04-14use hidden visibility for call from dlsym to internal __dlsymRich Felker-0/+1
2015-04-13dynamic linker bootstrap overhaulRich Felker-18/+0
this overhaul further reduces the amount of arch-specific code needed by the dynamic linker and removes a number of assumptions, including: - that symbolic function references inside libc are bound at link time via the linker option -Bsymbolic-functions. - that libc functions used by the dynamic linker do not require access to data symbols. - that static/internal function calls and data accesses can be made without performing any relocations, or that arch-specific startup code handled any such relocations needed. removing these assumptions paves the way for allowing itself to be built with stack protector (among other things), and is achieved by a three-stage bootstrap process: 1. relative relocations are processed with a flat function. 2. symbolic relocations are processed with no external calls/data. 3. main program and dependency libs are processed with a fully-functional libc/ldso. reduction in arch-specific code is achived through the following: - crt_arch.h, used for generating crt1.o, now provides the entry point for the dynamic linker too. - asm is no longer responsible for skipping the beginning of argv[] when ldso is invoked as a command. - the functionality previously provided by __reloc_self for heavily GOT-dependent RISC archs is now the arch-agnostic stage-1. - arch-specific relocation type codes are mapped directly as macros rather than via an inline translation function/switch statement.
2015-03-11add aarch64 portSzabolcs Nagy-0/+115
This adds complete aarch64 target support including bigendian subarch. Some of the long double math functions are known to be broken otherwise interfaces should be fully functional, but at this point consider this port experimental. Initial work on this port was done by Sireesh Tripurari and Kevin Bortis.