path: root/src/internal
AgeCommit message (Collapse)AuthorLines
2019-02-22add membarrier syscall wrapper, refactor dynamic tls install to use itRich Felker-1/+1
the motivation for this change is twofold. first, it gets the fallback logic out of the dynamic linker, improving code readability and organization. second, it provides application code that wants to use the membarrier syscall, which depends on preregistration of intent before the process becomes multithreaded unless unbounded latency is acceptable, with a symbol that, when linked, ensures that this registration happens.
2019-02-18install dynamic tls synchronously at dlopen, streamline accessRich Felker-0/+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.
2019-02-16rewrite __synccall in terms of global thread listRich Felker-1/+0
the __synccall mechanism provides stop-the-world synchronous execution of a callback in all threads of the process. it is used to implement multi-threaded setuid/setgid operations, since Linux lacks them at the kernel level, and for some other less-critical purposes. this change eliminates dependency on /proc/self/task to determine the set of live threads, which in addition to being an unwanted dependency and a potential point of resource-exhaustion failure, turned out to be inaccurate. test cases provided by Alexey Izbyshev showed that it could fail to reflect newly created threads. due to how the presignaling phase worked, this usually yielded a deadlock if hit, but in the worst case it could also result in threads being silently missed (allowed to continue running without executing the callback).
2019-02-15track all live threads in an AS-safe, fully-consistent linked listRich Felker-4/+8
the hard problem here is unlinking threads from a list when they exit without creating a window of inconsistency where the kernel task for a thread still exists and is still executing instructions in userspace, but is not reflected in the list. the magic solution here is getting rid of per-thread exit futex addresses (set_tid_address), and instead using the exit futex to unlock the global thread list. since pthread_join can no longer see the thread enter a detach_state of EXITED (which depended on the exit futex address pointing to the detach_state), it must now observe the unlocking of the thread list lock before it can unmap the joined thread and return. it doesn't actually have to take the lock. for this, a __tl_sync primitive is offered, with a signature that will allow it to be enhanced for quick return even under contention on the lock, if needed. for now, the exiting thread always performs a futex wake on its detach_state. a future change could optimize this out except when there is already a joiner waiting. initial/dynamic variants of detached state no longer need to be tracked separately, since the futex address is always set to the global list lock, not a thread-local address that could become invalid on detached thread exit. all detached threads, however, must perform a second sigprocmask syscall to block implementation-internal signals, since locking the thread list with them already blocked is not permissible. the arch-independent C version of __unmapself no longer needs to take a lock or setup its own futex address to release the lock, since it must necessarily be called with the thread list lock already held, guaranteeing exclusive access to the temporary stack. changes to libc.threads_minus_1 no longer need to be atomic, since they are guarded by the thread list lock. it is largely vestigial at this point, and can be replaced with a cheaper boolean indicating whether the process is multithreaded at some point in the future.
2019-02-15always block signals for starting new threads, refactor start argsRich Felker-11/+0
whether signals need to be blocked at thread start, and whether unblocking is necessary in the entry point function, has historically depended on intricacies of the cancellation design and on whether there are scheduling operations to perform on the new thread before its successful creation can be committed. future changes to track an AS-safe list of live threads will require signals to be blocked whenever changes are made to the list, so ... prior to commits b8742f32602add243ee2ce74d804015463726899 and 40bae2d32fd6f3ffea437fa745ad38a1fe77b27e, a signal mask for the entry function to restore was part of the pthread structure. it was removed to trim down the size of the structure, which both saved a small amount of stack space and improved code generation on archs where small immediate displacements are less costly than arbitrary ones, by limiting the range of offsets between the base of the thread structure, its members, and the thread pointer. these commits moved the saved mask to a special structure used only when special scheduling was needed, in which case the pthread_create caller and new thread had to synchronize with each other and could use this memory to pass a mask. this commit partially reverts the above two commits, but instead of putting the mask back in the pthread structure, it moves all "start argument" members out of the pthread structure, trimming it down further, and puts them in a separate structure passed on the new thread's stack. the code path for explicit scheduling of the new thread is also changed to synchronize with the calling thread in such a way to avoid spurious futex wakes.
2018-12-18add __timedwait backend workaround for old kernels where futex EINTRsRich Felker-0/+1
prior to linux 2.6.22, futex wait could fail with EINTR even for non-interrupting (SA_RESTART) signals. this was no problem provided the caller simply restarted the wait, but sem_[timed]wait is required by POSIX to return when interrupted by a signal. commit a113434cd68ce30642c4995b1caadcd084be6f09 introduced this behavior, and commit c0ed5a201b2bdb6d1896064bec0020c9973db0a1 reverted it based on a mistaken belief that it was not required. this belief stems from a bug in the specification: the description requires the function to return when interrupted, but the errors section marks EINTR as a "may fail" condition rather than a "shall fail" one. since there does seem to be significant value in the change made in commit c0ed5a201b2bdb6d1896064bec0020c9973db0a1, making it so that programs that call sem_wait without checking for EINTR don't silently make forward progress without obtaining the semaphore or treat it as a fatal error and abort, add a behind-the-scenes mechanism in the __timedwait backend to suppress EINTR in programs that have never installed interrupting signal handlers, and have sigaction track and report this state. this way the semaphore code is not cluttered by workarounds and can be updated (to be done in next commit) to reflect the high-level logic for conforming behavior. these changes are based loosely on a patch by Markus Wichmann, with the main changes being atomic update to flag object and moving the workaround from sem_timedwait to the __timedwait futex backend.
2018-10-20remove volatile qualification from category pointers in __locale_structRich Felker-1/+1
commit 63c188ec42e76ff768e81f6b65b11c68fc43351e missed making this change when switching from atomics to locking for modification of the global locale, leaving access to locale structures unnecessarily burdened with the restrictions of volatile. the volatile qualification was originally added in commit 56fbaa3bbe73f12af2bfbbcf2adb196e6f9fe264.
2018-10-20adapt setlocale to support possibility of failureRich Felker-0/+2
introduce a new LOC_MAP_FAILED sentinel for errors, since null pointers for a category's locale map indicate the C locale. at this time, __get_locale does not fail, so there should be no functional change by this commit.
2018-10-18adjust types in FILE struct to make line buffering check less expensiveRich Felker-4/+2
the choice of signed char for lbf was a theoretically space-saving hack that was not helping, and was unwantedly expensive. while comparing bytes against a byte-sized member sounds easy, the trick here was that the byte to be compared was unsigned while the lbf member was signed, making it possible to set lbf negative to disable line buffering. however, this imposed a requirement to promote both operands, zero-extending one and sign-extending the other, in order to compare them. to fix this, repurpose the waiters count slot (unused since commit c21f750727515602a9e84f2a190ee8a0a2aeb2a1). while we're at it, switch mode (orientation) from signed char to int as well. this makes no semantic difference (its only possible values are -1, 0, and 1) but it might help on archs where byte access is awkward.
2018-10-18optimize internal putc_unlocked macro used in putcRich Felker-1/+2
to check whether flush due to line buffering is needed, the int-type character argument must be truncated to unsigned char for comparison. if the original value is subsequently passed to __overflow, it must be preserved, adding to register pressure. since it doesn't matter, truncate all uses so the original value is no longer live.
2018-10-18fix wrong result for putc variants due to operator precedenceRich Felker-1/+1
the internal putc_unlocked macro was wrongly returning a meaningless boolean result rather than the written character or EOF. bug was found by reading (very surprising) asm.
2018-10-16move stdio locking MAYBE_WAITERS definition to stdio_impl.hRich Felker-0/+2
don't repeat definition in two places.
2018-10-12combine arch ABI's DTP_OFFSET into DTV pointersRich Felker-2/+3
as explained in commit 6ba5517a460c6c438f64d69464fdfc3269a4c91a, some archs use an offset (typicaly -0x8000) with their DTPOFF relocations, which __tls_get_addr needs to invert. on affected archs, which lack direct support for large immediates, this can cost multiple extra instructions in the hot path. instead, incorporate the DTP_OFFSET into the DTV entries. this means they are no longer valid pointers, so store them as an array of uintptr_t rather than void *; this also makes it easier to access slot 0 as a valid slot count. commit e75b16cf93ebbc1ce758d3ea6b2923e8b2457c68 left behind cruft in two places, __reset_tls and __tls_get_new, from back when it was possible to have uninitialized gap slots indicated by a null pointer in the DTV. since the concept of null pointer is no longer meaningful with an offset applied, remove this cruft. presently there are no archs with both TLSDESC and nonzero DTP_OFFSET, but the dynamic TLSDESC relocation code is also updated to apply an inverted offset to its offset field, so that the offset DTV would not impose a runtime cost in TLSDESC resolver functions.
2018-09-18increase default thread stack/guard sizeRich Felker-2/+2
stack size default is increased from 80k to 128k. this coincides with Linux's hard-coded default stack for the main thread (128k is initially committed; growth beyond that up to ulimit is contingent on additional allocation succeeding) and GNU ld's default PT_GNU_STACK size for FDPIC, at least on sh. guard size default is increased from 4k to 8k to reduce the risk of guard page jumping on overflow, since use of just over 4k of stack is common (PATH_MAX buffers, etc.).
2018-09-18limit the configurable default stack/guard size for threadsRich Felker-2/+5
limit to 8MB/1MB, repectively. since the defaults cannot be reduced once increased, excessively large settings would lead to an unrecoverably broken state. this change is in preparation to allow defaults to be increased via program headers at the linker level. creation of threads that really need larger sizes needs to be done with an explicit attribute.
2018-09-18fix deletion of pthread tsd keys that still have non-null values storedRich Felker-0/+3
per POSIX, deletion of a key for which some threads still have values stored is permitted, and newly created keys must initially hold the null value in all threads. these properties were not met by our implementation; if a key was deleted with values left and a new key was created in the same slot, the old values were still visible. moreover, due to lack of any synchronization in pthread_key_delete, there was a TOCTOU race whereby a concurrent pthread_exit could attempt to call a null destructor pointer for the newly orphaned value. this commit introduces a solution based on __synccall, stopping the world to zero out the values for deleted keys, but only does so lazily when all key slots have been exhausted. pthread_key_delete is split off into a separate translation unit so that static-linked programs which only create keys but never delete them will not pull in the __synccall machinery. a global rwlock is added to synchronize creation and deletion of keys with dtor execution. since the dtor execution loop now has to release and retake the lock around its call to each dtor, checks are made not to call the nodtor dummy function for keys which lack a dtor.
2018-09-16fix null pointer subtraction and comparison in stdioRich Felker-2/+2
morally, for null pointers a and b, a-b, a<b, and a>b should all be defined as 0; however, C does not define any of them. the stdio implementation makes heavy use of such pointer comparison and subtraction for buffer logic, and also uses null pos/base/end pointers to indicate that the FILE is not in the corresponding (read or write) mode ready for accesses through the buffer. all of the comparisons are fixed trivially by using != in place of the relational operators, since the opposite relation (e.g. pos>end) is logically impossible. the subtractions have been reviewed to check that they are conditional the stream being in the appropriate reading- or writing-through-buffer mode, with checks added where needed. in fgets and getdelim, the checks added should improve performance for unbuffered streams by avoiding a do-nothing call to memchr, and should be negligible for buffered streams.
2018-09-15fix undefined behavior in strto* via FILE buffer pointer abuseRich Felker-8/+40
in order to produce FILE objects to pass to the intscan/floatscan backends without any (prohibitively costly) extra buffering layer, the strto* functions set the FILE's rend (read end) buffer pointer to an invalid value at the end of the address space, or SIZE_MAX/2 past the beginning of the string. this led to undefined behavior comparing and subtracting the end pointer with the buffer position pointer (rpos). the comparison issue is easily eliminated by using != instead of <. however the subtractions require nontrivial changes: previously, f->shcnt stored the count that would have been read if consuming the whole buffer, which required an end pointer for the buffer. the purpose for this was that it allowed reading it and adding rpos-rend at any time to get the actual count so far, and required no adjustment at the time of __shgetc (actual function call) since the call would only happen when reaching the end of the buffer. to get rid of the dependency on rend, instead offset shcnt by buf-rpos (start of buffer) at the time of last __shlim/__shgetc call. this makes for slightly more work in __shgetc the function, but for the inline macro it's still just as easy to compute the current count. since the scan helper interfaces used here are a big hack, comments are added to document their contracts and what's going on with their implementations.
2018-09-13fix regression with compilers not incorporating C99 DR#289 resolutionRich Felker-1/+1
as originally published, the C99 syntax only allowed static index parameter declarators when a gratuitous parameter name was included. gcc 3, which some projects use for bootstrapping, is a supported C99 compiler, but does not have the fix to the standard incorporated, so edit the affected declaration to conform to the earlier buggy C99 syntax.
2018-09-12remove vis.h protected-visibility hackRich Felker-27/+0
since commit dc2f368e565c37728b0d620380b849c3a1ddd78f this has been disabled by default, but was left available in case users unhappy with the resulting size or performance regressions wanted to try to make it work. now that we make widespread use of hidden visibility for internal interfaces, this no longer makes sense. if any costly calls remain they can be fixed with hidden aliases.
2018-09-12split internal lock API out of libc.h, creating lock.hRich Felker-6/+9
this further reduces the number of source files which need to include libc.h and thereby be potentially exposed to libc global state and internals. this will also facilitate further improvements like adding an inline fast-path, if we want to do so later.
2018-09-12move misplaced __fork_handler declarationRich Felker-1/+1
pthread_atfork.c does not actually include pthread_impl.h and has no reason to, so it wasn't getting the declaration. move it to libc.h which is already included by both fork.c and pthread_atfork.c. this makes more sense anyway since the function has little to do with pthreads anyway aside from the name.
2018-09-12remove spurious inclusion of libc.h for LFS64 ABI aliasesRich Felker-6/+0
the LFS64 macro was not self-documenting and barely saved any characters. simply use weak_alias directly so that it's clear what's being done, and doesn't depend on a header to provide a strange macro.
2018-09-12reduce spurious inclusion of libc.hRich Felker-8/+7
libc.h was intended to be a header for access to global libc state and related interfaces, but ended up included all over the place because it was the way to get the weak_alias macro. most of the inclusions removed here are places where weak_alias was needed. a few were recently introduced for hidden. some go all the way back to when libc.h defined CANCELPT_BEGIN and _END, and all (wrongly implemented) cancellation points had to include it. remaining spurious users are mostly callers of the LOCK/UNLOCK macros and files that use the LFS64 macro to define the awful *64 aliases. in a few places, new inclusion of libc.h is added because several internal headers no longer implicitly include libc.h. declarations for __lockfile and __unlockfile are moved from libc.h to stdio_impl.h so that the latter does not need libc.h. putting them in libc.h made no sense at all, since the macros in stdio_impl.h are needed to use them correctly anyway.
2018-09-12remove unused __futex function and source fileRich Felker-2/+0
the direct syscall or various thin and mostly-inline wrappers around it are used instead internally. at some point a public futex function should be added, but it's not yet clear what the signature should be, and in the mean time this file is not useful.
2018-09-12declare and make hidden additional internal init/exit symbolsRich Felker-0/+4
2018-09-12declare and make hidden additional internal stdio symbolsRich Felker-0/+5
2018-09-12declare and make hidden more internal locale functionsRich Felker-0/+2
2018-09-12move additional pthread internal declarations to pthread_impl.h, hideRich Felker-0/+15
these were overlooked for various reasons in earlier stages.
2018-09-12apply hidden visibility to various remaining internal interfacesRich Felker-23/+23
2018-09-12apply hidden visibility to sigreturn code fragmentsRich Felker-1/+3
these were overlooked in the declarations overhaul work because they are not properly declared, and the current framework even allows their declared types to vary by arch. at some point this should be cleaned up, but I'm not sure what the right way would be.
2018-09-12apply hidden visibility to pthread internalsRich Felker-11/+11
2018-09-12apply hidden visibility to stdio internalsRich Felker-26/+26
2018-09-12apply hidden visibility to internal math functionsRich Felker-24/+24
this makes significant differences to codegen on archs with an expensive PLT-calling ABI; on i386 and gcc 7.3 for example, the sin and sinf functions no longer touch call-saved registers or the stack except for pushing outgoing arguments. performance is likely improved too, but no measurements were taken.
2018-09-12overhaul internally-public declarations using wrapper headersRich Felker-22/+6
commits leading up to this one have moved the vast majority of libc-internal interface declarations to appropriate internal headers, allowing them to be type-checked and setting the stage to limit their visibility. the ones that have not yet been moved are mostly namespace-protected aliases for standard/public interfaces, which exist to facilitate implementing plain C functions in terms of POSIX functionality, or C or POSIX functionality in terms of extensions that are not standardized. some don't quite fit this description, but are "internally public" interfacs between subsystems of libc. rather than create a number of newly-named headers to declare these functions, and having to add explicit include directives for them to every source file where they're needed, I have introduced a method of wrapping the corresponding public headers. parallel to the public headers in $(srcdir)/include, we now have wrappers in $(srcdir)/src/include that come earlier in the include path order. they include the public header they're wrapping, then add declarations for namespace-protected versions of the same interfaces and any "internally public" interfaces for the subsystem they correspond to. along these lines, the wrapper for features.h is now responsible for the definition of the hidden, weak, and weak_alias macros. this means source files will no longer need to include any special headers to access these features. over time, it is my expectation that the scope of what is "internally public" will expand, reducing the number of source files which need to include *_impl.h and related headers down to those which are actually implementing the corresponding subsystems, not just using them.
2018-09-12declare __getopt_msg in stdio_impl.hRich Felker-0/+2
it's not ideal, but the function is essentially an extended stdio function specialized to getopt's needs. the only reason it exists is avoiding pulling printf code into every program using getopt.
2018-09-12move __memalign declaration to malloc_impl.hRich Felker-0/+2
the malloc-implementation-private header is the only right place for this, because, being in the reserved namespace, __memalign is not interposable and thus not valid to use anywhere else. anything outside of the malloc implementation must call an appropriate-namespace public function (aligned_alloc or posix_memalign).
2018-09-12make arch __set_thread_area backends hiddenRich Felker-1/+1
this is not a public interface, and does not even necessarily match the syscall on all archs that have a syscall by that name. on archs where it's implemented in C, no action on the source file is needed; the hidden declaration in pthread_arch.h suffices.
2018-09-12make arch __clone backends hiddenRich Felker-1/+1
these are not a public interface and are not intended to be callable from anywhere but the public clone function or other places in libc.
2018-09-12move tlsdesc and internal dl function declarations to dynlink.hRich Felker-0/+10
2018-09-12move __stdio_exit_needed to stdio_impl.hRich Felker-0/+2
this functions is glue for linking dependency logic.
2018-09-12move __loc_is_allocated declaration to locale_impl.hRich Felker-0/+1
2018-09-12move declarations of tls setup/access functions to pthread_impl.hRich Felker-0/+6
it's already included in all places where these are needed, and aside from __tls_get_addr, they're all implementation internals.
2018-09-12move lgamma-related internal declarations to libm.hRich Felker-0/+4
2018-09-12move declarations for malloc internals to malloc_impl.hRich Felker-0/+4
2018-09-12improve machinery for ldso to report libc versionRich Felker-6/+3
eliminate gratuitous glue function for reporting the version, which was probably leftover from the old dynamic linker design which lacked a clear barrier for when/how it could access global data. put the declaration for the data object that replaces it in libc.h where it can be type checked.
2018-09-12make internal declarations for flockfile tracking functions checkableRich Felker-0/+5
logically these belong to the intersection of the stdio and pthread subsystems, and either place the declarations could go (stdio_impl.h or pthread_impl.h) requires a forward declaration for one of the argument types.
2018-09-12move and deduplicate declarations of __vdsosym to make it checkableRich Felker-0/+2
2018-09-12move and deduplicate declarations of __procfdname to make it checkableRich Felker-0/+4
syscall.h was chosen as the header to declare it, since its intended usage is alongside syscalls as a fallback for operations the direct syscall does not support.
2018-09-05remove leftover declarations for removed functions from pthread_impl.hRich Felker-4/+0