path: root/src/process
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2019-04-02use __strchrnul instead of strchr and strlen in execvpeFrediano Ziglio-2/+1
The result is the same but takes less code. Note that __execvpe calls getenv which calls __strchrnul so even using static output the size of the executable won't grow.
2019-02-15track all live threads in an AS-safe, fully-consistent linked listRich Felker-0/+1
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.
2018-09-12reduce spurious inclusion of libc.hRich Felker-5/+0
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 __vfork aliasRich Felker-28/+7
this was added so that posix_spawn and possibly other functionality could be implemented in terms of vfork, but that turned out to be unsafe. any such usage needs __clone with proper handling of stack lifetime.
2018-09-12overhaul internally-public declarations using wrapper headersRich Felker-4/+0
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.
2018-09-12rework mechanism for posix_spawnp calling posix_spawnRich Felker-19/+9
previously, a common __posix_spawnx backend was used that accepted an additional argument for the execve variant to call in the child. this moderately bloated up the posix_spawn function, shuffling arguments between stack and/or registers to call a 7-argument function from a 6-argument one. instead, tuck the exec function pointer in an unused part of the (large) pthread_spawnattr_t structure, and have posix_spawnp duplicate the attributes and fill in a pointer to __execvpe. the net code size change is minimal, but the weight is shifted to the "heavier" function which already pulls in more dependencies. as a bonus, we get rid of an external symbol (__posix_spawnx) that had no really good place for a declaration because it shouldn't have existed to begin with.
2018-09-12declare __syscall_ret as hidden in vfork asmRich Felker-0/+4
without this, it's plausible that assembler or linker could complain about an unsatisfiable relocation.
2018-09-12add arm asm for vforkPatrick Oppenlander-0/+13
2018-09-12move and deduplicate declarations of __procfdname to make it checkableRich Felker-2/+0
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.
2018-09-04implement fexecve in terms of execveat when it existsJoseph C. Sible-0/+5
This lets fexecve work even when /proc isn't mounted.
2018-08-28fix return value of system on failure to spawn child processRich Felker-1/+1
the value 0x7f00 (as if by _exit(127)) is specified only for the case where the child is created but then fails to exec the shell, since traditional fork+exec implementations do not admit reporting an error via errno in this case without additional machinery. it's unclear whether an implementation not subject to this failure mode needs to emulate it; one could read the standard as requiring that. if so, additional code will need to be added to map posix_spawn errors into the form system is expected to return. but for now, returning -1 to indicate an error is significantly better behavior than always reporting failures as if the shell failed to exec after fork.
2018-02-21convert execvp error handling to switch statementRich Felker-2/+9
this is more extensible if we need to consider additional errors, and more efficient as long as the compiler does not know it can cache the result of __errno_location (a surprisingly complex issue detailed in commit a603a75a72bb469c6be4963ed1b55fabe675fe15).
2018-02-21fix execvp failing on not-dir entries in PATH.Przemyslaw Pawelczyk-1/+1
It's better to make execvp continue PATH search on ENOTDIR rather than issuing an error. Bogus entries should not render rest of PATH invalid. Maintainer's note: POSIX seems to require the search to continue like this as part of XBD 8.3 Other Environment Variables. Only errors that conclusively determine non-existence are candidates for continuing; otherwise for consistency we have to report the error.
2017-11-10prevent fork's errno from being clobbered by atfork handlersBobby Bingham-3/+3
If the syscall fails, errno must be set correctly for the caller. There's no guarantee that the handlers registered with pthread_atfork won't clobber errno, so we need to ensure it gets set after they are called.
2017-11-05adjust posix_spawn dup2 action behavior to match future requirementsRich Felker-8/+12
the resolution to Austin Group issue #411 defined new semantics for the posix_spawn dup2 file action in the (previously useless) case where src and dest fd are equal. future issues will require the dup2 file action to remove the close-on-exec flag. without this change, passing fds to a child with posix_spawn while avoiding fd-leak races in a multithreaded parent required a complex dance with temporary fds. based on patch by Petr Skocik. changes were made to preserve the 80-column formatting of the function and to remove code that became unreachable as a result of the new functionality.
2017-10-19posix_spawn: use larger stack to cover worst-case in execvpeWill Dietz-1/+1
execvpe stack-allocates a buffer used to hold the full path (combination of a PATH entry and the program name) while searching through $PATH, so at least NAME_MAX+PATH_MAX is needed. The stack size can be made conditionally smaller (the current 1024 appears appropriate) should this larger size be burdensome in those situations.
2017-04-22have posix_spawnattr_setflags check for supported flagsRich Felker-0/+11
per POSIX, EINVAL is not a mandatory error, only an optional one. but reporting unsupported flags allows an application to fallback gracefully when a requested feature is not supported. this is not helpful now, but it may be in the future if additional flags are added. had this checking been present before, applications would have been able to check for the newly-added POSIX_SPAWN_SETSID feature (added in commit bb439bb17108b67f3df9c9af824d3a607b5b059d) at runtime.
2017-04-22implement new posix_spawn flag POSIX_SPAWN_SETSIDRich Felker-0/+4
this functionality has been adopted for inclusion in the next issue of POSIX as the result of Austin Group issue #1044. based on patch by Daurnimator.
2016-11-11add s390x portBobby Bingham-0/+8
2015-06-16switch to using trap number 31 for syscalls on shRich Felker-1/+1
nominally the low bits of the trap number on sh are the number of syscall arguments, but they have never been used by the kernel, and some code making syscalls does not even know the number of arguments and needs to pass an arbitrary high number anyway. sh3/sh4 traditionally used the trap range 16-31 for syscalls, but part of this range overlapped with hardware exceptions/interrupts on sh2 hardware, so an incompatible range 32-47 was chosen for sh2. using trap number 31 everywhere, since it's in the existing sh3/sh4 range and does not conflict with sh2 hardware, is a proposed unification of the kernel syscall convention that will allow binaries to be shared between sh2 and sh3/sh4. if this is not accepted into the kernel, we can refit the sh2 target with runtime selection mechanisms for the trap number, but doing so would be invasive and would entail non-trivial overhead.
2015-06-11add sh asm for vforkRich Felker-0/+23
2015-04-13remove remnants of support for running in no-thread-pointer modeRich Felker-1/+1
since 1.1.0, musl has nominally required a thread pointer to be setup. most of the remaining code that was checking for its availability was doing so for the sake of being usable by the dynamic linker. as of commit 71f099cb7db821c51d8f39dfac622c61e54d794c, this is no longer necessary; the thread pointer is now valid before any libc code (outside of dynamic linker bootstrap functions) runs. this commit essentially concludes "phase 3" of the "transition path for removing lazy init of thread pointer" project that began during the 1.1.0 release cycle.
2015-04-10optimize out setting up robust list with kernel when not neededRich Felker-1/+2
as a result of commit 12e1e324683a1d381b7f15dd36c99b37dd44d940, kernel processing of the robust list is only needed for process-shared mutexes. previously the first attempt to lock any owner-tracked mutex resulted in robust list initialization and a set_robust_list syscall. this is no longer necessary, and since the kernel's record of the robust list must now be cleared at thread exit time for detached threads, optimizing it out is more worthwhile than before too.
2015-02-03make execvp continue PATH search on EACCES rather than issuing an errrorRich Felker-1/+4
the specification for execvp itself is unclear as to whether encountering a file that cannot be executed due to EACCES during the PATH search is a mandatory error condition; however, XBD 8.3's specification of the PATH environment variable clarifies that the search continues until a file with "appropriate execution permissions" is found. since it seems undesirable/erroneous to report ENOENT rather than EACCES when an early path element has a non-executable file and all later path elements lack any file by the requested name, the new code stores a flag indicating that EACCES was seen and sets errno back to EACCES in this case.
2014-12-05use direct syscall rather than write function in posix_spawn childRich Felker-1/+1
the write function is a cancellation point and accesses thread-local state belonging to the calling thread in the parent process. since cancellation is blocked for the duration of posix_spawn, this is probably safe, but it's fragile and unnecessary. making the syscall directly is just as easy and clearly safe.
2014-12-05don't fail posix_spawn on failed closeRich Felker-2/+1
the resolution of austin group issue #370 removes the requirement that posix_spawn fail when the close file action is performed on an already-closed fd. since there are no other meaningful errors for close, just ignoring the return value completely is the simplest fix.
2014-07-05eliminate use of cached pid from thread structureRich Felker-1/+1
the main motivation for this change is to remove the assumption that the tid of the main thread is also the pid of the process. (the value returned by the set_tid_address syscall was used to fill both fields despite it semantically being the tid.) this is historically and presently true on linux and unlikely to change, but it conceivably could be false on other systems that otherwise reproduce the linux syscall api/abi. only a few parts of the code were actually still using the cached pid. in a couple places (aio and synccall) it was a minor optimization to avoid a syscall. caching could be reintroduced, but lazily as part of the public getpid function rather than at program startup, if it's deemed important for performance later. in other places (cancellation and pthread_kill) the pid was completely unnecessary; the tkill syscall can be used instead of tgkill. this is actually a rather subtle issue, since tgkill is supposedly a solution to race conditions that can affect use of tkill. however, as documented in the commit message for commit 7779dbd2663269b465951189b4f43e70839bc073, tgkill does not actually solve this race; it just limits it to happening within one process rather than between processes. we use a lock that avoids the race in pthread_kill, and the use in the cancellation signal handler is self-targeted and thus not subject to tid reuse races, so both are safe regardless of which syscall (tgkill or tkill) is used.
2014-07-01fix ungrammatical comment in posix_spawn codeRich Felker-3/+3
2014-05-30additional fixes for linux kernel apis with old syscalls removedRich Felker-0/+5
2014-05-29support linux kernel apis (new archs) with old syscalls removedRich Felker-2/+21
such archs are expected to omit definitions of the SYS_* macros for syscalls their kernels lack from arch/$ARCH/bits/syscall.h. the preprocessor is then able to select the an appropriate implementation for affected functions. two basic strategies are used on a case-by-case basis: where the old syscalls correspond to deprecated library-level functions, the deprecated functions have been converted to wrappers for the modern function, and the modern function has fallback code (omitted at the preprocessor level on new archs) to make use of the old syscalls if the new syscall fails with ENOSYS. this also improves functionality on older kernels and eliminates the incentive to program with deprecated library-level functions for the sake of compatibility with older kernels. in other situations where the old syscalls correspond to library-level functions which are not deprecated but merely lack some new features, such as the *at functions, the old syscalls are still used on archs which support them. this may change at some point in the future if or when fallback code is added to the new functions to make them usable (possibly with reduced functionality) on old kernels.
2014-05-24support kernels with no SYS_open syscall, only SYS_openatRich Felker-2/+1
open is handled specially because it is used from so many places, in so many variants (2 or 3 arguments, setting errno or not, and cancellable or not). trying to do it as a function would not only increase bloat, but would also risk subtle breakage. this is the first step towards supporting "new" archs where linux lacks "old" syscalls.
2014-04-20expose public execvpe interfaceM Farkas-Dyck-0/+3
2014-03-24always initialize thread pointer at program startRich Felker-3/+2
this is the first step in an overhaul aimed at greatly simplifying and optimizing everything dealing with thread-local state. previously, the thread pointer was initialized lazily on first access, or at program startup if stack protector was in use, or at certain random places where inconsistent state could be reached if it were not initialized early. while believed to be fully correct, the logic was fragile and non-obvious. in the first phase of the thread pointer overhaul, support is retained (and in some cases improved) for systems/situation where loading the thread pointer fails, e.g. old kernels. some notes on specific changes: - the confusing use of libc.main_thread as an indicator that the thread pointer is initialized is eliminated in favor of an explicit has_thread_pointer predicate. - sigaction no longer needs to ensure that the thread pointer is initialized before installing a signal handler (this was needed to prevent a situation where the signal handler caused the thread pointer to be initialized and the subsequent sigreturn cleared it again) but it still needs to ensure that implementation-internal thread-related signals are not blocked. - pthread tsd initialization for the main thread is deferred in a new manner to minimize bloat in the static-linked __init_tp code. - pthread_setcancelstate no longer needs special handling for the situation before the thread pointer is initialized. it simply fails on systems that cannot support a thread pointer, which are non-conforming anyway. - pthread_cleanup_push/pop now check for missing thread pointer and nop themselves out in this case, so stdio no longer needs to avoid the cancellable path when the thread pointer is not available. a number of cases remain where certain interfaces may crash if the system does not support a thread pointer. at this point, these should be limited to pthread interfaces, and the number of such cases should be fewer than before.
2014-02-23x32 port (diff against vanilla x86_64)rofl0r-1/+1
2014-02-23import vanilla x86_64 code as x32rofl0r-0/+12
2014-02-12make posix_spawn accept null pid pointer argumentsRich Felker-1/+1
this is a requirement in the specification that was overlooked.
2013-12-12include cleanups: remove unused headers and add feature test macrosSzabolcs Nagy-2/+2
2013-10-07add missing va_end in execl* for correcness and static code analyzersSzabolcs Nagy-0/+3
2013-10-03fix new environment always being null with execleRich Felker-2/+1
the va_arg call for the argv[]-terminating null pointer was missing, so this pointer was being wrongly used as the environment pointer. issue reported by Timo Teräs. proposed patch slightly modified to simplify the resulting code.
2013-08-09optimize posix_spawn to avoid spurious sigaction syscallsRich Felker-7/+21
the trick here is that sigaction can track for us which signals have ever had a signal handler set for them, and only those signals need to be considered for reset. this tracking mask may have false positives, since it is impossible to remove bits from it without race conditions. false negatives are not possible since the mask is updated with atomic operations prior to making the sigaction syscall. implementation-internal signals are set to SIG_IGN rather than SIG_DFL so that a signal raised in the parent (e.g. calling pthread_cancel on the thread executing pthread_spawn) does not have any chance make it to the child, where it would cause spurious termination by signal. this change reduces the minimum/typical number of syscalls in the child from around 70 to 4 (including execve). this should greatly improve the performance of posix_spawn and other interfaces which use it (popen and system). to facilitate these changes, sigismember is also changed to return 0 rather than -1 for invalid signals, and to return the actual status of implementation-internal signals. POSIX allows but does not require an error on invalid signal numbers, and in fact returning an error tends to confuse applications which wrongly assume the return value of sigismember is boolean.
2013-08-09fix missing errno from exec failure in posix_spawnRich Felker-0/+1
failures prior to the exec attempt were reported correctly, but on exec failure, the return value contained junk.
2013-08-08block signals during forkRich Felker-0/+3
there are several reasons for this. some of them are related to race conditions that arise since fork is required to be async-signal-safe: if fork or pthread_create is called from a signal handler after the fork syscall has returned but before the subsequent userspace code has finished, inconsistent state could result. also, there seem to be kernel and/or strace bugs related to arrival of signals during fork, at least on some versions, and simply blocking signals eliminates the possibility of such bugs.
2013-08-02debloat code that depends on /proc/self/fd/%d with shared functionRich Felker-3/+4
I intend to add more Linux workarounds that depend on using these pathnames, and some of them will be in "syscall" functions that, from an anti-bloat standpoint, should not depend on the whole snprintf framework.
2013-07-17make posix_spawn (and functions that use it) use CLONE_VFORK flagRich Felker-1/+2
this is both a minor scheduling optimization and a workaround for a difficult-to-fix bug in qemu app-level emulation. from the scheduling standpoint, it makes no sense to schedule the parent thread again until the child has exec'd or exited, since the parent will immediately block again waiting for it. on the qemu side, as regular application code running on an underlying libc, qemu cannot make arbitrary clone syscalls itself without confusing the underlying implementation. instead, it breaks them down into either fork-like or pthread_create-like cases. it was treating the code in posix_spawn as pthread_create-like, due to CLONE_VM, which caused horribly wrong behavior: CLONE_FILES broke the synchronization mechanism, CLONE_SIGHAND broke the parent's signals, and CLONE_THREAD caused the child's exec to end the parent -- if it hadn't already crashed. however, qemu special-cases CLONE_VFORK and emulates that with fork, even when CLONE_VM is also specified. this also gives incorrect semantics for code that really needs the memory sharing, but posix_spawn does not make use of the vm sharing except to avoid momentary double commit charge. programs using posix_spawn (including via popen) should now work correctly under qemu app-level emulation.
2013-04-26remove explicit locking to prevent __synccall setuid during posix_spawnRich Felker-13/+0
for the duration of the vm-sharing clone used by posix_spawn, all signals are blocked in the parent process, including implementation-internal signals. since __synccall cannot do anything until successfully signaling all threads, the fact that signals are blocked automatically yields the necessary safety. aside from debloating and general simplification, part of the motivation for removing the explicit lock is to simplify the synchronization logic of __synccall in hopes that it can be made async-signal-safe, which is needed to make setuid and setgid, which depend on __synccall, conform to the standard. whether this will be possible remains to be seen.
2013-03-24remove cruft from pre-posix_spawn version of the system functionRich Felker-6/+0
2013-02-17consistently use the internal name __environ for environRich Felker-4/+4
patch by Jens Gustedt. previously, the intended policy was to use __environ in code that must conform to the ISO C namespace requirements, and environ elsewhere. this policy was not followed in practice anyway, making things confusing. on top of that, Jens reported that certain combinations of link-time optimization options were breaking with the inconsistent references; this seems to be a compiler or linker bug, but having it go away is a nice side effect of the changes made here.
2013-02-03base system() on posix_spawnRich Felker-41/+26
this avoids duplicating the fragile logic for executing an external program without fork.
2013-02-03fix unsigned comparison bug in posix_spawnRich Felker-1/+1
read should never return anything but 0 or sizeof ec here, but if it does, we want to treat any other return as "success". then the caller will get back the pid and is responsible for waiting on it when it immediately exits.
2013-02-03overhaul posix_spawn to use CLONE_VM instead of vforkRich Felker-55/+125
the proposed change was described in detail in detail previously on the mailing list. in short, vfork is unsafe because: 1. the compiler could make optimizations that cause the child to clobber the parent's local vars. 2. strace is buggy and allows the vforking parent to run before the child execs when run under strace. the new design uses a close-on-exec pipe instead of vfork semantics to synchronize the parent and child so that the parent does not return before the child has finished using its arguments (and now, also its stack). this also allows reporting exec failures to the caller instead of giving the caller a child that mysteriously exits with status 127 on exec error. basic testing has been performed on both the success and failure code paths. further testing should be done.