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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.
2013-02-01fix up minor misplacement of restrict keyword in spawnattr sched stubsRich Felker-2/+2
2012-11-11add support for thread scheduling (POSIX TPS option)Rich Felker-0/+25
linux's sched_* syscalls actually implement the TPS (thread scheduling) functionality, not the PS (process scheduling) functionality which the sched_* functions are supposed to have. omitting support for the PS option (and having the sched_* interfaces fail with ENOSYS rather than omitting them, since some broken software assumes they exist) seems to be the only conforming way to do this on linux.
2012-11-08clean up sloppy nested inclusion from pthread_impl.hRich Felker-0/+1
this mirrors the stdio_impl.h cleanup. one header which is not strictly needed, errno.h, is left in pthread_impl.h, because since pthread functions return their error codes rather than using errno, nearly every single pthread function needs the errno constants. in a few places, rather than bringing in string.h to use memset, the memset was replaced by direct assignment. this seems to generate much better code anyway, and makes many functions which were previously non-leaf functions into leaf functions (possibly eliminating a great deal of bloat on some platforms where non-leaf functions require ugly prologue and/or epilogue).
2012-10-28system is a cancellation pointRich Felker-0/+3
ideally, system would also be cancellable while running the external command, but I cannot find any way to make that work without either leaking zombie processes or introducing behavior that is far outside what the standard specifies. glibc handles cancellation by killing the child process with SIGKILL, but this could be unsafe in that it could leave the data being manipulated by the command in an inconsistent state.
2012-10-19fix usage of locks with vforkRich Felker-2/+3
__release_ptc() is only valid in the parent; if it's performed in the child, the lock will be unlocked early then double-unlocked later, corrupting the lock state.
2012-10-18fix parent-memory-clobber in posix_spawn (environ)Rich Felker-9/+17
2012-10-18overhaul system() and popen() to use vfork; fix various related bugsRich Felker-29/+49
since we target systems without overcommit, special care should be taken that system() and popen(), like posix_spawn(), do not fail in processes whose commit charges are too high to allow ordinary forking. this in turn requires special precautions to ensure that the parent process's signal handlers do not end up running in the shared-memory child, where they could corrupt the state of the parent process. popen has also been updated to use pipe2, so it does not have a fd-leak race in multi-threaded programs. since pipe2 is missing on older kernels, (non-atomic) emulation has been added. some silly bugs in the old code should be gone too.
2012-10-15block uid/gid changes during posix_spawnRich Felker-0/+10
usage of vfork creates a situation where a process of lower privilege may momentarily have write access to the memory of a process of higher privilege. consider the case of a multi-threaded suid program which is calling posix_spawn in one thread while another thread drops the elevated privileges then runs untrusted (relative to the elevated privilege) code as the original invoking user. this untrusted code can then potentially modify the data the child process will use before calling exec, for example changing the pathname or arguments that will be passed to exec. note that if vfork is implemented as fork, the lock will not be held until the child execs, but since memory is not shared it does not matter.
2012-09-14use vfork if possible in posix_spawnRich Felker-1/+3
vfork is implemented as the fork syscall (with no atfork handlers run) on archs where it is not available, so this change does not introduce any change in behavior or regression for such archs.
2012-09-06use restrict everywhere it's required by c99 and/or posix 2008Rich Felker-18/+18
to deal with the fact that the public headers may be used with pre-c99 compilers, __restrict is used in place of restrict, and defined appropriately for any supported compiler. we also avoid the form [restrict] since older versions of gcc rejected it due to a bug in the original c99 standard, and instead use the form *restrict.
2012-02-06x86_64 vfork implementationRich Felker-0/+12
untested; should work.
2011-10-14support vfork on i386Rich Felker-0/+14
2011-10-14make available a namespace-safe vfork, if supportedRich Felker-1/+4
this may be useful to posix_spawn..?
2011-09-29fix various bugs in path and error handling in execvp/fexecveRich Felker-18/+29
2011-09-13fix various errors in function signatures/prototypes found by nszRich Felker-5/+8
2011-09-13add missing posix_spawnattr_init/destroy functionsRich Felker-0/+13
2011-08-06use weak aliases rather than function pointers to simplify some codeRich Felker-2/+8
2011-07-16ensure in fork that child gets its own new robust mutex listRich Felker-0/+1
2011-05-29fix backwards posix_spawn file action orderRich Felker-6/+10
2011-05-28add accidentally-omitted file needed for posix_spawn file actionsRich Felker-0/+10
2011-05-28add file actions support to posix_spawnRich Felker-2/+85
2011-05-28posix_spawn: honor POSIX_SPAWN_SETSIGDEF flagRich Felker-1/+3
2011-05-28initial implementation of posix_spawnRich Felker-0/+151
file actions are not yet implemented, but everything else should be mostly complete and roughly correct.
2011-04-27correct variadic prototypes for execl* familyRich Felker-15/+18
the old versions worked, but conflicted with programs which declared their own prototypes and generated warnings with some versions of gcc.
2011-04-20fix minor bugs due to incorrect threaded-predicate semanticsRich Felker-1/+2
some functions that should have been testing whether pthread_self() had been called and initialized the thread pointer were instead testing whether pthread_create() had been called and actually made the program "threaded". while it's unlikely any mismatch would occur in real-world problems, this could have introduced subtle bugs. now, we store the address of the main thread's thread descriptor in the libc structure and use its presence as a flag that the thread register is initialized. note that after fork, the calling thread (not necessarily the original main thread) is the new main thread.
2011-04-17clean up handling of thread/nothread mode, lockingRich Felker-1/+1