From 3d08cd331c1adcf0d917392f7e527b3f00511748 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Fri, 24 May 2024 06:52:22 +0200 Subject: Merging upstream version 6.8. Signed-off-by: Daniel Baumann --- man/man7/nptl.7 | 112 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 112 insertions(+) create mode 100644 man/man7/nptl.7 (limited to 'man/man7/nptl.7') diff --git a/man/man7/nptl.7 b/man/man7/nptl.7 new file mode 100644 index 0000000..8fc3046 --- /dev/null +++ b/man/man7/nptl.7 @@ -0,0 +1,112 @@ +.\" Copyright (c) 2015 by Michael Kerrisk +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" +.TH nptl 7 2024-05-02 "Linux man-pages (unreleased)" +.SH NAME +nptl \- Native POSIX Threads Library +.SH DESCRIPTION +NPTL (Native POSIX Threads Library) +is the GNU C library POSIX threads implementation that is used on modern +Linux systems. +.\" +.SS NPTL and signals +NPTL makes internal use of the first two real-time signals +(signal numbers 32 and 33). +One of these signals is used to support thread cancelation and POSIX timers +(see +.BR timer_create (2)); +the other is used as part of a mechanism that ensures all threads in +a process always have the same UIDs and GIDs, as required by POSIX. +These signals cannot be used in applications. +.P +To prevent accidental use of these signals in applications, +which might interfere with the operation of the NPTL implementation, +various glibc library functions and system call wrapper functions +attempt to hide these signals from applications, +as follows: +.IP \[bu] 3 +.B SIGRTMIN +is defined with the value 34 (rather than 32). +.IP \[bu] +The +.BR sigwaitinfo (2), +.BR sigtimedwait (2), +and +.BR sigwait (3) +interfaces silently ignore requests to wait for these two signals +if they are specified in the signal set argument of these calls. +.IP \[bu] +The +.BR sigprocmask (2) +and +.BR pthread_sigmask (3) +interfaces silently ignore attempts to block these two signals. +.IP \[bu] +The +.BR sigaction (2), +.BR pthread_kill (3), +and +.BR pthread_sigqueue (3) +interfaces fail with the error +.B EINVAL +(indicating an invalid signal number) if these signals are specified. +.IP \[bu] +.BR sigfillset (3) +does not include these two signals when it creates a full signal set. +.\" +.SS NPTL and process credential changes +At the Linux kernel level, +credentials (user and group IDs) are a per-thread attribute. +However, POSIX requires that all of the POSIX threads in a process +have the same credentials. +To accommodate this requirement, +the NPTL implementation wraps all of the system calls that +change process credentials with functions that, +in addition to invoking the underlying system call, +arrange for all other threads in the process to also change their credentials. +.P +The implementation of each of these system calls involves the use of +a real-time signal that is sent (using +.BR tgkill (2)) +to each of the other threads that must change its credentials. +Before sending these signals, the thread that is changing credentials +saves the new credential(s) and records the system call being employed +in a global buffer. +A signal handler in the receiving thread(s) fetches this information and +then uses the same system call to change its credentials. +.P +Wrapper functions employing this technique are provided for +.BR setgid (2), +.BR setuid (2), +.BR setegid (2), +.BR seteuid (2), +.BR setregid (2), +.BR setreuid (2), +.BR setresgid (2), +.BR setresuid (2), +and +.BR setgroups (2). +.\" FIXME . +.\" Maybe say something about vfork() not being serialized wrt set*id() APIs? +.\" https://sourceware.org/bugzilla/show_bug.cgi?id=14749 +.SH STANDARDS +For details of the conformance of NPTL to the POSIX standard, see +.BR pthreads (7). +.SH NOTES +POSIX says +.\" See POSIX.1-2008 specification of pthread_mutexattr_init() +that any thread in any process with access to the memory +containing a process-shared +.RB ( PTHREAD_PROCESS_SHARED ) +mutex can operate on that mutex. +However, on 64-bit x86 systems, the mutex definition for x86-64 +is incompatible with the mutex definition for i386, +.\" See sysdeps/x86/bits/pthreadtypes.h +meaning that 32-bit and 64-bit binaries can't share mutexes on x86-64 systems. +.SH SEE ALSO +.BR credentials (7), +.BR pthreads (7), +.BR signal (7), +.BR standards (7) -- cgit v1.2.3