libpsx(3) — Linux manual page


LIBPSX(3)               Linux Programmer's Manual              LIBPSX(3)

NAME         top

       psx_syscall3, psx_syscall6, psx_set_sensitivity - POSIX semantics
       for system calls

SYNOPSIS         top

       #include <sys/psx_syscall.h>

       long int psx_syscall3(long int syscall_nr, long int arg1, long int arg2, long int arg3);
       long int psx_syscall6(long int syscall_nr, long int arg1, long int arg2, long int arg3, long int arg4, long int arg5, long int arg6);
       int psx_set_sensitivity(psx_sensitivity_t sensitivity);

       Link with one of these:

       ld ... -lpsx -lpthread --wrap=pthread_create

       gcc ... -lpsx -lpthread -Wl,-wrap,pthread_create

DESCRIPTION         top

       The libpsx library attempts to fill a gap left by the pthreads(7)
       implementation on Linux. To be compliant POSIX threads, via the
       nptl(7) setxid mechanism glibc maintains consistent UID and GID
       credentials amongst all of the threads associated with the
       current process. However, other credential state is not supported
       by this abstraction. To support these extended kernel managed
       security attributes, libpsx provides a more generic pair of
       wrapping system call functions: psx_syscall3() and
       psx_syscall6().  Like the setxid mechanism, the coordination of
       thread state is mediated by a realtime signal. Whereas the
       nptl:setxid mechanism uses signo=33 (which is hidden by glibc
       below a redefined SIGRTMIN), libpsx inserts itself in the SIGSYS
       handler stack. It goes to great length to be the first such
       handler but acts as a pass-through for other SIGSYS uses.

       A linker trick of wrapping the pthread_create() call with a psx
       thread registration function is used to ensure libpsx can keep
       track of all pthreads.

       An inefficient macrology trick supports the psx_syscall() pseudo
       function which takes 1 to 7 arguments, depending on the needs of
       the caller. The macrology pads out the call to actually use
       psx_syscall3() or psx_syscall6() with zeros filling the missing
       arguments. While using this in source code will make it appear
       clean, the actual code footprint is larger. You are encouraged to
       use the more explicit psx_syscall3() and psx_syscall6() functions
       as needed.

       psx_set_sensitivity() changes the behavior of the mirrored system
       calls: PSX_IGNORE ensures that differences are ignored (the
       default behavior); PSX_WARNING prints a stderr notification about
       how the results differ; and PSX_ERROR prints the error details
       and generates a SIGSYS signal.

RETURN VALUE         top

       The return value for system call functions is generally the value
       returned by the kernel, or -1 in the case of an error. In such
       cases errno(3) is set to the detailed error value. The
       psx_syscall3() and psx_syscall6() functions attempt a single
       threaded system call and return immediately in the case of an
       error. Should this call succeed, then the same system calls are
       executed from a signal handler on each of the other threads of
       the process.

CONFORMING TO         top

       The needs of libcap(3) for POSIX semantics of capability
       manipulation. You can read more about why this is needed here:

REPORTING BUGS         top

       The libpsx library is distributed from where the release
       notes may already cover recent issues.  Please report newly
       discovered bugs via:

SEE ALSO         top

       libcap(3), pthreads(7) and nptl(7).

COLOPHON         top

       This page is part of the libcap (capabilities commands and
       library) project.  Information about the project can be found at
       ⟨⟩.  If you
       have a bug report for this manual page, send it to (please put "libcap" in the Subject line).
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on
       2022-12-17.  (At that time, the date of the most recent commit
       that was found in the repository was 2022-10-30.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to

                               2021-12-12                      LIBPSX(3)

Pages that refer to this page: cap_get_proc(3)cap_launch(3)libcap(3)