NAME

       psx_syscall3, psx_syscall6 - POSIX semantics for system calls

SYNOPSIS

       #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);

       Link with one of these:

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

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

DESCRIPTION

       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(3)  provides  a  more  generic  pair  of  wrapping  system  call  functions:  psx_syscall3(3)  and
       psx_syscall6(3).   Like  the setxid mechanism, the coordination of thread state is arranged by a realtime
       signal SIGRTMAX which is usurped for this process.

       A linker trick of wrapping the pthread_create() call with a psx thread registration function is  used  to
       allow  libpsx  to  keep  track of all pthreads. If that trick is not usable by your application, then the
       much more cumbersome and fragile <sys/psx_syscall.h> header file.

       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(3) or
       psx_syscall6(3) 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(3) and psx_syscall6(3) functions.

RETURN VALUE

       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

       The needs of libcap(3) for POSIX semantics of capability manipulation.

REPORTING BUGS

       Please report bugs via:

       https://bugzilla.kernel.org/buglist.cgi?component=libcap&list_id=1047723&product=Tools&resolution=---

SEE ALSO

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

                                                   2020-01-07                                          LIBPSX(3)