NAME

       psx_syscall3, psx_syscall6, psx_set_sensitivity - 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);
       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

       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

       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. You can read more
       about why this is needed here:

       https://sites.google.com/site/fullycapable/who-ordered-libpsx

REPORTING BUGS

       The libpsx library is distributed from  https://sites.google.com/site/fullycapable/  where
       the  release  notes  may already cover recent issues.  Please report newly discovered bugs
       via:

       https://bugzilla.kernel.org/buglist.cgi?component=libcap&list_id=1090757

SEE ALSO

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

                                            2021-12-12                                  LIBPSX(3)