Manpages - libpsx.3

psx_syscall3, psx_syscall6 - POSIX semantics for system calls

  #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

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.

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.

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

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

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