семантика POSIX для системных вызовов (POSIX semantics for system calls)
Имя (Name)
psx_syscall3, psx_syscall6 - POSIX semantics for system calls
Синопсис (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
Описание (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.
Возвращаемое значение (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.
Стандарты (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
Сообщение об ошибках (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
Смотри также (See also)
libcap(3), pthreads(7) and nptl(7).
