установить зависящее от архитектуры состояние потока (set architecture-specific thread state)
Имя (Name)
arch_prctl - set architecture-specific thread state
Синопсис (Synopsis)
#include <asm/prctl.h> /* Definition of ARCH_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <unistd.h>
int syscall(SYS_arch_prctl, int code, unsigned long addr);
int syscall(SYS_arch_prctl, int code, unsigned long *addr);
Note: glibc provides no wrapper for arch_prctl(), necessitating
the use of syscall(2).
Описание (Description)
arch_prctl() sets architecture-specific process or thread state.
code selects a subfunction and passes argument addr to it; addr
is interpreted as either an unsigned long for the "set"
operations, or as an unsigned long *, for the "get" operations.
Subfunctions for both x86 and x86-64 are:
ARCH_SET_CPUID (since Linux 4.12)
Enable (addr != 0) or disable (addr == 0) the cpuid
instruction for the calling thread. The instruction is
enabled by default. If disabled, any execution of a cpuid
instruction will instead generate a SIGSEGV signal. This
feature can be used to emulate cpuid results that differ
from what the underlying hardware would have produced
(e.g., in a paravirtualization setting).
The ARCH_SET_CPUID setting is preserved across fork(2) and
clone(2) but reset to the default (i.e., cpuid enabled) on
execve(2).
ARCH_GET_CPUID (since Linux 4.12)
Return the setting of the flag manipulated by
ARCH_SET_CPUID as the result of the system call (1 for
enabled, 0 for disabled). addr is ignored.
Subfunctions for x86-64 only are:
ARCH_SET_FS
Set the 64-bit base for the FS register to addr.
ARCH_GET_FS
Return the 64-bit base value for the FS register of the
calling thread in the unsigned long pointed to by addr.
ARCH_SET_GS
Set the 64-bit base for the GS register to addr.
ARCH_GET_GS
Return the 64-bit base value for the GS register of the
calling thread in the unsigned long pointed to by addr.
Возвращаемое значение (Return value)
On success, arch_prctl() returns 0; on error, -1 is returned, and
errno is set to indicate the error.
Ошибки (Error)
EFAULT addr points to an unmapped address or is outside the
process address space.
EINVAL code is not a valid subcommand.
ENODEV ARCH_SET_CPUID was requested, but the underlying hardware
does not support CPUID faulting.
EPERM addr is outside the process address space.
Стандарты (Conforming to)
arch_prctl() is a Linux/x86-64 extension and should not be used
in programs intended to be portable.
Примечание (Note)
arch_prctl() is supported only on Linux/x86-64 for 64-bit
programs currently.
The 64-bit base changes when a new 32-bit segment selector is
loaded.
ARCH_SET_GS is disabled in some kernels.
Context switches for 64-bit segment bases are rather expensive.
As an optimization, if a 32-bit TLS base address is used,
arch_prctl() may use a real TLS entry as if set_thread_area(2)
had been called, instead of manipulating the segment base
register directly. Memory in the first 2 GB of address space can
be allocated by using mmap(2) with the MAP_32BIT flag.
Because of the aforementioned optimization, using arch_prctl()
and set_thread_area(2) in the same thread is dangerous, as they
may overwrite each other's TLS entries.
FS may be already used by the threading library. Programs that
use ARCH_SET_FS directly are very likely to crash.
Смотри также (See also)
mmap(2), modify_ldt(2), prctl(2), set_thread_area(2)
AMD X86-64 Programmer's manual
