|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
ARCH_PRCTL(2) Linux Programmer's Manual ARCH_PRCTL(2)
arch_prctl - set architecture-specific thread state
#include <asm/prctl.h>
#include <sys/prctl.h>
int arch_prctl(int code, unsigned long addr);
int arch_prctl(int code, unsigned long *addr);
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 current 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
current 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
current thread in the unsigned long pointed to by addr.
On success, arch_prctl() returns 0; on error, -1 is returned, and
errno is set to indicate the error.
EFAULT addr points to an unmapped address or is outside the process
address space.
EINVAL code is not a valid subcommand.
EPERM addr is outside the process address space.
ENODEV ARCH_SET_CPUID was requested, but the underlying hardware does
not support CPUID faulting.
arch_prctl() is a Linux/x86-64 extension and should not be used in
programs intended to be portable.
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.
As of version 2.7, glibc provides no prototype for arch_prctl(). You
have to declare it yourself for now. This may be fixed in future
glibc versions.
FS may be already used by the threading library. Programs that use
ARCH_SET_FS directly are very likely to crash.
mmap(2), modify_ldt(2), prctl(2), set_thread_area(2)
AMD X86-64 Programmer's manual
This page is part of release 5.08 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2020-04-11 ARCH_PRCTL(2)
Pages that refer to this page: clone2(2) , __clone2(2) , clone(2) , clone3(2) , get_thread_area(2) , modify_ldt(2) , set_thread_area(2) , syscalls(2)
Copyright and license for this manual page