GNU/Linux |
CentOS 5.3 |
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arch_prctl(2) |
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arch_prctl − set architecture specific thread state
#include <asm/prctl.h>
#include <sys/prctl.h>
int arch_prctl(int code, unsigned long addr)
The arch_prctl() function sets architecture specific process or thread state. code selects a subfunction and passes argument addr to it.
Sub functions
for x86-64 are:
ARCH_SET_FS
Set the 64bit base for the FS register to addr.
ARCH_GET_FS
Return the 64bit base value for the FS register of the current thread in the unsigned long pointed to by the address parameter
ARCH_SET_GS
Set the 64bit base for the GS register to addr.
ARCH_GET_GS
Return the 64bit base value for the GS register of the current thread in the unsigned long pointed to by the address parameter.
arch_prctl() is only supported on Linux/x86-64 for 64bit programs currently.
The 64bit base changes when a new 32bit segment selector is loaded.
ARCH_SET_GS is disabled in some kernels.
Context switches for 64bit segment bases are rather expensive. It may be a faster alternative to set a 32bit base using a segment selector by setting up an LDT with modify_ldt(2) or using the set_thread_area(2) system call in a 2.5 kernel. arch_prctl() is only needed when you want to set bases that are larger than 4GB. Memory in the first 2GB of address space can be allocated by using mmap(2) with the MAP_32BIT flag.
As of version 2.3.5, 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.
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. |
Man page written by Andi Kleen.
arch_prctl() is a Linux/x86-64 extension and should not be used in programs intended to be portable.
mmap(2), modify_ldt(2), prctl(2), set_thread_area(2)
AMD X86-64 Programmer’s manual
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arch_prctl(2) | ![]() |