ARCH_PRCTLSection: Linux Programmer's Manual (2)
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NAMEarch_prctl - set architecture specific thread state
SYNOPSIS#include <asm/prctl.h> #include <sys/prctl.h>
DESCRIPTIONThe 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:
- Set the 64bit base for the FS register to addr.
- Return the 64bit base value for the FS register of the current thread in the unsigned long pointed to by the address parameter
- Set the 64bit base for the GS register to addr.
- Return the 64bit base value for the GS register of the current thread in the unsigned long pointed to by the address parameter.
RETURN VALUEOn sucess, arch_prctl() returns 0; on error, -1 is returned, and errno is set to indicate the error.
- addr points to an unmapped address or is outside the process address space.
- code is not a valid subcommand.
- addr is outside the process address space.
CONFORMING TOarch_prctl() is a Linux/x86-64 extension and should not be used in programs intended to be portable.
NOTESarch_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.
SEE ALSOmmap(2), modify_ldt(2), prctl(2), set_thread_area(2)
AMD X86-64 Programmer's manual