arch_prctl(2) -- Linux man page
NAMEarch_prctl - set architecture specific thread state
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.
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.
No prototype for arch_prctl in glibc 2.2. You have to declare it yourself for now. This will be fixed in future glibc versions.
- code is not a valid subcommand.
- addr is outside the process address space.
- addr points to an unmapped address or is outside the process address space.
AUTHORMan page written by Andi Kleen.
CONFORMANCEarch_prctl is a Linux/x86-64 extension and should not be used in programs intended to be portable.
SEE ALSOmmap(2), modify_ldt(2), prctl(2), set_thread_area(2)
AMD X86-64 Programmer's manual