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NAME

        arch_prctl - set architecture specific thread state
 

SYNOPSIS

        #include <asm/prctl.h>
 
        #include <sys/prctl.h>
 
        int arch_prctl(int code, unsigned long addr)
 

DESCRIPTION

        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.
 

NOTES

        arch_prctl()  is only supported on Linux/x86-64 for 64bit programs cur‐
        rently.
 
        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
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
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.
 

ERRORS

        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.
 

AUTHOR

        Man page written by Andi Kleen.
        arch_prctl() is a Linux/x86-64 extension and should not be used in pro‐
        grams intended to be portable.
set_thread_area(2)
 
        AMD X86-64 Programmer’s manual
 

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