NAME
i386_get_gsbase,
i386_set_gsbase —
manage i386 per-thread %gs base
address
SYNOPSIS
#include
<sys/types.h>
#include
<machine/sysarch.h>
int
i386_get_gsbase(void
**base);
int
i386_set_gsbase(void
*base);
DESCRIPTION
i386_get_gsbase()
copies the current base address of the segment that, by default, is
referenced by the %gs selector into the memory referenced by
base.
i386_set_gsbase()
sets the base address of the segment that, by default, is referenced by %gs
to the address base.
The segment base address is local to each thread. The initial thread of a new process inherits its segment base address from the parent thread. __tfork(3) sets the initial segment base address for threads that it creates.
Note:
Code using the
i386_get_gsbase()
and i386_set_gsbase() functions must be compiled
using -li386.
RETURN VALUES
Upon successful completion,
i386_get_gsbase() and
i386_set_gsbase() return 0. Otherwise, a value of -1
is returned and the global variable errno is set to
indicate the error.
ERRORS
i386_get_gsbase() will fail if:
- [
EFAULT] - base points outside the process's allocated address space.
SEE ALSO
Intel, i386 Microprocessor Programmer's Reference Manual.
WARNING
The ELF Thread-Local Storage ABI reserves %gs for its own use and
requires that the dynamic linker and thread library set it to reference
data-structures internal to and shared between them. Programs should use the
__thread storage class keyword instead of using these calls. To be maximally
portable, programs that require per-thread data should use the
pthread_key_create()
interface.