struct_user_regset(9) [suse man page]
STRUCT
USER_REGSET(9) Machine State STRUCT USER_REGSET(9) NAME
struct_user_regset - accessible thread CPU state SYNOPSIS
struct user_regset { user_regset_get_fn * get; user_regset_set_fn * set; user_regset_active_fn * active; user_regset_writeback_fn * writeback; unsigned int n; unsigned int size; unsigned int align; unsigned int bias; unsigned int core_note_type; }; MEMBERS
get Function to fetch values. set Function to store values. active Function to report if regset is active, or NULL. writeback Function to write data back to user memory, or NULL. n Number of slots (registers). size Size in bytes of a slot (register). align Required alignment, in bytes. bias Bias from natural indexing. core_note_type ELF note n_type value used in core dumps. DESCRIPTION
This data structure describes a machine resource we call a register set. This is part of the state of an individual thread, not necessarily actual CPU registers per se. A register set consists of a number of similar slots, given by n. Each slot is size bytes, and aligned to align bytes (which is at least size). These functions must be called only on the current thread or on a thread that is in TASK_STOPPED or TASK_TRACED state, that we are guaranteed will not be woken up and return to user mode, and that we have called wait_task_inactive on. (The target thread always might wake up for SIGKILL while these functions are working, in which case that thread's user_regset state might be scrambled.) The pos argument must be aligned according to align; the count argument must be a multiple of size. These functions are not responsible for checking for invalid arguments. When there is a natural value to use as an index, bias gives the difference between the natural index and the slot index for the register set. For example, x86 GDT segment descriptors form a regset; the segment selector produces a natural index, but only a subset of that index space is available as a regset (the TLS slots); subtracting bias from a segment selector index value computes the regset slot. If nonzero, core_note_type gives the n_type field (NT_* value) of the core file note in which this regset's data appears. NT_PRSTATUS is a special case in that the regset data starts at offsetof(struct elf_prstatus, pr_reg) into the note data; that is part of the per-machine ELF formats userland knows about. In other cases, the core file note contains exactly the whole regset (n * size) and nothing else. The core file note is normally omitted when there is an active function and it returns zero. Kernel Hackers Manual 2.6. July 2010 STRUCT USER_REGSET(9)
Check Out this Related Man Page
ARCH_PRCTL(2) Linux Programmer's Manual ARCH_PRCTL(2) 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); int arch_prctl(int code, unsigned long *addr); DESCRIPTION
arch_prctl() sets architecture-specific process or thread state. code selects a subfunction and passes argument addr to it; addr is inter- preted as either an unsigned long for the "set" operations, or as an unsigned long *, for the "get" operations. Subfunctions for x86-64 are: ARCH_SET_FS Set the 64-bit base for the FS register to addr. ARCH_GET_FS Return the 64-bit base value for the FS register of the current thread in the unsigned long pointed to by addr. ARCH_SET_GS Set the 64-bit base for the GS register to addr. ARCH_GET_GS Return the 64-bit base value for the GS register of the current thread in the unsigned long pointed to by addr. RETURN VALUE
On success, arch_prctl() returns 0; on error, -1 is returned, and errno is set to indicate the error. 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. CONFORMING TO
arch_prctl() is a Linux/x86-64 extension and should not be used in programs intended to be portable. NOTES
arch_prctl() is supported only on Linux/x86-64 for 64-bit programs currently. The 64-bit base changes when a new 32-bit segment selector is loaded. ARCH_SET_GS is disabled in some kernels. Context switches for 64-bit segment bases are rather expensive. As an optimization, if a 32-bit TLS base address is used, arch_prctl() may use a real TLS entry as if set_thread_area(2) had been called, instead of manipulating the segment base register directly. Memory in the first 2 GB of address space can be allocated by using mmap(2) with the MAP_32BIT flag. Because of the aforementioned optimization, using arch_prctl() and set_thread_area(2) in the same thread is dangerous, as they may over- write each other's TLS entries. As of version 2.7, 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. Programs that use ARCH_SET_FS directly are very likely to crash. SEE ALSO
mmap(2), modify_ldt(2), prctl(2), set_thread_area(2) AMD X86-64 Programmer's manual COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2017-09-15 ARCH_PRCTL(2)