From 399644e47874bff147afb19c89228901ac39340e Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 15 Apr 2024 21:40:15 +0200 Subject: Adding upstream version 6.05.01. Signed-off-by: Daniel Baumann --- man2/arch_prctl.2 | 176 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 176 insertions(+) create mode 100644 man2/arch_prctl.2 (limited to 'man2/arch_prctl.2') diff --git a/man2/arch_prctl.2 b/man2/arch_prctl.2 new file mode 100644 index 0000000..04a3633 --- /dev/null +++ b/man2/arch_prctl.2 @@ -0,0 +1,176 @@ +.\" Copyright (C) 2003 Andi Kleen +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH arch_prctl 2 2023-03-30 "Linux man-pages 6.05.01" +.SH NAME +arch_prctl \- set architecture-specific thread state +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.BR "#include " " /* Definition of " ARCH_* " constants */" +.BR "#include " " /* Definition of " SYS_* " constants */" +.B #include +.PP +.BI "int syscall(SYS_arch_prctl, int " code ", unsigned long " addr ); +.BI "int syscall(SYS_arch_prctl, int " code ", unsigned long *" addr ); +.fi +.PP +.IR Note : +glibc provides no wrapper for +.BR arch_prctl (), +necessitating the use of +.BR syscall (2). +.SH DESCRIPTION +.BR arch_prctl () +sets architecture-specific process or thread state. +.I code +selects a subfunction +and passes argument +.I addr +to it; +.I addr +is interpreted as either an +.I "unsigned long" +for the "set" operations, or as an +.IR "unsigned long\ *" , +for the "get" operations. +.PP +Subfunctions for both x86 and x86-64 are: +.TP +.BR ARCH_SET_CPUID " (since Linux 4.12)" +.\" commit e9ea1e7f53b852147cbd568b0568c7ad97ec21a3 +Enable +.RI ( "addr != 0" ) +or disable +.RI ( "addr == 0" ) +the +.I cpuid +instruction for the calling thread. +The instruction is enabled by default. +If disabled, any execution of a +.I cpuid +instruction will instead generate a +.B SIGSEGV +signal. +This feature can be used to emulate +.I cpuid +results that differ from what the underlying +hardware would have produced (e.g., in a paravirtualization setting). +.IP +The +.B ARCH_SET_CPUID +setting is preserved across +.BR fork (2) +and +.BR clone (2) +but reset to the default (i.e., +.I cpuid +enabled) on +.BR execve (2). +.TP +.BR ARCH_GET_CPUID " (since Linux 4.12)" +Return the setting of the flag manipulated by +.B ARCH_SET_CPUID +as the result of the system call (1 for enabled, 0 for disabled). +.I addr +is ignored. +.TP +Subfunctions for x86-64 only are: +.TP +.B ARCH_SET_FS +Set the 64-bit base for the +.I FS +register to +.IR addr . +.TP +.B ARCH_GET_FS +Return the 64-bit base value for the +.I FS +register of the calling thread in the +.I unsigned long +pointed to by +.IR addr . +.TP +.B ARCH_SET_GS +Set the 64-bit base for the +.I GS +register to +.IR addr . +.TP +.B ARCH_GET_GS +Return the 64-bit base value for the +.I GS +register of the calling thread in the +.I unsigned long +pointed to by +.IR addr . +.SH RETURN VALUE +On success, +.BR arch_prctl () +returns 0; on error, \-1 is returned, and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EFAULT +.I addr +points to an unmapped address or is outside the process address space. +.TP +.B EINVAL +.I code +is not a valid subcommand. +.TP +.B ENODEV +.B ARCH_SET_CPUID +was requested, but the underlying hardware does not support CPUID faulting. +.TP +.B EPERM +.I addr +is outside the process address space. +.\" .SH AUTHOR +.\" Man page written by Andi Kleen. +.SH STANDARDS +Linux/x86-64. +.SH NOTES +.BR arch_prctl () +is supported only on Linux/x86-64 for 64-bit programs currently. +.PP +The 64-bit base changes when a new 32-bit segment selector is loaded. +.PP +.B ARCH_SET_GS +is disabled in some kernels. +.PP +Context switches for 64-bit segment bases are rather expensive. +As an optimization, if a 32-bit TLS base address is used, +.BR arch_prctl () +may use a real TLS entry as if +.BR 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 +.BR mmap (2) +with the +.B MAP_32BIT +flag. +.PP +Because of the aforementioned optimization, using +.BR arch_prctl () +and +.BR set_thread_area (2) +in the same thread is dangerous, as they may overwrite each other's +TLS entries. +.PP +.I FS +may be already used by the threading library. +Programs that use +.B ARCH_SET_FS +directly are very likely to crash. +.SH SEE ALSO +.BR mmap (2), +.BR modify_ldt (2), +.BR prctl (2), +.BR set_thread_area (2) +.PP +AMD X86-64 Programmer's manual -- cgit v1.2.3