> some software needs fully functional per-thread %gs base address,
> hence the diff. limited testing shows no regressions.
> INTR_RESTORE_SELECTORS changes include:
> - %r11 is used to store curpcb instead of rdx that is used for
> wrmsr and gets trashed (it's safe to use %r11 because it's
> restored after INTR_RESTORE_SELECTORS gets called);
>
> - MSR_KERNELGSBASE needs to be updated instead of MSR_GSBASE
> so that we don't lose kernel gs.base stored in MSR_GSBASE
> and swapped by the swapgs.
>
> any objections? corrections?
>
> Index: sys/arch/amd64/amd64/cpu.c
> ===================================================================
> RCS file: /home/cvs/src/sys/arch/amd64/amd64/cpu.c,v
> retrieving revision 1.47
> diff -u -p -r1.47 cpu.c
> --- sys/arch/amd64/amd64/cpu.c 4 Apr 2012 18:44:22 -0000 1.47
> +++ sys/arch/amd64/amd64/cpu.c 13 Apr 2012 15:26:51 -0000
> @@ -682,6 +684,7 @@ cpu_init_msrs(struct cpu_info *ci)
> wrmsr(MSR_SFMASK, PSL_NT|PSL_T|PSL_I|PSL_C);
>
> ci->ci_cur_fsbase = 0;
> + ci->ci_cur_gsbase = (u_int64_t)ci;
> wrmsr(MSR_FSBASE, 0);
> wrmsr(MSR_GSBASE, (u_int64_t)ci);
> wrmsr(MSR_KERNELGSBASE, 0);
> Index: sys/arch/amd64/amd64/genassym.cf
> ===================================================================
> RCS file: /home/cvs/src/sys/arch/amd64/amd64/genassym.cf,v
> retrieving revision 1.28
> diff -u -p -r1.28 genassym.cf
> --- sys/arch/amd64/amd64/genassym.cf 13 Apr 2011 02:49:12 -0000 1.28
> +++ sys/arch/amd64/amd64/genassym.cf 13 Apr 2012 15:25:26 -0000
> @@ -86,6 +86,7 @@ member pcb_rsp
> member pcb_rbp
> member pcb_kstack
> member pcb_fsbase
> +member pcb_gsbase
> member pcb_onfault
> member pcb_fpcpu
> member pcb_pmap
> @@ -100,6 +101,7 @@ member tss_rsp0
> struct cpu_info
> member CPU_INFO_SCRATCH ci_scratch
> member CPU_INFO_CUR_FSBASE ci_cur_fsbase
> +member CPU_INFO_CUR_GSBASE ci_cur_gsbase
> member CPU_INFO_SELF ci_self
> member CPU_INFO_CPUID ci_cpuid
> member CPU_INFO_APICID ci_apicid
> Index: sys/arch/amd64/amd64/machdep.c
> ===================================================================
> RCS file: /home/cvs/src/sys/arch/amd64/amd64/machdep.c,v
> retrieving revision 1.152
> diff -u -p -r1.152 machdep.c
> --- sys/arch/amd64/amd64/machdep.c 13 Jan 2012 12:55:52 -0000 1.152
> +++ sys/arch/amd64/amd64/machdep.c 12 Apr 2012 16:41:18 -0000
> @@ -363,7 +363,7 @@ x86_64_proc0_tss_ldt_init(void)
>
> cpu_info_primary.ci_curpcb = pcb = &proc0.p_addr->u_pcb;
> pcb->pcb_cr0 = rcr0();
> - pcb->pcb_fsbase = 0;
> + pcb->pcb_fsbase = pcb->pcb_gsbase = 0;
> pcb->pcb_kstack = (u_int64_t)proc0.p_addr + USPACE - 16;
> proc0.p_md.md_regs = (struct trapframe *)pcb->pcb_kstack - 1;
>
> @@ -1022,6 +1022,7 @@ setregs(struct proc *p, struct exec_pack
> fpusave_proc(p, 0);
> p->p_md.md_flags &= ~MDP_USEDFPU;
> p->p_addr->u_pcb.pcb_fsbase = 0;
> + p->p_addr->u_pcb.pcb_gsbase = 0;
>
> tf = p->p_md.md_regs;
> tf->tf_ds = GSEL(GUDATA_SEL, SEL_UPL);
> Index: sys/arch/amd64/amd64/sys_machdep.c
> ===================================================================
> RCS file: /home/cvs/src/sys/arch/amd64/amd64/sys_machdep.c,v
> retrieving revision 1.12
> diff -u -p -r1.12 sys_machdep.c
> --- sys/arch/amd64/amd64/sys_machdep.c 13 Apr 2011 02:49:12 -0000
> 1.12
> +++ sys/arch/amd64/amd64/sys_machdep.c 12 Apr 2012 16:37:30 -0000
> @@ -159,6 +159,29 @@ amd64_set_fsbase(struct proc *p, void *a
> }
>
> int
> +amd64_get_gsbase(struct proc *p, void *args)
> +{
> + return copyout(&p->p_addr->u_pcb.pcb_gsbase, args,
> + sizeof(p->p_addr->u_pcb.pcb_gsbase));
> +}
> +
> +int
> +amd64_set_gsbase(struct proc *p, void *args)
> +{
> + int error;
> + uint64_t base;
> +
> + if ((error = copyin(args, &base, sizeof(base))) != 0)
> + return (error);
> +
> + if (base >= VM_MAXUSER_ADDRESS)
> + return (EINVAL);
> +
> + p->p_addr->u_pcb.pcb_gsbase = base;
> + return 0;
> +}
> +
> +int
> sys_sysarch(struct proc *p, void *v, register_t *retval)
> {
> struct sys_sysarch_args /* {
> @@ -196,12 +219,20 @@ sys_sysarch(struct proc *p, void *v, reg
> break;
> #endif
>
> - case AMD64_GET_FSBASE:
> + case AMD64_GET_FSBASE:
> error = amd64_get_fsbase(p, SCARG(uap, parms));
> break;
>
> - case AMD64_SET_FSBASE:
> + case AMD64_SET_FSBASE:
> error = amd64_set_fsbase(p, SCARG(uap, parms));
> + break;
> +
> + case AMD64_GET_GSBASE:
> + error = amd64_get_gsbase(p, SCARG(uap, parms));
> + break;
> +
> + case AMD64_SET_GSBASE:
> + error = amd64_set_gsbase(p, SCARG(uap, parms));
> break;
>
> default:
> Index: sys/arch/amd64/include/cpu.h
> ===================================================================
> RCS file: /home/cvs/src/sys/arch/amd64/include/cpu.h,v
> retrieving revision 1.72
> diff -u -p -r1.72 cpu.h
> --- sys/arch/amd64/include/cpu.h 4 Apr 2012 18:44:22 -0000 1.72
> +++ sys/arch/amd64/include/cpu.h 13 Apr 2012 15:25:13 -0000
> @@ -73,6 +73,7 @@ struct cpu_info {
>
> u_int64_t ci_scratch;
> u_int64_t ci_cur_fsbase;
> + u_int64_t ci_cur_gsbase;
>
> struct proc *ci_fpcurproc;
> struct proc *ci_fpsaveproc;
> Index: sys/arch/amd64/include/frameasm.h
> ===================================================================
> RCS file: /home/cvs/src/sys/arch/amd64/include/frameasm.h,v
> retrieving revision 1.6
> diff -u -p -r1.6 frameasm.h
> --- sys/arch/amd64/include/frameasm.h 4 Jul 2011 15:54:24 -0000
> 1.6
> +++ sys/arch/amd64/include/frameasm.h 13 Apr 2012 19:15:51 -0000
> @@ -56,16 +56,16 @@
>
> /*
> * Restore %ds, %es, %fs, and %gs, dealing with the FS.base MSR for
> - * %fs and doing the cli/swapgs for %gs. Uses %rax, %rcx, and %rdx
> + * %fs and doing the cli/swapgs for %gs. Uses %rax, %rcx, %rdx and %r11
> */
> #define INTR_RESTORE_SELECTORS
> \
> - movq CPUVAR(CURPCB),%rdx /* for below */ ; \
> + movq CPUVAR(CURPCB),%r11 /* for below */ ; \
> /* %es and %ds */ \
> movw TF_ES(%rsp),%es ; \
> movw $(GSEL(GUDATA_SEL, SEL_UPL)),%ax ; \
> movw %ax,%ds ; \
> /* Make sure both %fs and FS.base are the desired values */ \
> - movq PCB_FSBASE(%rdx),%rax ; \
> + movq PCB_FSBASE(%r11),%rax ; \
> cmpq $0,%rax ; \
> jne 96f ; \
> movw TF_FS(%rsp),%fs /* zero FS.base by setting %fs */ ; \
> @@ -81,7 +81,20 @@
> movl $MSR_FSBASE,%ecx ; \
> wrmsr ; \
> 98: movq %rax,CPUVAR(CUR_FSBASE) ; \
> -99: cli /* %fs done, so swapgs and do %gs */ ; \
> +99: /* Make sure GS.base is reset */ ; \
> + movq PCB_GSBASE(%r11),%rax ; \
> + cmpq $0,%rax ; \
> + jne 100f ; \
> + movq %rax,CPUVAR(CUR_GSBASE) ; \
> + jmp 101f ; \
> +100: cmpq CPUVAR(CUR_GSBASE),%rax
> ; \
> + je 101f ; \
> + movq %rax,CPUVAR(CUR_GSBASE) ; \
> + movq %rax,%rdx ; \
> + shrq $32,%rdx ; \
> + movl $MSR_KERNELGSBASE,%ecx ; \
> + wrmsr ; \
> +101: cli /* %gs done, do swapgs */
> ; \
> swapgs ; \
> movw TF_GS(%rsp),%gs
>
> Index: sys/arch/amd64/include/pcb.h
> ===================================================================
> RCS file: /home/cvs/src/sys/arch/amd64/include/pcb.h,v
> retrieving revision 1.12
> diff -u -p -r1.12 pcb.h
> --- sys/arch/amd64/include/pcb.h 10 Jul 2011 18:12:03 -0000 1.12
> +++ sys/arch/amd64/include/pcb.h 12 Apr 2012 17:28:16 -0000
> @@ -83,18 +83,19 @@ struct pcb {
> u_int64_t pcb_rbp;
> u_int64_t pcb_kstack; /* kernel stack address */
> u_int64_t pcb_fsbase; /* per-thread offset: %fs */
> + u_int64_t pcb_gsbase; /* per-thread offset: %gs */
> caddr_t pcb_onfault; /* copyin/out fault recovery */
> struct cpu_info *pcb_fpcpu; /* cpu holding our fp state. */
> struct pmap *pcb_pmap; /* back pointer to our pmap */
> int pcb_cr0; /* saved image of CR0 */
> };
>
> -/*
> - * The pcb is augmented with machine-dependent additional data for
> +/*
> + * The pcb is augmented with machine-dependent additional data for
> * core dumps. For the i386, there is nothing to add.
> - */
> + */
> struct md_coredump {
> long md_pad[8];
> -};
> +};
>
> #endif /* _MACHINE_PCB_H_ */
> Index: sys/arch/amd64/include/sysarch.h
> ===================================================================
> RCS file: /home/cvs/src/sys/arch/amd64/include/sysarch.h,v
> retrieving revision 1.10
> diff -u -p -r1.10 sysarch.h
> --- sys/arch/amd64/include/sysarch.h 13 Apr 2011 02:49:12 -0000 1.10
> +++ sys/arch/amd64/include/sysarch.h 12 Apr 2012 20:57:34 -0000
> @@ -16,6 +16,8 @@
> #define AMD64_PMC_READ 10
> #define AMD64_GET_FSBASE 11
> #define AMD64_SET_FSBASE 12
> +#define AMD64_GET_GSBASE 13
> +#define AMD64_SET_GSBASE 14
>
> struct amd64_iopl_args {
> int iopl;
> @@ -67,6 +69,8 @@ struct amd64_pmc_read_args {
> int amd64_iopl(struct proc *, void *, register_t *);
> int amd64_set_fsbase(struct proc *, void *);
> int amd64_get_fsbase(struct proc *, void *);
> +int amd64_set_gsbase(struct proc *, void *);
> +int amd64_get_gsbase(struct proc *, void *);
> #else
> int amd64_iopl(int);
> int amd64_get_ioperm(u_long *);
> @@ -76,6 +80,8 @@ int amd64_pmc_startstop(struct amd64_pmc
> int amd64_pmc_read(struct amd64_pmc_read_args *);
> int amd64_set_fsbase(void *);
> int amd64_get_fsbase(void **);
> +int amd64_set_gsbase(void *);
> +int amd64_get_gsbase(void **);
> int sysarch(int, void *);
> #endif
>
> Index: lib/libarch/amd64/Makefile
> ===================================================================
> RCS file: /home/cvs/src/lib/libarch/amd64/Makefile,v
> retrieving revision 1.10
> diff -u -p -r1.10 Makefile
> --- lib/libarch/amd64/Makefile 13 Apr 2011 02:49:12 -0000 1.10
> +++ lib/libarch/amd64/Makefile 13 Apr 2012 19:20:17 -0000
> @@ -3,15 +3,17 @@
>
> MANSUBDIR=amd64
> MAN+= amd64_iopl.2 amd64_get_ioperm.2 \
> - amd64_get_fsbase.2
> + amd64_get_fsbase.2 amd64_get_gsbase.2
> MLINKS+=amd64_get_ioperm.2 amd64_set_ioperm.2 \
> - amd64_get_fsbase.2 amd64_set_fsbase.2
> + amd64_get_fsbase.2 amd64_set_fsbase.2 \
> + amd64_get_gsbase.2 amd64_set_gsbase.2
>
> .if ${MACHINE_ARCH} == "amd64"
> .PATH: ${LIBC}/amd64
> NOPIC=
> SRCS+= amd64_iopl.c amd64_get_ioperm.c amd64_set_ioperm.c \
> - amd64_get_fsbase.c amd64_set_fsbase.c
> + amd64_get_fsbase.c amd64_set_fsbase.c \
> + amd64_get_gsbase.c amd64_set_gsbase.c
> .include <bsd.lib.mk>
> .else
> NOPROG=
> Index: lib/libarch/amd64/amd64_get_gsbase.2
> ===================================================================
> RCS file: lib/libarch/amd64/amd64_get_gsbase.2
> diff -N lib/libarch/amd64/amd64_get_gsbase.2
> --- /dev/null 1 Jan 1970 00:00:00 -0000
> +++ lib/libarch/amd64/amd64_get_gsbase.2 13 Apr 2012 19:24:18 -0000
> @@ -0,0 +1,87 @@
> +.\" $OpenBSD$
> +.\" $NetBSD: i386_get_ioperm.2,v 1.3 1996/02/27 22:57:17 jtc Exp $
> +.\"
> +.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
> +.\" All rights reserved.
> +.\"
> +.\" This code is derived from software contributed to The NetBSD
> Foundation
> +.\" by John T. Kohl and Charles M. Hannum.
> +.\"
> +.\" Redistribution and use in source and binary forms, with or without
> +.\" modification, are permitted provided that the following conditions
> +.\" are met:
> +.\" 1. Redistributions of source code must retain the above copyright
> +.\" notice, this list of conditions and the following disclaimer.
> +.\" 2. Redistributions in binary form must reproduce the above copyright
> +.\" notice, this list of conditions and the following disclaimer in
> the
> +.\" documentation and/or other materials provided with the
> distribution.
> +.\"
> +.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND
> CONTRIBUTORS
> +.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
> LIMITED
> +.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
> PARTICULAR
> +.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR
> CONTRIBUTORS BE
> +.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
> +.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
> +.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
> BUSINESS
> +.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
> IN
> +.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
> OTHERWISE)
> +.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
> OF THE
> +.\" POSSIBILITY OF SUCH DAMAGE.
> +.\"
> +.Dd $Mdocdate$
> +.Dt AMD64_GET_GSBASE 2 amd64
> +.Os
> +.Sh NAME
> +.Nm amd64_get_gsbase ,
> +.Nm amd64_set_gsbase
> +.Nd manage amd64 per-thread %gs base address
> +.Sh SYNOPSIS
> +.Fd #include <sys/types.h>
> +.Fd #include <machine/sysarch.h>
> +.Ft int
> +.Fn amd64_get_gsbase "void **base"
> +.Ft int
> +.Fn amd64_set_gsbase "void *base"
> +.Sh DESCRIPTION
> +.Fn amd64_get_gsbase
> +copies the current base address of the %gs segment into the memory
> +referenced by
> +.Fa base .
> +.Pp
> +.Fn amd64_set_gsbase
> +sets the base address of the %gs segment to the address
> +.Fa base .
> +.Pp
> +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.
> +.Xr __tfork 2
> +sets the initial segment base address for threads that it creates.
> +.Pp
> +.Sy Note:
> +Code using the
> +.Fn amd64_get_gsbase
> +and
> +.Fn amd64_set_gsbase
> +functions must be compiled using
> +.Cm -lamd64 .
> +.Sh RETURN VALUES
> +Upon successful completion,
> +.Fn amd64_get_gsbase
> +and
> +.Fn amd64_set_gsbase
> +return 0.
> +Otherwise, a value of \-1 is returned and the global variable
> +.Va errno
> +is set to indicate the error.
> +.Sh ERRORS
> +.Fn amd64_get_gsbase
> +will fail if:
> +.Bl -tag -width [EINVAL]
> +.It Bq Er EFAULT
> +.Fa base
> +points outside the process's allocated address space.
> +.El
> +.Sh SEE ALSO
> +.Xr __tfork 2 ,
> +.Xr fork 2
> Index: lib/libarch/amd64/amd64_get_gsbase.c
> ===================================================================
> RCS file: lib/libarch/amd64/amd64_get_gsbase.c
> diff -N lib/libarch/amd64/amd64_get_gsbase.c
> --- /dev/null 1 Jan 1970 00:00:00 -0000
> +++ lib/libarch/amd64/amd64_get_gsbase.c 13 Apr 2012 19:28:32 -0000
> @@ -0,0 +1,15 @@
> +/* $OpenBSD$ */
> +
> +/* Public domain. Written by Mike Belopuhov <mi...@openbsd.org> */
> +
> +#include <sys/cdefs.h>
> +#include <sys/types.h>
> +
> +#include <machine/segments.h>
> +#include <machine/sysarch.h>
> +
> +int
> +amd64_get_gsbase(void **base)
> +{
> + return sysarch(AMD64_GET_GSBASE, base);
> +}
> Index: lib/libarch/amd64/amd64_set_gsbase.c
> ===================================================================
> RCS file: lib/libarch/amd64/amd64_set_gsbase.c
> diff -N lib/libarch/amd64/amd64_set_gsbase.c
> --- /dev/null 1 Jan 1970 00:00:00 -0000
> +++ lib/libarch/amd64/amd64_set_gsbase.c 13 Apr 2012 19:28:19 -0000
> @@ -0,0 +1,15 @@
> +/* $OpenBSD$ */
> +
> +/* Public domain. Written by Mike Belopuhov <mi...@openbsd.org> */
> +
> +#include <sys/cdefs.h>
> +#include <sys/types.h>
> +
> +#include <machine/segments.h>
> +#include <machine/sysarch.h>
> +
> +int
> +amd64_set_gsbase(void *base)
> +{
> + return sysarch(AMD64_SET_GSBASE, &base);
> +}
> Index: lib/libpthread/Makefile
> ===================================================================
> RCS file: /home/cvs/src/regress/lib/libpthread/Makefile,v
> retrieving revision 1.38
> diff -u -p -r1.38 Makefile
> --- lib/libpthread/Makefile 13 Apr 2012 19:04:09 -0000 1.38
> +++ lib/libpthread/Makefile 14 Apr 2012 10:27:30 -0000
> @@ -12,6 +12,9 @@ SUBDIR= barrier blocked_close blocked_du
> readdir restart select semaphore setjmp setsockopt sigdeliver siginfo \
> siginterrupt signal signals signodefer sigsuspend sigwait sleep \
> socket stack stdarg stdio switch system
> +.if ${MACHINE_ARCH} == "amd64"
> +SUBDIR+=amd64_set_gsbase
> +.endif
>
> # Not available or disabled: fcntl, getaddrinfo, pause, pw, sigmask,
> stdfiles
>
> Index: lib/libpthread/amd64_set_gsbase/Makefile
> ===================================================================
> RCS file: lib/libpthread/amd64_set_gsbase/Makefile
> diff -N lib/libpthread/amd64_set_gsbase/Makefile
> --- /dev/null 1 Jan 1970 00:00:00 -0000
> +++ lib/libpthread/amd64_set_gsbase/Makefile 14 Apr 2012 10:54:33 -0000
> @@ -0,0 +1,10 @@
> +# $OpenBSD$
> +
> +PROG= amd64_set_gsbase
> +
> +LIBARCH= /usr/lib/libamd64.a
> +
> +LDADD+= ${LIBARCH}
> +DPADD+= ${LIBARCH}
> +
> +.include <bsd.regress.mk>
> Index: lib/libpthread/amd64_set_gsbase/amd64_set_gsbase.c
> ===================================================================
> RCS file: lib/libpthread/amd64_set_gsbase/amd64_set_gsbase.c
> diff -N lib/libpthread/amd64_set_gsbase/amd64_set_gsbase.c
> --- /dev/null 1 Jan 1970 00:00:00 -0000
> +++ lib/libpthread/amd64_set_gsbase/amd64_set_gsbase.c 14 Apr 2012
> 11:25:53 -0000
> @@ -0,0 +1,52 @@
> +/* $OpenBSD$ */
> +
> +/*
> + * Public domain. Written by Mike Belopuhov.
> + *
> + * Test amd64_set_gsbase and amd64_get_gsbase
> + */
> +
> +#include <sys/types.h>
> +#include <machine/sysarch.h>
> +#include <pthread.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include "test.h"
> +
> +#define NTHREADS 128
> +
> +void *
> +new_thread(void *arg)
> +{
> + int *val = NULL;
> +
> + amd64_set_gsbase(arg);
> +
> + pthread_yield();
> + sleep(arc4random_uniform(10));
> + pthread_yield();
> +
> + amd64_get_gsbase((void **)&val);
> +
> + ASSERT(val == arg);
> +
> + return (NULL);
> +}
> +
> +int
> +main(int argc, char *argv[])
> +{
> + pthread_t threads[NTHREADS];
> + int vals[NTHREADS];
> + int i;
> +
> + for (i = 0; i < NTHREADS; i++) {
> + CHECKr(pthread_create(&threads[i], NULL, new_thread,
> + (void *)&vals[i]));
> + }
> + for (i = 0; i < NTHREADS; i++) {
> + CHECKr(pthread_join(threads[i], NULL));
> + }
> + SUCCEED;
> +}
