git: 1a62e9bc0046 - main - Add <machine/tls.h> header to hold MD constants and helpers for TLS.

From: John Baldwin <jhb_at_FreeBSD.org>
Date: Thu, 09 Dec 2021 21:23:44 UTC
The branch main has been updated by jhb:

URL: https://cgit.FreeBSD.org/src/commit/?id=1a62e9bc0046bfe20f4dd785561e469ff73fd508

commit 1a62e9bc0046bfe20f4dd785561e469ff73fd508
Author:     John Baldwin <jhb@FreeBSD.org>
AuthorDate: 2021-12-09 21:17:13 +0000
Commit:     John Baldwin <jhb@FreeBSD.org>
CommitDate: 2021-12-09 21:17:13 +0000

    Add <machine/tls.h> header to hold MD constants and helpers for TLS.
    
    The header exports the following:
    
    - Definition of struct tcb.
    - Helpers to get/set the tcb for the current thread.
    - TLS_TCB_SIZE (size of TCB)
    - TLS_TCB_ALIGN (alignment of TCB)
    - TLS_VARIANT_I or TLS_VARIANT_II
    - TLS_DTV_OFFSET (bias of pointers in dtv[])
    - TLS_TP_OFFSET (bias of "thread pointer" relative to TCB)
    
    Note that TLS_TP_OFFSET does not account for if the unbiased thread
    pointer points to the start of the TCB (arm and x86) or the end of the
    TCB (MIPS, PowerPC, and RISC-V).
    
    Note also that for amd64, the struct tcb does not include the unused
    tcb_spare field included in the current structure in libthr.  libthr
    does not use this field, and the existing calls in libc and rtld that
    allocate a TCB for amd64 assume it is the size of 3 Elf_Addr's (and
    thus do not allocate room for tcb_spare).
    
    A <sys/_tls_variant_i.h> header is used by architectures using
    Variant I TLS which uses a common struct tcb.
    
    Reviewed by:    kib (older version of x86/tls.h), jrtc27
    Sponsored by:   The University of Cambridge, Google Inc.
    Differential Revision:  https://reviews.freebsd.org/D33351
---
 sys/amd64/include/tls.h   |  5 +++
 sys/arm/include/tls.h     | 55 ++++++++++++++++++++++++++++++++
 sys/arm64/include/tls.h   | 55 ++++++++++++++++++++++++++++++++
 sys/i386/include/tls.h    |  5 +++
 sys/mips/include/tls.h    | 44 +++++++++++++++++++++----
 sys/powerpc/include/tls.h | 66 ++++++++++++++++++++++++++++++++++++++
 sys/riscv/include/tls.h   | 60 +++++++++++++++++++++++++++++++++++
 sys/sys/_tls_variant_i.h  | 47 +++++++++++++++++++++++++++
 sys/x86/include/tls.h     | 81 +++++++++++++++++++++++++++++++++++++++++++++++
 9 files changed, 412 insertions(+), 6 deletions(-)

diff --git a/sys/amd64/include/tls.h b/sys/amd64/include/tls.h
new file mode 100644
index 000000000000..15a4a407c0e0
--- /dev/null
+++ b/sys/amd64/include/tls.h
@@ -0,0 +1,5 @@
+/*-
+ * This file is in the public domain.
+ */
+
+#include <x86/tls.h>
diff --git a/sys/arm/include/tls.h b/sys/arm/include/tls.h
new file mode 100644
index 000000000000..b3466896eb13
--- /dev/null
+++ b/sys/arm/include/tls.h
@@ -0,0 +1,55 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2005 David Xu <davidxu@freebsd.org>.
+ * All rights reserved.
+ *
+ * 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 AUTHOR ``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 AUTHOR 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.
+ */
+
+#ifndef _MACHINE_TLS_H_
+#define	_MACHINE_TLS_H_
+
+#include <sys/_tls_variant_i.h>
+#include <machine/sysarch.h>
+
+#define	TLS_DTV_OFFSET	0
+#define	TLS_TCB_ALIGN	8
+#define	TLS_TP_OFFSET	0
+
+static __inline void
+_tcb_set(struct tcb *tcb)
+{
+	sysarch(ARM_SET_TP, tcb);
+}
+
+static __inline struct tcb *
+_tcb_get(void)
+{
+	struct tcb *tcb;
+
+	__asm __volatile("mrc  p15, 0, %0, c13, c0, 3"		\
+	   		 : "=r" (tcb));
+	return (tcb);
+}
+
+#endif /* !_MACHINE_TLS_H_ */
diff --git a/sys/arm64/include/tls.h b/sys/arm64/include/tls.h
new file mode 100644
index 000000000000..a3ec7f7952e8
--- /dev/null
+++ b/sys/arm64/include/tls.h
@@ -0,0 +1,55 @@
+/*-
+ * Copyright (c) 2005 David Xu <davidxu@freebsd.org>.
+ * Copyright (c) 2014 the FreeBSD Foundation
+ * All rights reserved.
+ *
+ * Portions of this software were developed by Andrew Turner
+ * under sponsorship from the FreeBSD Foundation
+ *
+ * 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 AUTHOR ``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 AUTHOR 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.
+ */
+
+#ifndef _MACHINE_TLS_H_
+#define	_MACHINE_TLS_H_
+
+#include <sys/_tls_variant_i.h>
+
+#define	TLS_DTV_OFFSET	0
+#define	TLS_TCB_ALIGN	16
+#define	TLS_TP_OFFSET	0
+
+static __inline void
+_tcb_set(struct tcb *tcb)
+{
+	__asm __volatile("msr	tpidr_el0, %x0" :: "r" (tcb));
+}
+
+static __inline struct tcb *
+_tcb_get(void)
+{
+	struct tcb *tcb;
+
+	__asm __volatile("mrs	%x0, tpidr_el0" : "=r" (tcb));
+	return (tcb);
+}
+
+#endif /* !_MACHINE_TLS_H_ */
diff --git a/sys/i386/include/tls.h b/sys/i386/include/tls.h
new file mode 100644
index 000000000000..15a4a407c0e0
--- /dev/null
+++ b/sys/i386/include/tls.h
@@ -0,0 +1,5 @@
+/*-
+ * This file is in the public domain.
+ */
+
+#include <x86/tls.h>
diff --git a/sys/mips/include/tls.h b/sys/mips/include/tls.h
index c71507b773b0..c209983027b1 100644
--- a/sys/mips/include/tls.h
+++ b/sys/mips/include/tls.h
@@ -34,20 +34,52 @@
 #ifndef	__MIPS_TLS_H__
 #define	__MIPS_TLS_H__
 
+#include <sys/_tls_variant_i.h>
+#include <machine/sysarch.h>
+
 /*
  * TLS parameters
  */
 
-#define TLS_TP_OFFSET	0x7000
-#define TLS_DTV_OFFSET	0x8000
+#define	TLS_DTV_OFFSET	0x8000
+#define	TLS_TCB_ALIGN	8
+#define	TLS_TP_OFFSET	0x7000
 
-#ifdef __mips_n64
-#define TLS_TCB_SIZE	16
 #ifdef COMPAT_FREEBSD32
-#define TLS_TCB_SIZE32	8
+#define	TLS_TCB_SIZE32	8
 #endif
+
+#ifndef _KERNEL
+
+static __inline void
+_tcb_set(struct tcb *tcb)
+{
+	sysarch(MIPS_SET_TLS, tcb);
+}
+
+static __inline struct tcb *
+_tcb_get(void)
+{
+	struct tcb *tcb;
+
+#ifdef TLS_USE_SYSARCH
+	sysarch(MIPS_GET_TLS, &tcb);
 #else
-#define TLS_TCB_SIZE	8
+	__asm__ __volatile__ (
+	    ".set\tpush\n\t"
+#ifdef __mips_n64
+	    ".set\tmips64r2\n\t"
+#else
+	    ".set\tmips32r2\n\t"
+#endif
+	    "rdhwr\t%0, $29\n\t"
+	    ".set\tpop"
+	    : "=r" (tcb));
+	tcb = (struct tcb *)((uintptr_t)tcb - TLS_TP_OFFSET - TLS_TCB_SIZE);
+#endif
+	return (tcb);
+}
+
 #endif
 
 #endif	/* __MIPS_TLS_H__ */
diff --git a/sys/powerpc/include/tls.h b/sys/powerpc/include/tls.h
new file mode 100644
index 000000000000..745a83a910c4
--- /dev/null
+++ b/sys/powerpc/include/tls.h
@@ -0,0 +1,66 @@
+/*-
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
+ * Copyright 2004 by Peter Grehan. All rights reserved.
+ *
+ * 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.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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.
+ */
+
+#ifndef _MACHINE_TLS_H_
+#define	_MACHINE_TLS_H_
+
+#include <sys/_tls_variant_i.h>
+
+#define	TLS_DTV_OFFSET	0x8000
+#define	TLS_TCB_ALIGN	TLS_TCB_SIZE
+#define	TLS_TP_OFFSET	0x7000
+
+static __inline void
+_tcb_set(struct tcb *tcb)
+{
+#ifdef __powerpc64__
+	__asm __volatile("mr 13,%0" ::
+	    "r" ((uint8_t *)tcb + TLS_TP_OFFSET + TLS_TCB_SIZE));
+#else
+	__asm __volatile("mr 2,%0" ::
+	    "r" ((uint8_t *)tcb + TLS_TP_OFFSET + TLS_TCB_SIZE));
+#endif
+}
+
+static __inline struct tcb *
+_tcb_get(void)
+{
+	struct tcb *tcb;
+
+#ifdef __powerpc64__
+	__asm __volatile("addi %0,13,%1" : "=r" (tcb) :
+	    "i" (-(TLS_TP_OFFSET + TLS_TCB_SIZE)));
+#else
+	__asm __volatile("addi %0,2,%1" : "=r" (tcb) :
+	    "i" (-(TLS_TP_OFFSET + TLS_TCB_SIZE)));
+#endif
+	return (tcb);
+}
+
+#endif /* !_MACHINE_TLS_H_ */
diff --git a/sys/riscv/include/tls.h b/sys/riscv/include/tls.h
new file mode 100644
index 000000000000..4dd1fa8415ef
--- /dev/null
+++ b/sys/riscv/include/tls.h
@@ -0,0 +1,60 @@
+/*-
+ * Copyright (c) 2005 David Xu <davidxu@freebsd.org>
+ * Copyright (c) 2015 Ruslan Bukin <br@bsdpad.com>
+ * All rights reserved.
+ *
+ * Portions of this software were developed by SRI International and the
+ * University of Cambridge Computer Laboratory under DARPA/AFRL contract
+ * FA8750-10-C-0237 ("CTSRD"), as part of the DARPA CRASH research programme.
+ *
+ * Portions of this software were developed by the University of Cambridge
+ * Computer Laboratory as part of the CTSRD Project, with support from the
+ * UK Higher Education Innovation Fund (HEIF).
+ *
+ * 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 AUTHOR 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 AUTHOR 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.
+ */
+
+#ifndef _MACHINE_TLS_H_
+#define	_MACHINE_TLS_H_
+
+#include <sys/_tls_variant_i.h>
+
+#define	TLS_DTV_OFFSET	0x800
+#define	TLS_TCB_ALIGN	16
+#define	TLS_TP_OFFSET	0
+
+static __inline void
+_tcb_set(struct tcb *tcb)
+{
+	__asm __volatile("addi tp, %0, %1" :: "r" (tcb), "I" (TLS_TCB_SIZE));
+}
+
+static __inline struct tcb *
+_tcb_get(void)
+{
+	struct tcb *tcb;
+
+	__asm __volatile("addi %0, tp, %1" : "=r" (tcb) : "I" (-TLS_TCB_SIZE));
+	return (tcb);
+}
+
+#endif /* !_MACHINE_TLS_H_ */
diff --git a/sys/sys/_tls_variant_i.h b/sys/sys/_tls_variant_i.h
new file mode 100644
index 000000000000..0f83f121cc41
--- /dev/null
+++ b/sys/sys/_tls_variant_i.h
@@ -0,0 +1,47 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (c) 2005 David Xu <davidxu@freebsd.org>.
+ * All rights reserved.
+ *
+ * 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 AUTHOR ``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 AUTHOR 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.
+ */
+
+#ifndef _SYS_TLS_VARIANT_I_H_
+#define	_SYS_TLS_VARIANT_I_H_
+
+/*
+ * Variant I TLS uses the same TCB layout across architectures.
+ */
+
+#define	TLS_VARIANT_I
+
+struct pthread;
+
+struct tcb {
+	uintptr_t		*tcb_dtv;	/* required by rtld */
+	struct pthread		*tcb_thread;
+};
+
+#define	TLS_TCB_SIZE	sizeof(struct tcb)
+
+#endif /* !_SYS_TLS_VARIANT_I_H_ */
diff --git a/sys/x86/include/tls.h b/sys/x86/include/tls.h
new file mode 100644
index 000000000000..d4b631de10d0
--- /dev/null
+++ b/sys/x86/include/tls.h
@@ -0,0 +1,81 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (C) 2003 David Xu <davidxu@freebsd.org>
+ * Copyright (c) 2001 Daniel Eischen <deischen@freebsd.org>
+ * All rights reserved.
+ *
+ * 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. Neither the name of the author nor the names of its contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
+ */
+
+#ifndef _MACHINE_TLS_H_
+#define	_MACHINE_TLS_H_
+
+#include <x86/sysarch.h>
+
+#define	TLS_VARIANT_II
+
+struct pthread;
+
+/*
+ * Variant II tcb, first two members are required by rtld,
+ * %fs (amd64) / %gs (i386) points to the structure.
+ */
+struct tcb {
+	struct tcb		*tcb_self;	/* required by rtld */
+	uintptr_t		*tcb_dtv;	/* required by rtld */
+	struct pthread		*tcb_thread;
+};
+
+#define	TLS_DTV_OFFSET	0
+#ifdef __amd64__
+#define	TLS_TCB_ALIGN	16
+#else
+#define	TLS_TCB_ALIGN	4
+#endif
+#define	TLS_TCB_SIZE	sizeof(struct tcb)
+#define	TLS_TP_OFFSET	0
+
+static __inline void
+_tcb_set(struct tcb *tcb)
+{
+#ifdef __amd64__
+	amd64_set_fsbase(tcb);
+#else
+ 	i386_set_gsbase(tcb);
+#endif
+}
+
+static __inline struct tcb *
+_tcb_get(void)
+{
+	struct tcb *tcb;
+
+#ifdef __amd64__
+	__asm __volatile("movq %%fs:0, %0" : "=r" (tcb));
+#else
+	__asm __volatile("movl %%gs:0, %0" : "=r" (tcb));
+#endif
+	return (tcb);
+}
+
+#endif /* !_MACHINE_TLS_H_ */