libc/private/bionic_tls.h

/*
 * Copyright (C) 2008 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * 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 COPYRIGHT HOLDERS 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
 * COPYRIGHT OWNER 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 _SYS_TLS_H
#define _SYS_TLS_H

#include <sys/cdefs.h>

__BEGIN_DECLS

/** WARNING WARNING WARNING
 **
 ** This header file is *NOT* part of the public Bionic ABI/API
 ** and should not be used/included by user-serviceable parts of
 ** the system (e.g. applications).
 **
 ** It is only provided here for the benefit of the system dynamic
 ** linker and the OpenGL sub-system (which needs to access the
 ** pre-allocated slot directly for performance reason).
 **/

/* maximum number of elements in the TLS array */
#define BIONIC_TLS_SLOTS            64

/* note that slot 0, called TLS_SLOT_SELF must point to itself.
 * this is required to implement thread-local storage with the x86
 * Linux kernel, that reads the TLS from fs:[0], where 'fs' is a
 * thread-specific segment descriptor...
 */

/* Well known TLS slots */
#define TLS_SLOT_SELF               0
#define TLS_SLOT_THREAD_ID          1
#define TLS_SLOT_ERRNO              2

#define TLS_SLOT_OPENGL_API         3
#define TLS_SLOT_OPENGL             4

/* this slot is only used to pass information from the dynamic linker to
 * libc.so when the C library is loaded in to memory. The C runtime init
 * function will then clear it. Since its use is extremely temporary,
 * we reuse an existing location.
 */
#define  TLS_SLOT_BIONIC_PREINIT    (TLS_SLOT_ERRNO+1)

/* small technical note: it is not possible to call pthread_setspecific
 * on keys that are <= TLS_SLOT_MAX_WELL_KNOWN, which is why it is set to
 * TLS_SLOT_ERRNO.
 *
 * later slots like TLS_SLOT_OPENGL are pre-allocated through the use of
 * TLS_DEFAULT_ALLOC_MAP. this means that there is no need to use
 * pthread_key_create() to initialize them. on the other hand, there is
 * no destructor associated to them (we might need to implement this later)
 */
#define TLS_SLOT_MAX_WELL_KNOWN     TLS_SLOT_ERRNO

#define TLS_DEFAULT_ALLOC_MAP       0x0000001F

/* set the Thread Local Storage, must contain at least BIONIC_TLS_SLOTS pointers */
extern void __init_tls(void**  tls, void*  thread_info);

/* syscall only, do not call directly */
extern int __set_tls(void *ptr);

/* get the TLS */
#ifdef __arm__
/* The standard way to get the TLS is to call a kernel helper
 * function (i.e. a function provided at a fixed address in a
 * "magic page" mapped in all user-space address spaces ), which
 * contains the most appropriate code path for the target device.
 *
 * However, for performance reasons, we're going to use our own
 * machine code for the system's C shared library.
 *
 * We cannot use this optimization in the static version of the
 * C library, because we don't know where the corresponding code
 * is going to run.
 */
#  ifdef LIBC_STATIC

/* Use the kernel helper in static C library. */
  typedef volatile void* (__kernel_get_tls_t)(void);
#    define __get_tls() (*(__kernel_get_tls_t *)0xffff0fe0)()

#  else /* !LIBC_STATIC */
/* Use optimized code path.
 * Note that HAVE_ARM_TLS_REGISTER is build-specific
 * (it must match your kernel configuration)
 */
#    ifdef HAVE_ARM_TLS_REGISTER
 /* We can read the address directly from a coprocessor
  * register, which avoids touching the data cache
  * completely.
  */
#      define __get_tls() \
    ({ register unsigned int __val asm("r0"); \
       asm ("mrc p15, 0, r0, c13, c0, 3" : "=r"(__val) ); \
       (volatile void*)__val; })
#    else /* !HAVE_ARM_TLS_REGISTER */
 /* The kernel provides the address of the TLS at a fixed
  * address of the magic page too.
  */
#      define __get_tls() ( *((volatile void **) 0xffff0ff0) )
#    endif
#  endif /* !LIBC_STATIC */
#else /* !ARM */
extern void*  __get_tls( void );
#endif /* !ARM */

/* return the stack base and size, used by our malloc debugger */
extern void*  __get_stack_base(int  *p_stack_size);

__END_DECLS

#endif /* _SYS_TLS_H */