source: mainline/uspace/lib/c/generic/thread/tls.c@ 4ef27eb

/*
 * Copyright (c) 2006 Jakub Jermar
 * 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.
 * - 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.
 */

/** @addtogroup libc
 * @{
 */
/** @file
 *
 * Support for thread-local storage, as described in:
 *      Drepper U.: ELF Handling For Thread-Local Storage, 2005
 */

#include <assert.h>
#include <stdalign.h>
#include <stddef.h>
#include <align.h>
#include <tls.h>
#include <stdlib.h>
#include <str.h>
#include <macros.h>
#include <elf/elf.h>
#include <as.h>

#include <libarch/config.h>

#ifdef CONFIG_RTLD
#include <rtld/rtld.h>
#endif

#include "../private/libc.h"

#if !defined(CONFIG_TLS_VARIANT_1) && !defined(CONFIG_TLS_VARIANT_2)
#error Unknown TLS variant.
#endif

static ptrdiff_t _tcb_data_offset(const void* elf)
{
        const elf_segment_header_t *tls =
            elf_get_phdr(elf, PT_TLS);

        size_t tls_align = tls ? tls->p_align : 1;

#ifdef CONFIG_TLS_VARIANT_1
        return ALIGN_UP((ptrdiff_t) sizeof(tcb_t), tls_align);
#else
        size_t tls_size = tls ? tls->p_memsz : 0;
        return -ALIGN_UP((ptrdiff_t) tls_size, max(tls_align, alignof(tcb_t)));
#endif
}

/** Get address of static TLS block */
void *tls_get(void)
{
#ifdef CONFIG_RTLD
        assert(runtime_env == NULL);
#endif
        return (uint8_t *)__tcb_get() + _tcb_data_offset(__progsymbols.elfstart);
}

static tcb_t *tls_make_generic(const void *elf, void *(*alloc)(size_t, size_t))
{
        /*
         * See also rtld/module.c -> modules_process_tls(), where we have less
         * messy code for the dynamic-linking version of this.
         */
        assert(!elf_get_phdr(elf, PT_DYNAMIC));
#ifdef CONFIG_RTLD
        assert(runtime_env == NULL);
#endif

        const elf_segment_header_t *tls = elf_get_phdr(elf, PT_TLS);
        size_t tls_size = tls ? tls->p_memsz : 0;
        size_t tls_align = tls ? tls->p_align : 1;

        /*
         * We don't currently support alignment this big,
         * and neither should we need to.
         */
        assert(tls_align <= PAGE_SIZE);

#ifdef CONFIG_TLS_VARIANT_1
        size_t alloc_size =
            ALIGN_UP(sizeof(tcb_t), tls_align) + tls_size;
#else
        size_t alloc_size =
            ALIGN_UP(tls_size, max(tls_align, alignof(tcb_t))) + sizeof(tcb_t);
#endif

        void *area = alloc(max(tls_align, alignof(tcb_t)), alloc_size);
        if (!area)
                return NULL;

#ifdef CONFIG_TLS_VARIANT_1
        tcb_t *tcb = area;
        uint8_t *data = (uint8_t *)tcb + _tcb_data_offset(elf);
        memset(tcb, 0, sizeof(*tcb));
#else
        uint8_t *data = area;
        tcb_t *tcb = (tcb_t *) (data - _tcb_data_offset(elf));
        memset(tcb, 0, sizeof(tcb_t));
        tcb->self = tcb;
#endif

        if (!tls)
                return tcb;

        uintptr_t bias = elf_get_bias(elf);

        /*
         * FIXME: I couldn't convince myself this is correct, but I couldn't
         * find a case where it breaks either: if the actual alloc_size is
         * bigger than the requested size (tls->p_memsz), the alignment padding
         * will be placed at the beginning (because TLS is (at least sometimes?)
         * indexed with negative offsets from the TCB pointer).
         *
         * Now we will copy the initialization data to a position at the start of
         * the allocation, so if the padding has nonzero size, if think the initialization
         * data is now incorrectly offset by its size?
         *
         * Maybe a diagram helps explaining this?
         * |    allocation   |     |
         * | paddding | data | tcb |
         *   ^
         *   +--- we will copy the initialization data here
         *              ^
         *              +--- but the data should be actually here?
         */

        /* Copy thread local data from the initialization image. */
        memcpy(data, (void *)(tls->p_vaddr + bias), tls->p_filesz);
        /* Zero out the thread local uninitialized data. */
        memset(data + tls->p_filesz, 0, tls->p_memsz - tls->p_filesz);

        return tcb;
}

static void *early_alloc(size_t align, size_t alloc_size)
{
        assert(align <= PAGE_SIZE);
        alloc_size = ALIGN_UP(alloc_size, PAGE_SIZE);

        void *area = as_area_create(AS_AREA_ANY, alloc_size,
            AS_AREA_READ | AS_AREA_WRITE | AS_AREA_CACHEABLE, AS_AREA_UNPAGED);
        if (area == AS_MAP_FAILED)
                return NULL;
        return area;
}

/** Same as tls_make(), but uses as_area_create() instead of memalign().
 *  Only used in __libc_main() if the program was created by the kernel.
 */
tcb_t *tls_make_initial(const void *elf)
{
        return tls_make_generic(elf, early_alloc);
}

/** Create TLS (Thread Local Storage) data structures.
 *
 * @return Pointer to TCB.
 */
tcb_t *tls_make(const void *elf)
{
        // TODO: Always use rtld.

#ifdef CONFIG_RTLD
        if (runtime_env != NULL)
                return rtld_tls_make(runtime_env);
#endif

        return tls_make_generic(elf, memalign);
}

void tls_free(tcb_t *tcb)
{
#ifdef CONFIG_RTLD
        free(tcb->dtv);

        if (runtime_env != NULL) {
                tls_free_arch(tcb, runtime_env->tls_size, runtime_env->tls_align);
                return;
        }
#endif
        const elf_segment_header_t *tls =
            elf_get_phdr(__progsymbols.elfstart, PT_TLS);

        assert(tls != NULL);
        tls_free_arch(tcb,
            ALIGN_UP(tls->p_memsz, tls->p_align) + sizeof(tcb_t),
            max(tls->p_align, alignof(tcb_t)));
}

#ifdef CONFIG_TLS_VARIANT_1
/** Allocate TLS variant 1 data structures.
 *
 * @param data          Start of TLS section. This is an output argument.
 * @param size          Size of tdata + tbss section.
 * @return              Pointer to tcb_t structure.
 */
tcb_t *tls_alloc_variant_1(size_t size, size_t align)
{
        tcb_t *tcb = memalign(align, size);
        if (!tcb)
                return NULL;
        memset(tcb, 0, sizeof(tcb_t));
        return tcb;
}

/** Free TLS variant I data structures.
 *
 * @param tcb           Pointer to TCB structure.
 * @param size          This argument is ignored.
 */
void tls_free_variant_1(tcb_t *tcb, size_t size, size_t align)
{
        free(tcb);
}
#endif

#ifdef CONFIG_TLS_VARIANT_2
/** Allocate TLS variant II data structures.
 *
 * @param data          Pointer to pointer to thread local data. This is
 *                      actually an output argument.
 * @param size          Size of thread local data.
 * @param align         Alignment of thread local data.
 * @return              Pointer to TCB structure.
 */
tcb_t *tls_alloc_variant_2(size_t size, size_t align)
{
        void *data = memalign(align, size);
        if (data == NULL)
                return NULL;

        tcb_t *tcb = (tcb_t *) (data + size - sizeof(tcb_t));
        memset(tcb, 0, sizeof(tcb_t));
        tcb->self = tcb;
        return tcb;
}

/** Free TLS variant II data structures.
 *
 * @param tcb           Pointer to TCB structure.
 * @param size          Size of thread local data.
 * @param align         Alignment of thread local data.
 */
void tls_free_variant_2(tcb_t *tcb, size_t size, size_t align)
{
        if (tcb != NULL) {
                void *start = ((void *) tcb) + sizeof(tcb_t) - size;
                free(start);
        }
}
#endif

/** @}
 */