source: azure_iot_hub/trunk/musl-1.1.18/src/env/__init_tls.c@ 388

#include <elf.h>
#include <limits.h>
#include <sys/mman.h>
#include <string.h>
#include <stddef.h>
#include "pthread_impl.h"
#include "libc.h"
#include "atomic.h"
#include "syscall.h"

int __init_tp(void *p)
{
        pthread_t td = p;
        td->self = td;
        int r = __set_thread_area(TP_ADJ(p));
        if (r < 0) return -1;
        if (!r) libc.can_do_threads = 1;
        td->tid = __syscall(SYS_set_tid_address, &td->tid);
        td->locale = &libc.global_locale;
        td->robust_list.head = &td->robust_list.head;
        return 0;
}

static struct builtin_tls {
        char c;
        struct pthread pt;
        void *space[16];
} builtin_tls[1];
#define MIN_TLS_ALIGN offsetof(struct builtin_tls, pt)

static struct tls_module main_tls;

void *__copy_tls(unsigned char *mem)
{
        pthread_t td;
        struct tls_module *p;
        size_t i;
        void **dtv;

#ifdef TLS_ABOVE_TP
        dtv = (void **)(mem + libc.tls_size) - (libc.tls_cnt + 1);

        mem += -((uintptr_t)mem + sizeof(struct pthread)) & (libc.tls_align-1);
        td = (pthread_t)mem;
        mem += sizeof(struct pthread);

        for (i=1, p=libc.tls_head; p; i++, p=p->next) {
                dtv[i] = mem + p->offset;
                memcpy(dtv[i], p->image, p->len);
        }
#else
        dtv = (void **)mem;

        mem += libc.tls_size - sizeof(struct pthread);
        mem -= (uintptr_t)mem & (libc.tls_align-1);
        td = (pthread_t)mem;

        for (i=1, p=libc.tls_head; p; i++, p=p->next) {
                dtv[i] = mem - p->offset;
                memcpy(dtv[i], p->image, p->len);
        }
#endif
        dtv[0] = (void *)libc.tls_cnt;
        td->dtv = td->dtv_copy = dtv;
        return td;
}

#if ULONG_MAX == 0xffffffff
typedef Elf32_Phdr Phdr;
#else
typedef Elf64_Phdr Phdr;
#endif

#ifndef __c2__
__attribute__((__weak__, __visibility__("hidden")))
#endif
extern const size_t _DYNAMIC[];

static void static_init_tls(size_t *aux)
{
        unsigned char *p;
        size_t n;
        Phdr *phdr, *tls_phdr=0;
        size_t base = 0;
        void *mem;

        for (p=(void *)aux[AT_PHDR],n=aux[AT_PHNUM]; n; n--,p+=aux[AT_PHENT]) {
                phdr = (void *)p;
                if (phdr->p_type == PT_PHDR)
                        base = aux[AT_PHDR] - phdr->p_vaddr;
                if (phdr->p_type == PT_DYNAMIC && _DYNAMIC)
                        base = (size_t)_DYNAMIC - phdr->p_vaddr;
                if (phdr->p_type == PT_TLS)
                        tls_phdr = phdr;
        }

        if (tls_phdr) {
                main_tls.image = (void *)(base + tls_phdr->p_vaddr);
                main_tls.len = tls_phdr->p_filesz;
                main_tls.size = tls_phdr->p_memsz;
                main_tls.align = tls_phdr->p_align;
                libc.tls_cnt = 1;
                libc.tls_head = &main_tls;
        }

        main_tls.size += (-main_tls.size - (uintptr_t)main_tls.image)
                & (main_tls.align-1);
        if (main_tls.align < MIN_TLS_ALIGN) main_tls.align = MIN_TLS_ALIGN;
#ifndef TLS_ABOVE_TP
        main_tls.offset = main_tls.size;
#endif

        libc.tls_align = main_tls.align;
        libc.tls_size = 2*sizeof(void *) + sizeof(struct pthread)
                + main_tls.size + main_tls.align
                + MIN_TLS_ALIGN-1 & -MIN_TLS_ALIGN;

        if (libc.tls_size > sizeof builtin_tls) {
#ifndef SYS_mmap2
#define SYS_mmap2 SYS_mmap
#endif
                mem = (void *)__syscall(
                        SYS_mmap2,
                        0, libc.tls_size, PROT_READ|PROT_WRITE,
                        MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
                /* -4095...-1 cast to void * will crash on dereference anyway,
                 * so don't bloat the init code checking for error codes and
                 * explicitly calling a_crash(). */
        } else {
                mem = builtin_tls;
        }

        /* Failure to initialize thread pointer is always fatal. */
        if (__init_tp(__copy_tls(mem)) < 0)
                a_crash();
}

#ifndef __c2__
weak_alias(static_init_tls, __init_tls);
#else
void __init_tls(size_t *aux)
{
        static_init_tls(aux);
}
#endif