Add a "fork" of musl as //fusl.

fusl/src/env/__init_tls.c

+#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
+
+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_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();
+}
+
+weak_alias(static_init_tls, __init_tls);