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

fusl/src/env/__libc_start_main.c

+#include <elf.h>
+#include <poll.h>
+#include <fcntl.h>
+#include <signal.h>
+#include "syscall.h"
+#include "atomic.h"
+#include "libc.h"
+
+void __init_tls(size_t *);
+
+static void dummy(void) {}
+weak_alias(dummy, _init);
+
+__attribute__((__weak__, __visibility__("hidden")))
+extern void (*const __init_array_start)(void), (*const __init_array_end)(void);
+
+static void dummy1(void *p) {}
+weak_alias(dummy1, __init_ssp);
+
+#define AUX_CNT 38
+
+void __init_libc(char **envp, char *pn)
+{
+        size_t i, *auxv, aux[AUX_CNT] = { 0 };
+        __environ = envp;
+        for (i=0; envp[i]; i++);
+        libc.auxv = auxv = (void *)(envp+i+1);
+        for (i=0; auxv[i]; i+=2) if (auxv[i]<AUX_CNT) aux[auxv[i]] = auxv[i+1];
+        __hwcap = aux[AT_HWCAP];
+        __sysinfo = aux[AT_SYSINFO];
+        libc.page_size = aux[AT_PAGESZ];
+
+        if (pn) {
+                __progname = __progname_full = pn;
+                for (i=0; pn[i]; i++) if (pn[i]=='/') __progname = pn+i+1;
+        }
+
+        __init_tls(aux);
+        __init_ssp((void *)aux[AT_RANDOM]);
+
+        if (aux[AT_UID]==aux[AT_EUID] && aux[AT_GID]==aux[AT_EGID]
+                && !aux[AT_SECURE]) return;
+
+        struct pollfd pfd[3] = { {.fd=0}, {.fd=1}, {.fd=2} };
+#ifdef SYS_poll
+        __syscall(SYS_poll, pfd, 3, 0);
+#else
+        __syscall(SYS_ppoll, pfd, 3, &(struct timespec){0}, 0, _NSIG/8);
+#endif
+        for (i=0; i<3; i++) if (pfd[i].revents&POLLNVAL)
+                if (__sys_open("/dev/null", O_RDWR)<0)
+                        a_crash();
+        libc.secure = 1;
+}
+
+static void libc_start_init(void)
+{
+        _init();
+        uintptr_t a = (uintptr_t)&__init_array_start;
+        for (; a<(uintptr_t)&__init_array_end; a+=sizeof(void(*)()))
+                (*(void (**)())a)();
+}
+
+weak_alias(libc_start_init, __libc_start_init);
+
+int __libc_start_main(int (*main)(int,char **,char **), int argc, char **argv)
+{
+        char **envp = argv+argc+1;
+
+        __init_libc(envp, argv[0]);
+        __libc_start_init();
+
+        /* Pass control to the application */
+        exit(main(argc, argv, envp));
+        return 0;
+}