From 4abab5ad6c8465a7528ccdd5f49367da05f78bbd Mon Sep 17 00:00:00 2001
From: Vladimir Azarov <avm@intermediate-node.net>
Date: Tue, 1 Oct 2024 15:47:05 +0200
Subject: Initial version

---
 src/env/__libc_start_main.c | 97 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 src/env/__libc_start_main.c

(limited to 'src/env/__libc_start_main.c')

diff --git a/src/env/__libc_start_main.c b/src/env/__libc_start_main.c
new file mode 100644
index 0000000..c5b277b
--- /dev/null
+++ b/src/env/__libc_start_main.c
@@ -0,0 +1,97 @@
+#include <elf.h>
+#include <poll.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <unistd.h>
+#include "syscall.h"
+#include "atomic.h"
+#include "libc.h"
+
+static void dummy(void) {}
+weak_alias(dummy, _init);
+
+extern weak hidden 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
+
+#ifdef __GNUC__
+__attribute__((__noinline__))
+#endif
+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];
+	if (aux[AT_SYSINFO]) __sysinfo = aux[AT_SYSINFO];
+	libc.page_size = aux[AT_PAGESZ];
+
+	if (!pn) pn = (void*)aux[AT_EXECFN];
+	if (!pn) 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} };
+	int r =
+#ifdef SYS_poll
+	__syscall(SYS_poll, pfd, 3, 0);
+#else
+	__syscall(SYS_ppoll, pfd, 3, &(struct timespec){0}, 0, _NSIG/8);
+#endif
+	if (r<0) a_crash();
+	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 (**)(void))a)();
+}
+
+weak_alias(libc_start_init, __libc_start_init);
+
+typedef int lsm2_fn(int (*)(int,char **,char **), int, char **);
+static lsm2_fn libc_start_main_stage2;
+
+int __libc_start_main(int (*main)(int,char **,char **), int argc, char **argv,
+	void (*init_dummy)(), void(*fini_dummy)(), void(*ldso_dummy)())
+{
+	char **envp = argv+argc+1;
+
+	/* External linkage, and explicit noinline attribute if available,
+	 * are used to prevent the stack frame used during init from
+	 * persisting for the entire process lifetime. */
+	__init_libc(envp, argv[0]);
+
+	/* Barrier against hoisting application code or anything using ssp
+	 * or thread pointer prior to its initialization above. */
+	lsm2_fn *stage2 = libc_start_main_stage2;
+	__asm__ ( "" : "+r"(stage2) : : "memory" );
+	return stage2(main, argc, argv);
+}
+
+static int libc_start_main_stage2(int (*main)(int,char **,char **), int argc, char **argv)
+{
+	char **envp = argv+argc+1;
+	__libc_start_init();
+
+	/* Pass control to the application */
+	exit(main(argc, argv, envp));
+	return 0;
+}
-- 
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