user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/options/elf/generic/startup.cpp

@@ -0,0 +1,60 @@
+
+#include <errno.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <bits/ensure.h>
+#include <mlibc/elf/startup.h>
+#include <mlibc/environment.hpp>
+
+extern "C" size_t __init_array_start[];
+extern "C" size_t __init_array_end[];
+extern "C" size_t __preinit_array_start[];
+extern "C" size_t __preinit_array_end[];
+
+extern "C" uintptr_t *__dlapi_entrystack();
+
+namespace mlibc {
+
+exec_stack_data entry_stack;
+
+[[gnu::constructor]]
+void init_libc() {
+	mlibc::parse_exec_stack(__dlapi_entrystack(), &entry_stack);
+	mlibc::set_startup_data(entry_stack.argc, entry_stack.argv, entry_stack.envp);
+}
+
+void parse_exec_stack(void *opaque_sp, exec_stack_data *data) {
+	auto sp = reinterpret_cast<uintptr_t *>(opaque_sp);
+	data->argc = *sp++;
+	data->argv = reinterpret_cast<char **>(sp);
+	sp += data->argc; // Skip all arguments.
+	__ensure(!*sp); // Skip the terminating null element.
+	sp++;
+	data->envp = reinterpret_cast<char **>(sp);
+}
+
+// TODO: This does not have to be here; we could also move it to options/internal.
+void set_startup_data(int argc, char **argv, char **envp) {
+	if(argc) {
+		program_invocation_name = argv[0];
+
+		if(auto slash = strrchr(argv[0], '/'); slash) {
+			program_invocation_short_name = slash + 1;
+		}else{
+			program_invocation_short_name = argv[0];
+		}
+	}
+
+	// Initialize environ.
+	// TODO: Copy the arguments instead of pointing to them?
+	auto ev = envp;
+	while(*ev) {
+		auto fail = mlibc::putenv(*ev);
+		__ensure(!fail);
+		ev++;
+	}
+}
+
+} // namespace mlibc
+