user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/tests/rtld/scope2/libbar.c

@@ -0,0 +1,5 @@
+char *foo_baz_conflict(void);
+
+char *bar_calls_foo_baz_conflict(void) {
+	return foo_baz_conflict();
+}

user/include/mlibc/tests/rtld/scope2/libbaz.c

@@ -0,0 +1,3 @@
+char *foo_baz_conflict() {
+	return "resolved to baz";
+}

user/include/mlibc/tests/rtld/scope2/libfoo.c

@@ -0,0 +1,3 @@
+char *foo_baz_conflict() {
+	return "resolved to foo";
+}

user/include/mlibc/tests/rtld/scope2/meson.build

@@ -0,0 +1,9 @@
+libfoo = shared_library('foo', 'libfoo.c')
+libbar = shared_library('bar', 'libbar.c', build_rpath: test_rpath, link_with: libfoo)
+libbaz = shared_library('baz', 'libbaz.c')
+test_depends = [libfoo, libbar, libbaz]
+
+libfoo_native = shared_library('native-foo', 'libfoo.c', native: true)
+libbar_native = shared_library('native-bar', 'libbar.c', build_rpath: test_rpath, link_with: libfoo_native, native: true)
+libbaz_native = shared_library('native-baz', 'libbaz.c', native: true)
+test_native_depends = [libfoo_native, libbar_native, libbaz_native]

user/include/mlibc/tests/rtld/scope2/test.c

@@ -0,0 +1,38 @@
+#include <stddef.h>
+#include <dlfcn.h>
+#include <assert.h>
+#include <string.h>
+#include <stdio.h>
+
+#ifdef USE_HOST_LIBC
+#define LIBBAR "libnative-bar.so"
+#define LIBBAZ "libnative-baz.so"
+#else
+#define LIBBAR "libbar.so"
+#define LIBBAZ "libbaz.so"
+#endif
+
+typedef char *strfn(void);
+
+int main() {
+	void *baz = dlopen(LIBBAZ, RTLD_LAZY | RTLD_GLOBAL);
+	assert(baz);
+
+	// At this point, baz is loaded in the global scope. When we load bar locally,
+	// there is a relocation to `foo_baz_conflict` which is defined in both
+	// foo (which is a dependency of bar), and baz. In this case baz should win
+	// since we search the global scope first.
+
+	void *bar = dlopen(LIBBAR, RTLD_LAZY | RTLD_LOCAL);
+	assert(bar);
+
+	strfn *bfn = dlsym(bar, "bar_calls_foo_baz_conflict");
+	assert(!strcmp(bfn(), "resolved to baz"));
+
+	// TODO: Test RTLD_DEEPBIND and DT_SYMBOLIC once we implement it.
+
+	dlclose(bar);
+	dlclose(baz);
+
+	return 0;
+}