user: implement mlibc as the libc, finally.

It's finally done..

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

user/include/mlibc/options/lsb/generic/auxv.cpp

@@ -0,0 +1,59 @@
+
+#include <errno.h>
+#include <stdint.h>
+#include <sys/auxv.h>
+
+#include <bits/ensure.h>
+
+extern "C" uintptr_t *__dlapi_entrystack();
+
+int peekauxval(unsigned long type, unsigned long *out) {
+	// Find the auxiliary vector by skipping args and environment.
+	auto aux = __dlapi_entrystack();
+	aux += *aux + 1; // Skip argc and all arguments
+	__ensure(!*aux);
+	aux++;
+	while(*aux) // Now, we skip the environment.
+		aux++;
+	aux++;
+
+	// Parse the auxiliary vector.
+	while(true) {
+		auto value = aux + 1;
+		if(*aux == AT_NULL) {
+			errno = ENOENT;
+			return -1;
+		}else if(*aux == type) {
+			*out = *value;
+			return 0;
+		}
+		aux += 2;
+	}
+}
+
+unsigned long getauxval(unsigned long type) {
+	unsigned long value = 0;
+	if(peekauxval(type, &value))
+		return 0;
+	return value;
+}
+
+// XXX(qookie):
+// This is here because libgcc will call into __getauxval on glibc Linux
+// (which is what it believes we are due to the aarch64-linux-gnu toolchain)
+// in order to find AT_HWCAP to discover if LSE atomics are supported.
+//
+// This is not necessary on a custom Linux toolchain and is purely an artifact of
+// using the host toolchain.
+
+// __gnu_linux__ is the define checked by libgcc
+#if defined(__aarch64__) && defined(__gnu_linux__)
+
+extern "C" unsigned long __getauxval(unsigned long type) {
+	unsigned long value = 0;
+	if(peekauxval(type, &value))
+		return 0;
+	return value;
+}
+
+#endif