--- /dev/null
+//===-- Implementation of crt for aarch64 ---------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "config/linux/app.h"
+#include "include/sys/syscall.h"
+#include "src/__support/OSUtil/syscall.h"
+
+#include <linux/auxvec.h>
+#include <linux/elf.h>
+#include <stdint.h>
+
+extern "C" int main(int, char **, char **);
+
+// Source documentation:
+// https://github.com/ARM-software/abi-aa/tree/main/sysvabi64
+
+namespace __llvm_libc {
+
+AppProperties app;
+
+} // namespace __llvm_libc
+
+using __llvm_libc::app;
+
+struct Args {
+ // In the ARM64 ABI, arguments are usually passed in registers. x0 is a
+ // doubleword register, so this is 64 bit.
+ uint64_t argc;
+
+ // C++ Doesn't have flexible arrays: P1039 proposes to fix this, but for now
+ // we just fake it. Even if argc is zero, "argv[argc] shall be a null
+ // pointer" (ISO C 5.1.2.2.1) so one is fine.
+ uint64_t argv[1];
+};
+
+// TODO: Would be nice to use the aux entry structure from elf.h when available.
+struct AuxEntry {
+ uint64_t type;
+ uint64_t value;
+};
+
+extern "C" void _start() {
+ uintptr_t *frame_ptr =
+ reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
+
+ // Skip the Frame Pointer and the Link Register
+ // https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst
+ // Section 6.2.3
+
+ Args *args = reinterpret_cast<Args *>(frame_ptr + 2);
+
+ // After the argv array, is a 8-byte long NULL value before the array of env
+ // values. The end of the env values is marked by another 8-byte long NULL
+ // value. We step over it (the "+ 1" below) to get to the env values.
+ uint64_t *env_ptr = args->argv + args->argc + 1;
+ uint64_t *env_end_marker = env_ptr;
+ while (*env_end_marker)
+ ++env_end_marker;
+
+ // After the env array, is the aux-vector. The end of the aux-vector is
+ // denoted by an AT_NULL entry.
+ for (AuxEntry *aux_entry = reinterpret_cast<AuxEntry *>(env_end_marker + 1);
+ aux_entry->type != AT_NULL; ++aux_entry) {
+ switch (aux_entry->type) {
+ case AT_PAGESZ:
+ app.pageSize = aux_entry->value;
+ break;
+ default:
+ break; // TODO: Read other useful entries from the aux vector.
+ }
+ }
+
+ // TODO: Init TLS
+
+ __llvm_libc::syscall(SYS_exit,
+ main(args->argc, reinterpret_cast<char **>(args->argv),
+ reinterpret_cast<char **>(env_ptr)));
+}