blob: 335ca27073ea66b3e8a9d541499d775705d5e022 [file] [log] [blame]
// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "asm.h"
// Call the C _dl_start, which returns a dl_start_return_t containing the
// user entry point and its argument. Then jump to that entry point with
// the argument in the first argument register, pushing a zero return
// address and clearing the frame pointer register so the user entry point
// is the base of the call stack.
.hidden _start
// We can be pretty sure that we were started with the stack pointer
// correctly aligned, which is (rsp % 16) = 8 at function entry.
// Since we'd need to adjust down by 8 to make an immediate call with
// correct stack alignment, it's just as cheap to explicitly align and
// then we're resilient to process setup not having given us the
// ABI-required alignment, just in case.
and $-16,%rsp
xor %rbp,%rbp
call _dl_start
mov %rax,%rdi
push %rbp // Zero in the return address slot.
jmp *%rdx