| // 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 |
| ENTRY(_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 |
| END(_start) |
