| // Copyright 2023 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 <lib/arch/asm.h> |
| |
| // This defines the entry point in assembly, such that it calls: |
| // |
| // extern "C" int64_t TestStart(...); |
| // |
| // In the in-process version, that's a tail call so it returns directly to the |
| // in-process caller. In the separate-process version, the return value is |
| // passed to _exit. |
| |
| .function _start, global |
| |
| // This can assume the sp is already aligned to 16 by the kernel. |
| |
| #if defined(__aarch64__) |
| |
| mov x0, sp |
| #ifdef IN_PROCESS_TEST |
| b TestStart |
| #else |
| bl TestStart |
| // Return value in x0 is argument. |
| bl _exit |
| udf #0 |
| #endif |
| |
| #elif defined(__riscv) |
| |
| mv a0, sp |
| #ifdef IN_PROCESS_TEST |
| b TestStart |
| #else |
| call TestStart |
| // Return value in a0 is argument. |
| call _exit |
| unimp |
| #endif |
| |
| #elif defined(__x86_64__) |
| |
| mov %rsp, %rdi |
| // If called by ld-startup-tests.cc code, the return address is already in |
| // the word just below %rsp. If started otherwise, that word will be zero. |
| // Either way %rsp needs to be adjusted down to 8 mod 16 as a call would do |
| // by pushing the return address for the C calling convention. Instead of a |
| // call followed by a trap if it ever did return, just adjust %rsp down and |
| // jump so that either an original return address or a fault-inducing zero is |
| // the callee's return address. |
| sub $8, %rsp |
| #ifdef IN_PROCESS_TEST |
| jmp TestStart |
| #else |
| call TestStart |
| // Move the return value into the argument register. |
| mov %rax, %rdi |
| call _exit |
| ud2 |
| #endif |
| |
| #else |
| #error "unsupported machine" |
| #endif |
| |
| .end_function |
