1// Copyright 2021 the V8 project authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include "include/v8config.h"
6#include "src/trap-handler/trap-handler-simulator.h"
7
8#if V8_OS_DARWIN
9#define SYMBOL(name) "_" #name
10#else  // !V8_OS_DARWIN
11#define SYMBOL(name) #name
12#endif  // !V8_OS_DARWIN
13
14// Define the ProbeMemory function declared in trap-handler-simulators.h.
15asm(
16    ".globl " SYMBOL(ProbeMemory) "                 \n"
17    SYMBOL(ProbeMemory) ":                          \n"
18// First parameter (address) passed in %rdi on Linux/Mac, and %rcx on Windows.
19// The second parameter (pc) is unused here. It is read by the trap handler
20// instead.
21#if V8_OS_WIN
22    "  movb (%rcx), %al                             \n"
23#else
24    "  movb (%rdi), %al                             \n"
25#endif  // V8_OS_WIN
26    // Return 0 on success.
27    "  xorl %eax, %eax                              \n"
28    // Place an additional "ret" here instead of falling through to the one
29    // below, because (some) toolchain(s) on Mac set ".subsections_via_symbols",
30    // which can cause the "ret" below to be placed elsewhere. An alternative
31    // prevention would be to add ".alt_entry" (see
32    // https://reviews.llvm.org/D79926), but just adding a "ret" is simpler.
33    "  ret                                          \n"
34    ".globl " SYMBOL(v8_probe_memory_continuation) "\n"
35    SYMBOL(v8_probe_memory_continuation) ":         \n"
36    // If the trap handler continues here, it wrote the landing pad in %rax.
37    "  ret                                          \n");
38