push_registers_asm.cc

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// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
// Push all callee-saved registers to get them on the stack for conservative
// stack scanning.
//
// See asm/x64/push_registers_clang.cc for why the function is not generated
// using clang.
//
// Do not depend on V8_TARGET_OS_* defines as some embedders may override the
// GN toolchain (e.g. ChromeOS) and not provide them.
 
// We maintain 16-byte alignment at calls. There is an 4-byte return address
// on the stack and we push 28 bytes which maintains 16-byte stack alignment
// at the call.
//
// The following assumes cdecl calling convention.
// Source: https://en.wikipedia.org/wiki/X86_calling_conventions#cdecl
asm(
#ifdef _WIN32
    ".att_syntax                                        \n"
    ".globl _PushAllRegistersAndIterateStack            \n"
    "_PushAllRegistersAndIterateStack:                  \n"
#else   // !_WIN32
    ".globl PushAllRegistersAndIterateStack             \n"
    ".type PushAllRegistersAndIterateStack, %function   \n"
    ".hidden PushAllRegistersAndIterateStack            \n"
    "PushAllRegistersAndIterateStack:                   \n"
#endif  // !_WIN32
    // [ IterateStackCallback ]
    // [ StackVisitor*        ]
    // [ Stack*               ]
    // [ ret                  ]
    // ebp is callee-saved. Maintain proper frame pointer for debugging.
    "  push %ebp                                        \n"
    "  movl %esp, %ebp                                  \n"
    "  push %ebx                                        \n"
    "  push %esi                                        \n"
    "  push %edi                                        \n"
    // Save 3rd parameter (IterateStackCallback).
    "  movl 28(%esp), %ecx                              \n"
    // Pass 3rd parameter as esp (stack pointer).
    "  push %esp                                        \n"
    // Pass 2nd parameter (StackVisitor*).
    "  push 28(%esp)                                    \n"
    // Pass 1st parameter (Stack*).
    "  push 28(%esp)                                    \n"
    "  call *%ecx                                       \n"
    // Pop the callee-saved registers.
    "  addl $24, %esp                                   \n"
    // Restore rbp as it was used as frame pointer.
    "  pop %ebp                                         \n"
    "  ret                                              \n"
#if !defined(__APPLE__) && !defined(_WIN32)
    ".Lfunc_end0:                                       \n"
    ".size PushAllRegistersAndIterateStack, "
    ".Lfunc_end0-PushAllRegistersAndIterateStack\n"
#endif  // !defined(__APPLE__) && !defined(_WIN32)
    );