执行汇编函数触发Access violation异常，求原因及解决方法

Why You're Getting the Access Violation #

The root issue here is almost certainly incorrect code segment permissions or architecture mismatch:

• When you define your _CODE segment manually without specifying executable attributes or the correct bitness (32/64-bit), the linker might map this section to a memory page marked as non-executable. When the CPU tries to run mov eax, 2, it hits a permission barrier and throws the access violation.
• If your C++ code is compiled for x64 but your assembly is written for x86 (or vice versa), register usage and calling convention mismatches can also trigger this error—even swapping to rax/rcx won’t fix it if the underlying segment setup is wrong.

Fixed Assembly Code (x86 & x64) #

Let’s adjust your assembly to work properly for both architectures, with correct segment attributes:

For 32-bit (x86) MASM:

.386
.model flat, c ; Use C calling convention and flat memory model
.code ; Shorthand for properly configured executable segment

my_add_asm_call proc
    mov eax, 2
    mov ecx, 3
    add eax, ecx
    ret
my_add_asm_call endp

end

For 64-bit (x64) MASM:

.code ; Automatically sets up executable segment for x64

my_add_asm_call proc
    mov rax, 2
    mov rcx, 3
    add rax, rcx
    ret
my_add_asm_call endp

end

Key fixes here:

• .model flat, c (for x86) aligns the assembly with your C++ code’s memory model and calling convention.
• Using .code instead of manual _CODE SEGMENT automatically marks the section as executable, eliminating the permission error.
• For x64, the .code directive handles all necessary segment setup by default.

Basic Assembly Learning Guide #

Since you’re new to assembly, here’s a structured path to get started:

• Pick your target architecture first: Focus on x64 (modern systems) or x86 (simpler for basics) and stick to one until you grasp core concepts.
• Learn core registers: For x86, start with eax, ecx, esp (general-purpose and stack pointers). For x64, expand to rax, rcx, etc., and memorize which registers handle arguments/return values in your platform’s calling convention.
• Master calling conventions: For C/C++, learn cdecl (x86) and Microsoft’s x64 convention (or System V for Linux/macOS)—this dictates how arguments are passed, who cleans up the stack, and where return values go.
• Start small: Build simple functions like your my_add_asm_call first, then move to functions that take arguments and interact with C code.
• Use a debugger: Tools like Visual Studio Debugger (Windows) or GDB (Linux/macOS) let you step through assembly instructions, check register values, and pinpoint exactly where errors occur.
• Learn memory segment basics: Understand how code, data, and stack sections are mapped in memory, along with their permissions (executable, read-only, read-write)—this will help you avoid access violation errors long-term.

内容的提问来源于stack exchange，提问作者Narf the Mouse