Editing C++ (section)

====Interoperability between C++ and Assembly====
C++ provides two primary methods of integrating ASM code. 

1. Standalone assembly files – Assembly code is written separately and linked with C++ code.<ref>{{cite web |url=https://wiki.osdev.org/C%2B%2B_to_ASM_linkage_in_GCC |title=C++ to ASM linkage in GCC |website=OSDev Wiki |access-date=1 April 2025}}</ref>

2. [[Inline assembly]] – Assembly code is embedded within C++ code using compiler-specific extensions.

;Example Code for ASM Compatibility
* When calling an assembly function from C++, use <syntaxhighlight lang="C++" inline>extern "C"</syntaxhighlight> to prevent C++ name mangling.

<syntaxhighlight lang="cpp" line="1">
//main.cpp
import std;

extern "C" int add_asm(int, int);  // Declare the assembly function

int main() {
    int result = add_asm(5, 7);
    std::println("Result from ASM: {}", result);
    return 0;
}
</syntaxhighlight>

<syntaxhighlight lang="cpp" line="1">
#asm code using RISC-V architecture
.section .text
.global add_asm

add_asm:
    add a0, a0, a1  # Add first argument (a0) and second argument (a1), store in a0
    ret             # Return (a0 holds return value)
</syntaxhighlight>
*Global variables in assembly must be declared as <syntaxhighlight lang="C++" inline>extern</syntaxhighlight> in C++ and marked <code>.global</code> in assembly.
<syntaxhighlight lang="cpp" line="1">
// main.cpp
import std;

extern "C" int global_var;  // Declare global variable from assembly

int main() {
    std::println("Global variable from ASM: {}", global_var);
    return 0;
}
</syntaxhighlight>

<syntaxhighlight lang="cpp" line="1">
#asm using RISC-V architecture
.section .data
.global global_var
.align 4
global_var:
    .word 42   # Define integer value
</syntaxhighlight>

* Inline assembly allows embedding ASM directly in C++ using the <syntaxhighlight lang="C++" inline>asm</syntaxhighlight> keyword.

<syntaxhighlight lang="cpp" line="1">
//main.cpp (using GCC/CLANG compiler)
import std;

int main() {
    int x = 10, y = 20, sum;

    asm volatile (
        "add %0, %1, %2"
        : "=r" (sum)   // Output operand (stored in a register)
        : "r" (x), "r" (y) // Input operands (stored in registers)
    );

    std::println("Sum using inline ASM: {}", sum);
    return 0;
}
</syntaxhighlight>