How do I use the ARM assembler in XCode?

Question

Just for educational purposes, I would like to add a function to an existing iPhone app, written in ARM assembly. I don\'t need a tutorial on ARM assembly in general, becaus

Answer 1

I just started working with iOS. The first thing I tried to do was add asm code to my project and ran into the same problem. The static data is handled slightly differently in 64-bit mode. I discovered how to do it by looking at the assembler output of the compiler. The same .S file will be compiled as both 32 and 64-bit in Xcode, so prepare it like this:

        .globl         _myfunction
        .align         2

        my_constant_data:
              .byte 0,1,2,3,4,5,6,7

    #ifdef __arm__
        .thumb_func    _myfunction 
        .syntax        unified
        .code          16

    //
    // call from C as my myfunction()
    //
    _myfunction:
       ldr r0,=my_constant_data

    < write your thumb-2 code here >
       bx lr

    #else // or you can use #ifdef __arm64__
    //
    // Call from C as myfunction()
    //
    _myfunction:
       adrp x0, my_constant_data@PAGE
       add x0,x0, my_constant_data@PAGEOFF

    < write your Armv8 code here >
       ret

    #endif