Using Standard C Library function on ARM64 macOS assembly doesn't work after linking [duplicate]

Question

I'm on MacOS (Apple Silicon M4 processor, so, ARM64), and when trying to use puts from the standard C library:

 .global main // 1 main: // 2 stp x21, x30, [sp, -16]! // push onto stack // 3 mov x21, x1 // argc -> x0, argv -> x1 // 4 // 5 top: // 6 ldr x0, [x21], 8 // argv++, old value in x0 // 7 cbz x0, bottom // if *argv == NULL goto bottom // 8 bl puts // puts(*argv) // 9 b top // goto top // 10 // 11 bottom: // 12 ldp x21, x30, [sp], 16 // pop from stack // 13 mov x0, xzr // return 0 // 14 ret // 15 // 16 .end

It fails, and returns:

~/ clang -lc -arch arm64 test2.s -e main Undefined symbols for architecture arm64: "puts", referenced from: main in test2-8965bb.o ld: symbol(s) not found for architecture arm64 clang: error: linker command failed with exit code 1 (use -v to see invocation)

I have tried with the addition of the -lSystem flag, doesn't work, instead just returns a ld: warning: ignoring duplicate libraries: '-lSystem' warning.

Not sure what I did wrong, making it that I can't use libc (just in case, I have tried this:

#include <stdio.h> int main(){ puts("Hello, World!"); return 0; }

Whos assembly equivalent is:

 .section __TEXT,__text,regular,pure_instructions .build_version macos, 15, 0 sdk_version 15, 2 .globl _main ; -- Begin function main .p2align 2 _main: ; @main .cfi_startproc ; %bb.0: sub sp, sp, #32 stp x29, x30, [sp, #16] ; 16-byte Folded Spill add x29, sp, #16 .cfi_def_cfa w29, 16 .cfi_offset w30, -8 .cfi_offset w29, -16 mov w8, #0 ; =0x0 str w8, [sp, #8] ; 4-byte Folded Spill stur wzr, [x29, #-4] adrp x0, l_.str@PAGE add x0, x0, l_.str@PAGEOFF bl _puts ldr w0, [sp, #8] ; 4-byte Folded Reload ldp x29, x30, [sp, #16] ; 16-byte Folded Reload add sp, sp, #32 ret .cfi_endproc ; -- End function .section __TEXT,__cstring,cstring_literals l_.str: ; @.str .asciz "Hello, World!" .subsections_via_symbols

Which works just fine!)

Some help would be appreciated!

I have vague memories that Mac OS prefixes symbols with an underscore, so _puts. What does the assembly output of the C program use? — Shawn
– Shawn, Commented Jan 17 at 22:08
@Shawn it worked, just, does every function in libc have to be prefixed with an underscore? — Silicon
– Silicon, Commented Jan 17 at 22:18
@Silicon Every C language identifier is decorated with a leading underscore. — fuz
– fuz, Commented Jan 17 at 22:36
@Silicon This applies to all C code built for the macOS ABI, which is what mandates this decoration. If you build programs for ELF targets following the SysV ABI (such as Linux), there is no decoration. — fuz
– fuz, Commented Jan 17 at 22:48

Silicon · Accepted Answer · 2025-01-18 11:55:35Z

As @Shawn and @fuz mentioned, adding a prefixing _ is required for all C code built for the macOS ABI.

Therefore, the corrected code would become:

 .global main // 1 main: // 2 stp x21, x30, [sp, -16]! // push onto stack // 3 mov x21, x1 // argc -> x0, argv -> x1 // 4 // 5 top: // 6 ldr x0, [x21], 8 // argv++, old value in x0 // 7 cbz x0, bottom // if *argv == NULL goto bottom // 8 bl _puts // note that there is a `_` // 9 b top // goto top // 10 // 11 bottom: // 12 ldp x21, x30, [sp], 16 // pop from stack // 13 mov x0, xzr // return 0 // 14 ret // 15 // 16 .end

Fixed part:

bl _puts // with the addition of the leading `_`

Collectives™ on Stack Overflow

Using Standard C Library function on ARM64 macOS assembly doesn't work after linking [duplicate]

1 Answer 1

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Linked

Related