compilação – Compile Linux-ready assembly on OSX

Question:

I'm trying to study compilers, for that I have to compile an assembly of a language called howto with nasm.

the intermediate code generated by the howto compiler is as follows:

extern printf
segment .text
align 8
global main:function
main:
segment .rodata
align 8
_L1: db 'hello', 10, 0
segment .text
    mov rax, 0
    mov edi, $_L1
    call printf
    mov rax, 0
    ret

in the OSX terminal I do $ nasm -f macho out.asm , and I have a compilation error because of the main:function , if I remove the :function it ends with this first error when trying to compile again. One more error, but this time it just says I should use macho64 because of the system architecture, I try to compile with $ nasm -f macho64 out.asm and I get the error:

out.asm:11: error: Mach-O 64-bit format does not support 32-bit absolute addresses

After that I can't compile anymore, but if I use ELF64 I can create the out.o file.

From this point with the out.o file which I must compile with clang, I do $clang out.o -v to return all the verbose and I get the error:

Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)
Target: x86_64-apple-darwin14.4.0
Thread model: posix
  "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -dynamic -arch x86_64 -macosx_version_min 10.10.0 -o a.out out.o -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/6.1.0/lib/darwin/libclang_rt.osx.a
  ld: warning: ignoring file out.o, file was built for unsupported file format ( 0x7F 0x45 0x4C 0x46 0x02 0x01 0x01 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 ) which is not the architecture being linked (x86_64): out.o
Undefined symbols for architecture x86_64:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

From this point I can't go any further, I tried to link by ld with $ ld -e _main out.o and $ ld -e _main out.o -arch x86_64 but in these cases I get the error message:

Undefined symbols for architecture x86_64:
  "_main", referenced from:
     implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64

On linux, the compilation with $ nasm -f elf64 out.asm went without problems in the initial form of the code and $ gcc out.o also generated the a.out file which, when executed, returned the Hello response of the expected message. However, as I have to finish this project on OSX, I ask the community for help.

Answer:

I'm not sure what I'm saying!!! but here it goes anyway:

The architecture of intel 80-86 and descendants is a mess!

(unlike linux) on OSX the address space exceeds 2^32 so it doesn't usually support 32-bit absolute addressing.

update : Therefore: use 64bit registers or relative address:

64-bit registers:

global main
extern puts

segment .text
main:
    push rbp      ; (guardar o frame pointer -- *1)

    mov rax, 0
    mov rdi, _L1  ; usando o registo de 64 bits corresp ao edi
    call puts

    pop rbp       ; (retaurar o frame pointer -- *1)
    mov rax, 0    ; (return 0 do C)
    ret

_L1: 
   db "hello",  0

grades:

  • the *1 lines are not necessary for this case but are good practice…

  • I used puts instead of printf to make it simpler

alternatively — use relative addresses (no best practices…):

global main
extern puts

segment .text
main:
    mov eax, 0          ; registo de 32 bits correspondente ao rax
    lea edi, [rel _L1]  ; registo de 32 bits...             ao rdi
    call puts
    ret

_L1:
   db "hello",  0

Untested …I would expect these versions to work on both macho64 (OSX) and elf64 (linux). FEDERAL POLICE. tell me if it works: — I don't have 64bit machines to test

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