CODEWITHSUNDEEP
gccassemblynasmgnu-assembler
Martel
Martel

Reputation: 2734

Provide incbin path as a predefined macro in both NASM and GCC

I want to embed a binary file in an executable, in a way that is portable to both Windows and Linux.

For achieving this, I want to use an assembly file with the directive incbin. For example:

.intel_syntax noprefix


      .global _img0_start
      .global _img0_end
      .global _img0_size


_img0_start:   .incbin "img0.bin"
_img0_end:
_img0_size:    .quad  $ -  _img0_start

I can't know where the binary files will be before compiling the above assembly file, so I want to replace img0.bin by a macro, and define it within the command line arguments as if I were using the gcc option -D for defining a macro constant.

I have seen that there exists the -d Option: Pre-Define a Macro, that allows to do exactly the above but only for numeric values (I need to provide a path to a file). (font: https://www.nasm.us/doc/nasmdoc2.html#section-2.1.19)

Is there anything like -d, but that allows to define strings, and works for moth gas and nasm?

Upvotes: 2

Views: 1352

Answers (2)

Peter Cordes
Peter Cordes

Reputation: 364210

NASM macros and the C preprocessor both allow arbitrary strings.

NASM equ constants have to be integers, but %define foo eax or nasm '-DIMG="foo.bin"' both work.

Notice that the macro definition includes the double quotes. CPP makes it easy to expand a macro inside double quotes, but I didn't bother to check if NASM can easily do that.

It's normally easy to create a double-quoted string like that in Make or whatever.

;;; foo-nasm.asm  NASM source
incbin IMG

# foo-gas.S   GAS source (capital S gets GCC to run it through CPP)
.incbin IMG

hi.bin contains B8 68 69 00 00, the 32/64-bit machine code for mov eax, 'hi'

 $ gcc -c foo-gas.S -DIMG='"hi.bin"'            
 $ nasm -felf64 foo-nasm.asm -DIMG='"hi.bin"'       

$ disas foo-gas.o
...
0000000000000000 <.text>:
   0:   b8 68 69 00 00          mov    eax,0x6968

$ disas foo-nasm.o
...
0000000000000000 <.text>:
   0:   b8 68 69 00 00          mov    eax,0x6968

Upvotes: 1

Martel
Martel

Reputation: 2734

I have read more and I have realized that there is no need for a macro that expands to a string.

Instead, what can be done is just providing a fixed name for the binary file, in my case, img0.bin, and then use the -I option for providing extra paths for searching such file.

In other words, with the same assembly file as above (let it be assembly_file.s), just do:

gcc -c assembly_file.s -I<path_to_folder_that_contains_img0.bin> -o <output_file_name>

Upvotes: 2

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