17.2 Converting between Intel ASM syntax and AT&T syntax

Q: Where can I find an automated conversion tool to convert my Intel-style assembly code into a code acceptable by Gas?

Q: Where can I find a converter from AT&T assembly to Intel style?

A: A SED script which should do most of the conversion was posted to the DJGPP news group.

A program called TA2AS which can convert TASM assembly source to AT&T style can be found on the DJGPP server and on Oulu. TA2AS was written by Frank van Dijk of the Spirit group; if you have questions about this tool, you may contact Jan Oonk. The authors say that the program is far from finished, but the sources are available with the package so you can fix whatever is broken for your needs.

Another similar converter is Intel2Gas, available from its Web page.

Beginning with Binutils 2.10, Gas has an option that causes it to accept the Intel syntax, so you can use Gas to assembly Intel-style code.

Alternatively, here is what you can do to make your code linkable with DJGPP programs:

• Get and install NASM, a portable x86 assembler which supports most of the Intel syntax and can generate DJGPP-compatible COFF object files (as well as lots of other formats, such as Microsoft 16-bit OBJ and Win32, a.out, and ELF). It also supports Pentium and Pentium Pro opcodes, and MMX. NASM is free for non-commercial use (see the docs for commercial use restrictions) and can be compiled with DJGPP. NASM can be found on NASM Web site, which has links to official download sites. The maintainers of NASM are Jules and H. Peter Anvin.

  Be warned that NASM is not 100% identical to MASM or TASM. Even experienced assembly programmers might need some time to adapt to the slightly different flavor of NASM. If you want something much more similar to TASM, get JAS. JAS is available from OULU.

  Also note that NASM, or at least some of its versions, doesn't produce debug info in the format understood by GDB, which makes debugging NASM-assemblied code tedious (you might not be able to display source lines and refer to local symbols by name). Latest versions of NASM might correct this deficiency.

• For a small number of relatively short files, consider converting them with a smart editor (like Emacs or its work-alikes).
• Obtain a copy of Microsoft MASM 6.11. It has a -coff option to generate object code in COFF format which can be submitted to GCC, so you can compile your original source. You can also use the LIB32 librarian from Microsoft C8 to convert object files to COFF by putting them into a .lib library, then extracting them as COFF files. ²⁸ Note that, unless you link the MASM-generated object files with DJGPP's ld (as opposed to Microsoft's LINK /CO command), you won't be able to debug the resulting program, because the debug info is not in correct format. I'm also told that masm doesn't produce sections named ".text" and ".data", so you might need to hex-edit the section names in the object file manually.
• Use a disassembler to disassemble the object code, then convert it to the AT&T format either by hand or using TA2AS. One place to look for such a disassembler is on SimTel.NET mirrors.

Keep in mind that syntax is only one of the aspects of converting code written for DOS to DJGPP. You should also make sure your code doesn't violate any of the rules for protected-mode programming (see GPF in asm code).

If you need to perform the opposite conversion, from the AT&T style to the Intel style, try the Att2Intl converter written by Gregory Velichansky. Its output is intended for NASM or TASM. Att2Intl is available from Greg's home page.