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Re: Assembler Question

On Nov 28, 2007, at 11:44 AM, John Scheiderer wrote:
I want to learn Assembler on the Mac Intel platform, but I'm having a hard time finding any tutorials targeted for the Mac. I have an iMac G5 (which I know won't work), but I did setup a Darwin x86 PC that has the 'as' compiler, and I also installed 'nasm' (compiled successfully) from the most recent sources. The reason I installed 'nasm', is I noticed that Leopard now includes it in the Xcode install on my G5 machine.

I found some Hello World examples on the web, but none seem to work - they compile and link ok, but get error messages like "Bus error", etc.

As a test, I took an Objective-C program, and compiled it with gcc using the -S flag, which produced assembler code. When compiling the .s file using gcc, it produces an executable, so I suspect the examples I'm finding aren't error free.

Search <http://developer.apple.com> for "Mac OS X ABI Function Call Guide".

By your question, though, it sounds like you are a compiler writer, and that may not be quite enough.

You are most likely missing the setup for your main program, which has to push the stack base then call into itself (effectively) si the ret is to the caller of _main(). You may also be unaware that your linkages to libc need to be implemented as jump table entries so that dyld, which is loaded before the code starts running and invokes the crt1 statup code (see the "cctools" project in the Darwin sources).

This is easily visible in the assembly from a -S compile of a small "hello world" example that just outputs and exits.

-- Terry
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