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Re: preprocessing by gcc

From: Andi Hellmund <mail at andihellmund dot com>
To: PRASANTH RAJAGOPAL <prasanthris at gmail dot com>
Cc: gcc-help at gcc dot gnu dot org
Date: Tue, 31 May 2011 22:14:49 +0200
Subject: Re: preprocessing by gcc
References: <BANLkTikBQkdAm4YJTDYoQXWWyhaP9qY07w@mail.gmail.com>

Hi

I read the following:
Preprocessing - The *as* internal preprocessor:It does not do macro
processing, include file handling, or anything else you may get from
your C compiler's preprocessor.

Yes, that's true. The preprocessor of GNU as is not a pre-processor in the sense of the C compiler.

Now the way the toolchains are used, it appears that .S files are
preprocessed by the Assembler, because my MACROs in the .S are never
getting defined&  in the make files I see that the .S files are given
to Assembler.

There is a "convention" that .s are pure assembler-files which could be passed to the assembler directly, but .S files do contain pre-processor macros (known from C). So, the .S must be passed to the pre-processor before passing the output to the assembler.

The usual way is to NOT pass the .S file to 'as' but to pass it to 'gcc', e.g. gcc <file>.S -c. gcc will then do the steps as described above (preprocessor -> assembler).

Best regards,
Andi

References:
- preprocessing by gcc
  - From: PRASANTH RAJAGOPAL

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