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Re: [Tinycc-devel] preprocessor makes attributes disappear

From: Michael Matz
Subject: Re: [Tinycc-devel] preprocessor makes attributes disappear
Date: Fri, 6 Apr 2018 21:13:43 +0200 (CEST)
User-agent: Alpine 2.20 (LSU 67 2015-01-07)


On Thu, 5 Apr 2018, address@hidden wrote:

I made this test program which I expect to print all 0's, but it doesn't.

I noticed that after tcc -E the attributes have all disappeared.

Any idea what is stopping this from working? the attribute is documented and code gen seems to respect TOK_ALIGNED. I wasn't able to understand how it vanishes by looking at tccpp.c so advice would be welcome.

Yes, you stumbled over an artifact of the glibc standard headers. If used with a compiler that doesn't claim to be GCC (e.g. with TCC), you'll hit this snippet in /usr/include/sys/cdefs.h:

#if !defined __GNUC__ || __GNUC__ < 2
# define __attribute__(xyz)     /* Ignore */

Et voila, all your __attribute__ uses are defined away. Luckily the standard headers don't do the same with either __attribute (without the trailing double-underscore), so you can use that in your code. Alternatively you can do an '#undef __attribute__' after all standard headers are included. None of that helps for the __attribute__ uses in the standard headers themself (although they are optional anyway), for that you'd have to define __GNUC__ to 2 at least. But that has further ramifications as TCC is somewhat but not completely compatible with several GNU extensions.


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