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Re: [avr-libc-dev] [bug #36921] util/delay.h uses inline...

From: Joerg Wunsch
Subject: Re: [avr-libc-dev] [bug #36921] util/delay.h uses inline...
Date: Tue, 24 Jul 2012 17:44:21 +0200
User-agent: Mutt/1.5.20 (2009-06-14)

As David Brown wrote:

> Agreed - though it is possible that some parts might require gcc 
> extensions to C99.  What should be done if gcc extensions are not 
> required, but would allow the generation of better (smaller/faster) 
> code?  One possible situation here is when attributes such as "const" or 
> "pure" would allow better optimisation.

So far, I don't know of any of the GCC extensions which could not be
brought in by either escaping them with two underscores, or explicitly
declaring them being __extension__.  That way, you can still compile
the code with either -std=c89 -pedantic or -std=c99 -pedantic without
getting complaints.  After all, we (as "vendor" of a system library)
are the prime reason for allowing that kind of properly marked

> > Is it ok to have some modules that comply to C89, and others that can
> > never comply to C89?

I think it is.

> MISRA is currently based on C90/ANSI, AFAIK

Yes, that's the case.  From the preface of MISRA-C:2004:

"While producing MISRA-C:2004, the question of addressing the 1999 C
standard [8] arose.  At this time, only issues with MISRA-C:1998 are
addressed due to the limited support for C99 on embedded

> I think it is perfectly reasonable to make some modules C99-only (or 
> dependant on gcc extensions), if it leads to better/clearer code - but I 
> agree there should be a check on versions and a nice #error message 
> suggesting the use of "--std" flags.

So far, we've only got one header file that requires C99,
<util/atomic.h>.  It uses C99 for-internal variable declarations.
The compiler-produced error message when attempting to use it in
non-C99 mode (e.g. when defaulting to "gnu89") looks like:

foo.c: In function ‘tmr’:
foo.c:7:3: error: ‘for’ loop initial declarations are only allowed in C99 mode
foo.c:7:3: note: use option -std=c99 or -std=gnu99 to compile your code

I think that's clear enough to not requiere any additional #ifdef'ed
warnings in our own header file.

cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)

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