[parisc-linux] Building packages, problems with printf

[parisc-linux] Building packages, problems with printf

[Matthew Wilcox]

Something we've been running into when building packages is the problem
that printf is defined as a macro when using gcc 2.97.  This should be
resolved by doing the following:

#include <stdio.h>
#undef printf

fixing glibc to not do that seems to not be an option.  ANSI explicitly
allows any of the functions in libc to also be defined as macros.

-- 
Revolutions do not require corporate support.

Re: [parisc-linux] Building packages, problems with printf

[Alan Modra]

On Sun, 25 Mar 2001, Matthew Wilcox wrote:

> Something we've been running into when building packages is the problem
> that printf is defined as a macro when using gcc 2.97.  This should be
> resolved by doing the following:
> 
> #include <stdio.h>
> #undef printf

That's cheating!  The real fix is to turn

printf (foo_string,
#if SOMETHING
abc_param
#else
xyz_param
#endif
);

into

#if SOMETHING
printf (foo_string, abc_param);
#else
printf (foo_string, xyz_param);
#endif

Earn brownie points sending off proper fixes to package maintainers. :)

> fixing glibc to not do that seems to not be an option.  ANSI explicitly
> allows any of the functions in libc to also be defined as macros.

Alan
-- 
Linuxcare

Re: [parisc-linux] Building packages, problems with printf

[Matthew Wilcox]

On Mon, Mar 26, 2001 at 09:03:34AM +1000, Alan Modra wrote:
> That's cheating!  The real fix is to turn
> 
> printf (foo_string,
> #if SOMETHING
> abc_param
> #else
> xyz_param
> #endif
> );
> 
> into
> 
> #if SOMETHING
> printf (foo_string, abc_param);
> #else
> printf (foo_string, xyz_param);
> #endif
> 
> Earn brownie points sending off proper fixes to package maintainers. :)

Ah, but that doesn't cure netkit-telnet which is c++ and has a method called
printf which gets royally bollixed by this define.

Agreed that's a better solution though for the cases where it applies.

-- 
Revolutions do not require corporate support.

Re: [parisc-linux] Building packages, problems with printf

[Alan Cox]

> Earn brownie points sending off proper fixes to package maintainers. :)

Most package maintainers wont bother. printf as a macro breaks too much code
to be 'interesting' to fix. Many people take the address of printf for 
passing to functions using multiple I/O output methods

> > fixing glibc to not do that seems to not be an option.  ANSI explicitly
> > allows any of the functions in libc to also be defined as macros.

glibc may be ANSI compliant, its just useless if it does this. Useful and
standards compliant  interesect but dont 100% overlap

Alan

Re: [parisc-linux] Building packages, problems with printf

[Matthew Wilcox]

On Mon, Mar 26, 2001 at 12:42:46AM +0100, Alan Cox wrote:
> > Earn brownie points sending off proper fixes to package maintainers. :)
> 
> Most package maintainers wont bother. printf as a macro breaks too much code
> to be 'interesting' to fix. Many people take the address of printf for 
> passing to functions using multiple I/O output methods

you can still do that.  it's still an external function, but for
`optimisation' purposes calls to it go to fprintf.  i think this is a
worthless optimisation myself.

perhaps you can convince drepper of this?  :-)

-- 
Revolutions do not require corporate support.

Re: [parisc-linux] Building packages, problems with printf

[Steve Beattie]

On Mon, Mar 26, 2001 at 09:03:34AM +1000, Alan Modra wrote:
> On Sun, 25 Mar 2001, Matthew Wilcox wrote:
> 
> > Something we've been running into when building packages is the problem
> > that printf is defined as a macro when using gcc 2.97.  This should be
> > resolved by doing the following:
> > 
> > #include <stdio.h>
> > #undef printf
> 
> That's cheating!  The real fix is to turn
> 
> printf (foo_string,
> #if SOMETHING
> abc_param
> #else
> xyz_param
> #endif
> );
> 
> into
> 
> #if SOMETHING
> printf (foo_string, abc_param);
> #else
> printf (foo_string, xyz_param);
> #endif

Actually, another solution is:

(printf) (foo_string,
#if SOMETHING
abc_param
#else
xyz_param
#endif
);

The parentheses surrounding printf prevent macro expansion -- the C
standard explicitly states that it must. We discovered this in the
course of developing FormatGuard, a patch to glibc that turns printf
and the like into macros as a means of preventing format string attacks
(see http://www.immunix.org/formatguard.html for details).

-- 
Steve Beattie                               Don't trust programmers? 
<steve@wirex.net>                         Complete StackGuard distro at
http://immunix.org/~steve/                         immunix.org