linux-kernel - Re: [RFC PATCH] kconfig: introduce KCONFIG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Sat, 24 May 2008 17:20:51 -0700
From:	Steven Fuerst <sfuerst@...nford.edu>
To:	linux-kernel@...r.kernel.org
Cc:	"Tom Spink" <tspink@...il.com>
Subject: Re: [RFC PATCH] kconfig: introduce KCONFIG_* symbols for .c files

<snip>
> >
> > #include <stdio.h>
> >
> > #define CONFIG_FOO      1
> > /* #define CONFIG_BAR   1 */
> >
> > #define STR2(x) #x
> > #define STR(x) STR2(x)
> >
> > #define PASTE2(x, y) x##y
> > #define PASTE(x, y) PASTE2(x, y)
> >
> > #define KCONFIG2(x, y) STR(PASTE(CONFIG_, x))[y]
> > #define KCONFIG(x) (!((KCONFIG2(x, 0) == 'C') && \
> >                                        (KCONFIG2(x, 1) == 'O') && \
> >                                        (KCONFIG2(x, 2) == 'N') && \
> >                                        (KCONFIG2(x, 3) == 'F') && \
> >                                        (KCONFIG2(x, 4) == 'I') && \
> >                                        (KCONFIG2(x, 5) == 'G') && \
> >                                        (KCONFIG2(x, 6) == '_')))
> >
> > int main()
> > {
> >        if (KCONFIG(FOO)) printf("FOO\n");
> >        if (KCONFIG(BAR)) printf("BAR\n");
> >        return 0;
> > }
> >
> >
> > It of course assumes that the result of all defined macros you want to
> > test for do not start with "CONFIG_", so this doesn't work generally. 
> > However, nearly all of the time the arguement to KCONFIG() will be
> > defined to be "1" an integer, or some other known string that doesn't
> > begin with "CONFIG_", so this trick is fairly robust.
>
> I've seen worse abuse of the preprocessor[1]. ;-)

True...  Here's a "nicer" version, that even gets empty defines right.  I've 
checked that gcc is smart enough to compile away the constant string 
comparison.  The only thing wrong with this now is that it'll fail to get
#define CONFIG_BLAH	CONFIG_BLAH
correct, but that's a rather silly corner case.

#include <stdio.h>

#define CONFIG_FOO	1
/* #define CONFIG_BAR	1 */
#define CONFIG_BAZ

#define STR2(x) #x
#define STR(x) STR2(x)

#define PASTE(x, y) x##y

#define KCONFIG(x) \
	(__builtin_strcmp("Z" STR(PASTE(CONFIG_, x)), "ZCONFIG_" #x))

int main()
{
	if (KCONFIG(FOO)) printf("FOO\n");
	if (KCONFIG(BAR)) printf("BAR\n");
	if (KCONFIG(BAZ)) printf("BAZ\n");
	
	return 0;
}

Steven

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/