On Tue, Jan 7, 2014 at 6:55 AM, Sam Ravnborg <sam@xxxxxxxxxxxx> wrote: > On Mon, Jan 06, 2014 at 12:47:07PM -0800, Josh Triplett wrote: >> [CCing build-system folks and others likely to know about potential >> issues.] >> >> Does anyone have any objection to the use of "#pragma once" instead of >> the usual #ifndef-#define-...-#endif include guard? GCC, LLVM/clang, >> and the latest Sparse all support either method just fine. (I added >> support to Sparse myself.) Both have equivalent performance. "#pragma >> once" is simpler, and avoids the possibility of a typo in the defined >> guard symbol. > For kernel headers no concern. Just being cautious: Do we know the minimum gcc version that supports #pragma once? Furthermore I found this: | #pragma once does have one drawback (other than being non-standard) and | that is if you have the same file in different locations then the compiler will | think these are different files. http://stackoverflow.com/questions/787533/is-pragma-once-a-safe-include-guard With asm-generic and uapi, do we have multiple header files that deliberately use the same include guards? I know we have header files that deliberately don't have include guards (e.g. asm/unistd.h on some architectures). > For UAPI headers we should be more carefull - as we do not know which > compiler it ends up seeing - and what version. Furthermore some userspace may rely on doing #define XXX to avoid including a specific kernel header (yes, it's ugly). Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
