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Date: Fri, 19 Jan 2007 09:44:59 -0500 (EST) From: "Robert P. J. Day" <rpjday@...dspring.com> To: Adrian Bunk <bunk@...sta.de> cc: Pekka Enberg <penberg@...helsinki.fi>, Linux kernel mailing list <linux-kernel@...r.kernel.org> Subject: Re: can someone explain "inline" once and for all? On Fri, 19 Jan 2007, Adrian Bunk wrote: > On Fri, Jan 19, 2007 at 03:01:44PM +0200, Pekka Enberg wrote: > > On 1/19/07, Robert P. J. Day <rpjday@...dspring.com> wrote: > > >is there a simple explanation for how to *properly* define inline > > >routines in the kernel? and maybe this can be added to the > > >CodingStyle guide (he mused, wistfully). > > > > AFAIK __always_inline is the only reliable way to force inlining where > > it matters for correctness (for example, when playing tricks with > > __builtin_return_address like we do in the slab). > > > > Anything else is just a hint to the compiler that might be ignored if > > the optimizer thinks it knows better. > > With the current implementation in the kernel (and considering that > CONFIG_FORCED_INLINING was implemented in a way that it never had > any effect), __always_inline and inline are currently equivalent. right, and that last part explains that snippet i previously posted from include/asm-alpha/compiler.h ======================== #ifdef __KERNEL__ /* Some idiots over in <linux/compiler.h> thought inline should imply always_inline. This breaks stuff. We'll include this file whenever we run into such problems. */ ======================== which is a result of this from include/linux/compiler.h: ======================== #define inline inline __attribute__((always_inline)) #define __inline__ __inline__ __attribute__((always_inline)) #define __inline __inline __attribute__((always_inline)) which certainly seems to suggest that *ever* explicitly stating "always inline" is redundant, no? maybe i'm missing something critical here but this just seems wrong. > __always_inline is mostly an annotation that really bad things might > happen if the code doesn't get inlined. and that makes sense. it has no effect, it's more for just commenting. but it's still kind of misleading. rday - 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/
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