Re: [PATCH] Use -fno-unit-at-a-time if gcc supports it
From: David Mosberger-Tang (David.Mosberger_at_acm.org)
Date: 09/06/03
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To: Jan Hubicka <jh@suse.cz> Date: 06 Sep 2003 01:10:57 -0700
For what it's worth, it was straight-forward to get the ia64 linux
kernel to compile & boot with the latest gcc snapshot. I could make a
patch, if anyone cares, but it was mostly trival stuff: a small
cleanup in init_task.c and a few changes in init.h/compiler.h to use
"attribute ((used))".
Even the wait-channels seem to come out right, though I'm not sure
what's being done there is guaranteed to continue to work as the
compiler gets more aggressive...
--david
-- Interested in learning more about IA-64 Linux? Try http://www.lia64.org/book/ >>>>> On Sat, 06 Sep 2003 09:10:10 +0200, Jan Hubicka <jh@suse.cz> said: >> On Fri, 2003-09-05 at 11:17, Andreas Jaeger wrote: >> >> >> > Since unit-at-a-time has better inlining heuristics the better >> way is > to add the used attribute - but that takes some time. >> The short-term > solution would be to add the compiler flag, >> >> Won't we get a linker error if a static symbol is used but >> optimized-away? It shouldn't be hard to fix the n linker errors >> that crop up. Jan> Yes, you get linker error. You may also run into Jan> misscompilation assuiming that function is static and it is Jan> both called by hand in asm and by function call and there is Jan> missing attribute used and asmlinkage definition. In that case Jan> GCC would conclude to change into register calling convention Jan> on i386 breaking asm code. Jan> I would expect this to be rare as functions tends to be used Jan> either by assembly or by normal code but not by both. >> And why are we using static symbols in inline assembly outside >> of the compilation scope? Jan> The toplevel asm statements are common source of this at least Jan> in glibc. I didn't look much into the kernel sources. Jan> I would be very happy if someone did look on that. It may be Jan> well possible that implementing tricks you do currently with Jan> toplevel asm staements would need further extensions in GCC now Jan> and it would be nice to know about that. Jan> For instance it used to be possible to force function to go Jan> into given section by changing the section by hand, but now you Jan> have to use section attribute (that is cleaner anyway) >> Anyhow, if it generates an error, this isn't hard to fix. >> >> Here is the start... >> >> Robert Love >> >> >> --- linux-rml/include/linux/compiler.h Fri Sep 5 11:57:56 2003 >> +++ linux/include/linux/compiler.h Fri Sep 5 12:02:02 2003 @@ >> -74,6 +74,19 @@ #define __attribute_pure__ /* unimplemented */ >> #endif >> >> +/* + * As of gcc 3.2, we can mark a function as 'used' and gcc >> will assume that, + * even if it does not find a reference to it >> in any compilation unit. We + * need this for gcc 3.4 and >> beyond, which can optimize on a program-wide + * scope, and not >> just one file at a time, to avoid static symbols being + * >> discarded. + */ +#if (__GNUC__ == 3 && __GNUC_MINOR__ > 1) || >> __GNUC__ > 3 +#define __attribute_used__ __attribute__((used)) >> +#else +#define __attribute_used__ /* unimplemented */ +#endif + Jan> I believe there is little trick - attribute used works either Jan> for variables or functions. Functions can be marked as used Jan> only for GCC 3.4+ if I am right, so you may need Jan> __attribute_used_function__ and __attribute_used_variable__ Jan> macros for that. Jan> Honza >> /* This macro obfuscates arithmetic on a variable address so that >> gcc shouldn't recognize the original var, and make assumptions >> about it */ #define RELOC_HIDE(ptr, off) \ >> >> Jan> - To unsubscribe from this list: send the line "unsubscribe Jan> linux-kernel" in the body of a message to Jan> majordomo@vger.kernel.org More majordomo info at Jan> http://vger.kernel.org/majordomo-info.html Please read the FAQ Jan> at http://www.tux.org/lkml/ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
- Previous message: Benjamin Herrenschmidt: "Re: compile problems on PPC for 2.6.0-test4"
- Maybe in reply to: Andi Kleen: "[PATCH] Use -fno-unit-at-a-time if gcc supports it"
- Next in thread: David Mosberger: "Re: [PATCH] Use -fno-unit-at-a-time if gcc supports it"
- Reply: David Mosberger: "Re: [PATCH] Use -fno-unit-at-a-time if gcc supports it"
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