[tip:x86/urgent] x86: Document __phys_reloc_hide() usage in __pa_symbol()
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From: tip-bot for Namhyung Kim on 11 Aug 2010 03:50 Commit-ID: 8fd49936a8cac246fc9ed85508556c82cd44cf68 Gitweb: http://git.kernel.org/tip/8fd49936a8cac246fc9ed85508556c82cd44cf68 Author: Namhyung Kim <namhyung(a)gmail.com> AuthorDate: Wed, 11 Aug 2010 15:37:41 +0900 Committer: Ingo Molnar <mingo(a)elte.hu> CommitDate: Wed, 11 Aug 2010 08:43:49 +0200 x86: Document __phys_reloc_hide() usage in __pa_symbol() Until all supported versions of gcc recognize -fno-strict-overflow, we should keep the RELOC_HIDE() magic in __pa_symbol(). Comment it. Signed-off-by: Namhyung Kim <namhyung(a)gmail.com> LKML-Reference: <1281508661-29507-1-git-send-email-namhyung(a)gmail.com> Signed-off-by: Ingo Molnar <mingo(a)elte.hu> --- arch/x86/include/asm/page.h | 7 +++++++ 1 files changed, 7 insertions(+), 0 deletions(-) diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h index 625c3f0..8ca8283 100644 --- a/arch/x86/include/asm/page.h +++ b/arch/x86/include/asm/page.h @@ -37,6 +37,13 @@ static inline void copy_user_page(void *to, void *from, unsigned long vaddr, #define __pa_nodebug(x) __phys_addr_nodebug((unsigned long)(x)) /* __pa_symbol should be used for C visible symbols. This seems to be the official gcc blessed way to do such arithmetic. */ +/* + * We need __phys_reloc_hide() here because gcc may assume that there is no + * overflow during __pa() calculation and can optimize it unexpectedly. + * Newer versions of gcc provide -fno-strict-overflow switch to handle this + * case properly. Once all supported versions of gcc understand it, we can + * remove this Voodoo magic stuff. (i.e. once gcc3.x is deprecated) + */ #define __pa_symbol(x) __pa(__phys_reloc_hide((unsigned long)(x))) #define __va(x) ((void *)((unsigned long)(x)+PAGE_OFFSET)) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |