On Tue, May 01, 2007 at 02:43:30PM -0700, Linus Torvalds wrote: > > > On Tue, 1 May 2007, Josh Triplett wrote: > > > > Does this still apply? Do current versions of GCC still have this problem? > > If not, can the option and warning go away? > > Even if current versions of gcc don't triple the build time (and for the > kernel, I suspect it doesn't, because we've tried to clean up our header > files), the generated _code_ will invariably suck. FWIW, I do sparse runs on the fedora development kernels as part of our daily builds now, and of the latest ones at http://people.redhat.com/davej/kernels/Fedora/fc7/warnings.txt (concatenated warning logs from i586/i686/x86_64/ppc/ppc64/s390 builds) that 'expensive pointer subtraction' turns up 3705 times. Interestingly, 1873 of those instances are from include/linux/mm.h on the x86-64 build. It's complaining about this line... static __always_inline void *lowmem_page_address(struct page *page) { return __va(page_to_pfn(page) << PAGE_SHIFT); } ... unsigned long page_to_pfn(struct page *page) { return __page_to_pfn(page); } ... #define __page_to_pfn(page) ((unsigned long)((page) - mem_map) + \ ARCH_PFN_OFFSET) looks like the other two variants of __page_to_pfn also use similar arithmatic. Dave -- http://www.codemonkey.org.uk - To unsubscribe from this list: send the line "unsubscribe linux-sparse" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
