On Feb 7, 2008 1:04 AM, Ingo Molnar <[EMAIL PROTECTED]> wrote: > > * Yinghai Lu <[EMAIL PROTECTED]> wrote: > > > minor difference > > + trim_start = highest_pfn << PAGE_SHIFT; > > + trim_size = end_pfn << PAGE_SHIFT; > > > > could cause some problem with 32 bit kernel when mem > 4g. becase > > highest_pfn and end_pfn is unsigned long aka 32 bit ...could overflow. > > > > so need to assign thtem to tr, 32-bitim_start/trim_end at first > > or > > + trim_start = (u64)highest_pfn << PAGE_SHIFT; > > + trim_size = (u64)end_pfn << PAGE_SHIFT; > > indeed ... > > i think the 64-bit behavior of gcc is inherently dangerous, we had > numerous subtle bugs in that area. > > i think perhaps Sparse should be extended to warn about this. I think > any case where on _32-bit_ we have an 'unsigned long' that is shifted to > the left by any significant amount is clearly in danger of overflowing. > _Especially_ when the lvalue is 64-bit! > > or in other words, on any such construct: > > 64-bit lvalue = ... 32-bit value > > we should enforce _explicit_ (u64) conversions.
so you mean gcc will do some optimization to make + trim_start = highest_pfn; + trim_start <<= PAGE_SHIFT; to be + trim_start = highest_pfn << PAGE_SHIFT; looks scary... then gcc need to be fixed. YH -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
