On Wed, Feb 13, 2013 at 3:59 PM, Jakub Jelinek <ja...@redhat.com> wrote: > On Wed, Feb 13, 2013 at 11:32:00AM +0100, Jakub Jelinek wrote: >> On Wed, Feb 13, 2013 at 02:28:25PM +0400, Konstantin Serebryany wrote: >> > Right. In LLVM we test only with ASAN_FLEXIBLE_MAPPING_AND_OFFSET==1, >> > so this came unnoticed. >> > Fixed in r175049. >> ... >> >> This is ok, thanks. > > Unfortunately, it seems everything fails with that change :( on Linux. > The problem is that the default prelink library range for x86_64 is > 0x3000000000LL to 0x4000000000LL, and that unfortunately overlaps
Forgive my ignorance, what is the default prelink library range? > with the 0x7fff8000LL to 0x10007fff8000LL range that asan wants to use > for the shadow mapping. And the reason for that prelink default range is > that earlier (see e.g. > http://lwn.net/Articles/106177/ > ) Linux on x86_64 used much smaller virtual address space than it does now. > Not sure if there are still systems running pre-2.6.9 kernels or whenever the > PML4 > change made it into Linux kernel on x86-64 and whether people use prelink on > them. But in any case, even if I change the prelink range now (perhaps > conditionally on the size of address space detected by prelink), it will > still cause issues. > > So, either we need to revert that i386.c and asan_mapping.h (SHADOW_OFFSET) > change, or support non-contiguous shadow memory for the Linux x86-64 case. I suggest to either revert or (better) to support flexible mapping and revert the offset only in the gcc compiler module (leaving asan-rt unchanged). non-contiguous shadow memory sounds too scary and costly to support, not worth the benefit. > What could work is if we had: > > 0x000000000000 - 0x00007fff8000 low memory > 0x00007fff8000 - 0x00008fff7000 shadow mem for low memory > 0x00008fff7000 - 0x00067fff8000 protected > 0x00067fff8000 - 0x00087fff8000 shadow mem for mid memory > 0x00087fff8000 - 0x003000000000 protected > 0x003000000000 - 0x004000000000 mid memory > 0x004000000000 - 0x02008fff7000 protected > 0x02008fff7000 - 0x10007fff8000 shadow mem for high memory > 0x10007fff8000 - 0x7fffffffffff high memory > > asan_mapping.h then would need to introduce AddrIsInMidMem and > AddrIsInMidShadow inlines (perhaps defined to false for configurations > that don't need 3 part memory), use those in AddrIsInMem > and AddrIsInShadow, tweak AddrIsInShadowGap (as it has now more gaps) > for this configuration and tweak the mapping code. > > Jakub
