>On Monday 13 February 2017 11:56 AM, Atsushi Kumagai wrote: >> Hello Pratyush, >> >>> `makedumpfile --mem-usage /proc/kcore` has been broken after kaslr specific >>> modifications. I have proposed a kernel patch [0] which has been ACKed by >>> Andrew Morton and is available in next-2017020 now. Hopefully, it should be >>> part of upstream in v4.10 release. This kernel patch helps to fix this >>> issue for both the case of kaslr enabled and disabled. >>> >>> To seek other's feedback, I am sending makedumpfile patches before kernel >>> patch hits upstream. >> >> Thanks for taking care of this feature. >> I understand that the problem is: >> >> - phys_base is necessary for VtoP, but: >> - SYMBOL(phys_base) is unavailable since /proc/kcore doesn't export VMCOREINFO. >> - get_phys_base() doesn't work well since current PT_LOAD doesn't have valid p_paddr. > >Yes, this is what the problem is. > >> >> The new makedumpfile with this patches can show unexpected behavior since it >> will refer to invalid p_paddr(always 0). Of course, also current makedumpfile cannot >> work if phys_base isn't 0. >> >> If we don't have any way to get phys_base in 1st kernel environment, >> I think we should disable this feature in older kernel (e.g. by checking kernel version). > >Hummm..I had thought that distros with old kernel will backport kernel >patch and then can use this feature. If we disable it for older kernel, >then they will not be able to do it. > >would it be fine if I cc kernel patch to stable mailing list? It seems >that patch can be easily applied all older kernel. Even if there are some "supported" older kernels, there is no guarantee that all of the kernels provide valid p_paddr. So makedumpfile have to know whether the target kernel supports --mem-usage or not in older kernel. Is it possible to add a new stuff into PT_NOTE of /proc/kcore to signify the kernel supports --mem-usage ? Otherwise, my only idea is --force option for older kernel, expert user can use it if he is sure that the kernel has valid p_paddr. Thanks, Atsushi Kumagai
