On Wed, Oct 9, 2013 at 3:04 AM, HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx> wrote: > (2013/10/08 22:38), Dave Anderson wrote: >> >> >> >> ----- Original Message ----- >>> >>> (2013/10/07 22:21), Dave Anderson wrote: >>> >>>> ----- Original Message ----- >>>>> >>>>> (2013/10/03 22:47), Dave Anderson wrote: >>> >>> >>>>>> ----- Original Message ----- >>>>>>> >>>>>>> (2013/10/02 18:13), HATAYAMA Daisuke wrote: >>>>>>>> >>>>>>>> (2013/10/02 16:48), Kees Cook wrote: >>> >>> >>>>> >>>>> Thanks for detailed explanation. So, there's already a feature in crash >>>>> utility >>>>> to address relocation!, though it's better for me to try them to check >>>>> if >>>>> it's >>>>> really applicable to this feature. My concern is whether --reloc works >>>>> well >>>>> on x86_64 too, because relocation has never done on x86_64 ever, right? >>>> >>>> >>>> Correct. >>>> >>>>> Another concern is that in case of relocation, users need to additional >>>>> information >>>>> regarding runtime symbol information to crash utility. I want to avoid >>>>> additional >>>>> process, automation is preferable if possible. >>>> >>>> >>>> Right. As I mentioned in the case of 32-bit x86 dumpfiles, there is no >>>> automation >>>> available when CONFIG_PHYSICAL_START is larger than >>>> CONFIG_PHYSICAL_ALIGN. The user >>>> either has to be aware of their values in order to calculate the --reloc >>>> argument, >>>> or has to capture a copy of the /proc/kallsyms file on the crashed >>>> system. Typically >>>> users/distros using kdump changed their x86 configurations to avoid >>>> having to deal >>>> with that. >>>> >>> >>> Sorry, I don't understand why relocation size cannot be calculated when >>> CONFIG_PHYSICALSTART > CONFIG_PHYSICAL_ALIGN. Could you explain that? >> >> >> I just meant that when CONFIG_PHYSICAL_START > CONFIG_PHYSICAL_ALIGN, the >> 32-bit x86 kernel >> gets relocated (like the secondary kdump kernel), but that information is >> not readily available >> from the vmlinux/vmcore pair. >> > > My understanding on CONFIG_PHYSICAL_ALIGN was that starting address of > kernel text area > is always rounded up to CONFIG_PHYSICAL_ALIGN, only. Your explanation would > be part I don't > understand well. I'll reconsider it locally... > > >>> >>>>> I guess it's enough if there's runtime symbol addresses because we can >>>>> get relocated >>>>> offset value by comparing it with the compile-time symbol address >>>>> contained in >>>>> a given debuginfo file. Candidates for such symbols are the ones >>>>> contained in >>>>> VMCOREINFO note containing some symbol values for makedumpfile to refer >>>>> to mm-related >>>>> objects in kernel, which is always contained in vmcore generated by >>>>> current kdump and >>>>> also vmcores converted by makedumpfile from it. How about this idea? >>>> >>>> >>>> But how would that differ from using an incorrect (non-matching) vmlinux >>>> file? >>>> >>> >>> It seems to me almost similar to what crash currently does even if we do >>> relocation check. >>> The current check crash currently does is trial-and-error since there's >>> no information >>> indicating given vmcore and vmlinuxcertainly match well. >>> >>> For example, the process I imagine is: >>> >>> 1) try to match vmcore and vmlinux with no relocation. If fails, go >>> to 2). >>> 2) try to match vmcore and vmlinux with relocation. >>> >>> The two steps include symbol table initialization so it might actually be >>> difficult to >>> resume back from 2) to 1). >>> >>> Also, if gap due to phys_base and gap due to relocation can happen at the >>> same time, >>> calculating two values automatically might be futher complicated. So, it >>> would be better >>> to add relocation value in VMCOREINFO. Then, what crash utility sholud do >>> becomes very simple. >> >> >> Yes please... >> >> And while you're at it, the kernel's >> >> VMCOREINFO_SYMBOL(phys_base); >> >> is pretty much useless, at least w/respect to ELF vmcores, since we need >> to know its >> value in order to translate the address. And I don't think that >> makedumpfile uses >> it when it calculates the phys_base that it stores in compressed kdump >> headers. Why >> not put its value instead of its address? >> > > Yes, I've also noticed this fact. Anyway, I'll post a patch to improvement > this phys_base > and a patch to export relocation information in VMCOREINFO. Cool; can you keep me CCed on those patches? I'm interested in seeing and testing it too. Thanks! -Kees -- Kees Cook Chrome OS Security -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
