On Thu, Jun 23, 2016 at 12:44:12PM +0530, Pratyush Anand wrote: > Hi Takahiro, > > Thanks for your reply. > > On 22/06/2016:02:59:41 PM, AKASHI Takahiro wrote: > > On Mon, Jun 20, 2016 at 11:02:22AM +0530, Pratyush Anand wrote: > > > +Atsushi > > > > > > Hi Takahiro, > > > > > > On 16/06/2016:11:48:28 PM, Geoff Levand wrote: > > > > From: AKASHI Takahiro <takahiro.akashi at linaro.org> > > > > > > > > For the current crash utility, we need to know, at least, > > > > - kimage_voffset > > > > - PHYS_OFFSET > > > > to handle the contents of core dump file (/proc/vmcore) correctly due to > > > > the introduction of KASLR (CONFIG_RANDOMIZE_BASE) in v4.6. > > > > This patch puts them as VMCOREINFO's into the file. > > > > > > > > - VA_BITS > > > > is also added for makedumpfile command. > > > > > > Thanks for adding them. They are quite helpful for makedumpfile as well. > > > > > > > More VMCOREINFO's may be added later. > > > > > > Yes, we will need to pass VMCOREINFO_SYMBOL(_text) and VMCOREINFO_SYMBOL(_end) > > > in order to work with makedumpfile. > > > > I know that adding those symbols is the easiest way, but > > theoretically, if we know the physical address of "swapper_pg_dir", > > But, we know only it's virtual address. What I meant here is that, if we know the physical address of "swapper_pg_dir", we don't have to know neither of "_text", "_end", "kimage_voffset" nor "PHYS_OFFSET". I just wanted to ask you whether you thought of this possibility. > > > instead of its virtual address, we can access all the memory pointed to > > by any kernel virtual address. > > How do you rationalize that we need to know "_text" and "_end"? > > Well, we need some mechanism so that we can decide if an address can be > translated using linear mapping of virt_to_phys(). All the entries in MMU tables are based on "physical" addresses, and so we don't care whether a given address is in linear mapping or not in walking through MMU. See what I mean? Thanks, -Takahiro AKASHI > Alternatively, probably we can do like this: > -- Translate all address between "SYMBOL(swapper_pg_dir)" and "SYMBOL(swapper_pg_dir) > + SWAPPER_DIR_SIZE" using virt_to_phys() and now we can read values from > dumpfile using that physical address. This way we can get PGD/PMD/PUD values. > -- PTE values may lie out side this range, however that address should still be > linearly translatable. We can use virt_to_phys() macro from them as well. > > In summary, we can translate address of PGD/PMD/PUD/PTE using virt_to_phys() > and rest all can be translated using page table entries. > > ~Pratyush
