Re: [Crash-utility] kernel module parsing failure - mips

On Fri, Dec 02, 2016 at 04:06:20PM -0800, Sagar Borikar wrote: > With 7.1.7, crash is working for MIPS when all drivers are embedded > inside kernel. > When I make the driver loadable and panic the kernel, crash doesn't > locate some symbols correctly. > > please wait... (gathering module symbol data) > crash: invalid size request: 0 type: "pgd page" > > debugged further and find that PGD_ORDER provides incorrect number > due to which the PGD_SIZE macro results in 0. > > Just for fun, I replaced PGD_ORDER with 0(I know its incorrect) and it > went ahead but couldn't run "mod" command successfully as it threw > following error > > crash> mod > mod: cannot access vmalloc'd module memory In order to access vmalloc'd memory we need interpret the page tables correctly. This isn't needed when the modules are built in since then the memory will be in the direct-mapped kseg0 segment. So the "mod" failure is just a consequence of replacing PGD_ORDER with 0.

So the first error should be fixed properly before attempting "mod". What kernel version is this and what page size do to use?

Try running the "help -m" and "mach" commands (you can skip module loading with --no_modules to get to the crash> prompt) and check if the values for the various page table sizes and bits match what your kernel is using. crash> help -m ... pagesize: 4096 pageshift: 12 pagemask: fffffffffffff000 pageoffset: fff pgdir_shift: 22 ptrs_per_pgd: 1024 ptrs_per_pte: 1024 ... crash-mips> mach PAGE SIZE: 4096 _PAGE_PRESENT: 00000001 _PAGE_READ: 00000002 _PAGE_WRITE: 00000004 _PAGE_ACCESSED: 00000008 _PAGE_MODIFIED: 00000010 _PAGE_GLOBAL: 00000020 _PAGE_VALID: 00000040 _PAGE_DIRTY: 00000080

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