[Crash-utility] [PATCH v2] arm64: fix kernel memory map handling for kaslr-enabled kernel

[AKASHI Takahiro]

On Thu, May 26, 2016 at 03:09:55PM +0530, Pratyush Anand wrote:
> On 26/05/2016:05:13:30 PM, AKASHI Takahiro wrote:
> > On Wed, May 25, 2016 at 10:28:10AM -0400, Dave Anderson wrote:
> 
> [...]
> 
> > > > (This is the reason that I don't think we need a VMCOREINFO for
> > > > CONFIG_RANDOMIZE_BASE.)
> > > 
> > > Well, as long as there's a way to avoid that unnecessary/confusing
> > > warning message for non-KASLR new-vmemmap kernels.
> > > 
> > > I also wonder whether makedumpfile could use it?
> > 
> > -> Pratyush?
> 
> Since  second kernel's initrd cannot include a large file like VMLINUX, so
> makedumpfile should also work without passing '-x vmlinux'.  Therefore,
> makedumpfile will need some minimal symbol's values to be passed in vmcore.

I understand.
(but I wonder why makedumpfile doesn't utilize System.map nor .config.)

> IIUC, then you need to pass CONFIG_RANDOMIZE_BASE in order to calculate
> PHYS_OFFSET. If yes, then why not to pass PHYS_OFFSET itself into vmcore.

No, as I said in the discussions, I don't think that we need
CONFIG_RANDOMIZE_BASE *if* we can read a kernel symbol's value
from /proc/vmcore.

> Following numbers in vmcore [1] is helping me out in implementing __pa() and
> __va() for all page table sizes and levels.
> 
> VMCOREINFO_NUMBER(pgtable_levels);
> VMCOREINFO_NUMBER(va_bits);
> VMCOREINFO_NUMBER(page_shift);

Since We already have VMCOREINFO(PAGESIZE), we won't nedd page_shift.
As well, pgtable_levels can be determined by va_bits and PAGESIZE.
See arch/arm64/Kconfig.

> VMCOREINFO_NUMBER(phys_offset);
> VMCOREINFO_NUMBER(config_kasan);

Let me ask some questions.
* What kind of data in vmcore and how does makedumpfile access
  without vmlinux nor System.map?
* Why do you need CONFIG_KASAN?

Thanks,
-Takahiro AKASHI

> VMCOREINFO_NUMBER(kimage_voffset);
> 
> ~Pratyush
> 
> [1]
> https://github.com/pratyushanand/linux/blob/7011e478aae3e568cc8dca15b6c128fe728416f7/arch/arm64/kernel/machine_kexec.c#L275
> 
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-- 
Thanks,
-Takahiro AKASHI