[Crash-utility] [PATCH v2] arm64: fix the "pud page" crash for live system

[HAGIO KAZUHITO(萩尾 一仁)]

-----Original Message-----
> 1.) When I tested live system with "crash vmlinux /proc/kcore" in kernel v5.7,
>     I met the following crash issue:
>        ........................................
>        crash: seek error: kernel virtual address: ffff75e9fffff000  type: "pud page"
>        ........................................
> 
> 2.) The root cause is the PTOV does not work correctly for some kernel,
>     and then arm64_vtop_4level_4k() does not work correctly too.
> 
>     Why PTOV does not work?
> 
>     Because the physvirt_offset does not get the correct value.
> 
> 3.) This patch uses symbol_value_from_proc_kallsyms() to get the
>     virtual address of "physvirt_offset", and then uses
>     READMEM(,..,KCORE_USE_VADDR) to get the correct value of
>     "physvirt_offset".
> 
>     And also updates the ms->phys_offset which is initialized with
>     a wrong value in kernel version [5.4, 5.10).
> 
>     Also add more comments for arm64_calc_physvirt_offset().
> 
> Signed-off-by: Huang Shijie <shijie at os.amperecomputing.com>
> ---
> v1 --> v2:
> 	v1 tried to get the correct value for phys_offset,
> 	and then get the physvirt_offset correctly.
> 
> 	v2 tried to get the physvirt_offset correctly,
> 	and them update phys_offset correctly.
> 
> 	Tested this patch with kernel 5.7.

Thank you for the change.  The code looks good to me.

Acked-by: Kazuhito Hagio <k-hagio-ab at nec.com>

Lianbo, can we add the following with this?  it's missing in help -m.

@@ -1065,6 +1065,7 @@ arm64_dump_machdep_table(ulong arg)
                fprintf(fp, "        kimage_voffset: %016lx\n", ms->kimage_voffset);
        }
        fprintf(fp, "           phys_offset: %lx\n", ms->phys_offset);
+       fprintf(fp, "       physvirt_offset: %lx\n", ms->physvirt_offset);
        fprintf(fp, "__exception_text_start: %lx\n", ms->__exception_text_start);
        fprintf(fp, "  __exception_text_end: %lx\n", ms->__exception_text_end);
        fprintf(fp, " __irqentry_text_start: %lx\n", ms->__irqentry_text_start);

Thanks,
Kazu