[Crash-utility] [PATCHv5 1/3] crash-utility/arm64: store phy_offset and memstart_addr separately

[HAGIO KAZUHITO(萩尾 一仁)]

Hi Pingfan, Lianbo,

-----Original Message-----
> Hi, Pingfan
> 
> Thank you for the update.
> 
> > This bug connects with kernel commit 7bc1a0f9e176 ("arm64: mm: use
> > single quantity to represent the PA to VA translation"), memstart_addr
> > can be negative, which makes it different from real phys_offset. If
> > using memstart_addr to calculate the real paddr, the unreasonable paddr
> > will be got.
> 
> > Furthermore, in crash utility, PTOV() needs memstart_addr to calculate
> > VA from PA, while getting PFN offset in a dumpfile, phys_offset is
> > required.
> 
> As you mentioned above, the calculation formula has been changed, how to
> deal with the backward compatibility issue? Should we use kernel version
> to determine which code branch it should execute? Please correct me if I
> was wrong.

I'm not sure whether this is the same as Lianbo's concern, but my concern
is that if a kernel has the "physvirt_offset" variable, PTOV() looks to be
changed needlessly by the patch.  Does it work with such an old kernel?

static void
arm64_calc_physvirt_offset(void)
{
...
        ms->physvirt_offset = ms->phys_offset_nominal;

        if ((sp = kernel_symbol_search("physvirt_offset")) &&
                        machdep->machspec->kimage_voffset) {
                if (READMEM(pc->mfd, &physvirt_offset, sizeof(physvirt_offset),
                        sp->value, sp->value -
                        machdep->machspec->kimage_voffset) > 0) {
                                ms->physvirt_offset = physvirt_offset;  <<-- this case
                }
        }
}

-#define PTOV(X) \
-       ((unsigned long)(X) - (machdep->machspec->physvirt_offset))

+#define PTOV(X) \
+       (((unsigned long)(X) - (machdep->machspec->physvirt_offset)) | PAGE_OFFSET)


Maybe we can set ms->physvirt_offset to work with the current PTOV()
when no symbol?

Sorry that I cannot try the patch or ideas because of no machine.

Thanks,
Kazu