[Crash-utility] [PATCH] arm64: deduce the start address of kernel code, based on kernel version

[Pingfan Liu]

On Tue, Feb 22, 2022 at 10:19 AM HAGIO KAZUHITO(萩尾　一仁)
<k-hagio-ab at nec.com> wrote:
>
> Hi Pingfan,
>
> thanks for the patch.
>
> -----Original Message-----
> > After kernel commit e2a073dde921 ("arm64: omit [_text, _stext) from
> > permanent kernel mapping"), the range [_text, _stext] is reclaimed. But
> > the current crash code still assumes kernel starting from "_text".
> >
> > This change only affects the vmalloced area on arm64 and may result a
> > false in arm64_IS_VMALLOC_ADDR().
> >
> > Since vmcore has no extra information about this trival change, it can
> > only be deduced from kernel version, which means ms->kimage_text can not
> > be correctly initialized until kernel_init() finishes. This is fine
> > since there is no access to vmalloced area at this early stage.
> >
> > Signed-off-by: Pingfan Liu <piliu at redhat.com>
> > ---
> >  arm64.c  | 17 +++++++++++++++++
> >  defs.h   |  1 +
> >  kernel.c |  3 +++
> >  3 files changed, 21 insertions(+)
> >
> > diff --git a/arm64.c b/arm64.c
> > index 4f2c2b5..4aa971c 100644
> > --- a/arm64.c
> > +++ b/arm64.c
> > @@ -92,6 +92,21 @@ static void arm64_calc_VA_BITS(void);
> >  static int arm64_is_uvaddr(ulong, struct task_context *);
> >  static void arm64_calc_KERNELPACMASK(void);
> >
> > +/* called by kernel_init() */
> > +static void arm64_post_kernel_init(void)
> > +{
> > +     struct machine_specific *ms = machdep->machspec;
> > +     struct syment *sp;
> > +
> > +     if (THIS_KERNEL_VERSION >= LINUX(5,11,0))
> > +             sp = kernel_symbol_search("_stext");
> > +     else
> > +             sp = kernel_symbol_search("_text");
> > +
> > +     ms->kimage_text = (sp ? sp->value : 0);
> > +     sp = kernel_symbol_search("_end");
> > +     ms->kimage_end = (sp ? sp->value : 0);
> > +}
> >
> >  /*
> >   * Do all necessary machine-specific setup here. This is called several times
> > @@ -104,6 +119,7 @@ arm64_init(int when)
> >       char *string;
> >       struct machine_specific *ms;
> >
> > +     arch_post_kernel_init = arm64_post_kernel_init;
>
> Why is the arch_post_kernel_init needed, i.e. can't we put it in
> machdep_init(POST_GDB)?
>
Yeah, it is better to handle this issue in that place.

Thanks for the suggestion and I will send out V2 soon.

Regards,

Pingfan