Re: [Qemu-devel] [PATCH v2 5/7] kdump: add vmcoreinfo ELF note

[Dave Anderson]

----- Original Message -----
> Hi
> 
> On Thu, Jul 6, 2017 at 7:13 PM, Laszlo Ersek <address@hidden> wrote:
> > On 07/06/17 12:16, Marc-André Lureau wrote:
> >> kdump header provides offset and size of the vmcoreinfo ELF note,
> >> append it if available.
> >>
> >> Signed-off-by: Marc-André Lureau <address@hidden>
> >> ---
> >>  dump.c | 20 ++++++++++++++++++++
> >>  1 file changed, 20 insertions(+)
> >>
> >> diff --git a/dump.c b/dump.c
> >> index f699198204..dd416ad271 100644
> >> --- a/dump.c
> >> +++ b/dump.c
> >> @@ -839,6 +839,16 @@ static void create_header32(DumpState *s, Error
> >> **errp)
> >>      kh->dump_level = cpu_to_dump32(s, DUMP_LEVEL);
> >>
> >>      offset_note = DISKDUMP_HEADER_BLOCKS * block_size + size;
> >> +    if (s->vmcoreinfo) {
> >> +        uint64_t hsize, name_size, size_vmcoreinfo_desc,
> >> offset_vmcoreinfo;
> >> +
> >> +        get_note_sizes(s, s->vmcoreinfo, &hsize, &name_size,
> >> &size_vmcoreinfo_desc);
> >> +        offset_vmcoreinfo = offset_note + s->note_size -
> >> s->vmcoreinfo_size +
> >> +            (DIV_ROUND_UP(hsize, 4) + DIV_ROUND_UP(name_size, 4)) * 4;
> >> +        kh->offset_vmcoreinfo = cpu_to_dump64(s, offset_vmcoreinfo);
> >> +        kh->size_vmcoreinfo = cpu_to_dump32(s, size_vmcoreinfo_desc);
> >> +    }
> >> +
> >>      kh->offset_note = cpu_to_dump64(s, offset_note);
> >>      kh->note_size = cpu_to_dump32(s, s->note_size);
> >>
> >> @@ -939,6 +949,16 @@ static void create_header64(DumpState *s, Error
> >> **errp)
> >>      kh->dump_level = cpu_to_dump32(s, DUMP_LEVEL);
> >>
> >>      offset_note = DISKDUMP_HEADER_BLOCKS * block_size + size;
> >> +    if (s->vmcoreinfo) {
> >> +        uint64_t hsize, name_size, size_vmcoreinfo_desc,
> >> offset_vmcoreinfo;
> >> +
> >> +        get_note_sizes(s, s->vmcoreinfo, &hsize, &name_size,
> >> &size_vmcoreinfo_desc);
> >> +        offset_vmcoreinfo = offset_note + s->note_size -
> >> s->vmcoreinfo_size +
> >> +            (DIV_ROUND_UP(hsize, 4) + DIV_ROUND_UP(name_size, 4)) * 4;
> >> +        kh->offset_vmcoreinfo = cpu_to_dump64(s, offset_vmcoreinfo);
> >> +        kh->size_vmcoreinfo = cpu_to_dump64(s, size_vmcoreinfo_desc);
> >> +    }
> >> +
> >>      kh->offset_note = cpu_to_dump64(s, offset_note);
> >>      kh->note_size = cpu_to_dump64(s, s->note_size);
> >>
> >>
> >
> > I continue to think that this patch is unnecessary, but if you insist,

> > it does look OK to me.
> >
> > Reviewed-by: Laszlo Ersek <address@hidden>
> 
> Without it, crash doesn't read the vmcoreinfo PT_NOTE. And for some
> reason, the phys_base in the header wasn't enough (to be doubled
> checked).
>
> Any comment Dave about crash handling of vmcoreinfo in kdump files?

It just reads the kdump_sub_header's offset_vmcoreinfo and size_vmcoreinfo
fields to gather the vmcoreinfo data into a local buffer of memory, and
scans the strings for whatever it's looking for. 

With respect to phys_base, the only thing that might be of consequence
is this fairly recent change that's currently only in the github repo,
queued for crash-7.2.0:

  commit a4a538caca140a8e948bbdae2be311168db7a1eb
  Author: Dave Anderson <address@hidden>
  Date:   Tue May 2 16:51:53 2017 -0400

    Fix for Linux 4.10 and later kdump dumpfiles, or kernels that have
    backported commit 401721ecd1dcb0a428aa5d6832ee05ffbdbffbbe, titled
    "kexec: export the value of phys_base instead of symbol address".
    Without the patch, if the x86_64 "phys_base" value in the VMCOREINFO
    note is a negative decimal number, the crash session fails during
    session intialization with a "page excluded" or "seek error" when
    reading "page_offset_base".
    (address@hidden)

Also, crash-7.1.9 was the first version that started looking in the 
vmcoreinfo data for phys_base instead of in the kdump_sub_header.

Dave

> 
> 
> 
> --
> Marc-André Lureau
>