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

[Laszlo Ersek]

On 07/06/17 20:09, Dave Anderson wrote:
> 
> 
> ----- 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.

OK, if crash (or earlier versions of crash) need this QEMU patch, then
I'm fine with it -- my R-b stands.

Thanks
Laszlo