Hi On Sat, Jul 15, 2017 at 1:09 AM Michael S. Tsirkin <m...@redhat.com> wrote: > > On Sat, Jul 15, 2017 at 12:12:06AM +0200, Marc-André Lureau wrote: > > Hi > > > > On Fri, Jul 14, 2017 at 10:17 PM, Michael S. Tsirkin <m...@redhat.com> > > wrote: > > > On Fri, Jul 14, 2017 at 10:04:31PM +0200, Laszlo Ersek wrote: > > >> > It worries me that the format of this seems completely undefined > > >> > except in the patchset cover letter. > > >> > I don't think we should merge this before it is. > > >> > > >> I'm not sure what you mean, this patch adds "docs/specs/vmcoreinfo.txt". > > >> That file is the first level contract between the guest firmware > > >> (generally, via the linker/loader), the guest kernel driver > > >> (specifically), and QEMU (also specifically). > > >> > > >> The second level contract is the guest kernel's vmcoreinfo ELF note > > >> (which is pointed-to by the first level contract). The layout of that is > > >> specified elsewhere indeed (I don't think it belongs here). > > >> > > >> We've taken care not to trust anything coming from the guest kernel. > > >> > > >> Can you clarify please? > > >> > > >> Thanks > > >> Laszlo > > > > > > All there is is this: > > > > > > +Version 0 content: > > > + > > > + uint64 paddr: > > > + Physical address of the Linux vmcoreinfo ELF note. > > > + uint32 size: > > > + Size of the vmcoreinfo ELF note. > > > > > > It isn't defined here what is the Linux vmcoreinfo ELF note. > > > You want a bit more info so people trying to use it know where to start > > > and what they can get out of it. > > > > QEMU is not responsible for the content of the ELF note. All there is afaik > > is: > > > > https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-kernel-vmcoreinfo > > > > The rest you need to dig in the kernel code and git history I think. > > We need to do a good enough job to at least make it possible for people > to make use of it without reading your python code. > > Documentation/kdump/kdump.txt has a bit more information. > > All of the necessary information about the system kernel's core image > is > encoded in the ELF format, and stored in a reserved area of memory > before a crash. The physical address of the start of the ELF header is > passed to the dump-capture kernel through the elfcorehdr= boot > parameter. Optionally the size of the ELF header can also be passed > when using the elfcorehdr=[size[KMG]@]offset[KMG] syntax. > > > With the dump-capture kernel, you can access the memory image through > /proc/vmcore. This exports the dump as an ELF-format file that you can > write out using file copy commands such as cp or scp. Further, you can > use analysis tools such as the GNU Debugger (GDB) and the Crash tool > to > debug the dump file. This method ensures that the dump pages are > correctly > ordered. > > I know where to find it but most people likely won't be able to. >
What do you learn from that regarding vmcoreinfo? That is it being used by kdump? and that you can use gdb/crash, that we already use to analyse our dumps. > > BTW why does it pass ELF header size? Any idea? https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d3bf37955d46718ee1a7f1fc69f953d2328ba7c2
