----- Original Message -----
> From: Wen Congyang <wency@xxxxxxxxxxxxxx>
> Subject: Re: question about phys_base
> Date: Thu, 16 Feb 2012 09:16:28 +0800
>
> > At 02/16/2012 12:17 AM, Dave Anderson Wrote:
> >>
> >>
> >> ----- Original Message -----
> >>> Hi, Dave
> >>>
> >>> I am implementing a new dump command in the qemu. The vmcore's
> >>> format is elf(like kdump). And I try to provide phys_base in
> >>> the PT_LOAD. But if the os uses the first vcpu do kdump, the
> >>> value of phys_base is wrong.
> >>>
> >>> I find a function x86_64_virt_phys_base() in crash's code.
> >>> Is it OK to call this function first? If the function
> >>> successes, we do not calculate phys_base according to PT_LOAD.
> >>
> >> I'm presuming that the qemu-generated ELF file is essentially
> >> a "clone" of a kdump ELF file, and therefore the initialization
> >> sequence would be:
> >>
> >> main()
> >> machdep_init(PRE_GDB)
> >> x86_64_init(PRE_GDB)
> >> x86_64_calc_phys_base()
> >>
> >> where it should fall into this part:
> >>
> >> if ((vd = get_kdump_vmcore_data())) {
> >> for (i = 0; i < vd->num_pt_load_segments; i++) {
> >> phdr = vd->load64 + i;
> >> if ((phdr->p_vaddr >= __START_KERNEL_map) &&
> >> !(IS_VMALLOC_ADDR(phdr->p_vaddr))) {
> >>
> >> machdep->machspec->phys_base =
> >> phdr->p_paddr -
> >> (phdr->p_vaddr &
> >> ~(__START_KERNEL_map));
> >>
> >> if (CRASHDEBUG(1)) {
> >> fprintf(fp, "p_vaddr: %lx
> >> p_paddr: %lx -> ",
> >> phdr->p_vaddr,
> >> phdr->p_paddr);
> >> fprintf(fp, "phys_base:
> >> %lx\n\n",
> >> machdep->machspec->phys_base);
> >> }
> >> break;
> >> }
> >> }
> >>
> >> return;
> >> }
> >>
> >> Question: will the qemu-generated ELF header contain a PT_LOAD segment that
> >> describes the mapped __START_KERNEL_map region?
> >>
> >> If the __START_KERNEL_map PT_LOAD segment does *not* exist, then the code above
> >> would fall through to the "return", and I suppose that you could call
> >> x86_64_virt_phys_base() there instead.
> >>
> >> If there *is* a __START_KERNEL_map PT_LOAD segment, are you saying that
> >> the calculation above would incorrectly calculate phys_base?
> >
> > Because it is hard to calculate phys_base in qemu side. I try to do it like
> > the function get_kernel_base() in qemu.c. But if the os uses the vcpu to do
> > kdump, the phys_base is for the second kernel, not the first kernel. Another
> > problem is that it is for linux, and we donot which the guest is.
> >
>
> For the another problem, I don't know whether the way of checking the
> type of running OS that is typically used, exists now, how about
> letting users to specify the format through command-line? For example
> --elf or --os=linux. Users who try to generate vmcore must know what
> kind of OS is running, so I guess they can choose proper ones.
>
> Of couse, if such way exists, it should be used.
>
> >>
> >> Ideally, there would be some other "differentiator" between qemu-generated
> >> and kdump-generated ELF headers -- while still being a KDUMP clone in all
> >> other respects. (Maybe an ELF NOTE?) And then preferably, that differentiator
> >> could be used to separate the code, i.e., something like:
> >
> > The qemu-generated ELF headers may be the same as kdump-generated ELF headers.
> >
> > Thanks
> > Wen Congyang
>
> kdump ELF vmcore has further VMCOREINFO.
>
> $ readelf -n
> /media/pub3/vmcores/vmcore-2.6.35.14-106.fc14.x86_64-10000-threads
>
> Notes at offset 0x000001c8 with length 0x00000838:
> Owner Data size Description
> CORE 0x00000150 NT_PRSTATUS (prstatus structure)
> CORE 0x00000150 NT_PRSTATUS (prstatus structure)
> VMCOREINFO 0x00000557 Unknown note type:
> (0x00000000)
>
> But diskdump/netdump ELF vmcore doesn't, so crash could possibly get
> confused against this.
>
> OTOH, I think qemu's CPU state information, CPUX86State structure, is
> very useful debugging information. Because kvmdump format has the same
> information, if this information is lost, this can be thouht of as a
> kind of feature regression. So, how adding the information as new note
> information? Then, this can help crash to distinguish the vmcore from
> the original kdump's.
>
> Thanks.
> HATAYAMA, Daisuke
Right -- that would be a good idea. In fact I thought I read that
someone on the qemu-devel list had suggested that Wen do just that.
Dave
>
> >>
> >> if (qemu_generated_ELF_kdump() {
> >> x86_64_virt_phys_base();
> >> return;
> >> }
> >>
> >> if ((vd = get_kdump_vmcore_data())) {
> >> for (i = 0; i < vd->num_pt_load_segments; i++) {
> >> phdr = vd->load64 + i;
> >> if ((phdr->p_vaddr >= __START_KERNEL_map)
> >> &&
> >> ...
> >>
> >> Would that be possible?
> >>
> >> Dave
> >>
> >>
> >
> >
>
>
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