Re: [Crash-utility] question about phys_base
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.
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
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