Re: [Crash-utility] question about phys_base
----- 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?
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:
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