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 > >