On 12/09/16 at 10:25pm, Baoquan He wrote: > On 12/09/16 at 03:40pm, Pratyush Anand wrote: > > > > - page_dir = SYMBOL(init_level4_pgt); > > > > + page_dir = SYMBOL(init_level4_pgt) - __START_KERNEL_map + phys_base; > > > > > > I found that this change breaks the backward compatibility for > > > kernel 2.6.21 or older since phys_base was introduced in kernel 2.6.22 > > > by the commit below: > > > > > > commit 1ab60e0f72f71ec54831e525a3e1154f1c092408 > > > Author: Vivek Goyal <vgoyal at in.ibm.com> > > > Date: Wed May 2 19:27:07 2007 +0200 > > > > > > [PATCH] x86-64: Relocatable Kernel Support > > > > > > There is no problem if phys_base is always 0 in older kernel, but > > > get_phys_base_x86_64() calculates "phys_base = 0x100000" from my vmcore: > > This is really awkward. Checked code, found PAGE_OFFSET is > 0xffff810000000000 before 2.6.26, then changed to 0xffff880000000000 > after that. Can we check the page_offset calculated from pt_load > segments, meanwhile check if has VMCOREINFO and osrelease after 2.6.21. > > With both of above condition, we could set phys_vase to 0. Not sure if > this can solve the existing problem. I meant making a judgement: if (page_offset == 0xffff810000000000 && info->kernel_version > KERNEL_VERSION(2, 6, 21)) info->phys_base = 0; > > > > > > > Type Offset VirtAddr PhysAddr > > > FileSiz MemSiz Flags Align > > > NOTE 0x0000000000000190 0x0000000000000000 0x0000000000000000 > > > 0x0000000000000590 0x0000000000000590 0 > > > LOAD 0x0000000000000720 0xffffffff80000000 0x0000000000100000 // CONFIG_PHYSICAL_START = 0x100000 > > > 0x00000000008b2000 0x00000000008b2000 RWE 0 > > > LOAD 0x00000000008b2720 0xffff810000000000 0x0000000000000000 > > > 0x00000000000a0000 0x00000000000a0000 RWE 0 > > > LOAD 0x0000000000952720 0xffff810000100000 0x0000000000100000 > > > 0x0000000000f00000 0x0000000000f00000 RWE 0 > > > LOAD 0x0000000001852720 0xffff810005000000 0x0000000005000000 > > > 0x00000000caf70000 0x00000000caf70000 RWE 0 > > > LOAD 0x00000000cc7c2720 0xffff810100000000 0x0000000100000000 > > > 0x0000000070000000 0x0000000070000000 RWE 0 > > > > > > Of course we shouldn't use that invalid phys_base: > > > > > > crash> sym init_level4_pgt > > > ffffffff80101000 (T) init_level4_pgt > > > crash> vtop ffffffff80101000 > > > VIRTUAL PHYSICAL > > > ffffffff80101000 101000 // just "VIRTUAL - __START_KERNEL_map" > > > > > > PML4 DIRECTORY: ffffffff80101000 > > > PAGE DIRECTORY: 103027 > > > PUD: 103ff0 => 105027 > > > PMD: 105000 => 1e3 > > > PAGE: 0 (2MB) > > > > > > PTE PHYSICAL FLAGS > > > 1e3 0 (PRESENT|RW|ACCESSED|DIRTY|PSE|GLOBAL) > > > > > > PAGE PHYSICAL MAPPING INDEX CNT FLAGS > > > ffff810005004838 101000 0 0 1 400 > > > crash> > > > > > > At first I thought about setting 0 to phys_base if the kernel is > > > older than 2.6.22, but unfortunately we can't get the kernel version > > > before getting correct phys_base since VtoP is necessary to read > > > system_utsname. > > > (and 2.6.21 doesn't have VMCOREINFO, OSRELEASE can't be used too.) > > > > We can use this fact may be. So, when has_vmcoreinfo() is false we can > > consider it as old kernel and can set phys_start as 0. > > > > > > Bao, any opnion? > > > > ~Pratyush
