>On Saturday 10 December 2016 07:03 AM, bhe at redhat.com wrote:
>> On 12/10/16 at 09:29am, Baoquan He wrote:
>>> 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:
>>>
>>
>> Sorry, should be:
>> if (page_offset == 0xffff810000000000 && !info->kernel_version > KERNEL_VERSION(2, 6, 21))
>> info->phys_base = 0;
>>
>
>
>But you can not read kernel_version because those version does not have
>VMCOREINFO. So, has_vmcoreinfo() still need to be used.
Thanks for your comments, using has_vmcoreinfo() sounds like a good approach,
but not perfect way. VMCOREINFO has been introduced since 2.6.24,
2.6.22 and 2.6.23 don't have VMCOREINFO but have phys_base.
Conversely, 2.6.22 and 2.6.23 require vmlinux, so we can confirm the existence of
phys_base with that. My idea is:
diff --git a/arch/x86_64.c b/arch/x86_64.c
index 010ea10..893cd51 100644
--- a/arch/x86_64.c
+++ b/arch/x86_64.c
@@ -67,6 +67,14 @@ get_phys_base_x86_64(void)
return TRUE;
}
+ /* linux-2.6.21 or older don't have phys_base, should be set to 0. */
+ if (!has_vmcoreinfo()) {
+ SYMBOL_INIT(phys_base, "phys_base");
+ if (SYMBOL(phys_base) == NOT_FOUND_SYMBOL) {
+ return TRUE;
+ }
+ }
+
for (i = 0; get_pt_load(i, &phys_start, NULL, &virt_start, NULL); i++) {
if (virt_start >= __START_KERNEL_map) {
This fix may resolve my issue, but now I have another question that
"Is the logic of get_phys_base_x86_64() correct in any kernel configuration ?"
I mean I'm worried about the possibility that another offset gets mixed with
the result of get_phys_base_x86_64() like my 2.6.21 case.
After phys_base was introduced, does it always equal to the offset which can be
calculated from PT_LOAD headers ?
Thanks,
Atsushi Kumagai
>
>~Pratyush
>
>>>>
>>>>>>
>>>>>> 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
>
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