Re: [Qemu-devel] [RFC][PATCH 07/16 v6] target-i386: Add API to add extra memory mapping

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-02-15 06:19, Wen Congyang wrote:
> At 02/15/2012 01:35 AM, Jan Kiszka Wrote:
>> On 2012-02-09 04:24, Wen Congyang wrote:
>>> Crash needs extra memory mapping to determine phys_base.
>>>
>>> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
>>> ---
>>>  cpu-all.h               |    2 ++
>>>  target-i386/arch-dump.c |   43 +++++++++++++++++++++++++++++++++++++++++++
>>>  2 files changed, 45 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/cpu-all.h b/cpu-all.h
>>> index efb5ba3..290c43a 100644
>>> --- a/cpu-all.h
>>> +++ b/cpu-all.h
>>> @@ -530,10 +530,12 @@ int cpu_write_elf64_note(int fd, CPUState *env, int cpuid,
>>>                           target_phys_addr_t *offset);
>>>  int cpu_write_elf32_note(int fd, CPUState *env, int cpuid,
>>>                           target_phys_addr_t *offset);
>>> +int cpu_add_extra_memory_mapping(MemoryMappingList *list);
>>>  #else
>>>  #define cpu_get_memory_mapping(list, env)
>>>  #define cpu_write_elf64_note(fd, env, cpuid, offset) ({ -1; })
>>>  #define cpu_write_elf32_note(fd, env, cpuid, offset) ({ -1; })
>>> +#define cpu_add_extra_memory_mapping(list) ({ 0; })
>>>  #endif
>>>  
>>>  #endif /* CPU_ALL_H */
>>> diff --git a/target-i386/arch-dump.c b/target-i386/arch-dump.c
>>> index 4c0ff77..d96f6ae 100644
>>> --- a/target-i386/arch-dump.c
>>> +++ b/target-i386/arch-dump.c
>>> @@ -495,3 +495,46 @@ int cpu_write_elf32_note(int fd, CPUState *env, int cpuid,
>>>  {
>>>      return x86_write_elf32_note(fd, env, cpuid, offset);
>>>  }
>>> +
>>> +/* This function is copied from crash */
>>
>> And what does it do there and here? I suppose it is Linux-specific - any
>> version? This should be documented and encoded in the function name.
>>
>>> +static target_ulong get_phys_base_addr(CPUState *env, target_ulong *base_vaddr)
>>> +{
>>> +    int i;
>>> +    target_ulong kernel_base = -1;
>>> +    target_ulong last, mask;
>>> +
>>> +    for (i = 30, last = -1; (kernel_base == -1) && (i >= 20); i--) {
>>> +        mask = ~((1LL << i) - 1);
>>> +        *base_vaddr = env->idt.base & mask;
>>> +        if (*base_vaddr == last) {
>>> +            continue;
>>> +        }
>>> +
>>> +        kernel_base = cpu_get_phys_page_debug(env, *base_vaddr);
>>> +        last = *base_vaddr;
>>> +    }
>>> +
>>> +    return kernel_base;
>>> +}
>>> +
>>> +int cpu_add_extra_memory_mapping(MemoryMappingList *list)
>>
>> Again, what does "extra" mean? Probably guest-specific, no?
> 
> crash will calculate the phys_base according to the virtual address and physical
> address stored in the PT_LOAD.

Crash is a Linux-only tool, dump must not be restricted to that guest -
but could contain transparent extensions of the file format if needed.

> 
> If the vmcore is generated by 'virsh dump'(use migration to implement dumping),
> crash calculates the phys_base according to idt.base. The function get_phys_base_addr()
> uses the same way to calculates the phys_base.

Hmm, where are those special registers (idt, gdt, tr etc.) stored in the
vmcore file, BTW?

> 
> I think crash may work without this. I will verify it.

Does gdb require this?

Jan

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