Sorry for late reply.
(2013/04/30 4:51), Vivek Goyal wrote:
> On Sat, Apr 13, 2013 at 09:21:46AM +0900, HATAYAMA Daisuke wrote:
>> Treat memory chunks referenced by PT_LOAD program header entries in
>> page-size boundary in vmcore_list. Formally, for each range [start,
>> end], we set up the corresponding vmcore object in vmcore_list to
>> [rounddown(start, PAGE_SIZE), roundup(end, PAGE_SIZE)].
>>
>> This change affects layout of /proc/vmcore. The gaps generated by the
>> rearrangement are newly made visible to applications as
>> holes. Concretely, they are two ranges [rounddown(start, PAGE_SIZE),
>> start] and [end, roundup(end, PAGE_SIZE)].
>
> Sorry did not understand this part. So if end is not page aligned, then
> we roundup(end, PAGE_SIZE) and increase the PT_LOAD size accordingly?
> Similarly for start, we do roundown().
>
> - Can you really rounddown() start? Then you will have to change start
> virtual address in program header and that's not really a good idea.
>
No, there's no need to change paddr in program header. Pleaes notice
that difference between what objects in vc_list refer to and what
PT_LOAD program headers refer to. The former covers not only kernel
memory but also the extra memory, while the latter the kernel memory only.
> - So this extra memory for end, we read from old memory and not fill
> with zeros?
Yes. The extra memory is not covered by any program header, i.e. hole.
The extra memory is not modified at all, exported with no change; if it
is used by BIOS, users can see BIOS data there. This design comes from
the discussion with Erick.
>
>>
>> Signed-off-by: HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com>
>> ---
>>
>> fs/proc/vmcore.c | 26 ++++++++++++++++++++------
>> 1 files changed, 20 insertions(+), 6 deletions(-)
>>
>> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
>> index 029bdc0..cd0f9d9 100644
>> --- a/fs/proc/vmcore.c
>> +++ b/fs/proc/vmcore.c
>> @@ -477,16 +477,23 @@ static int __init process_ptload_program_headers_elf64(char *elfptr,
>> vmcore_off = elfsz + roundup(phdr_ptr->p_memsz, PAGE_SIZE);
>>
>> for (i = 0; i < ehdr_ptr->e_phnum; i++, phdr_ptr++) {
>> + u64 paddr, start, end, size;
>> +
>> if (phdr_ptr->p_type != PT_LOAD)
>> continue;
>>
>> + paddr = phdr_ptr->p_offset;
>> + start = rounddown(paddr, PAGE_SIZE);
>> + end = roundup(paddr + phdr_ptr->p_memsz, PAGE_SIZE);
>> + size = end - start;
>> +
>> /* Add this contiguous chunk of memory to vmcore list.*/
>> - if (vmcore_add(vc_list, phdr_ptr->p_offset, phdr_ptr->p_memsz))
>> + if (vmcore_add(vc_list, start, size))
>> return -ENOMEM;
>>
>> /* Update the program header offset. */
>> - phdr_ptr->p_offset = vmcore_off;
>> - vmcore_off = vmcore_off + phdr_ptr->p_memsz;
>> + phdr_ptr->p_offset = vmcore_off + (paddr - start);
>
> What's paddr-start. Why following is not sufficient.
>
> phdr_ptr->p_offset = vmcore_off
>
(paddr - start) is offset of the memory program header refers to, from
which kernel memory starts. Pictrically:
vmcore_off +----------------------+
| extra memory |
| (non kernel memory) |
phdr->p_offset = +----------------------+
vmcore_off + (paddr - start) | |\
| kernel memory | phdr->p_memsz
| |/
+----------------------+
| extra memory |
| (non kernel memory) |
vmcore_off + size +----------------------+
--
Thanks.
HATAYAMA, Daisuke
