On Thu, Feb 14, 2013 at 07:12:32PM +0900, HATAYAMA Daisuke wrote: > Objects exported from ELF note segments are in fact located apart from > each other on old memory. But on /proc/vmcore they are exported as a > single ELF note segment. To satisfy mmap()'s page-size boundary > requirement, copy them in a page-size aligned buffer allocated by > __get_free_pages() on 2nd kernel and remap the buffer to user-space. > > The buffer for ELF note segments is added to vmcore_list as the object > of VMCORE_2ND_KERNEL type. > > Copy of ELF note segments is done in two pass: first pass tries to > calculate real total size of ELF note segments, and then 2nd pass > copies the segment data into the buffer of the real total size. Ok, this is the part I am not very happy with. I don't like the idea of copying notes into second kernel. It has potential to bloat our memory usage requirements in second kernel. For example, we allocate a 4K page for each cpu and a huge machine say 4096 cpu, 16MB of more memory is required. Not that it is big concern for a 4K cpu machine, still if we can avoid copying notes from previous kernel, it will be good. So the problem is that note size from previous kernel might not be page aligned. And in /proc/vmcore view all the notes are supposed to be contiguous. Thinking loud. - Can we introduce multiple PT_NOTE program headers. One for each note data. I am not sure if this will break existing user space tools like gdb, crash etc. - Or can we pad the notes with a new note type say "VMCORE_PAD". This is similar to "VMCOREINFO" just that it is used for padding to make sure notes can be page aligned. User space tools should simple ignore the VMCORE_PAD notes and move on to next note. I think I like second idea better and given the fact that gdb did not break with introduction of "VMCOREINFO" note type, it should not break when we introduce another note type. If this works, you don't have to copy notes in second kernel? Eric, do you have any thoughts on this. What makes more sense. Thanks Vivek
