Re: [Crash-utility] [PATCH v4] Use register value in elf note NT_PRSTATUS to do backtrace

Hi Dave and all, Sent on 2011-5-7 0:11, Dave Anderson wrote: >> 2) Dump notes related information including total number of notes, their >> buffers' pointer value and finally offset in the dump file. >> 3) Move nt_prstatus_percpu and nt_prstatus_percpu to diskdump_data struct. >> However, bt command may need sp/ip from the notes later, so I guess >> the buffer should not be freed after diskdump_read_header(). > > I wish I had understood the s390x implementation a bit better when I > reviewed your v2 patch. Currently read_dump_header() malloc's a > single "notes_buf" buffer and copies the complete ELF notes section > from the dumpfile into it. I believe (but am not completely sure) that > the s390x code references pieces of that buffer, and that's why they > originally kept the "notes_buf" buffer permanently allocated. That > being the case, the "notes_buf" pointer should be moved to the > diskdump header. > > Anyway, in the case of x86/x86_64, your patch: > > (1) malloc's dd->nt_prstatus_percpu as an array of pointers, > (2) malloc's a bunch of individual per-cpu ELF prstatus buffers, and > then copies the ELF data from the "notes_buf" buffer into > each per-cpu buffer. > (4) puts a pointer to each per-cpu buffer into each dd->nt_prstatus_percpu > pointer. > > But given that the original "notes_buf" buffer is permanent, your patch > should only have to store per-cpu pointers into the original note_buf > buffer -- rather than redundantly malloc'ing a bunch of new buffers that > contain copies of what's already permanently available. So I would suggest > setting it up like this: > > dd->nt_prstatus_percpu[cpu] => points into relevant "notes_buf" > location > Oh, sorry for my misunderstood. Since we will later refer to ip/sp value in the notes_buf, we should keep the notes_buf permanently and do not free them at the end of read_diskdump_header. s390x don't have such problem because the notes are copied to the s390x_cpu_vec when processing notes_buf.

So just as what you suggested, notes_buf was moved to diskdump header in the attached v4 patch and nt_prstatus_percpu will store the address in notes_buf then.