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

> 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