K 10
svn:author
V 3
jhb
K 8
svn:date
V 27
2018-07-25T17:28:36.027028Z
K 7
svn:log
V 1661
Fixes for kgdb including initial FreeBSD/arm support.

- Improve fallback handling for the read of pcb_size.

  If for some reason kgdb has only the kernel's debug info, a read of
  pcb_size will simply return 0, resulting in an exception when unwinding
  the stack of a thread that was on a CPU at the time the dump was
  created.  In this case, fall back to using sizeof(struct pcb).
- Always supply a value for the PC register on x86.

  A thread's PCB may have been swapped out, and a dummy value ensures that
  we don't get an exception while enumerating threads in a dump.
- Mark all 64-bit address bits as valid for aarch64 kernels.

  ARMv8 supports pointer tagging in which case the upper 8 bits of VAs are
  ignored, but FreeBSD kernels are linked such that they depend on those
  upper 8 bits being set to 1.  GDB was stripping those bits by default
  causing KVAs to be mapped to invalid addresses.
- Rework kgdb -w support to only open /dev/mem writable.

  Don't depend on the gdb global 'write_files' option which tries to
  rewrite the kernel binary on close which can crash.  Instead, add an
  optional '-w' flag to 'target vmcore' which opens the vmcore with
  O_RDWR instead of O_RDONLY.  Change the kgdb '-w' option to set this
  flag in the nested 'target vmcore' command rather than passing the
  global '-w' option to gdb.
- Garbage collect old code for reading dumptid.
- First cut at FreeBSD/arm kernel support.

  Tested on live kernel on my RPi, but not against a crashdump, and only
  trapframes from userland, not a nested trap.

Submitted by:	markj (1, 2)
Approved by:	kan
Differential Revision:	https://reviews.freebsd.org/D16013

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