Store core dump notes for all valid register sets for FreeBSD processes.

[jhb]

Summary

In particular, use a generic wrapper around struct regset rather than
requiring per-regset helpers. This helper replaces the MI
elfN(note_prstatus) and elfN(note_fpregset) helpers. It also
removes the need to explicitly dump NT_ARM_ADDR_MASK in the arm64
__elfN(dump_thread).

Sponsored by: University of Cambridge, Google, Inc.

[jhb]

I've tested this on both 32-bit arm and aarch64. I'm also working on testing this on amd64. For !aarch64 it effects NT_PRSTATUS and NT_FPREGSET. The goal of this is that one can simple define a new regset with a get method and it will then be dumped for all threads in core dumps without needing code in elf_dump_thread().

[markj]

sys/kern/imgact_elf.c

2336

Assert SV_ABI_FREEBSD is clear in sv->sv_flags?

[jhb]

sys/kern/imgact_elf.c

2336

I kind of suspect I could even assert that regsetp isn't NULL here entirely (or not bother asserting and just let it fault). Non-FreeBSD ABIs don't use this function (the caller writes out FreeBSD-specific NT_THRMISC, etc.).

[jhb]

Tested on amd64 (both 32-bit and 64-bit processes).