LoongArch: Add hardware breakpoints/watchpoints support

Use perf framework to manage hardware instruction and data breakpoints.
LoongArch defines hardware watchpoint functions for instruction fetch
and load/store operations, after the software configures hardware watchpoints
for instruction fetch and load/store operations. The processor hardware will
monitor the access address of the instruction fetch and load/store operation,
and will trigger the exception of the watchpoint when it meets the conditions
set by the watchpoint.

The hardware monitoring points for instruction fetching and load/store operations
each have a register for the overall configuration of all monitoring points,
a register for recording the status of all monitoring points, and four registers
required for configuration of each watchpoint individually.

Watchpoint related control status register chapters:
https://github.com/loongson/LoongArch-Documentation/relea...
LoongArch-Vol1-v1.02-CN.pdf

Initial version has the following limitations:
- no support for virtualization

Can be tested: e.g.
1. see samples/hw_breakpoint and register_wide_hw_breakpoint.
2. ptrace(PTRACE_SINGLESTEP/..., pid, NULL, NULL)
3. ptrace (PTRACE_SETREGSET, tid, ... , ...)

TODO:
- Add hardware breakpoints/watchpoints for gdb, kgdb

Changes v1 -> v2:
Suggested by Huacai:
- Use irqentry_enter()/irqentry_exit() instead of
  exception_enter()/exception_exit().
- Add ptrace interface to expose hw-breakpoints to debuggers.
- Use 2022-2023.
- Some other changes.

Changes v2 -> v3:
Suggested by Jinyang:
- get_num_brps/wrps, decode/encode_ctrl_reg which the function
  returns directly.
- Remove irrelevant content from the first patch.
- Use macros to avoid using magic values directly.
- Add new arg to indicate it is breakpoint or watchpoint
  to avoid function coupling.
- Remove redundant tab.
- Modify the breakpoint/watchpoint_handler function type to void.
- Some other changes.

Changes v3 -> v4:
Suggested by Jinyang:
- Add judgment prevent rd == pc from causing single step to fail to stop.
- Add code comments to improve readability.
- Use macros in csr_write32.

Qing Zhang (3):
  LoongArch: Add hardware breakpoints/watchpoints support
  LoongArch: Add ptrace single step support
  LoongArch: ptrace: expose hardware breakpoints to debuggers

 arch/loongarch/Kconfig                     |   1 +
 arch/loongarch/include/asm/hw_breakpoint.h | 145 ++++++
 arch/loongarch/include/asm/inst.h          |  39 ++
 arch/loongarch/include/asm/loongarch.h     |  35 +-
 arch/loongarch/include/asm/processor.h     |  14 +-
 arch/loongarch/include/asm/ptrace.h        |   2 +
 arch/loongarch/include/asm/switch_to.h     |   1 +
 arch/loongarch/include/uapi/asm/ptrace.h   |   9 +
 arch/loongarch/kernel/Makefile             |   1 +
 arch/loongarch/kernel/hw_breakpoint.c      | 544 +++++++++++++++++++++
 arch/loongarch/kernel/process.c            |   7 +
 arch/loongarch/kernel/ptrace.c             | 484 ++++++++++++++++++
 arch/loongarch/kernel/traps.c              |  38 +-
 include/uapi/linux/elf.h                   |   2 +
 14 files changed, 1301 insertions(+), 21 deletions(-)
 create mode 100644 arch/loongarch/include/asm/hw_breakpoint.h
 create mode 100644 arch/loongarch/kernel/hw_breakpoint.c

-- 
2.36.0