[PATCH v5 0/3] LoongArch: Add hardware breakpoints/watchpoints support

From: Qing Zhang
Date: Sat Feb 18 2023 - 01:39:34 EST


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/releases/download/2022.08.12/
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.

Changes v4 -> v5:
Suggested by Xuerui and Youling:
- add better comments
- Use TASK_SIZE to adapt to different address lengths in user mode
- Modify the jirl judgment condition
- Modify commit information

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 | 38 ++
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 | 41 +-
include/uapi/linux/elf.h | 2 +
14 files changed, 1303 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