[PATCH v4 0/2] riscv: Introduce support for hardware break/watchpoints

[Himanshu Chauhan]

This patchset adds support of hardware breakpoints and watchpoints in RISC-V
architecture. The framework is built on top of perf subsystem and SBI debug
trigger extension.

Currently following features are not supported and are in works:
 - Ptrace support
 - Single stepping
 - Virtualization of debug triggers

The SBI debug trigger extension proposal can be found in Chapter-19 of SBI specification:
https://github.com/riscv-non-isa/riscv-sbi-doc/releases/download/v3.0/riscv-sbi.pdf

The Sdtrig ISA is part of RISC-V debug specification which can be found at:
https://github.com/riscv/riscv-debug-spec

Changes from v3:
	- Rebased to v7.1-rc3.
	- For watchpoints, check tdata1.hit via SBI_EXT_DBTR_TRIG_READ and
	  keep STVAL-based matching as fallback.
	- Improved watchpoint matching when STVAL reports the lowest accessed
	  address for wider memory accesses.
	- Program execute breakpoints with SIZE=0 (match any size) to avoid
	  misses with 16-bit/compressed instruction addresses.
	- Updated RISCV selftest to avoid deadlock by replacing unbounded
	  sem_wait() with sem_timedwait() timeout handling.
	- Updated RISCV selftest breakpoint function so it cannot be inlined
	  or optimized away.

Changes from v2:
	- Rebased to v7.0-rc1
	- Fixed the warnings from `checkpatch.pl --strict` run.

Changes from v1:
	- The patch that adds the extension and the function IDs defined by the extension is
	  already merged. So this patch builds on top of that.
	- Added breakpoint test application in self tests to test debug triggers

How to use:
~~~~~~~~~~~
OpenSBI:
https://github.com/riscv-software-src/opensbi.git

Qemu:
https://github.com/qemu/qemu.git

Linux Kernel:
You can pull v7.1-rc3 branch from Linus' Tree and apply these patches.

How to test:
~~~~~~~~~~~
>From the Linux kernel directory issue the following command:
make -C tools/testing/selftests/breakpoints/

This will make a binary named breakpoint_test_riscv under the same directory.
Load it on the machine and run. Sample output is given below:

/ # /apps/breakpoint_test_riscv
Breakpoint triggered!
Breakpoint test passed!
Watchpoint triggered!
Watchpoint test passed!

Himanshu Chauhan (2):
  riscv: Introduce support for hardware break/watchpoints
  riscv: Add breakpoint and watchpoint test for riscv

 arch/riscv/Kconfig                            |   1 +
 arch/riscv/include/asm/hw_breakpoint.h        | 332 ++++++++
 arch/riscv/include/asm/kdebug.h               |   3 +-
 arch/riscv/kernel/Makefile                    |   1 +
 arch/riscv/kernel/hw_breakpoint.c             | 736 ++++++++++++++++++
 arch/riscv/kernel/traps.c                     |   6 +
 tools/testing/selftests/breakpoints/Makefile  |   5 +
 .../breakpoints/breakpoint_test_riscv.c       | 214 +++++
 8 files changed, 1297 insertions(+), 1 deletion(-)
 create mode 100644 arch/riscv/include/asm/hw_breakpoint.h
 create mode 100644 arch/riscv/kernel/hw_breakpoint.c
 create mode 100644 tools/testing/selftests/breakpoints/breakpoint_test_riscv.c

-- 
2.43.0