Re: [PATCH v5 0/3] riscv: Introduce support for hardware break/watchpoints

[Himanshu Chauhan]

Hi Jesse,

On Fri, Jul 24, 2026 at 7:20 PM Jesse Taube <jtaubepe@xxxxxxxxxx> wrote:
>
> On Thu, Jul 23, 2026 at 4:49 AM Himanshu Chauhan
> <himanshu.chauhan@xxxxxxxxxxxxxxxx> wrote:
> >
> > 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.
>
> Hello, its nice to see you working on this project again,
> can you keep me and Charlie Jenkins <thecharlesjenkins@xxxxxxxxx> in cc please

Will do!

> This set doesnt seem to be a continuation on my set, but does it pass the tests
> i wrote there?

You were building on top of my (these) patches. I don't want to push
everything at once. I like incremental work which is independent and
easier to review.
While I have perf, single stepping, and virtualized breakpoint patches
ready and in line, I am planning to push these first. I will make all
the patches see the light of the day.
You are welcome to review!

> On patch 8 i wrote the comment
> "The selftest fails as register_user_hw_breakpoint seemingly does not
> call arch_install_hw_breakpoint. The test also seems to fail on arm64
> in the same way when I tested it."
> https://lore.kernel.org/all/20250822174715.1269138-9-jesse@xxxxxxxxxxxx/
> https://patchwork.kernel.org/project/linux-riscv/list/?series=994750&state=*
>
> Thanks,
> Jesse Taube
>
> >
> > 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 v4:
> >         - Rebased to v7.2-rc4
> >         - Fixed rv32 build error
> >         - Added pr_fmt to print KBUILD_MODNAME
> >         - Changed type of shmem_pa to phys_addr_t
> >         - Use per_cpu_ptr_to_phys instead of __pa per-cpu allocated mem
> >         - Print successful registration/unregistration message when no error
> >         - Added RISC-V DEBUGGING section in MAINTAINER file and added myself as maintainer
> >         - Fixed crawled in warnings from checkpatch.pl --strict run
> >
> > 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 v7.2-rc4 tag 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 (3):
> >   riscv: Introduce support for hardware break/watchpoints
> >   riscv: Add breakpoint and watchpoint test for riscv
> >   MAINTAINERS: Add entry for RISC-V Debugging
> >
> >  MAINTAINERS                                   |   9 +
> >  arch/riscv/Kconfig                            |   1 +
> >  arch/riscv/include/asm/hw_breakpoint.h        | 337 ++++++++
> >  arch/riscv/include/asm/kdebug.h               |   3 +-
> >  arch/riscv/kernel/Makefile                    |   1 +
> >  arch/riscv/kernel/hw_breakpoint.c             | 738 ++++++++++++++++++
> >  arch/riscv/kernel/traps.c                     |   6 +
> >  tools/testing/selftests/breakpoints/Makefile  |   5 +
> >  .../breakpoints/breakpoint_test_riscv.c       | 214 +++++
> >  9 files changed, 1313 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
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-riscv
> >
>