[PATCH v3 2/2] riscv: Add breakpoint and watchpoint test for riscv

[Ilya Mamay]

Hi Himanshu,

I have been working on a system that guarantees the successful installation of
hardware breakpoints in a tracee process (or ensures perf_event_open fails in
the tracer otherwise). While using your patches for testing, I noticed two
critical issues in the current implementation:

1) The test_func is a static empty function, which means the compiler may inline
it or optimize it away entirely. If this happens, the hardware breakpoint will
never fire.

2) Potential Deadlock: The test uses sem_wait to wait for the breakpoint to
trigger. If the breakpoint fails to fire, the test will hang indefinitely.

Regards,
Ilya

On Mon, Feb 23, 2026 at 10:19:18AM +0530, Himanshu Chauhan wrote:
> Add self test for riscv architecture. It uses ptrace to ptrace framework
> to set/unset break/watchpoint and uses signals to check triggers.
> 
> Signed-off-by: Himanshu Chauhan <himanshu.chauhan at oss.qualcomm.com>
> ---
>  tools/testing/selftests/breakpoints/Makefile  |   5 +
>  .../breakpoints/breakpoint_test_riscv.c       | 174 ++++++++++++++++++
>  2 files changed, 179 insertions(+)
>  create mode 100644 tools/testing/selftests/breakpoints/breakpoint_test_riscv.c
> 
> diff --git a/tools/testing/selftests/breakpoints/Makefile b/tools/testing/selftests/breakpoints/Makefile
> index 9ec2c78de8ca..97ab746908d8 100644
> --- a/tools/testing/selftests/breakpoints/Makefile
> +++ b/tools/testing/selftests/breakpoints/Makefile
> @@ -12,5 +12,10 @@ ifneq (,$(filter $(ARCH),aarch64 arm64))
>  TEST_GEN_PROGS += breakpoint_test_arm64
>  endif
>  
> +ifneq (,$(filter $(ARCH),riscv))
> +CFLAGS += -static
> +TEST_GEN_PROGS += breakpoint_test_riscv
> +endif
> +
>  include ../lib.mk
>  
> diff --git a/tools/testing/selftests/breakpoints/breakpoint_test_riscv.c b/tools/testing/selftests/breakpoints/breakpoint_test_riscv.c
> new file mode 100644
> index 000000000000..e07f6fb1cfbd
> --- /dev/null
> +++ b/tools/testing/selftests/breakpoints/breakpoint_test_riscv.c
> @@ -0,0 +1,174 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2026 Qualcomm Technologies, Inc.
> + *
> + * Author: Himanshu Chauhan <himanshu.chauhan at oss.qualcomm.com>
> + */
> +
> +#define _GNU_SOURCE
> +#include <linux/perf_event.h>    /* Definition of PERF_* constants */
> +#include <linux/hw_breakpoint.h> /* Definition of HW_* constants */
> +#include <sys/syscall.h>         /* Definition of SYS_* constants */
> +#include <unistd.h>
> +#include <stdbool.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <sys/ioctl.h>
> +#include <time.h>
> +#include <fcntl.h>
> +#include <signal.h>
> +#include <sys/mman.h>
> +#include <string.h>
> +#include <semaphore.h>
> +
> +static int gfd;
> +sem_t ib_mtx, wp_mtx;
> +static int bp_triggered, wp_triggered;
> +
> +int setup_bp(bool is_x, void *addr, int sig)
> +{
> +	struct perf_event_attr pe;
> +	int fd;
> +
> +	memset(&pe, 0, sizeof(struct perf_event_attr));
> +	pe.type = PERF_TYPE_BREAKPOINT;
> +	pe.size = sizeof(struct perf_event_attr);
> +
> +	pe.config = 0;
> +	pe.bp_type = is_x ? HW_BREAKPOINT_X : HW_BREAKPOINT_W;
> +	pe.bp_addr = (unsigned long)addr;
> +	pe.bp_len = sizeof(long);
> +
> +	pe.sample_period = 1;
> +	pe.sample_type = PERF_SAMPLE_IP;
> +	pe.wakeup_events = 1;
> +
> +	pe.disabled = 1;
> +	pe.exclude_kernel = 1;
> +	pe.exclude_hv = 1;
> +
> +	fd = syscall(SYS_perf_event_open, &pe, 0, -1, -1, 0);
> +	if (fd < 0) {
> +		printf("Failed to open event: %llx\n", pe.config);
> +		return -1;
> +	}
> +
> +	fcntl(fd, F_SETFL, O_RDWR | O_NONBLOCK | O_ASYNC);
> +	fcntl(fd, F_SETSIG, sig);
> +	fcntl(fd, F_SETOWN, getpid());
> +
> +	ioctl(fd, PERF_EVENT_IOC_RESET, 0);
> +
> +	return fd;
> +}
> +
> +static void sig_handler_bp(int signum, siginfo_t *oh, void *uc)
> +{
> +	int ret;
> +
> +	bp_triggered++;
> +
> +	printf("Breakpoint triggered!\n");
> +	ioctl(gfd, PERF_EVENT_IOC_DISABLE, 0);
> +	ret = sem_post(&ib_mtx);
> +	if (ret) {
> +		printf("Failed to report BP success\n");
> +		return;
> +	}
> +}
> +
> +static void sig_handler_wp(int signum, siginfo_t *oh, void *uc)
> +{
> +	int ret;
> +
> +	printf("Watchpoint triggered!\n");
> +	ioctl(gfd, PERF_EVENT_IOC_DISABLE, 0);
> +	wp_triggered++;
> +
> +	ret = sem_post(&wp_mtx);
> +
> +	if (ret) {
> +		printf("Failed to report WP success\n");
> +		return;
> +	}
> +}
> +
> +static void test_func(void)
> +{
> +}
> +
> +static int trigger_bp(void)
> +{
> +	struct sigaction sa;
> +
> +	memset(&sa, 0, sizeof(struct sigaction));
> +	sa.sa_sigaction = (void *)sig_handler_bp;
> +	sa.sa_flags = SA_SIGINFO;
> +
> +	if (sigaction(SIGIO, &sa, NULL) < 0) {
> +		printf("Failed to setup signal handler\n");
> +		return -1;
> +	}
> +
> +	gfd = setup_bp(1, test_func, SIGIO);
> +
> +	if (gfd < 0) {
> +		printf("Failed to setup breakpoint.\n");
> +		return -1;
> +	}
> +
> +	ioctl(gfd, PERF_EVENT_IOC_ENABLE, 0);
> +
> +	test_func();
> +
> +	ioctl(gfd, PERF_EVENT_IOC_DISABLE, 0);
> +
> +	close(gfd);
> +}
> +
> +static int trigger_wp(void)
> +{
> +	struct sigaction sa;
> +	unsigned long test_data;
> +
> +	memset(&sa, 0, sizeof(struct sigaction));
> +	sa.sa_sigaction = (void *)sig_handler_wp;
> +	sa.sa_flags = SA_SIGINFO;
> +
> +	if (sigaction(SIGUSR1, &sa, NULL) < 0) {
> +		printf("Failed to setup signal handler\n");
> +		return -1;
> +	}
> +
> +	gfd = setup_bp(0, &test_data, SIGUSR1);
> +
> +	if (gfd < 0) {
> +		printf("Failed to setup watchpoint\n");
> +		return -1;
> +	}
> +
> +	ioctl(gfd, PERF_EVENT_IOC_ENABLE, 0);
> +	test_data = 0xdeadbeef;
> +	ioctl(gfd, PERF_EVENT_IOC_DISABLE, 0);
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +	struct sigaction sa;
> +
> +	sem_init(&ib_mtx, 0, 0);
> +	trigger_bp();
> +	sem_wait(&ib_mtx);
> +
> +	if (bp_triggered)
> +		printf("Breakpoint test passed!\n");
> +
> +	sem_init(&wp_mtx, 0, 0);
> +	trigger_wp();
> +	sem_wait(&wp_mtx);
> +
> +	if (wp_triggered)
> +		printf("Watchpoint test passed!\n");
> +
> +	return 0;
> +}
> -- 
> 2.43.0
> 
> 
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