1. Patchew
  2. linux
  3. [PATCH v2 00/18] mm/ksw: Introduce real-time Kernel Stack Watch debugging tool
  4. View patch

[PATCH v2 06/18] perf/hw_breakpoint: add arch-independent hw_breakpoint_modify_local()

Jinchao Wang posted 18 patches 5 months, 1 week ago
There is a newer version of this series
[PATCH v2 06/18] perf/hw_breakpoint: add arch-independent hw_breakpoint_modify_local()
Posted by Jinchao Wang 5 months, 1 week ago 
Introduce hw_breakpoint_modify_local() as a generic helper to modify an
existing hardware breakpoint. The function invokes
hw_breakpoint_arch_parse() and delegates the reinstall step to the
architecture via arch_reinstall_hw_breakpoint().

A weak default implementation of arch_reinstall_hw_breakpoint() is
provided, returning -EOPNOTSUPP on architectures without support.

This makes the interface arch-independent while allowing x86 (and others)
to provide their own implementation.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
 include/linux/hw_breakpoint.h |  1 +
 kernel/events/hw_breakpoint.c | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
index db199d653dd1..9453b5bdb443 100644
--- a/include/linux/hw_breakpoint.h
+++ b/include/linux/hw_breakpoint.h
@@ -67,6 +67,7 @@ extern int
 modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
 				bool check);
 
+int hw_breakpoint_modify_local(struct perf_event *bp, struct perf_event_attr *attr);
 /*
  * Kernel breakpoints are not associated with any particular thread.
  */
diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index 8ec2cb688903..ff428739f71e 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -983,6 +983,24 @@ static void hw_breakpoint_del(struct perf_event *bp, int flags)
 	arch_uninstall_hw_breakpoint(bp);
 }
 
+int hw_breakpoint_modify_local(struct perf_event *bp, struct perf_event_attr *attr)
+{
+	int err;
+
+	err = hw_breakpoint_arch_parse(bp, attr, counter_arch_bp(bp));
+	if (err)
+		return err;
+
+	return arch_reinstall_hw_breakpoint(bp);
+}
+EXPORT_SYMBOL(hw_breakpoint_modify_local);
+
+/* weak fallback for arches without support */
+__weak int arch_reinstall_hw_breakpoint(struct perf_event *bp)
+{
+	return -EOPNOTSUPP;
+}
+
 static void hw_breakpoint_start(struct perf_event *bp, int flags)
 {
 	bp->hw.state = 0;
-- 
2.43.0
Re: [PATCH v2 06/18] perf/hw_breakpoint: add arch-independent hw_breakpoint_modify_local()
Posted by kernel test robot 5 months ago 
Hi Jinchao,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Jinchao-Wang/mm-ksw-add-build-system-support/20250904-082544
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20250904002126.1514566-7-wangjinchao600%40gmail.com
patch subject: [PATCH v2 06/18] perf/hw_breakpoint: add arch-independent hw_breakpoint_modify_local()
config: sh-randconfig-001-20250905 (https://download.01.org/0day-ci/archive/20250906/202509060154.f5xlnJ2n-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 15.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250906/202509060154.f5xlnJ2n-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509060154.f5xlnJ2n-lkp@intel.com/

All errors (new ones prefixed by >>):

   kernel/events/hw_breakpoint.c: In function 'hw_breakpoint_modify_local':
>> kernel/events/hw_breakpoint.c:994:16: error: implicit declaration of function 'arch_reinstall_hw_breakpoint'; did you mean 'arch_uninstall_hw_breakpoint'? [-Wimplicit-function-declaration]
     994 |         return arch_reinstall_hw_breakpoint(bp);
         |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
         |                arch_uninstall_hw_breakpoint
   kernel/events/hw_breakpoint.c: At top level:
   kernel/events/hw_breakpoint.c:999:12: warning: no previous prototype for 'arch_reinstall_hw_breakpoint' [-Wmissing-prototypes]
     999 | __weak int arch_reinstall_hw_breakpoint(struct perf_event *bp)
         |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +994 kernel/events/hw_breakpoint.c

   985	
   986	int hw_breakpoint_modify_local(struct perf_event *bp, struct perf_event_attr *attr)
   987	{
   988		int err;
   989	
   990		err = hw_breakpoint_arch_parse(bp, attr, counter_arch_bp(bp));
   991		if (err)
   992			return err;
   993	
 > 994		return arch_reinstall_hw_breakpoint(bp);
   995	}
   996	EXPORT_SYMBOL(hw_breakpoint_modify_local);
   997	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Re: [PATCH v2 06/18] perf/hw_breakpoint: add arch-independent hw_breakpoint_modify_local()
Posted by kernel test robot 5 months ago 
Hi Jinchao,

kernel test robot noticed the following build warnings:

[auto build test WARNING on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Jinchao-Wang/mm-ksw-add-build-system-support/20250904-082544
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20250904002126.1514566-7-wangjinchao600%40gmail.com
patch subject: [PATCH v2 06/18] perf/hw_breakpoint: add arch-independent hw_breakpoint_modify_local()
config: sh-randconfig-001-20250905 (https://download.01.org/0day-ci/archive/20250905/202509052351.KuHBWdAF-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 15.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250905/202509052351.KuHBWdAF-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509052351.KuHBWdAF-lkp@intel.com/

All warnings (new ones prefixed by >>):

   kernel/events/hw_breakpoint.c: In function 'hw_breakpoint_modify_local':
   kernel/events/hw_breakpoint.c:994:16: error: implicit declaration of function 'arch_reinstall_hw_breakpoint'; did you mean 'arch_uninstall_hw_breakpoint'? [-Wimplicit-function-declaration]
     994 |         return arch_reinstall_hw_breakpoint(bp);
         |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
         |                arch_uninstall_hw_breakpoint
   kernel/events/hw_breakpoint.c: At top level:
>> kernel/events/hw_breakpoint.c:999:12: warning: no previous prototype for 'arch_reinstall_hw_breakpoint' [-Wmissing-prototypes]
     999 | __weak int arch_reinstall_hw_breakpoint(struct perf_event *bp)
         |            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~


vim +/arch_reinstall_hw_breakpoint +999 kernel/events/hw_breakpoint.c

   997	
   998	/* weak fallback for arches without support */
 > 999	__weak int arch_reinstall_hw_breakpoint(struct perf_event *bp)
  1000	{
  1001		return -EOPNOTSUPP;
  1002	}
  1003	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Re: [PATCH v2 06/18] perf/hw_breakpoint: add arch-independent hw_breakpoint_modify_local()
Posted by Peter Zijlstra 5 months, 1 week ago 
On Thu, Sep 04, 2025 at 08:21:03AM +0800, Jinchao Wang wrote:
> Introduce hw_breakpoint_modify_local() as a generic helper to modify an
> existing hardware breakpoint. The function invokes
> hw_breakpoint_arch_parse() and delegates the reinstall step to the
> architecture via arch_reinstall_hw_breakpoint().
> 
> A weak default implementation of arch_reinstall_hw_breakpoint() is
> provided, returning -EOPNOTSUPP on architectures without support.
> 
> This makes the interface arch-independent while allowing x86 (and others)
> to provide their own implementation.
> 
> Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
> ---
>  include/linux/hw_breakpoint.h |  1 +
>  kernel/events/hw_breakpoint.c | 18 ++++++++++++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
> index db199d653dd1..9453b5bdb443 100644
> --- a/include/linux/hw_breakpoint.h
> +++ b/include/linux/hw_breakpoint.h
> @@ -67,6 +67,7 @@ extern int
>  modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
>  				bool check);
>  
> +int hw_breakpoint_modify_local(struct perf_event *bp, struct perf_event_attr *attr);
>  /*
>   * Kernel breakpoints are not associated with any particular thread.
>   */
> diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
> index 8ec2cb688903..ff428739f71e 100644
> --- a/kernel/events/hw_breakpoint.c
> +++ b/kernel/events/hw_breakpoint.c
> @@ -983,6 +983,24 @@ static void hw_breakpoint_del(struct perf_event *bp, int flags)
>  	arch_uninstall_hw_breakpoint(bp);
>  }
>  
> +int hw_breakpoint_modify_local(struct perf_event *bp, struct perf_event_attr *attr)
> +{
> +	int err;
> +
> +	err = hw_breakpoint_arch_parse(bp, attr, counter_arch_bp(bp));
> +	if (err)
> +		return err;
> +
> +	return arch_reinstall_hw_breakpoint(bp);
> +}
> +EXPORT_SYMBOL(hw_breakpoint_modify_local);
> +
> +/* weak fallback for arches without support */
> +__weak int arch_reinstall_hw_breakpoint(struct perf_event *bp)
> +{
> +	return -EOPNOTSUPP;
> +}

Again, so much fail :/

So we have:

{register,modify,unregister}_user_hw_breakpoint()

and

{register,unregister}_wide_hw_breakpoint()

And you choose to extend this latter with hw_breakpoint_modify_local()
instead of sticking with the naming scheme and say adding:

modify_wide_hw_breakpoint_local().

Also, again, that EXPORT is a fail, these other interfaces are all
EXPORT_SYMBOL_GPL().

Also note that modify_user_hw_breakpoint() doesn't seem to need new arch
hooks. Yet you fail to explain why you think you do.
Re: [PATCH v2 06/18] perf/hw_breakpoint: add arch-independent hw_breakpoint_modify_local()
Posted by Jinchao Wang 5 months ago 
On Thu, Sep 04, 2025 at 08:44:48AM +0200, Peter Zijlstra wrote:
> On Thu, Sep 04, 2025 at 08:21:03AM +0800, Jinchao Wang wrote:
> > Introduce hw_breakpoint_modify_local() as a generic helper to modify an
> > existing hardware breakpoint. The function invokes
> > hw_breakpoint_arch_parse() and delegates the reinstall step to the
> > architecture via arch_reinstall_hw_breakpoint().
> > 
> > A weak default implementation of arch_reinstall_hw_breakpoint() is
> > provided, returning -EOPNOTSUPP on architectures without support.
> > 
> > This makes the interface arch-independent while allowing x86 (and others)
> > to provide their own implementation.
> > 
> > Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
> > ---
> >  include/linux/hw_breakpoint.h |  1 +
> >  kernel/events/hw_breakpoint.c | 18 ++++++++++++++++++
> >  2 files changed, 19 insertions(+)
> > 
> > diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
> > index db199d653dd1..9453b5bdb443 100644
> > --- a/include/linux/hw_breakpoint.h
> > +++ b/include/linux/hw_breakpoint.h
> > @@ -67,6 +67,7 @@ extern int
> >  modify_user_hw_breakpoint_check(struct perf_event *bp, struct perf_event_attr *attr,
> >  				bool check);
> >  
> > +int hw_breakpoint_modify_local(struct perf_event *bp, struct perf_event_attr *attr);
> >  /*
> >   * Kernel breakpoints are not associated with any particular thread.
> >   */
> > diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
> > index 8ec2cb688903..ff428739f71e 100644
> > --- a/kernel/events/hw_breakpoint.c
> > +++ b/kernel/events/hw_breakpoint.c
> > @@ -983,6 +983,24 @@ static void hw_breakpoint_del(struct perf_event *bp, int flags)
> >  	arch_uninstall_hw_breakpoint(bp);
> >  }
> >  
> > +int hw_breakpoint_modify_local(struct perf_event *bp, struct perf_event_attr *attr)
> > +{
> > +	int err;
> > +
> > +	err = hw_breakpoint_arch_parse(bp, attr, counter_arch_bp(bp));
> > +	if (err)
> > +		return err;
> > +
> > +	return arch_reinstall_hw_breakpoint(bp);
> > +}
> > +EXPORT_SYMBOL(hw_breakpoint_modify_local);
> > +
> > +/* weak fallback for arches without support */
> > +__weak int arch_reinstall_hw_breakpoint(struct perf_event *bp)
> > +{
> > +	return -EOPNOTSUPP;
> > +}
> 
> Again, so much fail :/
> 

> So we have:
> 
> {register,modify,unregister}_user_hw_breakpoint()
> 
> and
> 
> {register,unregister}_wide_hw_breakpoint()
> 
> And you choose to extend this latter with hw_breakpoint_modify_local()
> instead of sticking with the naming scheme and say adding:
> 
> modify_wide_hw_breakpoint_local().
> 
> Also, again, that EXPORT is a fail, these other interfaces are all
> EXPORT_SYMBOL_GPL().
> 
Thanks for your patience.

I was misled by another family:
  - hw_breakpoint_add
  - hw_breakpoint_del
  - hw_breakpoint_start
  - hw_breakpoint_stop

Since this logic was also added in the wprobe series by Masami, I will
adopt his version instead.
> Also note that modify_user_hw_breakpoint() doesn't seem to need new arch
> hooks. Yet you fail to explain why you think you do.
Thanks for feedback, I will study existing code to better handle the arch
dependencies.

Patchew 2.1-devel-b67e4c2

© 2016 - 2026 Red Hat, Inc.