[PATCH 1/3] coresight: Add config flag to enable branch broadcast

[PATCH 1/3] coresight: Add config flag to enable branch broadcast

[James Clark]

When enabled, all taken branch addresses are output, even if the branch
was because of a direct branch instruction. This enables reconstruction
of the program flow without having access to the memory image of the
code being executed.

Use bit 8 for the config option which would be the correct bit for
programming ETMv3. Although branch broadcast can't be enabled on ETMv3
because it's not in the define ETM3X_SUPPORTED_OPTIONS, using the
correct bit might help prevent future collisions or allow it to be
enabled if needed.

Signed-off-by: James Clark <james.clark@arm.com>
---
 drivers/hwtracing/coresight/coresight-etm-perf.c   | 2 ++
 drivers/hwtracing/coresight/coresight-etm4x-core.c | 9 +++++++++
 include/linux/coresight-pmu.h                      | 2 ++
 3 files changed, 13 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
index c039b6ae206f..43bbd5dc3d3b 100644
--- a/drivers/hwtracing/coresight/coresight-etm-perf.c
+++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
@@ -52,6 +52,7 @@ static DEFINE_PER_CPU(struct coresight_device *, csdev_src);
  * The PMU formats were orignally for ETMv3.5/PTM's ETMCR 'config';
  * now take them as general formats and apply on all ETMs.
  */
+PMU_FORMAT_ATTR(branch_broadcast, "config:"__stringify(ETM_OPT_BRANCH_BROADCAST));
 PMU_FORMAT_ATTR(cycacc,		"config:" __stringify(ETM_OPT_CYCACC));
 /* contextid1 enables tracing CONTEXTIDR_EL1 for ETMv4 */
 PMU_FORMAT_ATTR(contextid1,	"config:" __stringify(ETM_OPT_CTXTID));
@@ -97,6 +98,7 @@ static struct attribute *etm_config_formats_attr[] = {
 	&format_attr_sinkid.attr,
 	&format_attr_preset.attr,
 	&format_attr_configid.attr,
+	&format_attr_branch_broadcast.attr,
 	NULL,
 };
 
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index bf18128cf5de..d2bafb50c66a 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -692,6 +692,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
 		ret = cscfg_csdev_enable_active_config(csdev, cfg_hash, preset);
 	}
 
+	/* branch broadcast - enable if selected and supported */
+	if (attr->config & BIT(ETM_OPT_BRANCH_BROADCAST)) {
+		if (!drvdata->trcbb) {
+			ret = -EINVAL;
+			goto out;
+		} else
+			config->cfg |= BIT(ETM4_CFG_BIT_BB);
+	}
+
 out:
 	return ret;
 }
diff --git a/include/linux/coresight-pmu.h b/include/linux/coresight-pmu.h
index 4ac5c081af93..6c2fd6cc5a98 100644
--- a/include/linux/coresight-pmu.h
+++ b/include/linux/coresight-pmu.h
@@ -18,6 +18,7 @@
  * ETMv3.5/PTM doesn't define ETMCR config bits with prefix "ETM3_" and
  * directly use below macros as config bits.
  */
+#define ETM_OPT_BRANCH_BROADCAST 8
 #define ETM_OPT_CYCACC		12
 #define ETM_OPT_CTXTID		14
 #define ETM_OPT_CTXTID2		15
@@ -25,6 +26,7 @@
 #define ETM_OPT_RETSTK		29
 
 /* ETMv4 CONFIGR programming bits for the ETM OPTs */
+#define ETM4_CFG_BIT_BB         3
 #define ETM4_CFG_BIT_CYCACC	4
 #define ETM4_CFG_BIT_CTXTID	6
 #define ETM4_CFG_BIT_VMID	7
-- 
2.28.0

[PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[James Clark]

Maintain consistency with the other options by failing to open when they
aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
requested but not supported by hardware.

The consequence of not doing this is that the user may not be
aware that they are not enabling the feature as it is silently disabled.

Signed-off-by: James Clark <james.clark@arm.com>
---
 drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index d2bafb50c66a..0a9bb943a5e5 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
 	}
 
 	/* return stack - enable if selected and supported */
-	if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
-		/* bit[12], Return stack enable bit */
-		config->cfg |= BIT(12);
-
+	if (attr->config & BIT(ETM_OPT_RETSTK)) {
+		if (!drvdata->retstack) {
+			ret = -EINVAL;
+			goto out;
+		} else {
+			/* bit[12], Return stack enable bit */
+			config->cfg |= BIT(12);
+		}
+	}
 	/*
 	 * Set any selected configuration and preset.
 	 *
-- 
2.28.0

[PATCH 3/3] perf cs-etm: Update deduction of TRCCONFIGR register for branch broadcast

[James Clark]

Now that a config flag for branch broadcast has been added, take it into
account when trying to deduce what the driver would have programmed the
TRCCONFIGR register to.

Signed-off-by: James Clark <james.clark@arm.com>
---
 tools/include/linux/coresight-pmu.h | 2 ++
 tools/perf/arch/arm/util/cs-etm.c   | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/tools/include/linux/coresight-pmu.h b/tools/include/linux/coresight-pmu.h
index 4ac5c081af93..6c2fd6cc5a98 100644
--- a/tools/include/linux/coresight-pmu.h
+++ b/tools/include/linux/coresight-pmu.h
@@ -18,6 +18,7 @@
  * ETMv3.5/PTM doesn't define ETMCR config bits with prefix "ETM3_" and
  * directly use below macros as config bits.
  */
+#define ETM_OPT_BRANCH_BROADCAST 8
 #define ETM_OPT_CYCACC		12
 #define ETM_OPT_CTXTID		14
 #define ETM_OPT_CTXTID2		15
@@ -25,6 +26,7 @@
 #define ETM_OPT_RETSTK		29
 
 /* ETMv4 CONFIGR programming bits for the ETM OPTs */
+#define ETM4_CFG_BIT_BB         3
 #define ETM4_CFG_BIT_CYCACC	4
 #define ETM4_CFG_BIT_CTXTID	6
 #define ETM4_CFG_BIT_VMID	7
diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
index 293a23bf8be3..c7ef4e9b4a3a 100644
--- a/tools/perf/arch/arm/util/cs-etm.c
+++ b/tools/perf/arch/arm/util/cs-etm.c
@@ -527,6 +527,9 @@ static u64 cs_etmv4_get_config(struct auxtrace_record *itr)
 	if (config_opts & BIT(ETM_OPT_CTXTID2))
 		config |= BIT(ETM4_CFG_BIT_VMID) |
 			  BIT(ETM4_CFG_BIT_VMID_OPT);
+	if (config_opts & BIT(ETM_OPT_BRANCH_BROADCAST))
+		config |= BIT(ETM4_CFG_BIT_BB);
+
 	return config;
 }
 
-- 
2.28.0

Re: [PATCH 1/3] coresight: Add config flag to enable branch broadcast

[Suzuki K Poulose]

On 08/12/2021 16:09, James Clark wrote:
> When enabled, all taken branch addresses are output, even if the branch
> was because of a direct branch instruction. This enables reconstruction
> of the program flow without having access to the memory image of the
> code being executed.
> 
> Use bit 8 for the config option which would be the correct bit for
> programming ETMv3. Although branch broadcast can't be enabled on ETMv3
> because it's not in the define ETM3X_SUPPORTED_OPTIONS, using the
> correct bit might help prevent future collisions or allow it to be
> enabled if needed.
> 
> Signed-off-by: James Clark <james.clark@arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-etm-perf.c   | 2 ++
>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 9 +++++++++
>   include/linux/coresight-pmu.h                      | 2 ++
>   3 files changed, 13 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index c039b6ae206f..43bbd5dc3d3b 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -52,6 +52,7 @@ static DEFINE_PER_CPU(struct coresight_device *, csdev_src);
>    * The PMU formats were orignally for ETMv3.5/PTM's ETMCR 'config';
>    * now take them as general formats and apply on all ETMs.
>    */
> +PMU_FORMAT_ATTR(branch_broadcast, "config:"__stringify(ETM_OPT_BRANCH_BROADCAST));
>   PMU_FORMAT_ATTR(cycacc,		"config:" __stringify(ETM_OPT_CYCACC));
>   /* contextid1 enables tracing CONTEXTIDR_EL1 for ETMv4 */
>   PMU_FORMAT_ATTR(contextid1,	"config:" __stringify(ETM_OPT_CTXTID));
> @@ -97,6 +98,7 @@ static struct attribute *etm_config_formats_attr[] = {
>   	&format_attr_sinkid.attr,
>   	&format_attr_preset.attr,
>   	&format_attr_configid.attr,
> +	&format_attr_branch_broadcast.attr,
>   	NULL,
>   };
>   
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index bf18128cf5de..d2bafb50c66a 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -692,6 +692,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>   		ret = cscfg_csdev_enable_active_config(csdev, cfg_hash, preset);
>   	}
>   
> +	/* branch broadcast - enable if selected and supported */
> +	if (attr->config & BIT(ETM_OPT_BRANCH_BROADCAST)) {
> +		if (!drvdata->trcbb) {
> +			ret = -EINVAL;
> +			goto out;
> +		} else
> +			config->cfg |= BIT(ETM4_CFG_BIT_BB);

nit: For consistent styling, I would recommend to wrap the else case
also in { }.

Otherwise looks good to me.

Suzuki

Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[Suzuki K Poulose]

On 08/12/2021 16:09, James Clark wrote:
> Maintain consistency with the other options by failing to open when they
> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
> requested but not supported by hardware.
> 
> The consequence of not doing this is that the user may not be
> aware that they are not enabling the feature as it is silently disabled.
> 
> Signed-off-by: James Clark <james.clark@arm.com>
> ---
>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
>   1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index d2bafb50c66a..0a9bb943a5e5 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>   	}
>   
>   	/* return stack - enable if selected and supported */
> -	if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
> -		/* bit[12], Return stack enable bit */
> -		config->cfg |= BIT(12);
> -
> +	if (attr->config & BIT(ETM_OPT_RETSTK)) {
> +		if (!drvdata->retstack) {
> +			ret = -EINVAL;
> +			goto out;
> +		} else {
> +			/* bit[12], Return stack enable bit */
> +			config->cfg |= BIT(12);
> +		}

nit: While at this, please could you change the hard coded value
to ETM4_CFG_BIT_RETSTK ?

Otherwise, looks good to me

Suzuki

Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[James Clark]

On 09/12/2021 11:00, Suzuki K Poulose wrote:
> On 08/12/2021 16:09, James Clark wrote:
>> Maintain consistency with the other options by failing to open when they
>> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
>> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
>> requested but not supported by hardware.
>>
>> The consequence of not doing this is that the user may not be
>> aware that they are not enabling the feature as it is silently disabled.
>>
>> Signed-off-by: James Clark <james.clark@arm.com>
>> ---
>>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> index d2bafb50c66a..0a9bb943a5e5 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>>       }
>>         /* return stack - enable if selected and supported */
>> -    if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
>> -        /* bit[12], Return stack enable bit */
>> -        config->cfg |= BIT(12);
>> -
>> +    if (attr->config & BIT(ETM_OPT_RETSTK)) {
>> +        if (!drvdata->retstack) {
>> +            ret = -EINVAL;
>> +            goto out;
>> +        } else {
>> +            /* bit[12], Return stack enable bit */
>> +            config->cfg |= BIT(12);
>> +        }
> 
> nit: While at this, please could you change the hard coded value
> to ETM4_CFG_BIT_RETSTK ?
> 
I started changing them all because I had trouble searching for bits by name but then
I thought it would snowball into a bigger change so I undid it.

I think I'll just go and do it now if it's an issue here.

> Otherwise, looks good to me
> 
> Suzuki

Re: [PATCH 3/3] perf cs-etm: Update deduction of TRCCONFIGR register for branch broadcast

[Leo Yan]

On Wed, Dec 08, 2021 at 04:09:07PM +0000, James Clark wrote:
> Now that a config flag for branch broadcast has been added, take it into
> account when trying to deduce what the driver would have programmed the
> TRCCONFIGR register to.
> 
> Signed-off-by: James Clark <james.clark@arm.com>
> ---
>  tools/include/linux/coresight-pmu.h | 2 ++
>  tools/perf/arch/arm/util/cs-etm.c   | 3 +++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/tools/include/linux/coresight-pmu.h b/tools/include/linux/coresight-pmu.h
> index 4ac5c081af93..6c2fd6cc5a98 100644
> --- a/tools/include/linux/coresight-pmu.h
> +++ b/tools/include/linux/coresight-pmu.h
> @@ -18,6 +18,7 @@
>   * ETMv3.5/PTM doesn't define ETMCR config bits with prefix "ETM3_" and
>   * directly use below macros as config bits.
>   */
> +#define ETM_OPT_BRANCH_BROADCAST 8

I checked ETMv3 architecture spec (ARM IHI 0014Q), its bit 8 is "branch
output" for all branch address outputting.  I am not sure if it is the
same thing between ETMv3's "branch output" and ETMv4's "branch
broadcasting", but it makes sense for me to use bit 8 as an unified
config bit to control these two options for ETMv3 and ETMv4
respectively.

Just note, I understand this patch set is to enable branch broadcasting
for entire memory region rather than using any comparators (see
TRCBBCTLR) to limit branch broadcasting ranges.  This is fine for me and
we could enable ranges later.

Reviewed-by: Leo Yan <leo.yan@linaro.org>

>  #define ETM_OPT_CYCACC		12
>  #define ETM_OPT_CTXTID		14
>  #define ETM_OPT_CTXTID2		15
> @@ -25,6 +26,7 @@
>  #define ETM_OPT_RETSTK		29
>  
>  /* ETMv4 CONFIGR programming bits for the ETM OPTs */
> +#define ETM4_CFG_BIT_BB         3
>  #define ETM4_CFG_BIT_CYCACC	4
>  #define ETM4_CFG_BIT_CTXTID	6
>  #define ETM4_CFG_BIT_VMID	7
> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> index 293a23bf8be3..c7ef4e9b4a3a 100644
> --- a/tools/perf/arch/arm/util/cs-etm.c
> +++ b/tools/perf/arch/arm/util/cs-etm.c
> @@ -527,6 +527,9 @@ static u64 cs_etmv4_get_config(struct auxtrace_record *itr)
>  	if (config_opts & BIT(ETM_OPT_CTXTID2))
>  		config |= BIT(ETM4_CFG_BIT_VMID) |
>  			  BIT(ETM4_CFG_BIT_VMID_OPT);
> +	if (config_opts & BIT(ETM_OPT_BRANCH_BROADCAST))
> +		config |= BIT(ETM4_CFG_BIT_BB);
> +
>  	return config;
>  }
>  
> -- 
> 2.28.0
> 

Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[Mathieu Poirier]

Hi James,

On Thu, Dec 09, 2021 at 11:13:55AM +0000, James Clark wrote:
> 
> 
> On 09/12/2021 11:00, Suzuki K Poulose wrote:
> > On 08/12/2021 16:09, James Clark wrote:
> >> Maintain consistency with the other options by failing to open when they
> >> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
> >> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
> >> requested but not supported by hardware.
> >>
> >> The consequence of not doing this is that the user may not be
> >> aware that they are not enabling the feature as it is silently disabled.
> >>
> >> Signed-off-by: James Clark <james.clark@arm.com>
> >> ---
> >>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
> >>   1 file changed, 9 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >> index d2bafb50c66a..0a9bb943a5e5 100644
> >> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
> >>       }
> >>         /* return stack - enable if selected and supported */
> >> -    if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
> >> -        /* bit[12], Return stack enable bit */
> >> -        config->cfg |= BIT(12);
> >> -
> >> +    if (attr->config & BIT(ETM_OPT_RETSTK)) {
> >> +        if (!drvdata->retstack) {
> >> +            ret = -EINVAL;
> >> +            goto out;
> >> +        } else {
> >> +            /* bit[12], Return stack enable bit */
> >> +            config->cfg |= BIT(12);
> >> +        }
> > 
> > nit: While at this, please could you change the hard coded value
> > to ETM4_CFG_BIT_RETSTK ?
> > 
> I started changing them all because I had trouble searching for bits by name but then
> I thought it would snowball into a bigger change so I undid it.
> 
> I think I'll just go and do it now if it's an issue here.

I can apply this set right away and you send another patch to fix all hard coded
bitfields or you can send another revision with all 4 patches included in it
(bitfields fix plus these 3).  Just let me know what you want to do.  And next
time please add a cover letter.

Thanks,
Mathieu

> 
> > Otherwise, looks good to me
> > 
> > Suzuki

Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[Mike Leach]

Hi James,

A couple of points - relating mainly to docs:

1. Activating branch broadcast overrides any setting of return stack.
As a minimum there needs to be a documentation update to reflect this
-Setting both options is not prohibited in hardware - and in the case
where we can use branch broadcast over a range both are then relevant.

2. A documented note to reflect that choosing this option will result
in a significant increase in the amount of trace generated - possible
danger of overflows, or less actual instructions covered. In addition
perhaps documents could reflect the intended use-case for this option,
given the disadvantages.

3. Has this been tested in a situation where it will be of use?
Testing against static code images will show the same decoded trace
output as not using branch broadcast. (although the packet dumps will
show additional output)

Given a primary use is for situations where code is patched or
dynamically altered at runtime - then this can affect the full decode
output. If the code is being patched to only alter the branch
addresses then decode should work against static images.
If, however, we are tracing code that adds in new branches, on top of
NOPs for example, then the decoding against the original static image
will be wrong, as the image will have the NOPs, rather than the branch
instructions so the apparent location of E atoms will be in a
different position to the actual code. Is there anything in perf that
will ensure that the patched code is presented to the decoder?

If there are potential decode issues - these too need documenting.

Other than the documents and testing,  I cannot see any issues with
this patch set in terms of setting and enabling the option.

Regards

Mike


On Fri, 10 Dec 2021 at 17:22, Mathieu Poirier
<mathieu.poirier@linaro.org> wrote:
>
> Hi James,
>
> On Thu, Dec 09, 2021 at 11:13:55AM +0000, James Clark wrote:
> >
> >
> > On 09/12/2021 11:00, Suzuki K Poulose wrote:
> > > On 08/12/2021 16:09, James Clark wrote:
> > >> Maintain consistency with the other options by failing to open when they
> > >> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
> > >> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
> > >> requested but not supported by hardware.
> > >>
> > >> The consequence of not doing this is that the user may not be
> > >> aware that they are not enabling the feature as it is silently disabled.
> > >>
> > >> Signed-off-by: James Clark <james.clark@arm.com>
> > >> ---
> > >>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
> > >>   1 file changed, 9 insertions(+), 4 deletions(-)
> > >>
> > >> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > >> index d2bafb50c66a..0a9bb943a5e5 100644
> > >> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > >> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > >> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
> > >>       }
> > >>         /* return stack - enable if selected and supported */
> > >> -    if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
> > >> -        /* bit[12], Return stack enable bit */
> > >> -        config->cfg |= BIT(12);
> > >> -
> > >> +    if (attr->config & BIT(ETM_OPT_RETSTK)) {
> > >> +        if (!drvdata->retstack) {
> > >> +            ret = -EINVAL;
> > >> +            goto out;
> > >> +        } else {
> > >> +            /* bit[12], Return stack enable bit */
> > >> +            config->cfg |= BIT(12);
> > >> +        }
> > >
> > > nit: While at this, please could you change the hard coded value
> > > to ETM4_CFG_BIT_RETSTK ?
> > >
> > I started changing them all because I had trouble searching for bits by name but then
> > I thought it would snowball into a bigger change so I undid it.
> >
> > I think I'll just go and do it now if it's an issue here.
>
> I can apply this set right away and you send another patch to fix all hard coded
> bitfields or you can send another revision with all 4 patches included in it
> (bitfields fix plus these 3).  Just let me know what you want to do.  And next
> time please add a cover letter.
>
> Thanks,
> Mathieu
>
> >
> > > Otherwise, looks good to me
> > >
> > > Suzuki



-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK

Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[James Clark]

On 10/12/2021 17:22, Mathieu Poirier wrote:
> Hi James,
> 
> On Thu, Dec 09, 2021 at 11:13:55AM +0000, James Clark wrote:
>>
>>
>> On 09/12/2021 11:00, Suzuki K Poulose wrote:
>>> On 08/12/2021 16:09, James Clark wrote:
>>>> Maintain consistency with the other options by failing to open when they
>>>> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
>>>> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
>>>> requested but not supported by hardware.
>>>>
>>>> The consequence of not doing this is that the user may not be
>>>> aware that they are not enabling the feature as it is silently disabled.
>>>>
>>>> Signed-off-by: James Clark <james.clark@arm.com>
>>>> ---
>>>> � drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
>>>> � 1 file changed, 9 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>> index d2bafb50c66a..0a9bb943a5e5 100644
>>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>>>> ����� }
>>>> � ����� /* return stack - enable if selected and supported */
>>>> -��� if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
>>>> -������� /* bit[12], Return stack enable bit */
>>>> -������� config->cfg |= BIT(12);
>>>> -
>>>> +��� if (attr->config & BIT(ETM_OPT_RETSTK)) {
>>>> +������� if (!drvdata->retstack) {
>>>> +����������� ret = -EINVAL;
>>>> +����������� goto out;
>>>> +������� } else {
>>>> +����������� /* bit[12], Return stack enable bit */
>>>> +����������� config->cfg |= BIT(12);
>>>> +������� }
>>>
>>> nit: While at this, please could you change the hard coded value
>>> to ETM4_CFG_BIT_RETSTK ?
>>>
>> I started changing them all because I had trouble searching for bits by name but then
>> I thought it would snowball into a bigger change so I undid it.
>>
>> I think I'll just go and do it now if it's an issue here.
> 
> I can apply this set right away and you send another patch to fix all hard coded
> bitfields or you can send another revision with all 4 patches included in it
> (bitfields fix plus these 3).  Just let me know what you want to do.  And next
> time please add a cover letter.

I think I would like to hold off for a bit based on Mike's feedback. Seems like I may
need to make a change about return stacks.

Thanks
James

> 
> Thanks,
> Mathieu
> 
>>
>>> Otherwise, looks good to me
>>>
>>> Suzuki

Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[James Clark]

On 13/12/2021 09:48, Mike Leach wrote:
> Hi James,
> 
> A couple of points - relating mainly to docs:
> 

Hi Mike,

Thanks for the feedback. I was in the process of adding some docs and
ran into this https://lkml.org/lkml/2021/12/16/1087 so I went to fix
that first. Now I will add some more details and resubmit.

> 1. Activating branch broadcast overrides any setting of return stack.
> As a minimum there needs to be a documentation update to reflect this
> -Setting both options is not prohibited in hardware - and in the case
> where we can use branch broadcast over a range both are then relevant.
> 

Do you mean that if branch broadcast and return stacks are both requested,
but branch broadcast is limited to a range, return stacks will only be
available outside that branch broadcast range? But if branch broadcast is
enabled for all ranges there will be no return stacks at all?

> 2. A documented note to reflect that choosing this option will result
> in a significant increase in the amount of trace generated - possible
> danger of overflows, or less actual instructions covered. In addition
> perhaps documents could reflect the intended use-case for this option,
> given the disadvantages.
> 

Will do.

> 3. Has this been tested in a situation where it will be of use?
> Testing against static code images will show the same decoded trace
> output as not using branch broadcast. (although the packet dumps will
> show additional output)> 
> Given a primary use is for situations where code is patched or
> dynamically altered at runtime - then this can affect the full decode
> output. If the code is being patched to only alter the branch
> addresses then decode should work against static images.
> If, however, we are tracing code that adds in new branches, on top of
> NOPs for example, then the decoding against the original static image
> will be wrong, as the image will have the NOPs, rather than the branch
> instructions so the apparent location of E atoms will be in a
> different position to the actual code. Is there anything in perf that
> will ensure that the patched code is presented to the decoder?
> 
> If there are potential decode issues - these too need documenting.
> 

I'm not sure this should be a blocking issue for this set. Branch broadcast
could already be enabled by setting the mode via sysfs. And the perf decode
part isn't necessarily a step in the workflow, maybe someone wants to gather
data for another tool.

I will do some testing after this change though, but I imagine we would have
had issues reported it it wasn't working already which lowers the priority.

James

> Other than the documents and testing,  I cannot see any issues with
> this patch set in terms of setting and enabling the option.
> 
> Regards
> 
> Mike
> 
> 
> On Fri, 10 Dec 2021 at 17:22, Mathieu Poirier
> <mathieu.poirier@linaro.org> wrote:
>>
>> Hi James,
>>
>> On Thu, Dec 09, 2021 at 11:13:55AM +0000, James Clark wrote:
>>>
>>>
>>> On 09/12/2021 11:00, Suzuki K Poulose wrote:
>>>> On 08/12/2021 16:09, James Clark wrote:
>>>>> Maintain consistency with the other options by failing to open when they
>>>>> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
>>>>> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
>>>>> requested but not supported by hardware.
>>>>>
>>>>> The consequence of not doing this is that the user may not be
>>>>> aware that they are not enabling the feature as it is silently disabled.
>>>>>
>>>>> Signed-off-by: James Clark <james.clark@arm.com>
>>>>> ---
>>>>>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
>>>>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>> index d2bafb50c66a..0a9bb943a5e5 100644
>>>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>>>>>       }
>>>>>         /* return stack - enable if selected and supported */
>>>>> -    if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
>>>>> -        /* bit[12], Return stack enable bit */
>>>>> -        config->cfg |= BIT(12);
>>>>> -
>>>>> +    if (attr->config & BIT(ETM_OPT_RETSTK)) {
>>>>> +        if (!drvdata->retstack) {
>>>>> +            ret = -EINVAL;
>>>>> +            goto out;
>>>>> +        } else {
>>>>> +            /* bit[12], Return stack enable bit */
>>>>> +            config->cfg |= BIT(12);
>>>>> +        }
>>>>
>>>> nit: While at this, please could you change the hard coded value
>>>> to ETM4_CFG_BIT_RETSTK ?
>>>>
>>> I started changing them all because I had trouble searching for bits by name but then
>>> I thought it would snowball into a bigger change so I undid it.
>>>
>>> I think I'll just go and do it now if it's an issue here.
>>
>> I can apply this set right away and you send another patch to fix all hard coded
>> bitfields or you can send another revision with all 4 patches included in it
>> (bitfields fix plus these 3).  Just let me know what you want to do.  And next
>> time please add a cover letter.
>>
>> Thanks,
>> Mathieu
>>
>>>
>>>> Otherwise, looks good to me
>>>>
>>>> Suzuki
> 
> 
> 

Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[Mike Leach]

Hi James

On Fri, 17 Dec 2021 at 09:41, James Clark <james.clark@arm.com> wrote:
>
>
>
> On 13/12/2021 09:48, Mike Leach wrote:
> > Hi James,
> >
> > A couple of points - relating mainly to docs:
> >
>
> Hi Mike,
>
> Thanks for the feedback. I was in the process of adding some docs and
> ran into this https://lkml.org/lkml/2021/12/16/1087 so I went to fix
> that first. Now I will add some more details and resubmit.
>
> > 1. Activating branch broadcast overrides any setting of return stack.
> > As a minimum there needs to be a documentation update to reflect this
> > -Setting both options is not prohibited in hardware - and in the case
> > where we can use branch broadcast over a range both are then relevant.
> >
>
> Do you mean that if branch broadcast and return stacks are both requested,
> but branch broadcast is limited to a range, return stacks will only be
> available outside that branch broadcast range? But if branch broadcast is
> enabled for all ranges there will be no return stacks at all?
>

Correct - you may want to branch broadcast over a small ranges, but
otherwise use return stack to decrease the amount of trace in other
areas.
Once the complex config sets are accepted upstream then this set-up
will be possible by writing a config to do this.

> > 2. A documented note to reflect that choosing this option will result
> > in a significant increase in the amount of trace generated - possible
> > danger of overflows, or less actual instructions covered. In addition
> > perhaps documents could reflect the intended use-case for this option,
> > given the disadvantages.
> >
>
> Will do.
>
> > 3. Has this been tested in a situation where it will be of use?
> > Testing against static code images will show the same decoded trace
> > output as not using branch broadcast. (although the packet dumps will
> > show additional output)>
> > Given a primary use is for situations where code is patched or
> > dynamically altered at runtime - then this can affect the full decode
> > output. If the code is being patched to only alter the branch
> > addresses then decode should work against static images.
> > If, however, we are tracing code that adds in new branches, on top of
> > NOPs for example, then the decoding against the original static image
> > will be wrong, as the image will have the NOPs, rather than the branch
> > instructions so the apparent location of E atoms will be in a
> > different position to the actual code. Is there anything in perf that
> > will ensure that the patched code is presented to the decoder?
> >
> > If there are potential decode issues - these too need documenting.
> >
>
> I'm not sure this should be a blocking issue for this set. Branch broadcast
> could already be enabled by setting the mode via sysfs. And the perf decode
> part isn't necessarily a step in the workflow, maybe someone wants to gather
> data for another tool.
>

Someone could set this in sysfs - when collecting data via sysfs.  In
this case they would not be using perf for decode anyway as you say.

What you have added here is a new method for perf to set this feature
and perf always starts off with a clean configuration - then adds
according to command line options.
Therefore this will be the first time anyone will have been able to
set this for a perf session.

It there are potential limitations, then we need to be clear about
them - then users of perf, and other hypothetical tools can make a
good choice about if this option is appropriate - and we avoid mailing
list complaints (or at least can point to the docs) if users find
issues that they were warned about!

> I will do some testing after this change though, but I imagine we would have
> had issues reported it it wasn't working already which lowers the priority.
>

really depends on what was tested! If it is being used over static
code then the subsequent decode will be fine,

Regards

Mike

> James
>
> > Other than the documents and testing,  I cannot see any issues with
> > this patch set in terms of setting and enabling the option.
> >
> > Regards
> >
> > Mike
> >
> >
> > On Fri, 10 Dec 2021 at 17:22, Mathieu Poirier
> > <mathieu.poirier@linaro.org> wrote:
> >>
> >> Hi James,
> >>
> >> On Thu, Dec 09, 2021 at 11:13:55AM +0000, James Clark wrote:
> >>>
> >>>
> >>> On 09/12/2021 11:00, Suzuki K Poulose wrote:
> >>>> On 08/12/2021 16:09, James Clark wrote:
> >>>>> Maintain consistency with the other options by failing to open when they
> >>>>> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
> >>>>> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
> >>>>> requested but not supported by hardware.
> >>>>>
> >>>>> The consequence of not doing this is that the user may not be
> >>>>> aware that they are not enabling the feature as it is silently disabled.
> >>>>>
> >>>>> Signed-off-by: James Clark <james.clark@arm.com>
> >>>>> ---
> >>>>>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
> >>>>>   1 file changed, 9 insertions(+), 4 deletions(-)
> >>>>>
> >>>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >>>>> index d2bafb50c66a..0a9bb943a5e5 100644
> >>>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >>>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> >>>>> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
> >>>>>       }
> >>>>>         /* return stack - enable if selected and supported */
> >>>>> -    if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
> >>>>> -        /* bit[12], Return stack enable bit */
> >>>>> -        config->cfg |= BIT(12);
> >>>>> -
> >>>>> +    if (attr->config & BIT(ETM_OPT_RETSTK)) {
> >>>>> +        if (!drvdata->retstack) {
> >>>>> +            ret = -EINVAL;
> >>>>> +            goto out;
> >>>>> +        } else {
> >>>>> +            /* bit[12], Return stack enable bit */
> >>>>> +            config->cfg |= BIT(12);
> >>>>> +        }
> >>>>
> >>>> nit: While at this, please could you change the hard coded value
> >>>> to ETM4_CFG_BIT_RETSTK ?
> >>>>
> >>> I started changing them all because I had trouble searching for bits by name but then
> >>> I thought it would snowball into a bigger change so I undid it.
> >>>
> >>> I think I'll just go and do it now if it's an issue here.
> >>
> >> I can apply this set right away and you send another patch to fix all hard coded
> >> bitfields or you can send another revision with all 4 patches included in it
> >> (bitfields fix plus these 3).  Just let me know what you want to do.  And next
> >> time please add a cover letter.
> >>
> >> Thanks,
> >> Mathieu
> >>
> >>>
> >>>> Otherwise, looks good to me
> >>>>
> >>>> Suzuki
> >
> >
> >



-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK

Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[James Clark]

On 09/12/2021 11:13, James Clark wrote:
> 
> 
> On 09/12/2021 11:00, Suzuki K Poulose wrote:
>> On 08/12/2021 16:09, James Clark wrote:
>>> Maintain consistency with the other options by failing to open when they
>>> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
>>> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
>>> requested but not supported by hardware.
>>>
>>> The consequence of not doing this is that the user may not be
>>> aware that they are not enabling the feature as it is silently disabled.
>>>
>>> Signed-off-by: James Clark <james.clark@arm.com>
>>> ---
>>>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
>>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>> index d2bafb50c66a..0a9bb943a5e5 100644
>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>>>       }
>>>         /* return stack - enable if selected and supported */
>>> -    if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
>>> -        /* bit[12], Return stack enable bit */
>>> -        config->cfg |= BIT(12);
>>> -
>>> +    if (attr->config & BIT(ETM_OPT_RETSTK)) {
>>> +        if (!drvdata->retstack) {
>>> +            ret = -EINVAL;
>>> +            goto out;
>>> +        } else {
>>> +            /* bit[12], Return stack enable bit */
>>> +            config->cfg |= BIT(12);
>>> +        }
>>
>> nit: While at this, please could you change the hard coded value
>> to ETM4_CFG_BIT_RETSTK ?
>>
> I started changing them all because I had trouble searching for bits by name but then
> I thought it would snowball into a bigger change so I undid it.
> 
> I think I'll just go and do it now if it's an issue here.

Hi Suzuki,

I started on this and I think the only worthwhile change is to make them all consistent
with sysreg.h. As in have xxx_SHIFT and xxx_MASK style definitions like:

  #define TRCCONFIGR_INSTP0_SHIFT		1
  #define TRCCONFIGR_INSTPO_MASK		GENMASK(1,0)

This has been done for SPE and some of the new ETM stuff. If that sounds right to you
I will go and do it as a followup patch to this one. It is quite a bit change so I can
see maybe we don't want to do it? (Personally I would vote to do it)

James

> 
>> Otherwise, looks good to me
>>
>> Suzuki

Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[Suzuki K Poulose]

On 07/01/2022 15:10, James Clark wrote:
> 
> 
> On 09/12/2021 11:13, James Clark wrote:
>>
>>
>> On 09/12/2021 11:00, Suzuki K Poulose wrote:
>>> On 08/12/2021 16:09, James Clark wrote:
>>>> Maintain consistency with the other options by failing to open when they
>>>> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
>>>> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
>>>> requested but not supported by hardware.
>>>>
>>>> The consequence of not doing this is that the user may not be
>>>> aware that they are not enabling the feature as it is silently disabled.
>>>>
>>>> Signed-off-by: James Clark <james.clark@arm.com>
>>>> ---
>>>>    drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
>>>>    1 file changed, 9 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>> index d2bafb50c66a..0a9bb943a5e5 100644
>>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>>>>        }
>>>>          /* return stack - enable if selected and supported */
>>>> -    if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
>>>> -        /* bit[12], Return stack enable bit */
>>>> -        config->cfg |= BIT(12);
>>>> -
>>>> +    if (attr->config & BIT(ETM_OPT_RETSTK)) {
>>>> +        if (!drvdata->retstack) {
>>>> +            ret = -EINVAL;
>>>> +            goto out;
>>>> +        } else {
>>>> +            /* bit[12], Return stack enable bit */
>>>> +            config->cfg |= BIT(12);
>>>> +        }
>>>
>>> nit: While at this, please could you change the hard coded value
>>> to ETM4_CFG_BIT_RETSTK ?
>>>
>> I started changing them all because I had trouble searching for bits by name but then
>> I thought it would snowball into a bigger change so I undid it.
>>
>> I think I'll just go and do it now if it's an issue here.
> 
> Hi Suzuki,
> 
> I started on this and I think the only worthwhile change is to make them all consistent
> with sysreg.h. As in have xxx_SHIFT and xxx_MASK style definitions like:
> 
>    #define TRCCONFIGR_INSTP0_SHIFT		1
>    #define TRCCONFIGR_INSTPO_MASK		GENMASK(1,0)
> 
> This has been done for SPE and some of the new ETM stuff. If that sounds right to you
> I will go and do it as a followup patch to this one. It is quite a bit change so I can
> see maybe we don't want to do it? (Personally I would vote to do it)

Yes, please go ahead with that. Thanks for taking it up !

Suzuki

Re: [PATCH 2/3] coresight: Fail to open with return stacks if they are unavailable

[James Clark]

On 17/12/2021 11:52, Mike Leach wrote:
> Hi James
> 
> On Fri, 17 Dec 2021 at 09:41, James Clark <james.clark@arm.com> wrote:
>>
>>
>>
>> On 13/12/2021 09:48, Mike Leach wrote:
>>> Hi James,
>>>
>>> A couple of points - relating mainly to docs:
>>>
>>
>> Hi Mike,
>>
>> Thanks for the feedback. I was in the process of adding some docs and
>> ran into this https://lkml.org/lkml/2021/12/16/1087 so I went to fix
>> that first. Now I will add some more details and resubmit.
>>
>>> 1. Activating branch broadcast overrides any setting of return stack.
>>> As a minimum there needs to be a documentation update to reflect this
>>> -Setting both options is not prohibited in hardware - and in the case
>>> where we can use branch broadcast over a range both are then relevant.
>>>
>>
>> Do you mean that if branch broadcast and return stacks are both requested,
>> but branch broadcast is limited to a range, return stacks will only be
>> available outside that branch broadcast range? But if branch broadcast is
>> enabled for all ranges there will be no return stacks at all?
>>
> 
> Correct - you may want to branch broadcast over a small ranges, but
> otherwise use return stack to decrease the amount of trace in other
> areas.
> Once the complex config sets are accepted upstream then this set-up
> will be possible by writing a config to do this.
> 
>>> 2. A documented note to reflect that choosing this option will result
>>> in a significant increase in the amount of trace generated - possible
>>> danger of overflows, or less actual instructions covered. In addition
>>> perhaps documents could reflect the intended use-case for this option,
>>> given the disadvantages.
>>>
>>
>> Will do.
>>
>>> 3. Has this been tested in a situation where it will be of use?
>>> Testing against static code images will show the same decoded trace
>>> output as not using branch broadcast. (although the packet dumps will
>>> show additional output)>
>>> Given a primary use is for situations where code is patched or
>>> dynamically altered at runtime - then this can affect the full decode
>>> output. If the code is being patched to only alter the branch
>>> addresses then decode should work against static images.
>>> If, however, we are tracing code that adds in new branches, on top of
>>> NOPs for example, then the decoding against the original static image
>>> will be wrong, as the image will have the NOPs, rather than the branch
>>> instructions so the apparent location of E atoms will be in a
>>> different position to the actual code. Is there anything in perf that
>>> will ensure that the patched code is presented to the decoder?
>>>
>>> If there are potential decode issues - these too need documenting.
>>>
>>
>> I'm not sure this should be a blocking issue for this set. Branch broadcast
>> could already be enabled by setting the mode via sysfs. And the perf decode
>> part isn't necessarily a step in the workflow, maybe someone wants to gather
>> data for another tool.
>>
> 
> Someone could set this in sysfs - when collecting data via sysfs.  In
> this case they would not be using perf for decode anyway as you say.
> 
> What you have added here is a new method for perf to set this feature
> and perf always starts off with a clean configuration - then adds
> according to command line options.
> Therefore this will be the first time anyone will have been able to
> set this for a perf session.
> 
> It there are potential limitations, then we need to be clear about
> them - then users of perf, and other hypothetical tools can make a
> good choice about if this option is appropriate - and we avoid mailing
> list complaints (or at least can point to the docs) if users find
> issues that they were warned about!
> 
>> I will do some testing after this change though, but I imagine we would have
>> had issues reported it it wasn't working already which lowers the priority.
>>
> 
> really depends on what was tested! If it is being used over static
> code then the subsequent decode will be fine,
> 

I've posted v2 of this change with some docs changes. I also did some testing
around JITed code in java to see if there were any bad errors which I put
in the cover letter. Although I think the main point of adding this format
flag for perf is to open another avenue of testing or for people who just want
to look at the raw trace manually for now.

James

> Regards
> 
> Mike
> 
>> James
>>
>>> Other than the documents and testing,  I cannot see any issues with
>>> this patch set in terms of setting and enabling the option.
>>>
>>> Regards
>>>
>>> Mike
>>>
>>>
>>> On Fri, 10 Dec 2021 at 17:22, Mathieu Poirier
>>> <mathieu.poirier@linaro.org> wrote:
>>>>
>>>> Hi James,
>>>>
>>>> On Thu, Dec 09, 2021 at 11:13:55AM +0000, James Clark wrote:
>>>>>
>>>>>
>>>>> On 09/12/2021 11:00, Suzuki K Poulose wrote:
>>>>>> On 08/12/2021 16:09, James Clark wrote:
>>>>>>> Maintain consistency with the other options by failing to open when they
>>>>>>> aren't supported. For example ETM_OPT_TS, ETM_OPT_CTXTID2 and the newly
>>>>>>> added ETM_OPT_BRANCH_BROADCAST all return with -EINVAL if they are
>>>>>>> requested but not supported by hardware.
>>>>>>>
>>>>>>> The consequence of not doing this is that the user may not be
>>>>>>> aware that they are not enabling the feature as it is silently disabled.
>>>>>>>
>>>>>>> Signed-off-by: James Clark <james.clark@arm.com>
>>>>>>> ---
>>>>>>>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++----
>>>>>>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>>>> index d2bafb50c66a..0a9bb943a5e5 100644
>>>>>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>>>>>> @@ -674,10 +674,15 @@ static int etm4_parse_event_config(struct coresight_device *csdev,
>>>>>>>       }
>>>>>>>         /* return stack - enable if selected and supported */
>>>>>>> -    if ((attr->config & BIT(ETM_OPT_RETSTK)) && drvdata->retstack)
>>>>>>> -        /* bit[12], Return stack enable bit */
>>>>>>> -        config->cfg |= BIT(12);
>>>>>>> -
>>>>>>> +    if (attr->config & BIT(ETM_OPT_RETSTK)) {
>>>>>>> +        if (!drvdata->retstack) {
>>>>>>> +            ret = -EINVAL;
>>>>>>> +            goto out;
>>>>>>> +        } else {
>>>>>>> +            /* bit[12], Return stack enable bit */
>>>>>>> +            config->cfg |= BIT(12);
>>>>>>> +        }
>>>>>>
>>>>>> nit: While at this, please could you change the hard coded value
>>>>>> to ETM4_CFG_BIT_RETSTK ?
>>>>>>
>>>>> I started changing them all because I had trouble searching for bits by name but then
>>>>> I thought it would snowball into a bigger change so I undid it.
>>>>>
>>>>> I think I'll just go and do it now if it's an issue here.
>>>>
>>>> I can apply this set right away and you send another patch to fix all hard coded
>>>> bitfields or you can send another revision with all 4 patches included in it
>>>> (bitfields fix plus these 3).  Just let me know what you want to do.  And next
>>>> time please add a cover letter.
>>>>
>>>> Thanks,
>>>> Mathieu
>>>>
>>>>>
>>>>>> Otherwise, looks good to me
>>>>>>
>>>>>> Suzuki
>>>
>>>
>>>
> 
> 
> 

Re: [PATCH 3/3] perf cs-etm: Update deduction of TRCCONFIGR register for branch broadcast

[James Clark]

On 10/12/2021 02:41, Leo Yan wrote:
> On Wed, Dec 08, 2021 at 04:09:07PM +0000, James Clark wrote:
>> Now that a config flag for branch broadcast has been added, take it into
>> account when trying to deduce what the driver would have programmed the
>> TRCCONFIGR register to.
>>
>> Signed-off-by: James Clark <james.clark@arm.com>
>> ---
>>  tools/include/linux/coresight-pmu.h | 2 ++
>>  tools/perf/arch/arm/util/cs-etm.c   | 3 +++
>>  2 files changed, 5 insertions(+)
>>
>> diff --git a/tools/include/linux/coresight-pmu.h b/tools/include/linux/coresight-pmu.h
>> index 4ac5c081af93..6c2fd6cc5a98 100644
>> --- a/tools/include/linux/coresight-pmu.h
>> +++ b/tools/include/linux/coresight-pmu.h
>> @@ -18,6 +18,7 @@
>>   * ETMv3.5/PTM doesn't define ETMCR config bits with prefix "ETM3_" and
>>   * directly use below macros as config bits.
>>   */
>> +#define ETM_OPT_BRANCH_BROADCAST 8
> 
> I checked ETMv3 architecture spec (ARM IHI 0014Q), its bit 8 is "branch
> output" for all branch address outputting.  I am not sure if it is the
> same thing between ETMv3's "branch output" and ETMv4's "branch
> broadcasting", but it makes sense for me to use bit 8 as an unified
> config bit to control these two options for ETMv3 and ETMv4
> respectively.
> 
> Just note, I understand this patch set is to enable branch broadcasting
> for entire memory region rather than using any comparators (see
> TRCBBCTLR) to limit branch broadcasting ranges.  This is fine for me and
> we could enable ranges later.
> 
> Reviewed-by: Leo Yan <leo.yan@linaro.org>

Hi Leo,

Thanks for the review, I've posted v2, but I only put your reviewed by tag
on this commit because I wasn't sure if you meant for the full set. Please
take another look

Thanks
James

> 
>>  #define ETM_OPT_CYCACC		12
>>  #define ETM_OPT_CTXTID		14
>>  #define ETM_OPT_CTXTID2		15
>> @@ -25,6 +26,7 @@
>>  #define ETM_OPT_RETSTK		29
>>  
>>  /* ETMv4 CONFIGR programming bits for the ETM OPTs */
>> +#define ETM4_CFG_BIT_BB         3
>>  #define ETM4_CFG_BIT_CYCACC	4
>>  #define ETM4_CFG_BIT_CTXTID	6
>>  #define ETM4_CFG_BIT_VMID	7
>> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
>> index 293a23bf8be3..c7ef4e9b4a3a 100644
>> --- a/tools/perf/arch/arm/util/cs-etm.c
>> +++ b/tools/perf/arch/arm/util/cs-etm.c
>> @@ -527,6 +527,9 @@ static u64 cs_etmv4_get_config(struct auxtrace_record *itr)
>>  	if (config_opts & BIT(ETM_OPT_CTXTID2))
>>  		config |= BIT(ETM4_CFG_BIT_VMID) |
>>  			  BIT(ETM4_CFG_BIT_VMID_OPT);
>> +	if (config_opts & BIT(ETM_OPT_BRANCH_BROADCAST))
>> +		config |= BIT(ETM4_CFG_BIT_BB);
>> +
>>  	return config;
>>  }
>>  
>> -- 
>> 2.28.0
>>