[PATCH v3 0/4] coresight: Add config flag to enable branch broadcast

[PATCH v3 0/4] coresight: Add config flag to enable branch broadcast

[James Clark]

Apologies for the delay.

Changes since v2:

 * Pick up some of Mike's review tags
 * Add a comment explaining rationale for not opening the event when BB isn't
   supported
 * Extend docs to say that Perf doesn't support decode when binaries are
   modified
 * Drop Perf side patches that were already merged

Thanks
James

James Clark (4):
  coresight: Add config flag to enable branch broadcast
  Documentation: coresight: Turn numbered subsections into real
    subsections
  Documentation: coresight: Link config options to existing
    documentation
  Documentation: coresight: Expand branch broadcast documentation

 .../coresight/coresight-etm4x-reference.rst   | 17 +++++-
 Documentation/trace/coresight/coresight.rst   | 56 +++++++++++++++++--
 .../hwtracing/coresight/coresight-etm-perf.c  |  2 +
 .../coresight/coresight-etm4x-core.c          | 14 +++++
 include/linux/coresight-pmu.h                 |  2 +
 5 files changed, 85 insertions(+), 6 deletions(-)

-- 
2.28.0

[PATCH v3 1/4] 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>
Reviewed-by: Mike Leach <mike.leach@linaro.org>
---
 drivers/hwtracing/coresight/coresight-etm-perf.c   |  2 ++
 drivers/hwtracing/coresight/coresight-etm4x-core.c | 14 ++++++++++++++
 include/linux/coresight-pmu.h                      |  2 ++
 3 files changed, 18 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 87299e99dabb..cf249ecad5a5 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -696,6 +696,20 @@ 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) {
+			/*
+			 * Missing BB support could cause silent decode errors
+			 * so fail to open if it's not supported.
+			 */
+			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 v3 2/4] Documentation: coresight: Turn numbered subsections into real subsections

[James Clark]

This is to allow them to be referenced in a later commit. There was
also a mistake where sysFS was introduced as section 2, but numbered
as section 1. And vice versa for 'Using perf framework'. This can't
happen with unnumbered sections.

Signed-off-by: James Clark <james.clark@arm.com>
Reviewed-by: Mike Leach <mike.leach@linaro.org>
---
 Documentation/trace/coresight/coresight.rst | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst
index a15571d96cc8..db66ff45ff4c 100644
--- a/Documentation/trace/coresight/coresight.rst
+++ b/Documentation/trace/coresight/coresight.rst
@@ -339,7 +339,8 @@ Preference is given to the former as using the sysFS interface
 requires a deep understanding of the Coresight HW.  The following sections
 provide details on using both methods.
 
-1) Using the sysFS interface:
+Using the sysFS interface
+~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Before trace collection can start, a coresight sink needs to be identified.
 There is no limit on the amount of sinks (nor sources) that can be enabled at
@@ -446,7 +447,8 @@ wealth of possibilities that coresight provides.
     Instruction     0       0x8026B588      E8BD8000        true    LDM      sp!,{pc}
     Timestamp                                       Timestamp: 17107041535
 
-2) Using perf framework:
+Using perf framework
+~~~~~~~~~~~~~~~~~~~~
 
 Coresight tracers are represented using the Perf framework's Performance
 Monitoring Unit (PMU) abstraction.  As such the perf framework takes charge of
@@ -495,7 +497,11 @@ More information on the above and other example on how to use Coresight with
 the perf tools can be found in the "HOWTO.md" file of the openCSD gitHub
 repository [#third]_.
 
-2.1) AutoFDO analysis using the perf tools:
+Advanced perf framework usage
+-----------------------------
+
+AutoFDO analysis using the perf tools
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 perf can be used to record and analyze trace of programs.
 
@@ -513,7 +519,8 @@ The --itrace option controls the type and frequency of synthesized events
 Note that only 64-bit programs are currently supported - further work is
 required to support instruction decode of 32-bit Arm programs.
 
-2.2) Tracing PID
+Tracing PID
+~~~~~~~~~~~
 
 The kernel can be built to write the PID value into the PE ContextID registers.
 For a kernel running at EL1, the PID is stored in CONTEXTIDR_EL1.  A PE may
@@ -547,7 +554,7 @@ wants to trace PIDs for both host and guest, the two configs "contextid1" and
 
 
 Generating coverage files for Feedback Directed Optimization: AutoFDO
----------------------------------------------------------------------
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 'perf inject' accepts the --itrace option in which case tracing data is
 removed and replaced with the synthesized events. e.g.
-- 
2.28.0

[PATCH v3 3/4] Documentation: coresight: Link config options to existing documentation

[James Clark]

In order to document the newly added branch_broadcast option, create a
table that links all of the config option formats to any existing docs.
That way when the branch broadcast docs are expanded they are accessible
from both places.

Signed-off-by: James Clark <james.clark@arm.com>
Reviewed-by: Mike Leach <mike.leach@linaro.org>
---
 .../coresight/coresight-etm4x-reference.rst   |  4 ++
 Documentation/trace/coresight/coresight.rst   | 39 +++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/Documentation/trace/coresight/coresight-etm4x-reference.rst b/Documentation/trace/coresight/coresight-etm4x-reference.rst
index d25dfe86af9b..0439b4006227 100644
--- a/Documentation/trace/coresight/coresight-etm4x-reference.rst
+++ b/Documentation/trace/coresight/coresight-etm4x-reference.rst
@@ -650,6 +650,7 @@ Bit assignments shown below:-
     parameter is set this value is applied to the currently indexed
     address range.
 
+.. _coresight-branch-broadcast:
 
 **bit (4):**
     ETM_MODE_BB
@@ -657,6 +658,7 @@ Bit assignments shown below:-
 **description:**
     Set to enable branch broadcast if supported in hardware [IDR0].
 
+.. _coresight-cycle-accurate:
 
 **bit (5):**
     ETMv4_MODE_CYCACC
@@ -678,6 +680,7 @@ Bit assignments shown below:-
 **description:**
     Set to enable virtual machine ID tracing if supported [IDR2].
 
+.. _coresight-timestamp:
 
 **bit (11):**
     ETMv4_MODE_TIMESTAMP
@@ -685,6 +688,7 @@ Bit assignments shown below:-
 **description:**
     Set to enable timestamp generation if supported [IDR0].
 
+.. _coresight-return-stack:
 
 **bit (12):**
     ETM_MODE_RETURNSTACK
diff --git a/Documentation/trace/coresight/coresight.rst b/Documentation/trace/coresight/coresight.rst
index db66ff45ff4c..803a224dbb0e 100644
--- a/Documentation/trace/coresight/coresight.rst
+++ b/Documentation/trace/coresight/coresight.rst
@@ -585,6 +585,45 @@ sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tuto
 	Bubble sorting array of 30000 elements
 	5806 ms
 
+Config option formats
+~~~~~~~~~~~~~~~~~~~~~
+
+The following strings can be provided between // on the perf command line to enable various options.
+They are also listed in the folder /sys/bus/event_source/devices/cs_etm/format/
+
+.. list-table::
+   :header-rows: 1
+
+   * - Option
+     - Description
+   * - branch_broadcast
+     - Session local version of the system wide setting:
+       :ref:`ETM_MODE_BB <coresight-branch-broadcast>`
+   * - contextid
+     - See `Tracing PID`_
+   * - contextid1
+     - See `Tracing PID`_
+   * - contextid2
+     - See `Tracing PID`_
+   * - configid
+     - Selection for a custom configuration. This is an implementation detail and not used directly,
+       see :ref:`trace/coresight/coresight-config:Using Configurations in perf`
+   * - preset
+     - Override for parameters in a custom configuration, see
+       :ref:`trace/coresight/coresight-config:Using Configurations in perf`
+   * - sinkid
+     - Hashed version of the string to select a sink, automatically set when using the @ notation.
+       This is an internal implementation detail and is not used directly, see `Using perf
+       framework`_.
+   * - cycacc
+     - Session local version of the system wide setting: :ref:`ETMv4_MODE_CYCACC
+       <coresight-cycle-accurate>`
+   * - retstack
+     - Session local version of the system wide setting: :ref:`ETM_MODE_RETURNSTACK
+       <coresight-return-stack>`
+   * - timestamp
+     - Session local version of the system wide setting: :ref:`ETMv4_MODE_TIMESTAMP
+       <coresight-timestamp>`
 
 How to use the STM module
 -------------------------
-- 
2.28.0

[PATCH v3 4/4] Documentation: coresight: Expand branch broadcast documentation

[James Clark]

Now that there is a way of enabling branch broadcast via perf, mention
the possible use cases and known limitations.

Signed-off-by: James Clark <james.clark@arm.com>
---
 .../trace/coresight/coresight-etm4x-reference.rst   | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/Documentation/trace/coresight/coresight-etm4x-reference.rst b/Documentation/trace/coresight/coresight-etm4x-reference.rst
index 0439b4006227..fb7578fd9372 100644
--- a/Documentation/trace/coresight/coresight-etm4x-reference.rst
+++ b/Documentation/trace/coresight/coresight-etm4x-reference.rst
@@ -656,7 +656,18 @@ Bit assignments shown below:-
     ETM_MODE_BB
 
 **description:**
-    Set to enable branch broadcast if supported in hardware [IDR0].
+    Set to enable branch broadcast if supported in hardware [IDR0]. The primary use for this feature
+    is when code is patched dynamically at run time and the full program flow may not be able to be
+    reconstructed using only conditional branches.
+
+    There is currently no support in Perf for supplying modified binaries to the decoder, so this
+    feature is only inteded to be used for debugging purposes or with a 3rd party tool.
+
+    Choosing this option will result in a significant increase in the amount of trace generated -
+    possible danger of overflows, or fewer instructions covered. Note, that this option also
+    overrides any setting of :ref:`ETM_MODE_RETURNSTACK <coresight-return-stack>`, so where a branch
+    broadcast range overlaps a return stack range, return stacks will not be available for that
+    range.
 
 .. _coresight-cycle-accurate:
 
-- 
2.28.0

Re: [PATCH v3 4/4] Documentation: coresight: Expand branch broadcast documentation

[Mike Leach]

On Wed, 11 May 2022 at 15:46, James Clark <james.clark@arm.com> wrote:
>
> Now that there is a way of enabling branch broadcast via perf, mention
> the possible use cases and known limitations.
>
> Signed-off-by: James Clark <james.clark@arm.com>
> ---
>  .../trace/coresight/coresight-etm4x-reference.rst   | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/trace/coresight/coresight-etm4x-reference.rst b/Documentation/trace/coresight/coresight-etm4x-reference.rst
> index 0439b4006227..fb7578fd9372 100644
> --- a/Documentation/trace/coresight/coresight-etm4x-reference.rst
> +++ b/Documentation/trace/coresight/coresight-etm4x-reference.rst
> @@ -656,7 +656,18 @@ Bit assignments shown below:-
>      ETM_MODE_BB
>
>  **description:**
> -    Set to enable branch broadcast if supported in hardware [IDR0].
> +    Set to enable branch broadcast if supported in hardware [IDR0]. The primary use for this feature
> +    is when code is patched dynamically at run time and the full program flow may not be able to be
> +    reconstructed using only conditional branches.
> +
> +    There is currently no support in Perf for supplying modified binaries to the decoder, so this
> +    feature is only inteded to be used for debugging purposes or with a 3rd party tool.
> +
> +    Choosing this option will result in a significant increase in the amount of trace generated -
> +    possible danger of overflows, or fewer instructions covered. Note, that this option also
> +    overrides any setting of :ref:`ETM_MODE_RETURNSTACK <coresight-return-stack>`, so where a branch
> +    broadcast range overlaps a return stack range, return stacks will not be available for that
> +    range.
>
>  .. _coresight-cycle-accurate:
>
> --
> 2.28.0
>

Reviewed-by: Mike Leach<mike.leach@linaro.org>
-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK

Re: [PATCH v3 0/4] coresight: Add config flag to enable branch broadcast

[Suzuki K Poulose]

Hi James,



On 11/05/2022 15:45, James Clark wrote:
> Apologies for the delay.
> 
> Changes since v2:
> 
>   * Pick up some of Mike's review tags
>   * Add a comment explaining rationale for not opening the event when BB isn't
>     supported
>   * Extend docs to say that Perf doesn't support decode when binaries are
>     modified
>   * Drop Perf side patches that were already merged
> 
> Thanks
> James
> 
> James Clark (4):
>    coresight: Add config flag to enable branch broadcast
>    Documentation: coresight: Turn numbered subsections into real
>      subsections
>    Documentation: coresight: Link config options to existing
>      documentation
>    Documentation: coresight: Expand branch broadcast documentation


The series looks good to me. Apologies, this missed the 5.19 window.
I will queue this for 5.20 at -rc1.


Suzuki

> 
>   .../coresight/coresight-etm4x-reference.rst   | 17 +++++-
>   Documentation/trace/coresight/coresight.rst   | 56 +++++++++++++++++--
>   .../hwtracing/coresight/coresight-etm-perf.c  |  2 +
>   .../coresight/coresight-etm4x-core.c          | 14 +++++
>   include/linux/coresight-pmu.h                 |  2 +
>   5 files changed, 85 insertions(+), 6 deletions(-)
>