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From: James Clark <james.clark@arm.com>
To: suzuki.poulose@arm.com, mathieu.poirier@linaro.org,
	coresight@lists.linaro.org, mike.leach@linaro.org
Cc: leo.yan@linaro.com, James Clark <james.clark@arm.com>,
	Leo Yan <leo.yan@linaro.org>,
	linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v3 4/4] Documentation: coresight: Expand branch broadcast documentation
Date: Wed, 11 May 2022 15:46:01 +0100	[thread overview]
Message-ID: <20220511144601.2257870-5-james.clark@arm.com> (raw)
In-Reply-To: <20220511144601.2257870-1-james.clark@arm.com>

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


WARNING: multiple messages have this Message-ID (diff)
From: James Clark <james.clark@arm.com>
To: suzuki.poulose@arm.com, mathieu.poirier@linaro.org,
	coresight@lists.linaro.org, mike.leach@linaro.org
Cc: leo.yan@linaro.com, James Clark <james.clark@arm.com>,
	Leo Yan <leo.yan@linaro.org>,
	linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v3 4/4] Documentation: coresight: Expand branch broadcast documentation
Date: Wed, 11 May 2022 15:46:01 +0100	[thread overview]
Message-ID: <20220511144601.2257870-5-james.clark@arm.com> (raw)
In-Reply-To: <20220511144601.2257870-1-james.clark@arm.com>

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


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  parent reply	other threads:[~2022-05-11 14:46 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-11 14:45 [PATCH v3 0/4] coresight: Add config flag to enable branch broadcast James Clark
2022-05-11 14:45 ` James Clark
2022-05-11 14:45 ` [PATCH v3 1/4] " James Clark
2022-05-11 14:45   ` James Clark
2022-05-11 14:45 ` [PATCH v3 2/4] Documentation: coresight: Turn numbered subsections into real subsections James Clark
2022-05-11 14:45   ` James Clark
2022-05-11 14:46 ` [PATCH v3 3/4] Documentation: coresight: Link config options to existing documentation James Clark
2022-05-11 14:46   ` James Clark
2022-05-11 14:46 ` James Clark [this message]
2022-05-11 14:46   ` [PATCH v3 4/4] Documentation: coresight: Expand branch broadcast documentation James Clark
2022-05-18  9:28   ` Mike Leach
2022-05-18  9:28     ` Mike Leach
2022-05-25 10:06 ` [PATCH v3 0/4] coresight: Add config flag to enable branch broadcast Suzuki K Poulose
2022-05-25 10:06   ` Suzuki K Poulose

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