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authorJames Clark <james.clark@arm.com>2022-05-11 15:46:01 +0100
committerSuzuki K Poulose <suzuki.poulose@arm.com>2022-07-06 16:32:08 +0100
commit774daad3c0d800f84f3abd725bd66f9ff04b42c6 (patch)
tree8fa92c9103566d3fdd1cc2ba57ef1b373d16a6b1 /Documentation/trace
parent32ee00d86e90c9bc9fa453deadbbfe87a921ea70 (diff)
Documentation: coresight: Expand branch broadcast documentation
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> Reviewed-by: Mike Leach<mike.leach@linaro.org> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> Link: https://lore.kernel.org/r/20220511144601.2257870-5-james.clark@arm.com
Diffstat (limited to 'Documentation/trace')
-rw-r--r--Documentation/trace/coresight/coresight-etm4x-reference.rst13
1 files changed, 12 insertions, 1 deletions
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: