From 774daad3c0d800f84f3abd725bd66f9ff04b42c6 Mon Sep 17 00:00:00 2001 From: James Clark Date: Wed, 11 May 2022 15:46:01 +0100 Subject: 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 Reviewed-by: Mike Leach Signed-off-by: Suzuki K Poulose Link: https://lore.kernel.org/r/20220511144601.2257870-5-james.clark@arm.com --- Documentation/trace/coresight/coresight-etm4x-reference.rst | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) (limited to 'Documentation/trace/coresight') 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 `, so where a branch + broadcast range overlaps a return stack range, return stacks will not be available for that + range. .. _coresight-cycle-accurate: -- cgit v1.2.3