On Wed, 11 May 2022 at 15:46, James Clark <james.clark@xxxxxxx> 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@xxxxxxx> > --- > .../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@xxxxxxxxxx> -- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK
