[PATCH v1 5/7] docs: mark intention to deprecate TCG tracing functionality

Alex Bennée alex.bennee at linaro.org
Wed May 5 09:22:57 UTC 2021

Currently attempts to add a new TCG trace events results in failures
to build. Previous discussions have suggested maybe it's time to mark
the feature as deprecated and push people towards using plugins.

Signed-off-by: Alex Bennée <alex.bennee at linaro.org>
Cc: Luis Vilanova <vilanova at imperial.ac.uk>
Cc: Stefan Hajnoczi <stefanha at redhat.com>
 docs/devel/tcg-plugins.rst |  2 ++
 docs/devel/tracing.rst     |  7 +++++++
 docs/system/deprecated.rst | 13 +++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/docs/devel/tcg-plugins.rst b/docs/devel/tcg-plugins.rst
index 18c6581d85..edf04e3091 100644
--- a/docs/devel/tcg-plugins.rst
+++ b/docs/devel/tcg-plugins.rst
@@ -3,6 +3,8 @@
    Copyright (c) 2019, Linaro Limited
    Written by Emilio Cota and Alex Bennée
+.. _tcgplugin-ref:
 QEMU TCG Plugins
diff --git a/docs/devel/tracing.rst b/docs/devel/tracing.rst
index ba83954899..6b0f46cd54 100644
--- a/docs/devel/tracing.rst
+++ b/docs/devel/tracing.rst
@@ -414,6 +414,13 @@ disabled, this check will have no performance impact.
+.. warning::
+   The ability to add new TCG trace points relies on a having a good
+   understanding of the TCG internals. In the meantime TCG plugins
+   have been introduced which solve many of the same problems with
+   more of a focus on analysing guest code. See :ref:`tcgplugin-ref`
+   for more details.
 Guest code generated by TCG can be traced by defining an event with the "tcg"
 event property. Internally, this property generates two events:
 "<eventname>_trans" to trace the event at translation time, and
diff --git a/docs/system/deprecated.rst b/docs/system/deprecated.rst
index 80cae86252..0c9d3c1e1e 100644
--- a/docs/system/deprecated.rst
+++ b/docs/system/deprecated.rst
@@ -312,6 +312,19 @@ The ``I7200`` guest CPU relies on the nanoMIPS ISA, which is deprecated
 (the ISA has never been upstreamed to a compiler toolchain). Therefore
 this CPU is also deprecated.
+TCG introspection features
+TCG trace-events (since 6.1)
+The ability to add new TCG trace points has bit rotted and as the
+feature can be replicated with TCG plugins it will be deprecated. If
+any user is currently using this feature and needs help with
+converting to using TCG plugins they should contact the qemu-devel
+mailing list.
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