[PATCH 4/4] Documentation: gcov: document MC/DC condition coverage support

[Sasha Levin <sashal@kernel.org>]

Add a section documenting MC/DC support, including the GCC 14
requirement, how to view condition coverage data with gcov --conditions,
and the 64-condition-per-expression limitation.

Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 Documentation/dev-tools/gcov.rst | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/Documentation/dev-tools/gcov.rst b/Documentation/dev-tools/gcov.rst
index 075df6a4598d8..57b9345060c5e 100644
--- a/Documentation/dev-tools/gcov.rst
+++ b/Documentation/dev-tools/gcov.rst
@@ -180,6 +180,31 @@ b) gcov is run on the BUILD machine
       [user@build] gcov -o /tmp/coverage/tmp/out/init main.c
 
 
+MC/DC Coverage
+--------------
+
+When using GCC 14 or later with ``CONFIG_GCOV_CONDITION_COVERAGE=y``,
+Modified Condition/Decision Coverage (MC/DC) data is collected alongside
+standard branch coverage. MC/DC verifies that each condition in a
+decision independently affects the decision's outcome.
+
+To view MC/DC data, use::
+
+    gcov --conditions -o /sys/kernel/debug/gcov/path/to/dir file.c
+
+MC/DC coverage is required by safety standards such as DO-178C
+(avionics) and ISO 26262 (automotive).
+
+GCC's condition coverage implementation has a limit of 64 conditions per
+boolean expression, due to the use of 64-bit bitmasks internally.
+Expressions exceeding this limit cannot be instrumented and will produce
+a compiler warning. This does not affect the correctness of the kernel;
+those expressions simply will not have MC/DC coverage data.
+
+Note that MC/DC instrumentation increases binary size and execution
+overhead compared to standard gcov profiling.
+
+
 Note on compilers
 -----------------
 
-- 
2.51.0