Merge branch 'eyraud/378' into 'master'

Document common instrumentation error

Closes #378

See merge request eng/das/cov/gnatcoverage!886

Closes eng/das/cov/gnatcoverage#378

Author: Jugst3r

doc/gnatcov/src_traces.rst

@@ -335,11 +335,11 @@ with N > 0 to specify the desired level of concurrency.
 
 .. _Dump_Triggers:
 
-Output strategies for main units
---------------------------------
+Output strategies for coverage information
+------------------------------------------
 
-The choice of a ``--dump-trigger``/``--dump-channel`` pair for main units
-depends on the runtime environment available to your program.
+The choice of a ``--dump-trigger``/``--dump-channel`` pair for coverage
+information dump depends on the runtime environment available to your program.
 
 For a native program with access to a full Ada runtime and the associated
 coverage runtime, ``--dump-channel=bin-file`` is the recommended choice as it
@@ -1545,3 +1545,17 @@ under ``ccg_gnatcov_rts/`` for the sources already present before the gprbuild
 invocation, and under ``ccg_gnatcov_rts/obj-gnatcov_rts.static`` for the sources
 generated by CCG. The C sources generated from the instrumented Ada sources will
 be available in the object directory of their corresponding project.
+
+Common instrumentation errors
+=============================
+
+Linker error when building instrumented application
+---------------------------------------------------
+
+If the build of the instrumented programs fails with an undefined reference to a
+gnatcov defined symbol (e.g. "xcov_buf_stmt_<slug>"), it usually means that the
+list of coverage buffers that contain coverage data is not in the closure of the
+main. This is typically the case when the main was not instrumented as such, or
+when using the manual dump-trigger and inserting a dump buffer annotation in
+a source that is not in the main closure. Refer to :ref:`Dump_Triggers` for more
+information.