+** Typical errors
+If the test suite shows failures such as the following one
+
+ .../bison/lib/getopt.h:196:8: error: redefinition of 'struct option'
+ /usr/include/getopt.h:54:8: error: previous definition of 'struct option'
+
+it probably means that some file was compiled without
+AT_DATA_SOURCE_PROLOGUE. This error is due to the fact that our -I options
+pick up gnulib's replacement headers, such as getopt.h, and this will go
+wrong if config.h was not included first.
+
+See tests/local.at for details.
+
+** make maintainer-check-valgrind
+This target uses valgrind both to check bison, and the generated parsers.
+
+This is not mature on Mac OS X. First, Valgrind does support the way bison
+calls m4, so Valgrind cannot be used to check bison on Mac OS X.
+
+Second, there are many errors that come from the platform itself, not from
+bison. build-aux/darwin11.4.0.valgrind addresses some of them.
+
+Third, valgrind issues warnings such as:
+
+ --99312:0:syswrap- WARNING: Ignoring sigreturn( ..., UC_RESET_ALT_STACK );
+
+which cause the test to fail uselessly. It is hard to ignore these errors
+with a major overhaul of the way instrumentation is performed in the test
+suite. So currently, do not try to run valgrind on Mac OS X.
+