configure.py support coverage profiles on standrad build modes

We already have a dedicated coverage build, however, this build is
dedicated mostly for coverage in boost and standalone unit tests.
This added configuration option will compile every configured
build mode with coverage profiling support (excluding 'coverage' mode).
It also does targeted profiling that is narrowed down only to ScyllaDB
code and doesn't instrument seastar and testing code, this should give
a more accurate coverage reporting and also impact performance less, as
one example, the reactor loop in seastar will not be profiled (along
with everything else).
The targeted profiling is done with the help of the newly added
`coverage_sources.list` file which excludes all seastar sub directories
from the profiling.
Also an extra measure is taken to make sure that the seastar
library will not be linked with the coverage framework
(so it will not dump confusing empty profiles).
Some of the seastar headers are still going to be included in the
profile since they are indirectly included by profiled source files in
order to remove them from the final report a processing step on the
resulting profile will need to take place.

A note about expected performance impact:
It is expected to have minimal impact on performance since the
instrumentation adds counter increments without locking.
Ref: https://clang.llvm.org/docs/UsersManual.html#cmdoption-fprofile-update
This means that the numbers themselves are less reliable but all covered
lines are guarantied to have at least non-zero value.

Signed-off-by: Eliran Sinvani <eliransin@scylladb.com>

configure.py

@@ -778,8 +778,11 @@ arg_parser.add_argument('--list-artifacts', dest='list_artifacts', action='store
 arg_parser.add_argument('--date-stamp', dest='date_stamp', type=str,
                         help='Set datestamp for SCYLLA-VERSION-GEN')
 arg_parser.add_argument('--use-cmake', action='store_true', help='Use CMake as the build system')
+arg_parser.add_argument('--coverage', action = 'store_true', help = 'Compile scylla with coverage instrumentation')
 args = arg_parser.parse_args()
 
+PROFILES_LIST_FILE_NAME = "coverage_sources.list"
+
 if args.list_artifacts:
     for artifact in sorted(all_artifacts):
         print(artifact)
@@ -1418,6 +1421,15 @@ tests_not_using_seastar_test_framework = set([
     'test/unit/cross_shard_barrier_test',
 ]) | pure_boost_tests
 
+
+COVERAGE_INST_FLAGS = ['-fprofile-instr-generate', '-fcoverage-mapping', f'-fprofile-list=./{PROFILES_LIST_FILE_NAME}']
+if args.coverage:
+    for _, mode in filter(lambda m: m[0] != "coverage", modes.items()):
+        mode['cxx_ld_flags'] += ' ' + ' '.join(COVERAGE_INST_FLAGS)
+        mode['cxx_ld_flags'] = mode['cxx_ld_flags'].strip()
+        mode['cxxflags'] += ' ' + ' '.join(COVERAGE_INST_FLAGS)
+        mode['cxxflags'] = mode['cxxflags'].strip()
+
 for t in tests_not_using_seastar_test_framework:
     if t not in scylla_tests:
         raise Exception("Test %s not found in scylla_tests" % (t))
@@ -1671,13 +1683,19 @@ def real_relpath(path, start):
 def configure_seastar(build_dir, mode, mode_config):
     seastar_build_dir = os.path.join(build_dir, mode, 'seastar')
 
+    seastar_cxx_ld_flags = mode_config['cxx_ld_flags']
+    # We want to "undo" coverage for seastar if we have it enabled.
+    if args.coverage:
+        for flag in COVERAGE_INST_FLAGS:
+            seastar_cxx_ld_flags = seastar_cxx_ld_flags.replace(' ' + flag, '')
+            seastar_cxx_ld_flags = seastar_cxx_ld_flags.replace(flag, '')
     seastar_cmake_args = [
         '-DCMAKE_BUILD_TYPE={}'.format(mode_config['cmake_build_type']),
         '-DCMAKE_C_COMPILER={}'.format(args.cc),
         '-DCMAKE_CXX_COMPILER={}'.format(args.cxx),
         '-DCMAKE_EXPORT_NO_PACKAGE_REGISTRY=ON',
         '-DSeastar_CXX_FLAGS=SHELL:{}'.format(mode_config['lib_cflags']),
-        '-DSeastar_LD_FLAGS={}'.format(semicolon_separated(mode_config['lib_ldflags'], mode_config['cxx_ld_flags'])),
+        '-DSeastar_LD_FLAGS={}'.format(semicolon_separated(mode_config['lib_ldflags'], seastar_cxx_ld_flags)),
         '-DSeastar_CXX_DIALECT=gnu++20',
         '-DSeastar_API_LEVEL=7',
         '-DSeastar_UNUSED_RESULT_ERROR=ON',

coverage_sources.list

@@ -0,0 +1,8 @@
+# Those tests are testing header files so we have no choice but to instrument them
+source:test/boost/small_vector_test\.cc=allow
+source:test/boost/anchorless_list_test\.cc=allow
+
+# Don't instrument files that are part of the testing framework itself.
+source:test/*\.*=skip
+
+default:allow