Implement `-fsanitize-coverage-whitelist` and `-fsanitize-coverage-blacklist` for clang

[tuktuk]

Summary

This commit adds two command-line options to clang.
These options let the user decide which functions will receive SanitizerCoverage instrumentation.
This is most useful in the libFuzzer use case, where it enables targeted coverage-guided fuzzing.

Patch by Yannis Juglaret of DGA-MI, Rennes, France

libFuzzer tests its target against an evolving corpus, and relies on SanitizerCoverage instrumentation to collect the code coverage information that drives corpus evolution. Currently, libFuzzer collects such information for all functions of the target under test, and adds to the corpus every mutated sample that finds a new code coverage path in any function of the target. We propose instead to let the user specify which functions' code coverage information is relevant for building the upcoming fuzzing campaign's corpus. To this end, we add two new command line options for clang, enabling targeted coverage-guided fuzzing with libFuzzer. We see targeted coverage guided fuzzing as a simple way to leverage libFuzzer for big targets with thousands of functions or multiple dependencies. We publish this patch as work from DGA-MI of Rennes, France, with proper authorization from the hierarchy.

Targeted coverage-guided fuzzing can accelerate bug finding for two reasons. First, the compiler will avoid costly instrumentation for non-relevant functions, accelerating fuzzer execution for each call to any of these functions. Second, the built fuzzer will produce and use a more accurate corpus, because it will not keep the samples that find new coverage paths in non-relevant functions.

The two new command line options are -fsanitize-coverage-whitelist and -fsanitize-coverage-blacklist. They accept files in the same format as the existing -fsanitize-blacklist option https://clang.llvm.org/docs/SanitizerSpecialCaseList.html#format. The new options influence SanitizerCoverage so that it will only instrument a subset of the functions in the target. We explain these options in detail in clang/docs/SanitizerCoverage.rst.

Consider now the woff2 fuzzing example from the libFuzzer tutorial https://github.com/google/fuzzer-test-suite/blob/master/tutorial/libFuzzerTutorial.md. We are aware that we cannot conclude much from this example because mutating compressed data is generally a bad idea, but let us use it anyway as an illustration for its simplicity. Let us use an empty blacklist together with one of the three following whitelists:

# (a)
src:*
fun:*

# (b)
src:SRC/*
fun:*

# (c)
src:SRC/src/woff2_dec.cc
fun:*

Running the built fuzzers shows how many instrumentation points the compiler adds, the fuzzer will output XXX PCs. Whitelist (a) is the instrument-everything whitelist, it produces 11912 instrumentation points. Whitelist (b) focuses coverage to instrument woff2 source code only, ignoring the dependency code for brotli (de)compression; it produces 3984 instrumented instrumentation points. Whitelist (c) focuses coverage to only instrument functions in the main file that deals with WOFF2 to TTF conversion, resulting in 1056 instrumentation points.

For experimentation purposes, we ran each fuzzer approximately 100 times, single process, with the initial corpus provided in the tutorial. We let the fuzzer run until it either found the heap buffer overflow or went out of memory. On this simple example, whitelists (b) and (c) found the heap buffer overflow more reliably and 5x faster than whitelist (a). The average execution times when finding the heap buffer overflow were as follows: (a) 904 s, (b) 156 s, and (c) 176 s.

We explain these results by the fact that WOFF2 to TTF conversion calls the brotli decompression algorithm's functions, which are mostly irrelevant for finding bugs in WOFF2 font reconstruction but nevertheless instrumented and used by whitelist (a) to guide fuzzing. This results in longer execution time for these functions and a partially irrelevant corpus. Contrary to whitelist (a), whitelists (b) and (c) will execute brotli-related functions without instrumentation overhead, and ignore new code paths found in them. This results in faster bug finding for WOFF2 font reconstruction.

The results for whitelist (b) are similar to the ones for whitelist (c). Indeed, WOFF2 to TTF conversion calls functions that are mostly located in SRC/src/woff2_dec.cc. The 2892 extra instrumentation points allowed by whitelist (b) do not tamper with bug finding, even though they are mostly irrelevant, simply because most of these functions do not get called. We get a slightly faster average time for bug finding with whitelist (b), which might indicate that some of the extra instrumentation points are actually relevant, or might just be random noise.

[lebedev.ri]

Test coverage missing.

[tuktuk]

I followed Roman Lebedev's advice and adapted the sanitizer_coverage_no_prune.cc test to create a sanitizer_coverage_whitelist_blacklist.cc test under make check_sanitizer. I can only try the test on a Linux machine, and it passes on that machine.

[morehouse]

Thanks for the patch! Seems like a useful feature for targeted fuzzing.

clang/docs/SanitizerCoverage.rst

310

The wording makes it sound like there may be exceptions to the expected whitelist/blacklist behavior. But IIUC the paragraph is meant to explain the typical use case. Can we make this more explicit?

e.g.,

A common use case is to have the whitelist list folders and source files ... while the blacklist ...

Or maybe we don't need this paragraph at all...

clang/include/clang/Driver/Options.td

978

For fsanitize_blacklist we only support -fsanitize-blacklist=. Let's do the same for these lists to keep things simple.

clang/lib/CodeGen/BackendUtil.cpp

218

Please run clang-format --style=LLVM on the patch.

clang/lib/Driver/SanitizerArgs.cpp

743

The two cases have lots of overlapping code. Let's try to coalesce.

759

Let's try to coalesce here too. Maybe a helper function? Then we could also use it for the sanitizer blacklist.

compiler-rt/test/sanitizer_common/TestCases/sanitizer_coverage_whitelist_blacklist.cc

60 ↗

(On Diff #206006)

Can we also test with -fsanitize=inline-8bit-counters, since that is what libFuzzer uses by default?

llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp

192

Nit: Preferred style is no curly braces for one-statement ifs.

[tuktuk]

I followed Matt Morehouse's advice: mainly, I adapted the test so that it uses libFuzzer's default SanitizerCoverage options instead of trace-pc, and I rewrote some parts of the code to make it less redundant.

[morehouse]

LGTM

[tuktuk]

Thanks for the reviews.

[• dende]

This is a really useful feature for fuzzing bigger software projects and the review was accepted. Any plans to merge this?

[xwlin222]

Think so, and when can this feature be merge to the mainline? look forward it.

In D63616#1809697, @dende wrote:

This is a really useful feature for fuzzing bigger software projects and the review was accepted. Any plans to merge this?

[eternalsakura]

In D63616#1562824, @tuktuk wrote:

Thanks for the reviews.

Hi, @tuktuk. I want to use this function on the latest llvm, but now the code has been modified, this patch is no longer valid, can you take a look, thank you very much. : )

[tuktuk]

Thank you for your interest in this feature! It is unfortunate indeed that the patch was not merged when accepted, so here is an update that matches the current status of the code base.

Dear reviewers, can you please make sure that this time, the patch gets merged if accepted?
Also, this time I was unable to run the new test that this patch adds from within the test system, because of my limited understanding; so I gave up and followed the test myself, command by command.
Am I missing an additional step for test integration, after adding the test file?
Thanks a lot.

[vitalybuka]

clang/lib/CodeGen/BackendUtil.cpp

218

it should be -style=file
"arc diff" should also invoke clang-format, check utils/arcanist/clang-format.sh

[morehouse]

Thanks again for the patch. Sorry about the delay in landing it; I'll work on it today.

[morehouse]

In D63616#1961449, @tuktuk wrote:

Am I missing an additional step for test integration, after adding the test file?

Just tried locally and I think you need to rename to file from *.cc to *.cpp. Then it will run during ninja check-sanitizer.

I did that and the test fails for me.

--
Exit Code: 1 

Command Output (stderr): 
--
Expected 14 lines, got 28.

--

Please take a look and fix it.

compiler-rt/test/sanitizer_common/TestCases/sanitizer_coverage_whitelist_blacklist.cc

8 ↗

(On Diff #255032)

Please use %t or %T in temp file names so that they get cleaned up properly.

[tuktuk]

I was indeed able to run the test again after changing its name to .cpp, thank you for your help. I have restored XFAIL lines from the original sanitizer_coverage_no_prune.cpp that I should not have deleted. Now the test passes again. Also the test now uses %t to work in a subdirectory like sanitizer_coverage_symbolize.cpp does.

[tuktuk]

I forgot to apply clang-format on clang/lib/Driver/SanitizerArgs.cpp, now it should be OK.

[morehouse]

LGTM

clang/docs/SanitizerCoverage.rst

.. code-block:: c++
   // Val is the second argument of division.
   void __sanitizer_cov_trace_div4(uint32_t Val);
   void __sanitizer_cov_trace_div8(uint64_t Val);
 
   // Called before a GetElemementPtr (GEP) instruction
   // for every non-constant array index.
   void __sanitizer_cov_trace_gep(uintptr_t Idx);
 
+Partially disabling instrumentation
+===================================
+
+It is sometimes useful to tell SanitizerCoverage to instrument only a subset of the
+functions in your target.
+With ``-fsanitize-coverage-whitelist=whitelist.txt``
+and ``-fsanitize-coverage-blacklist=blacklist.txt``,
+you can specify such a subset through the combination of a whitelist and a blacklist.
+
+SanitizerCoverage will only instrument functions that satisfy two conditions.
+First, the function should belong to a source file with a path that is both whitelisted
+and not blacklisted.
+Second, the function should have a mangled name that is both whitelisted and not blacklisted.
+
+The whitelist and blacklist format is similar to that of the sanitizer blacklist format.
+The default whitelist will match every source file and every function.
+The default blacklist will match no source file and no function.
+
+In most cases, the whitelist will list the folders or source files for which you want
+instrumentation and allow all function names, while the blacklist will opt out some specific
+files or functions that the whitelist loosely allowed.
+
+Here is an example whitelist:
+
+.. code-block:: none
+
+  # Enable instrumentation for a whole folder
+  src:bar/*
+  # Enable instrumentation for a specific source file
+  src:foo/a.cpp
+  # Enable instrumentation for all functions in those files
+  fun:*
+
+And an example blacklist:
+
+.. code-block:: none
+
+  # Disable instrumentation for a specific source file that the whitelist allowed
+  src:bar/b.cpp
+  # Disable instrumentation for a specific function that the whitelist allowed
+  fun:*myFunc*
+
+The use of ``*`` wildcards above is required because function names are matched after mangling.
+Without the wildcards, one would have to write the whole mangled name.
+
+Be careful that the paths of source files are matched exactly as they are provided on the clang
+command line.
+For example, the whitelist above would include file ``bar/b.cpp`` if the path was provided
+exactly like this, but would it would fail to include it with other ways to refer to the same
+file such as ``./bar/b.cpp``, or ``bar\b.cpp`` on Windows.
+So, please make sure to always double check that your lists are correctly applied.
+
 Default implementation
 ======================
 
 The sanitizer run-time (AddressSanitizer, MemorySanitizer, etc) provide a
 default implementations of some of the coverage callbacks.
 You may use this implementation to dump the coverage on disk at the process
 exit.
 

clang/include/clang/Basic/CodeGenOptions.h

public:
   /// Set of XRay instrumentation kinds to emit.
   XRayInstrSet XRayInstrumentationBundle;
 
   std::vector<std::string> DefaultFunctionAttrs;
 
   /// List of dynamic shared object files to be loaded as pass plugins.
   std::vector<std::string> PassPlugins;
 
+  /// Path to whitelist file specifying which objects
+  /// (files, functions) should exclusively be instrumented
+  /// by sanitizer coverage pass.
+  std::vector<std::string> SanitizeCoverageWhitelistFiles;
+
+  /// Path to blacklist file specifying which objects
+  /// (files, functions) listed for instrumentation by sanitizer
+  /// coverage pass should actually not be instrumented.
+  std::vector<std::string> SanitizeCoverageBlacklistFiles;
+
 public:
   // Define accessors/mutators for code generation options of enumeration type.
 #define CODEGENOPT(Name, Bits, Default)
 #define ENUM_CODEGENOPT(Name, Type, Bits, Default) \
   Type get##Name() const { return static_cast<Type>(Name); } \
   void set##Name(Type Value) { Name = static_cast<unsigned>(Value); }
 #include "clang/Basic/CodeGenOptions.def"
 

clang/include/clang/Basic/DiagnosticDriverKinds.td

 def err_drv_missing_arg_mtp : Error<
   "missing argument to '%0'">;
 def err_drv_invalid_libcxx_deployment : Error<
   "invalid deployment target for -stdlib=libc++ (requires %0 or later)">;
 def err_drv_invalid_argument_to_fdebug_prefix_map : Error<
   "invalid argument '%0' to -fdebug-prefix-map">;
 def err_drv_malformed_sanitizer_blacklist : Error<
   "malformed sanitizer blacklist: '%0'">;
+def err_drv_malformed_sanitizer_coverage_whitelist : Error<
+  "malformed sanitizer coverage whitelist: '%0'">;
+def err_drv_malformed_sanitizer_coverage_blacklist : Error<
+  "malformed sanitizer coverage blacklist: '%0'">;
 def err_drv_duplicate_config : Error<
   "no more than one option '--config' is allowed">;
 def err_drv_config_file_not_exist : Error<
   "configuration file '%0' does not exist">;
 def err_drv_config_file_not_found : Error<
   "configuration file '%0' cannot be found">;
 def note_drv_config_file_searched_in : Note<
   "was searched for in the directory: %0">;

clang/include/clang/Driver/Options.td

def fsanitize_coverage
     : CommaJoined<["-"], "fsanitize-coverage=">,
       Group<f_clang_Group>,
       HelpText<"Specify the type of coverage instrumentation for Sanitizers">;
 def fno_sanitize_coverage
     : CommaJoined<["-"], "fno-sanitize-coverage=">,
       Group<f_clang_Group>, Flags<[CoreOption, DriverOption]>,
       HelpText<"Disable specified features of coverage instrumentation for "
                "Sanitizers">, Values<"func,bb,edge,indirect-calls,trace-bb,trace-cmp,trace-div,trace-gep,8bit-counters,trace-pc,trace-pc-guard,no-prune,inline-8bit-counters">;
+def fsanitize_coverage_whitelist_EQ : Joined<["-"], "fsanitize-coverage-whitelist=">,
+    Group<f_clang_Group>, Flags<[CoreOption, DriverOption]>,
+    HelpText<"Restrict sanitizer coverage instrumentation exclusively to modules and functions that match the provided special case list, except the blacklisted ones">;
+def fsanitize_coverage_whitelist : Separate<["-"], "fsanitize-coverage-whitelist">,
+    Group<f_Group>, Flags<[CoreOption, DriverOption]>, Alias<fsanitize_coverage_whitelist_EQ>;
+def fsanitize_coverage_blacklist_EQ : Joined<["-"], "fsanitize-coverage-blacklist=">,
+    Group<f_clang_Group>, Flags<[CoreOption, DriverOption]>,
+    HelpText<"Disable sanitizer coverage instrumentation for modules and functions that match the provided special case list, even the whitelisted ones">;
+def fsanitize_coverage_blacklist : Separate<["-"], "fsanitize-coverage-blacklist">,
+    Group<f_Group>, Flags<[CoreOption, DriverOption]>, Alias<fsanitize_coverage_blacklist_EQ>;
 def fsanitize_memory_track_origins_EQ : Joined<["-"], "fsanitize-memory-track-origins=">,
                                         Group<f_clang_Group>,
                                         HelpText<"Enable origins tracking in MemorySanitizer">;
 def fsanitize_memory_track_origins : Flag<["-"], "fsanitize-memory-track-origins">,
                                      Group<f_clang_Group>,
                                      HelpText<"Enable origins tracking in MemorySanitizer">;
 def fno_sanitize_memory_track_origins : Flag<["-"], "fno-sanitize-memory-track-origins">,
                                         Group<f_clang_Group>,

clang/include/clang/Driver/SanitizerArgs.h

 class SanitizerArgs {
   SanitizerSet Sanitizers;
   SanitizerSet RecoverableSanitizers;
   SanitizerSet TrapSanitizers;
 
   std::vector<std::string> BlacklistFiles;
   std::vector<std::string> ExtraDeps;
   int CoverageFeatures = 0;
+  std::vector<std::string> CoverageWhitelistFiles;
+  std::vector<std::string> CoverageBlacklistFiles;
   int MsanTrackOrigins = 0;
   bool MsanUseAfterDtor = true;
   bool CfiCrossDso = false;
   bool CfiICallGeneralizePointers = false;
   int AsanFieldPadding = 0;
   bool SharedRuntime = false;
   bool AsanUseAfterScope = true;
   bool AsanPoisonCustomArrayCookie = false;

clang/lib/CodeGen/BackendUtil.cpp

static void addSanitizerCoveragePass(const PassManagerBuilder &Builder,
   Opts.TraceGep = CGOpts.SanitizeCoverageTraceGep;
   Opts.Use8bitCounters = CGOpts.SanitizeCoverage8bitCounters;
   Opts.TracePC = CGOpts.SanitizeCoverageTracePC;
   Opts.TracePCGuard = CGOpts.SanitizeCoverageTracePCGuard;
   Opts.NoPrune = CGOpts.SanitizeCoverageNoPrune;
   Opts.Inline8bitCounters = CGOpts.SanitizeCoverageInline8bitCounters;
   Opts.PCTable = CGOpts.SanitizeCoveragePCTable;
   Opts.StackDepth = CGOpts.SanitizeCoverageStackDepth;
-  PM.add(createSanitizerCoverageModulePass(Opts));
+  PM.add(createSanitizerCoverageModulePass(Opts, CGOpts.SanitizeCoverageWhitelistFiles, CGOpts.SanitizeCoverageBlacklistFiles));
 }
 
 // Check if ASan should use GC-friendly instrumentation for globals.
 // First of all, there is no point if -fdata-sections is off (expect for MachO,
 // where this is not a factor). Also, on ELF this feature requires an assembler
 // extension that only works with -integrated-as at the moment.
 static bool asanUseGlobalsGC(const Triple &T, const CodeGenOptions &CGOpts) {
   if (!CGOpts.SanitizeAddressGlobalsDeadStripping)

clang/lib/Driver/SanitizerArgs.cpp

if (!(CoverageFeatures & InsertionPointTypes)) {
     if (CoverageFeatures &
         (CoverageTracePC | CoverageTracePCGuard | CoverageInline8bitCounters))
       CoverageFeatures |= CoverageEdge;
 
     if (CoverageFeatures & CoverageStackDepth)
       CoverageFeatures |= CoverageFunc;
   }
 
+  // Parse -fsanitize-coverage-{white,black}list options.
+  for (const auto *Arg : Args) {
+    if (Arg->getOption().matches(options::OPT_fsanitize_coverage_whitelist_EQ)) {
+      Arg->claim();
+      std::string CWLPath = Arg->getValue();
+      if (llvm::sys::fs::exists(CWLPath)) {
+        CoverageWhitelistFiles.push_back(CWLPath);
+        ExtraDeps.push_back(CWLPath);
+      } else {
+        D.Diag(clang::diag::err_drv_no_such_file) << CWLPath;
+      }
+    } else if (Arg->getOption().matches(options::OPT_fsanitize_coverage_blacklist_EQ)) {
+      Arg->claim();
+      std::string CBLPath = Arg->getValue();
+      if (llvm::sys::fs::exists(CBLPath)) {
+        CoverageBlacklistFiles.push_back(CBLPath);
+        ExtraDeps.push_back(CBLPath);
+      } else {
+        D.Diag(clang::diag::err_drv_no_such_file) << CBLPath;
+      }
+    }
+  }
+  // Validate whitelist and blacklist format.
+  if (CoverageWhitelistFiles.size() > 0) {
+    std::string WLError;
+    std::unique_ptr<llvm::SpecialCaseList> SCL(
+        llvm::SpecialCaseList::create(CoverageWhitelistFiles, WLError));
+    if (!SCL.get())
+      D.Diag(clang::diag::err_drv_malformed_sanitizer_coverage_whitelist) << WLError;
+  }
+  if (CoverageBlacklistFiles.size() > 0) {
+    std::string BLError;
+    std::unique_ptr<llvm::SpecialCaseList> SCL(
+        llvm::SpecialCaseList::create(CoverageBlacklistFiles, BLError));
+    if (!SCL.get())
+      D.Diag(clang::diag::err_drv_malformed_sanitizer_coverage_blacklist) << BLError;
+  }
+
   SharedRuntime =
       Args.hasFlag(options::OPT_shared_libsan, options::OPT_static_libsan,
                    TC.getTriple().isAndroid() || TC.getTriple().isOSFuchsia() ||
                        TC.getTriple().isOSDarwin());
 
   ImplicitCfiRuntime = TC.getTriple().isAndroid();
 
   if (AllAddedKinds & SanitizerKind::Address) {
std::pair<int, const char *> CoverageFlags[] = {
     std::make_pair(CoveragePCTable, "-fsanitize-coverage-pc-table"),
     std::make_pair(CoverageNoPrune, "-fsanitize-coverage-no-prune"),
     std::make_pair(CoverageStackDepth, "-fsanitize-coverage-stack-depth")};
   for (auto F : CoverageFlags) {
     if (CoverageFeatures & F.first)
       CmdArgs.push_back(F.second);
   }
 
+  // Forward coverage whitelist and blacklist
+  for (const auto &CWLPath : CoverageWhitelistFiles) {
+    SmallString<64> CoverageWhitelistOpt("-fsanitize-coverage-whitelist=");
+    CoverageWhitelistOpt += CWLPath;
+    CmdArgs.push_back(Args.MakeArgString(CoverageWhitelistOpt));
+  }
+  for (const auto &CBLPath : CoverageBlacklistFiles) {
+    SmallString<64> CoverageBlacklistOpt("-fsanitize-coverage-blacklist=");
+    CoverageBlacklistOpt += CBLPath;
+    CmdArgs.push_back(Args.MakeArgString(CoverageBlacklistOpt));
+  }
+
   if (TC.getTriple().isOSWindows() && needsUbsanRt()) {
     // Instruct the code generator to embed linker directives in the object file
     // that cause the required runtime libraries to be linked.
     CmdArgs.push_back(Args.MakeArgString(
         "--dependent-lib=" + TC.getCompilerRT(Args, "ubsan_standalone")));
     if (types::isCXX(InputType))
       CmdArgs.push_back(Args.MakeArgString(
           "--dependent-lib=" + TC.getCompilerRT(Args, "ubsan_standalone_cxx")));

clang/lib/Frontend/CompilerInvocation.cpp

static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.SanitizeCoverageTracePCGuard =
       Args.hasArg(OPT_fsanitize_coverage_trace_pc_guard);
   Opts.SanitizeCoverageNoPrune = Args.hasArg(OPT_fsanitize_coverage_no_prune);
   Opts.SanitizeCoverageInline8bitCounters =
       Args.hasArg(OPT_fsanitize_coverage_inline_8bit_counters);
   Opts.SanitizeCoveragePCTable = Args.hasArg(OPT_fsanitize_coverage_pc_table);
   Opts.SanitizeCoverageStackDepth =
       Args.hasArg(OPT_fsanitize_coverage_stack_depth);
+  Opts.SanitizeCoverageWhitelistFiles = Args.getAllArgValues(OPT_fsanitize_coverage_whitelist_EQ);
+  Opts.SanitizeCoverageBlacklistFiles = Args.getAllArgValues(OPT_fsanitize_coverage_blacklist_EQ);
   Opts.SanitizeMemoryTrackOrigins =
       getLastArgIntValue(Args, OPT_fsanitize_memory_track_origins_EQ, 0, Diags);
   Opts.SanitizeMemoryUseAfterDtor =
       Args.hasFlag(OPT_fsanitize_memory_use_after_dtor,
                    OPT_fno_sanitize_memory_use_after_dtor,
                    false);
   Opts.SanitizeMinimalRuntime = Args.hasArg(OPT_fsanitize_minimal_runtime);
   Opts.SanitizeCfiCrossDso = Args.hasArg(OPT_fsanitize_cfi_cross_dso);

llvm/include/llvm/Transforms/Instrumentation.h

struct SanitizerCoverageOptions {
   bool NoPrune = false;
   bool StackDepth = false;
 
   SanitizerCoverageOptions() = default;
 };
 
 // Insert SanitizerCoverage instrumentation.
 ModulePass *createSanitizerCoverageModulePass(
-    const SanitizerCoverageOptions &Options = SanitizerCoverageOptions());
+    const SanitizerCoverageOptions &Options = SanitizerCoverageOptions(),
+    const std::vector<std::string>& WhitelistFiles = std::vector<std::string>(),
+    const std::vector<std::string>& BlacklistFiles = std::vector<std::string>());
 
 /// Calculate what to divide by to scale counts.
 ///
 /// Given the maximum count, calculate a divisor that will scale all the
 /// weights to strictly less than std::numeric_limits<uint32_t>::max().
 static inline uint64_t calculateCountScale(uint64_t MaxCount) {
   return MaxCount < std::numeric_limits<uint32_t>::max()
              ? 1

llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp

 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Mangler.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/SpecialCaseList.h"
 #include "llvm/Transforms/Instrumentation.h"
 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
 #include "llvm/Transforms/Utils/ModuleUtils.h"
 
 using namespace llvm;
 
 #define DEBUG_TYPE "sancov"
 
if (!Options.TracePCGuard && !Options.TracePC &&
       !Options.Inline8bitCounters && !Options.StackDepth)
     Options.TracePCGuard = true; // TracePCGuard is default.
   return Options;
 }
 
 class SanitizerCoverageModule : public ModulePass {
 public:
   SanitizerCoverageModule(
-      const SanitizerCoverageOptions &Options = SanitizerCoverageOptions())
+      const SanitizerCoverageOptions &Options = SanitizerCoverageOptions(),
+      const std::vector<std::string>& WhitelistFiles = std::vector<std::string>(),
+      const std::vector<std::string>& BlacklistFiles = std::vector<std::string>())
       : ModulePass(ID), Options(OverrideFromCL(Options)) {
+    if (WhitelistFiles.size() > 0) {
+      Whitelist = SpecialCaseList::createOrDie(WhitelistFiles);
+    }
+    if (BlacklistFiles.size() > 0) {
+      Blacklist = SpecialCaseList::createOrDie(BlacklistFiles);
+    }
     initializeSanitizerCoverageModulePass(*PassRegistry::getPassRegistry());
   }
   bool runOnModule(Module &M) override;
   bool runOnFunction(Function &F);
   static char ID; // Pass identification, replacement for typeid
   StringRef getPassName() const override { return "SanitizerCoverageModule"; }
 
   void getAnalysisUsage(AnalysisUsage &AU) const override {
private:
 
   GlobalVariable *FunctionGuardArray;  // for trace-pc-guard.
   GlobalVariable *Function8bitCounterArray;  // for inline-8bit-counters.
   GlobalVariable *FunctionPCsArray;  // for pc-table.
   SmallVector<GlobalValue *, 20> GlobalsToAppendToUsed;
   SmallVector<GlobalValue *, 20> GlobalsToAppendToCompilerUsed;
 
   SanitizerCoverageOptions Options;
+
+  std::unique_ptr<SpecialCaseList> Whitelist;
+  std::unique_ptr<SpecialCaseList> Blacklist;
 };
 
 } // namespace
 
 std::pair<Value *, Value *>
 SanitizerCoverageModule::CreateSecStartEnd(Module &M, const char *Section,
                                            Type *Ty) {
   GlobalVariable *SecStart =
if (TargetTriple.isOSBinFormatCOFF()) {
     appendToUsed(M, CtorFunc);
   }
   return CtorFunc;
 }
 
 bool SanitizerCoverageModule::runOnModule(Module &M) {
   if (Options.CoverageType == SanitizerCoverageOptions::SCK_None)
     return false;
+  if (Whitelist &&
+      !Whitelist->inSection("coverage", "src", M.getSourceFileName()))
+    return false;
+  if (Blacklist &&
+      Blacklist->inSection("coverage", "src", M.getSourceFileName()))
+    return false;
   C = &(M.getContext());
   DL = &M.getDataLayout();
   CurModule = &M;
   CurModuleUniqueId = getUniqueModuleId(CurModule);
   TargetTriple = Triple(M.getTargetTriple());
   FunctionGuardArray = nullptr;
   Function8bitCounterArray = nullptr;
   FunctionPCsArray = nullptr;
bool SanitizerCoverageModule::runOnFunction(Function &F) {
   if (isa<UnreachableInst>(F.getEntryBlock().getTerminator()))
     return false;
   // Don't instrument functions using SEH for now. Splitting basic blocks like
   // we do for coverage breaks WinEHPrepare.
   // FIXME: Remove this when SEH no longer uses landingpad pattern matching.
   if (F.hasPersonalityFn() &&
       isAsynchronousEHPersonality(classifyEHPersonality(F.getPersonalityFn())))
     return false;
+  if (Whitelist && !Whitelist->inSection("coverage", "fun", F.getName()))
+    return false;
+  if (Blacklist && Blacklist->inSection("coverage", "fun", F.getName()))
+    return false;
   if (Options.CoverageType >= SanitizerCoverageOptions::SCK_Edge)
     SplitAllCriticalEdges(F, CriticalEdgeSplittingOptions().setIgnoreUnreachableDests());
   SmallVector<Instruction *, 8> IndirCalls;
   SmallVector<BasicBlock *, 16> BlocksToInstrument;
   SmallVector<Instruction *, 8> CmpTraceTargets;
   SmallVector<Instruction *, 8> SwitchTraceTargets;
   SmallVector<BinaryOperator *, 8> DivTraceTargets;
   SmallVector<GetElementPtrInst *, 8> GepTraceTargets;
INITIALIZE_PASS_BEGIN(SanitizerCoverageModule, "sancov",
                       false, false)
 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 INITIALIZE_PASS_DEPENDENCY(PostDominatorTreeWrapperPass)
 INITIALIZE_PASS_END(SanitizerCoverageModule, "sancov",
                     "SanitizerCoverage: TODO."
                     "ModulePass",
                     false, false)
 ModulePass *llvm::createSanitizerCoverageModulePass(
-    const SanitizerCoverageOptions &Options) {
-  return new SanitizerCoverageModule(Options);
+    const SanitizerCoverageOptions &Options,
+    const std::vector<std::string>& WhitelistFiles,
+    const std::vector<std::string>& BlacklistFiles) {
+  return new SanitizerCoverageModule(Options, WhitelistFiles, BlacklistFiles);
 }