[libFuzzer] Disable implicit builtin knowledge about memcmp-like functions when -fsanitize=fuzzer-no-link is given.

Summary: This patch disables implicit builtin knowledge about memcmp-like functions when compiling the program for fuzzing, i.e., when -fsanitize=fuzzer(-no-link) is given. This allows libFuzzer to always intercept memcmp-like functions as it effectively disables optimizing calls to such functions into different forms. This is done by adding a set of flags (-fno-builtin-memcmp and others) in the clang driver. Individual -fno-builtin-* flags previously used in several libFuzzer tests are now removed, as it is now done automatically in the clang driver.

Reviewers: morehouse, hctim

Subscribers: cfe-commits, #sanitizers

Tags: #clang, #sanitizers

Differential Revision: https://reviews.llvm.org/D83987

Author: dokyungs

clang/lib/Driver/SanitizerArgs.cpp

@@ -1088,6 +1088,22 @@ void SanitizerArgs::addArgs(const ToolChain &TC, const llvm::opt::ArgList &Args,
       Sanitizers.has(SanitizerKind::Address))
     CmdArgs.push_back("-fno-assume-sane-operator-new");
 
+  // libFuzzer wants to intercept calls to certain library functions, so the
+  // following -fno-builtin-* flags force the compiler to emit interposable
+  // libcalls to these functions. Other sanitizers effectively do the same thing
+  // by marking all library call sites with NoBuiltin attribute in their LLVM
+  // pass. (see llvm::maybeMarkSanitizerLibraryCallNoBuiltin)
+  if (Sanitizers.has(SanitizerKind::FuzzerNoLink)) {
+    CmdArgs.push_back("-fno-builtin-memcmp");
+    CmdArgs.push_back("-fno-builtin-strncmp");
+    CmdArgs.push_back("-fno-builtin-strcmp");
+    CmdArgs.push_back("-fno-builtin-strncasecmp");
+    CmdArgs.push_back("-fno-builtin-strcasecmp");
+    CmdArgs.push_back("-fno-builtin-strstr");
+    CmdArgs.push_back("-fno-builtin-strcasestr");
+    CmdArgs.push_back("-fno-builtin-memmem");
+  }
+
   // Require -fvisibility= flag on non-Windows when compiling if vptr CFI is
   // enabled.
   if (Sanitizers.hasOneOf(CFIClasses) && !TC.getTriple().isOSWindows() &&

compiler-rt/test/fuzzer/memcmp.test

@@ -2,7 +2,7 @@ UNSUPPORTED: freebsd
 RUN: %cpp_compiler %S/MemcmpTest.cpp -o %t-MemcmpTest
 RUN: not %run %t-MemcmpTest               -seed=1 -runs=10000000   2>&1 | FileCheck %s
 
-RUN: %cpp_compiler -fno-sanitize=address -fno-builtin-memcmp %S/MemcmpTest.cpp -o %t-NoAsanMemcmpTest
+RUN: %cpp_compiler -fno-sanitize=address %S/MemcmpTest.cpp -o %t-NoAsanMemcmpTest
 RUN: not %run %t-MemcmpTest               -seed=1 -runs=10000000   2>&1 | FileCheck %s
 
 CHECK: BINGO

compiler-rt/test/fuzzer/memcmp64.test

@@ -2,7 +2,7 @@ UNSUPPORTED: freebsd
 RUN: %cpp_compiler %S/Memcmp64BytesTest.cpp -o %t-Memcmp64BytesTest
 RUN: not %run %t-Memcmp64BytesTest        -seed=1 -runs=1000000   2>&1 | FileCheck %s
 
-RUN: %cpp_compiler -fno-sanitize=address -fno-builtin-memcmp %S/Memcmp64BytesTest.cpp -o %t-NoAsanMemcmp64BytesTest
+RUN: %cpp_compiler -fno-sanitize=address %S/Memcmp64BytesTest.cpp -o %t-NoAsanMemcmp64BytesTest
 RUN: not %run %t-Memcmp64BytesTest        -seed=1 -runs=1000000   2>&1 | FileCheck %s
 
 CHECK: BINGO

compiler-rt/test/fuzzer/strcmp.test

@@ -2,7 +2,7 @@ UNSUPPORTED: freebsd
 RUN: %cpp_compiler %S/StrcmpTest.cpp -o %t-StrcmpTest
 RUN: not %run %t-StrcmpTest               -seed=1 -runs=2000000   2>&1 | FileCheck %s
 
-RUN: %cpp_compiler -fno-sanitize=address -fno-builtin-strcmp %S/StrcmpTest.cpp -o %t-NoAsanStrcmpTest
+RUN: %cpp_compiler -fno-sanitize=address %S/StrcmpTest.cpp -o %t-NoAsanStrcmpTest
 RUN: not %run %t-StrcmpTest               -seed=1 -runs=2000000   2>&1 | FileCheck %s
 
 CHECK: BINGO

compiler-rt/test/fuzzer/strncmp.test

@@ -2,7 +2,7 @@ UNSUPPORTED: freebsd
 RUN: %cpp_compiler %S/StrncmpTest.cpp -o %t-StrncmpTest
 RUN: not %run %t-StrncmpTest              -seed=2 -runs=10000000   2>&1 | FileCheck %s
 
-RUN: %cpp_compiler -fno-sanitize=address -fno-builtin-strncmp %S/StrncmpTest.cpp -o %t-NoAsanStrncmpTest
+RUN: %cpp_compiler -fno-sanitize=address %S/StrncmpTest.cpp -o %t-NoAsanStrncmpTest
 RUN: not %run %t-StrncmpTest              -seed=2 -runs=10000000   2>&1 | FileCheck %s
 
 CHECK: BINGO

compiler-rt/test/fuzzer/strstr.test

@@ -2,7 +2,7 @@ UNSUPPORTED: freebsd
 RUN: %cpp_compiler %S/StrstrTest.cpp -o %t-StrstrTest
 RUN: not %run %t-StrstrTest               -seed=1 -runs=2000000   2>&1 | FileCheck %s
 
-RUN: %cpp_compiler -fno-sanitize=address -fno-builtin-strstr %S/StrstrTest.cpp -o %t-NoAsanStrstrTest
+RUN: %cpp_compiler -fno-sanitize=address %S/StrstrTest.cpp -o %t-NoAsanStrstrTest
 RUN: not %run %t-StrstrTest               -seed=1 -runs=2000000   2>&1 | FileCheck %s
 
 CHECK: BINGO