[llvm] 2e74b6d - [llvm-cov gcov] Don't require NUL terminator when reading files

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2020-07-19T00:31:52-07:00
New Revision: 2e74b6d80f347203ae17ec8b09e6b3e86ff6c179

URL: https://github.com/llvm/llvm-project/commit/2e74b6d80f347203ae17ec8b09e6b3e86ff6c179
DIFF: https://github.com/llvm/llvm-project/commit/2e74b6d80f347203ae17ec8b09e6b3e86ff6c179.diff

LOG: [llvm-cov gcov] Don't require NUL terminator when reading files

.gcno, .gcda and source files can be modified while we are reading them. If the
concurrent modification of a file being read nullifies the NUL terminator
assumption, llvm-cov can trip over an assertion failure in MemoryBuffer::init.
This is not so rare - the source files can be in an editor and .gcda can be
written by an running process (if the process forks, when .gcda gets written is
probably more unpredictable).

There is no accompanying test because an assertion failure requires data
races with some involved setting.

Added: 
    

Modified: 
    llvm/lib/ProfileData/GCOV.cpp
    llvm/tools/llvm-cov/gcov.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/ProfileData/GCOV.cpp b/llvm/lib/ProfileData/GCOV.cpp
index 71ea44a1a722..7b97723da60c 100644
--- a/llvm/lib/ProfileData/GCOV.cpp
+++ b/llvm/lib/ProfileData/GCOV.cpp
@@ -522,8 +522,11 @@ class LineConsumer {
 public:
   LineConsumer() = default;
   LineConsumer(StringRef Filename) {
+    // Open source files without requiring a NUL terminator. The concurrent
+    // modification may nullify the NUL terminator condition.
     ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
-        MemoryBuffer::getFileOrSTDIN(Filename);
+        MemoryBuffer::getFileOrSTDIN(Filename, -1,
+                                     /*RequiresNullTerminator=*/false);
     if (std::error_code EC = BufferOrErr.getError()) {
       errs() << Filename << ": " << EC.message() << "\n";
       Remaining = "";

diff  --git a/llvm/tools/llvm-cov/gcov.cpp b/llvm/tools/llvm-cov/gcov.cpp
index 7a1dbbfe9338..d99e792c68a9 100644
--- a/llvm/tools/llvm-cov/gcov.cpp
+++ b/llvm/tools/llvm-cov/gcov.cpp
@@ -43,8 +43,10 @@ static void reportCoverage(StringRef SourceFile, StringRef ObjectDir,
                          : InputGCDA;
   GCOVFile GF;
 
+  // Open .gcda and .gcda without requiring a NUL terminator. The concurrent
+  // modification may nullify the NUL terminator condition.
   ErrorOr<std::unique_ptr<MemoryBuffer>> GCNO_Buff =
-      MemoryBuffer::getFileOrSTDIN(GCNO);
+      MemoryBuffer::getFileOrSTDIN(GCNO, -1, /*RequiresNullTerminator=*/false);
   if (std::error_code EC = GCNO_Buff.getError()) {
     errs() << GCNO << ": " << EC.message() << "\n";
     return;
@@ -56,7 +58,7 @@ static void reportCoverage(StringRef SourceFile, StringRef ObjectDir,
   }
 
   ErrorOr<std::unique_ptr<MemoryBuffer>> GCDA_Buff =
-      MemoryBuffer::getFileOrSTDIN(GCDA);
+      MemoryBuffer::getFileOrSTDIN(GCDA, -1, /*RequiresNullTerminator=*/false);
   if (std::error_code EC = GCDA_Buff.getError()) {
     if (EC != errc::no_such_file_or_directory) {
       errs() << GCDA << ": " << EC.message() << "\n";