Support: chunk writing on Linux

This is a workaround for large file writes.  It has been witnessed that
write(2) failing with EINVAL (22) due to a large value (>2G).  Thanks to
James Knight for the help with coming up with a sane test case.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305846 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/Unix/Program.inc

@@ -449,11 +449,22 @@ bool llvm::sys::commandLineFitsWithinSystemLimits(StringRef Program, ArrayRef<co
   size_t ArgLength = Program.size() + 1;
   for (ArrayRef<const char*>::iterator I = Args.begin(), E = Args.end();
        I != E; ++I) {
-    ArgLength += strlen(*I) + 1;
+    size_t length = strlen(*I);
+
+    // Ensure that we do not exceed the MAX_ARG_STRLEN constant on Linux, which
+    // does not have a constant unlike what the man pages would have you
+    // believe. Since this limit is pretty high, perform the check
+    // unconditionally rather than trying to be aggressive and limiting it to
+    // Linux only.
+    if (length >= (32 * 4096))
+      return false;
+
+    ArgLength += length + 1;
     if (ArgLength > size_t(HalfArgMax)) {
       return false;
     }
   }
+
   return true;
 }
 }

lib/Support/raw_ostream.cpp

@@ -548,7 +548,11 @@ void raw_fd_ostream::write_impl(const char *Ptr, size_t Size) {
   pos += Size;
 
 #ifndef LLVM_ON_WIN32
+#if defined(__linux__)
+  bool ShouldWriteInChunks = true;
+#else
   bool ShouldWriteInChunks = false;
+#endif
 #else
   // Writing a large size of output to Windows console returns ENOMEM. It seems
   // that, prior to Windows 8, WriteFile() is redirecting to WriteConsole(), and

unittests/Support/CommandLineTest.cpp

@@ -13,6 +13,7 @@
 #include "llvm/Config/config.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/Program.h"
 #include "llvm/Support/StringSaver.h"
 #include "gtest/gtest.h"
 #include <fstream>
@@ -546,6 +547,11 @@ TEST(CommandLineTest, GetRegisteredSubcommands) {
   }
 }
 
+TEST(CommandLineTest, ArgumentLimit) {
+  std::string args(32 * 4096, 'a');
+  EXPECT_FALSE(llvm::sys::commandLineFitsWithinSystemLimits("cl", args.data()));
+}
+
 TEST(CommandLineTest, ResponseFiles) {
   llvm::SmallString<128> TestDir;
   std::error_code EC =