libLLVMSupport: Generate random block of arbitrary size

[evgeny777]

Summary

ruiu suggested doing this here:
https://reviews.llvm.org/D23349

[davide]

A couple of comments on the Unix bits. I'm not familiar with the Windows bits, one between Michael and rnk should sign-off that part before it goes in.

lib/Support/RandomNumberGenerator.cpp

79

POSIX read() could return less bytes than you requested, or just failing, and you might want to handle that case.

80

Also, close() can fail (so you might want to check errno in that case and propagate that back to the caller instead of swallowing it).

[evgeny777]

Added additional error checking

[evgeny777]

Any comments on this?

[aaron.ballman]

Some minor nits, but LGTM

RandomNumberGenerator.cpp

68 ↗

(On Diff #68707)

No need to specify the W version explicitly here. You can pass nullptr rather than 0 as well.

Unix/Unix.h

52 ↗

(On Diff #68707)

Formatting of this line doesn't match the formatting of the other lines in the file.

include/llvm/Support/RandomNumberGenerator.h

 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_RANDOMNUMBERGENERATOR_H_
 #define LLVM_SUPPORT_RANDOMNUMBERGENERATOR_H_
 
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/DataTypes.h" // Needed for uint64_t on Windows.
 #include <random>
+#include <system_error>
 
 namespace llvm {
 class StringRef;
 
 /// A random number generator.
 ///
 /// Instances of this class should not be shared across threads. The
 /// seed should be set by passing the -rng-seed=<uint64> option. Use
private:
   std::mt19937_64 Generator;
 
   // Noncopyable.
   RandomNumberGenerator(const RandomNumberGenerator &other) = delete;
   RandomNumberGenerator &operator=(const RandomNumberGenerator &other) = delete;
 
   friend class Module;
 };
+
+// Get random vector of specified size
+std::error_code getRandomBytes(void *Buffer, size_t Size);
 }
 
 #endif

lib/Support/RandomNumberGenerator.cpp

 // the C++11 <random> facilities.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/RandomNumberGenerator.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
+#ifdef LLVM_ON_WIN32
+#include "Windows/WindowsSupport.h"
+#else
+#include "Unix/Unix.h"
+#endif
 
 using namespace llvm;
 
 #define DEBUG_TYPE "rng"
 
 // Tracking BUG: 19665
 // http://llvm.org/bugs/show_bug.cgi?id=19665
 //
RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
 
   std::seed_seq SeedSeq(Data.begin(), Data.end());
   Generator.seed(SeedSeq);
 }
 
 uint_fast64_t RandomNumberGenerator::operator()() {
   return Generator();
 }
+
+// Get random vector of specified size
+std::error_code getRandomBytes(void *Buffer, size_t Size) {
+#ifdef LLVM_ON_WIN32
+  HCRYPTPROV hProvider;
+  if (CryptAcquireContextW(&hProvider, 0, 0, PROV_RSA_FULL,
+                           CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
+    ScopedCryptContext ScopedHandle(hProvider);
+    if (CryptGenRandom(hProvider, Size, Buffer))
+      return std::error_code();
+  }
+  return std::error_code(GetLastError(), std::system_category());
+#else
+  int Fd = open("/dev/urandom", O_RDONLY);
+  if (Fd == -1)
+    return std::error_code(errno, std::system_category());
+  read(Fd, Buffer, Size);
+  close(Fd);
+  return std::error_code();
+#endif
+}

lib/Support/Unix/Unix.h

 # include <sys/time.h>
 #endif
 #include <time.h>
 
 #ifdef HAVE_DLFCN_H
 # include <dlfcn.h>
 #endif
 
+#ifdef HAVE_FCNTL_H
+#include <fcntl.h>
+#endif
+
 /// This function builds an error message into \p ErrMsg using the \p prefix
 /// string and the Unix error number given by \p errnum. If errnum is -1, the
 /// default then the value of errno is used.
 /// @brief Make an error message
 ///
 /// If the error number can be converted to a string, it will be
 /// separated from prefix by ": ".
 static inline bool MakeErrMsg(