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 ↗

(On Diff #68546)

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

80 ↗

(On Diff #68546)

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

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

Unix/Unix.h

52

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

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, static_cast<BYTE *>(Buffer)))
+      return std::error_code();
+  }
+  return std::error_code(GetLastError(), std::system_category());
+#else
+  int Fd = open("/dev/urandom", O_RDONLY);
+  if (Fd != -1) {
+    std::error_code Ret;
+    ssize_t BytesRead = read(Fd, Buffer, Size);
+    if (BytesRead == -1)
+      Ret = std::error_code(errno, std::system_category());
+    else if (BytesRead != static_cast<ssize_t>(Size))
+      Ret = std::error_code(EIO, std::system_category());
+    if (close(Fd) == -1)
+      Ret = std::error_code(errno, std::system_category());
+
+    return Ret;
+  }
+  return std::error_code(errno, std::system_category());
+#endif
+}

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(