[Stdlib] Fix Linux detection for malloc_size. Silence const cast warnings. Fix Linux implementation in Random.cpp to actually compile.

Author: mikeash

stdlib/public/SwiftShims/LibcShims.h

@@ -81,22 +81,31 @@ static inline int _swift_stdlib_memcmp(const void *s1, const void *s2,
   return memcmp(s1, s2, n);
 }
 
+// Casting helper. This code needs to work when included from C or C++.
+// Casting away const with a C-style cast warns in C++. Use a const_cast
+// there.
+#ifdef __cplusplus
+#define CONST_CAST(type, value) const_cast<type>(value)
+#else
+#define CONST_CAST(type, value) (type)value
+#endif
+
 // Non-standard extensions
 #if defined(__APPLE__)
 static inline __swift_size_t _swift_stdlib_malloc_size(const void *ptr) {
   extern __swift_size_t malloc_size(const void *);
   return malloc_size(ptr);
 }
-#elif defined(__GNU_LIBRARY__) || defined(__CYGWIN__) || defined(__ANDROID__) \
+#elif defined(__linux__) || defined(__CYGWIN__) || defined(__ANDROID__) \
    || defined(__HAIKU__) || defined(__FreeBSD__)
 static inline __swift_size_t _swift_stdlib_malloc_size(const void *ptr) {
   extern __swift_size_t malloc_usable_size(void *ptr);
-  return malloc_usable_size((void *)ptr);
+  return malloc_usable_size(CONST_CAST(void *, ptr));
 }
 #elif defined(_WIN32)
 static inline __swift_size_t _swift_stdlib_malloc_size(const void *ptr) {
   extern __swift_size_t _msize(void *ptr);
-  return _msize(const_cast<void *>(ptr));
+  return _msize(CONST_CAST(void *, ptr));
 }
 #else
 #error No malloc_size analog known for this platform/libc.

stdlib/public/stubs/Random.cpp

@@ -23,6 +23,7 @@
 #pragma comment(lib, "Bcrypt.lib")
 #else
 #include <errno.h>
+#include <fcntl.h>
 #include <unistd.h>
 #endif
 
@@ -36,6 +37,7 @@
 
 #include <stdlib.h>
 
+#include "swift/Runtime/Debug.h"
 #include "swift/Runtime/Mutex.h"
 #include "../SwiftShims/Random.h"
 
@@ -91,12 +93,12 @@ void swift::swift_stdlib_random(void *buf, __swift_size_t nbytes) {
 
     if (actual_nbytes == -1) {
       static const int fd = 
-        WHILE_EINTR(_swift_stdlib_open("/dev/urandom", O_RDONLY | O_CLOEXEC, 0));
+        WHILE_EINTR(open("/dev/urandom", O_RDONLY | O_CLOEXEC, 0));
 
       if (fd != -1) {
         static StaticMutex mutex;
         mutex.withLock([&] {
-          actual_nbytes = WHILE_EINTR(_swift_stdlib_read(fd, buf, nbytes));
+          actual_nbytes = WHILE_EINTR(read(fd, buf, nbytes));
         });
       }
     }