Reduce code duplication for obtaining libc file name

Author: simonrozsival

src/native/libs/System.Native/pal_dynamicload.c

@@ -7,32 +7,13 @@
 #include <dlfcn.h>
 #include <string.h>
 
-#if HAVE_GNU_LIBNAMES_H
-#include <gnu/lib-names.h>
-#endif
-
 void* SystemNative_LoadLibrary(const char* filename)
 {
-    // Check whether we have been requested to load 'libc'. If that's the case, then:
-    // * For Linux, use the full name of the library that is defined in <gnu/lib-names.h> by the
-    //   LIBC_SO constant. The problem is that calling dlopen("libc.so") will fail for libc even
-    //   though it works for other libraries. The reason is that libc.so is just linker script
-    //   (i.e. a test file).
-    //   As a result, we have to use the full name (i.e. lib.so.6) that is defined by LIBC_SO.
-    // * For macOS, use constant value absolute path "/usr/lib/libc.dylib".
-    // * For FreeBSD, use constant value "libc.so.7".
-    // * For rest of Unices, use constant value "libc.so".
+    // Check whether we have been requested to load 'libc'. If that's the case, then use the
+    // correct file name based on the current platform.
     if (strcmp(filename, "libc") == 0)
     {
-#if defined(__APPLE__)
-        filename = "/usr/lib/libc.dylib";
-#elif defined(__FreeBSD__)
-        filename = "libc.so.7";
-#elif defined(LIBC_SO)
-        filename = LIBC_SO;
-#else
-        filename = "libc.so";
-#endif
+        filename = LIBC_FILENAME;
     }
 
     return dlopen(filename, RTLD_LAZY);

src/native/libs/System.Native/pal_dynamicload.h

@@ -6,6 +6,29 @@
 #include "pal_compiler.h"
 #include "pal_types.h"
 
+#if HAVE_GNU_LIBNAMES_H
+#include <gnu/lib-names.h>
+#endif
+
+// libc file name:
+// * For Linux, use the full name of the library that is defined in <gnu/lib-names.h> by the
+//   LIBC_SO constant. The problem is that calling dlopen("libc.so") will fail for libc even
+//   though it works for other libraries. The reason is that libc.so is just linker script
+//   (i.e. a test file).
+//   As a result, we have to use the full name (i.e. lib.so.6) that is defined by LIBC_SO.
+// * For macOS, use constant value absolute path "/usr/lib/libc.dylib".
+// * For FreeBSD, use constant value "libc.so.7".
+// * For rest of Unices, use constant value "libc.so".
+#if defined(__APPLE__)
+#define LIBC_FILENAME "/usr/lib/libc.dylib"
+#elif defined(__FreeBSD__)
+#define LIBC_FILENAME "libc.so.7"
+#elif defined(LIBC_SO)
+#define LIBC_FILENAME LIBC_SO
+#else
+#define LIBC_FILENAME "libc.so"
+#endif
+
 PALEXPORT void* SystemNative_LoadLibrary(const char* filename);
 
 PALEXPORT void* SystemNative_GetProcAddress(void* handle, const char* symbol);

src/native/libs/System.Native/pal_interfaceaddresses.c

@@ -7,6 +7,7 @@
 #include "pal_utilities.h"
 #include "pal_safecrt.h"
 #include "pal_networking.h"
+#include "pal_dynamicload.h"
 
 #include <stdlib.h>
 #include <sys/types.h>
@@ -55,13 +56,6 @@
 #endif
 #endif
 
-#if !HAVE_GETIFADDRS
-#include <dlfcn.h>
-#if HAVE_GNU_LIBNAMES_H
-#include <gnu/lib-names.h>
-#endif
-#endif
-
 // Convert mask to prefix length e.g. 255.255.255.0 -> 24
 // mask parameter is pointer to buffer where address starts and length is
 // buffer length e.g. 4 for IPv4 and 16 for IPv6.
@@ -139,17 +133,7 @@ static bool ensure_getifaddrs_impl_available() {
     {
         loading_getifaddrs_already_attempted = true;
 
-#if defined(__APPLE__)
-        const char *libc_path = "/usr/lib/libc.dylib";
-#elif defined(__FreeBSD__)
-        const char *libc_path = "libc.so.7";
-#elif defined(LIBC_SO)
-        const char *libc_path = LIBC_SO;
-#else
-        const char *libc_path = "libc.so";
-#endif
-
-        void *libc = dlopen(libc_path, RTLD_NOW);
+        void *libc = dlopen(LIBC_FILENAME, RTLD_NOW);
         if (libc)
         {
             getifaddrs_impl = (getifaddrs_fptr)dlsym(libc, "getifaddrs");