From e3cce7c178bfdf35d82450903c9c69ee98f6d6db Mon Sep 17 00:00:00 2001
From: stephentoub <stoub@microsoft.com>
Date: Thu, 16 Jul 2015 09:10:56 -0400
Subject: [PATCH] Update DllImport logic to support lack of "lib" prefix

Today the runtime supports automatically appending an appropriate
suffix (e.g. ".so", ".dylib", etc.) for the library name provided
to DllImport.  This commit adds support for also prepending the
standard library prefix "lib".
---
 src/pal/src/loader/module.cpp | 46 +++++++++++++++++++++++--------------------
 1 file changed, 25 insertions(+), 21 deletions(-)

diff --git a/src/pal/src/loader/module.cpp b/src/pal/src/loader/module.cpp
index 1e7c224..2073977 100644
--- a/src/pal/src/loader/module.cpp
+++ b/src/pal/src/loader/module.cpp
@@ -1314,7 +1314,7 @@ static HMODULE LOADLoadLibrary(LPCSTR shortAsciiName, BOOL fDynamic)
 {
     CHAR fullLibraryName[MAX_PATH];
     MODSTRUCT *module = NULL;
-    void *dl_handle;
+    void *dl_handle = NULL;
     DWORD dwError;
     DWORD retval;
 
@@ -1339,29 +1339,33 @@ static HMODULE LOADLoadLibrary(LPCSTR shortAsciiName, BOOL fDynamic)
     // See if file can be dlopen()ed; this should work even if it's already loaded
     {
         // See GetProcAddress for an explanation why we leave the PAL.
-        PAL_LeaveHolder holder;
-        dl_handle = dlopen(shortAsciiName, RTLD_LAZY | RTLD_NOLOAD); 
-        if (!dl_handle)
+        PAL_LeaveHolder holder; 
+        
+        // P/Invokes are often declared with variations on the actual library name.
+        // For example, it's common to leave off the extension/suffix of the library
+        // even if it has one, or to leave off a prefix like "lib" even if it has one
+        // (both of these are done typically to smooth over cross-platform differences). 
+        // We try to dlopen with such variations on the original.
+        const char* const formatStrings[4] = // used with args: PAL_SHLIB_PREFIX, shortAsciiName, PAL_SHLIB_SUFFIX
         {
-            dl_handle = dlopen(shortAsciiName, RTLD_LAZY);
-        }
-
-        // P/Invoke calls are often defined without an extension in the name of the 
-        // target library. So if we failed to load the specified library, try adding
-        // a proper extension and load the library again.
-        if (!dl_handle)
+            "%s%s%s",     // prefix+name+suffix
+            "%.0s%s%.0s", // name
+            "%.0s%s%s",   // name+suffix
+            "%s%s%.0s",   // prefix+name
+        };
+        const int skipPrefixing = strchr(shortAsciiName, '/') != NULL; // skip prefixing if the name is actually a path
+        for (int i = 0; i < 4; i++)
         {
-            if (snprintf(fullLibraryName, MAX_PATH, "%s%s", shortAsciiName, PAL_SHLIB_SUFFIX) < MAX_PATH)
+           if (skipPrefixing && (i == 0 || i == 3)) // 0th and 3rd strings include prefixes
+               continue;
+           
+            if (!dl_handle &&
+                snprintf(fullLibraryName, MAX_PATH, formatStrings[i], PAL_SHLIB_PREFIX, shortAsciiName, PAL_SHLIB_SUFFIX) < MAX_PATH &&
+                ((dl_handle = dlopen(fullLibraryName, RTLD_LAZY | RTLD_NOLOAD)) || 
+                 (dl_handle = dlopen(fullLibraryName, RTLD_LAZY))))
             {
-                dl_handle = dlopen(fullLibraryName, RTLD_LAZY | RTLD_NOLOAD); 
-                if (!dl_handle)
-                {
-                    dl_handle = dlopen(fullLibraryName, RTLD_LAZY);
-                }
-                if (dl_handle)
-                {
-                    shortAsciiName = fullLibraryName;
-                }
+                shortAsciiName = fullLibraryName;
+                break;
             }
         }
     }
-- 
2.7.4