Add AssemblyLoadContext.LoadUnmanagedDllFromPathfor use by overriders of AssemblyLoadContext.LoadUnmanagedDll

LoadUnmanagedDllFromPath needs to call LoadLibrary or dlopen, and return the system handle to the library through LoadUnmanagedDll. Outside Windows, when LoadUnmanagedDll returns a system handle to a library, the handle needs to be registered with PAL's module list for lifetime management. From that point on, the system handle is tracked as part of the PAL handle.

To handle both of the above, I have refactored module.cpp!LOADLoadLibrary into a LoadLibraryDirect portion and a RegisterLibrary component.

    LoadLibraryDirect loads the specified library directly using the system call, without appending or prepending anything to the library name
    RegisterLibrary registers a system library handle with PAL to get a PAL handle

This patch contains the necessary changes to coreclr and mscorlib. Tests will be added separately, after the new APIs are published and can be consumed.

Fixes dotnet/coreclr#935
Part of dotnet/coreclr#937 and dotnet/corefx#3054

See https://github.com/dotnet/coreclr/pull/1500

[tfs-changeset: 1529692]

1 files changed, 13 insertions, 0 deletions

diff --git a/src/pal/inc/pal.h b/src/pal/inc/pal.h
index 6f88513d29..e995549a4f 100644
--- a/src/pal/inc/pal.h
+++ b/src/pal/inc/pal.h
@@ -3658,6 +3658,19 @@ LoadLibraryExW(
         IN /*Reserved*/ HANDLE hFile,
         IN DWORD dwFlags);
 
+PALIMPORT
+HMODULE
+PALAPI
+PAL_LoadLibraryDirect(
+         IN LPCWSTR lpLibFileName);
+
+PALIMPORT
+HMODULE
+PALAPI
+PAL_RegisterLibraryDirect(
+         IN HMODULE dl_handle,
+         IN LPCWSTR lpLibFileName);
+
 /*++
 Function:
   PAL_LOADLoadPEFile