[Host] Respect LLVM_LIBDIR_SUFFIX when looking for LLDB plugins on Linux

[mgorny]

Summary

Fix the Linux plugin lookup path to include appropriate libdir suffix
for the system. To accomplish this, store the value of
LLVM_LIBDIR_SUFFIX in lldb/Host/Config.h as LLDB_LIBDIR_SUFFIX,
and use this variable when defining the plugin path.

[mgorny]

Disclaimer: I have never seen a plugin for LLDB. I've just noticed the wrong path in strace output and fixed it ;-).

[labath]

We have one plugin in-tree (tools/intel-features), but I'm not sure if anyone uses/installs it.

In any case, the change seems like the right thing to do.

[clayborg]

source/Host/linux/HostInfoLinux.cpp

208

Is there no setting that sets the start of the path here ("/usr/lib")? Not sure how open source projects handle this, but it seems that this should be a build setting that defaults to "/usr/lib" and can be modified?

[clayborg]

See inlined comment

[mgorny]

source/Host/linux/HostInfoLinux.cpp

208

Well, yes, this is something that could be possibly be done but TBH I don't really know how exactly it should be done. For autoconf projects, you generally do something like -Dbindir=$(bindir) in the Makefile. For CMake projects, I suppose this could be CMAKE_INSTALL_PREFIX, except I don't know if it has any corner cases. AFAIK clang uses path relative to executable to find compiler-rt, so maybe that would be revelant here as well.

In other words, I went for fixing the most obvious bug, and leaving the harder (yet less frequent) problem to somebody else.

[clayborg]

Looks good.

include/lldb/Host/Config.h.cmake

 //===-- Config.h -----------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLDB_HOST_CONFIG_H
 #define LLDB_HOST_CONFIG_H
 
 #cmakedefine LLDB_CONFIG_TERMIOS_SUPPORTED
 
 #cmakedefine LLDB_DISABLE_POSIX
 
+#define LLDB_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}"
+
 #cmakedefine01 HAVE_SYS_EVENT_H
 
 #cmakedefine01 HAVE_PPOLL
 
 #cmakedefine01 HAVE_SIGACTION
 
 #cmakedefine01 HAVE_PROCESS_VM_READV
 
 #cmakedefine01 HAVE_NR_PROCESS_VM_READV
 
 #cmakedefine HAVE_LIBCOMPRESSION
 
 #endif // #ifndef LLDB_HOST_CONFIG_H

source/Host/linux/HostInfoLinux.cpp

 //===-- HostInfoLinux.cpp ---------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
+#include "lldb/Host/Config.h"
 #include "lldb/Host/linux/HostInfoLinux.h"
 #include "lldb/Utility/Log.h"
 
 #include "llvm/Support/Threading.h"
 
 #include <limits.h>
 #include <stdio.h>
 #include <string.h>
bool HostInfoLinux::ComputeSupportExeDirectory(FileSpec &file_spec) {
   if (HostInfoPosix::ComputeSupportExeDirectory(file_spec) &&
       file_spec.IsAbsolute() && file_spec.Exists())
     return true;
   file_spec.GetDirectory() = GetProgramFileSpec().GetDirectory();
   return !file_spec.GetDirectory().IsEmpty();
 }
 
 bool HostInfoLinux::ComputeSystemPluginsDirectory(FileSpec &file_spec) {
-  FileSpec temp_file("/usr/lib/lldb/plugins", true);
+  FileSpec temp_file("/usr/lib" LLDB_LIBDIR_SUFFIX "/lldb/plugins", true);
   file_spec.GetDirectory().SetCString(temp_file.GetPath().c_str());
   return true;
 }
 
 bool HostInfoLinux::ComputeUserPluginsDirectory(FileSpec &file_spec) {
   // XDG Base Directory Specification
   // http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
   // If XDG_DATA_HOME exists, use that, otherwise use ~/.local/share/lldb.