RFC & help: Retrieve programmatically the plugin directory name.

[Basile STARYNKEVITCH <basile at starynkevitch dot net>]

Hello All,

The attached patch to trunk 154643 provides a way to retrieve programmatically the plugin directory name.

See http://gcc.gnu.org/ml/gcc-patches/2009-06/msg01545.html & http://gcc.gnu.org/ml/gcc/2009-11/msg00655.html

The intent is that some plugins may find useful to get some of their configuration files within the plugin/ directory as 
returned by the command
   gcc -print-file-name=plugin

So this patch provides a plugin_directory_name () function to retrieve programmatically that directory.
It works in a similar way to the add_standard_paths function of gcc/incpath.c by calling make_relative_prefix with a 
dummy filename.

Unfortunately, it does not seems to work as expected. My intuitive feeling is that gcc should in fact pass some argument 
[like -iplugindir] to cc1, computed from the prefix and the spec file. Unfortunately, I don't understand these.

So this patch is *not* OK but I am still asking for help.

#### bad gcc/ChangeLog entry: ####
2009-11-25  Basile Starynkevitch  <basile@starynkevitch.net>

	* gcc-plugin.h (plugin_directory_name): Added new declaration.

	* plugin.c: Includes prefix.h & cppdefault.h.
	(plugind_directory_name): Added new function.

	* Makefile.in (plugin.o): also depends upon prefix.h & cppdefault.h.



#### bad gcc/testsuite/ChangeLog entry: ####
2009-11-25  Basile Starynkevitch  <basile@starynkevitch.net>
	* plugdir-test-1.c: Added new test case for plugin_directory_name.
	* plugdir_plugin.c: ditto.
	* plugin.exp: ditto.

#####################

My general feeling is that GCC passes, in particular plugin provided passes, may legitimately need to access files 
within the GCC installation file tree, and I feel that we are lacking some functions (or at least documentations) to 
make that easy from within cc1 and plugins.

Once suich a plugin_directory_name function exists and is working, it is quite easy to patch plugin.c so that 
-fplugin=foo is a simpler way to pass -fplugin=`gcc -print-file-name=plugin`/libexec/foo.so [notice the backquote for 
the shell].

Comments and suggestions are welcome.

Regards.
--
Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
8, rue de la Faiencerie, 92340 Bourg La Reine, France
*** opinions {are only mines, sont seulement les miennes} ***

Index: gcc-trunk-bstarynk/gcc/doc/plugins.texi
===================================================================
--- gcc-trunk-bstarynk/gcc/doc/plugins.texi	(revision 154643)
+++ gcc-trunk-bstarynk/gcc/doc/plugins.texi	(working copy)
@@ -348,6 +348,9 @@ On most systems, you can query this @code{plugin}
 invoking @command{gcc -print-file-name=plugin} (replace if needed
 @command{gcc} with the appropriate program path).
 
+Inside plugins, this @code{plugin} directory name can be queried by
+calling @code{plugin_directory_name ()}.
+
 The following GNU Makefile excerpt shows how to build a simple plugin:
 
 @smallexample
Index: gcc-trunk-bstarynk/gcc/testsuite/gcc.dg/plugin/plugdir-test-1.c
===================================================================
--- gcc-trunk-bstarynk/gcc/testsuite/gcc.dg/plugin/plugdir-test-1.c	(revision 0)
+++ gcc-trunk-bstarynk/gcc/testsuite/gcc.dg/plugin/plugdir-test-1.c	(revision 0)
@@ -0,0 +1,7 @@
+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+int main (int argc, char **argv) 
+{ 
+  return 0;  
+}
Index: gcc-trunk-bstarynk/gcc/testsuite/gcc.dg/plugin/plugdir_plugin.c
===================================================================
--- gcc-trunk-bstarynk/gcc/testsuite/gcc.dg/plugin/plugdir_plugin.c	(revision 0)
+++ gcc-trunk-bstarynk/gcc/testsuite/gcc.dg/plugin/plugdir_plugin.c	(revision 0)
@@ -0,0 +1,42 @@
+/* This test plugin just displays the plugin directory. */
+#include "gcc-plugin.h"
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "toplev.h"
+#include "basic-block.h"
+#include "gimple.h"
+#include "tree.h"
+#include "tree-pass.h"
+#include "intl.h"
+#include "plugin-version.h"
+
+int plugin_is_GPL_compatible;
+
+
+static void 
+start_callback (void *gcc_data, void *user_data)
+{
+  inform (UNKNOWN_LOCATION, "plugin directory is %s", 
+	  plugin_directory_name ());
+}
+
+/* The initialization routine exposed to and called by GCC. The spec of this
+   function is defined in gcc/gcc-plugin.h.
+
+   PLUGIN_NAME - name of the plugin (useful for error reporting)
+   ARGC        - the size of the ARGV array
+   ARGV        - an array of key-value argument pair
+
+   Returns 0 if initialization finishes successfully.
+
+   Note that this function needs to be named exactly "plugin_init".  */
+
+int
+plugin_init (struct plugin_name_args *plugin_info,
+             struct plugin_gcc_version *version)
+{
+  register_callback ("plugdir", PLUGIN_START_UNIT, &start_callback, NULL);
+  return 0;
+}
Index: gcc-trunk-bstarynk/gcc/testsuite/gcc.dg/plugin/plugin.exp
===================================================================
--- gcc-trunk-bstarynk/gcc/testsuite/gcc.dg/plugin/plugin.exp	(revision 154643)
+++ gcc-trunk-bstarynk/gcc/testsuite/gcc.dg/plugin/plugin.exp	(working copy)
@@ -51,6 +51,7 @@ set plugin_test_list [list \
     { ggcplug.c ggcplug-test-1.c } \
     { one_time_plugin.c one_time-test-1.c } \
     { start_unit_plugin.c start_unit-test-1.c } \
+    { plugdir_plugin.c plugdir-test-1.c } \
     { finish_unit_plugin.c finish_unit-test-1.c } \
 ]
 
Index: gcc-trunk-bstarynk/gcc/gcc-plugin.h
===================================================================
--- gcc-trunk-bstarynk/gcc/gcc-plugin.h	(revision 154643)
+++ gcc-trunk-bstarynk/gcc/gcc-plugin.h	(working copy)
@@ -137,4 +137,8 @@ extern void register_callback (const char *plugin_
                                plugin_callback_func callback,
                                void *user_data);
 
+/* Retrieve the plugin directory name, as returned by the
+   -fprint-file-name=plugin argument to the gcc program. */
+extern const char* plugin_directory_name (void);
+
 #endif /* GCC_PLUGIN_H */
Index: gcc-trunk-bstarynk/gcc/plugin.c
===================================================================
--- gcc-trunk-bstarynk/gcc/plugin.c	(revision 154643)
+++ gcc-trunk-bstarynk/gcc/plugin.c	(working copy)
@@ -38,6 +38,8 @@ along with GCC; see the file COPYING3.  If not see
 #include "intl.h"
 #include "plugin.h"
 #include "timevar.h"
+#include "prefix.h"
+#include "cppdefault.h"
 #include "ggc.h"
 
 #ifdef ENABLE_PLUGIN
@@ -686,3 +688,37 @@ plugin_default_version_check (struct plugin_gcc_ve
     return false;
   return true;
 }
+
+/* Retrieve the plugin directory name, using the make_relative_prefix
+   utility function, which expects a program name, not a directory
+   name.  So we use "plugin-dummy" as the ``program'' name.  */
+const char* 
+plugin_directory_name (void)
+{
+  struct stat dirst;
+  const char* dummyplugin;
+  char* relocprefix;
+  static char* plugdirname;
+  /* When called more than once, return the memoized result. */
+  if (plugdirname)
+    return plugdirname;
+  /* We are doing like add_standard_paths from incpath.c. */
+  dummyplugin = 
+    gcc_exec_prefix?
+    concat (gcc_exec_prefix, "plugin-dummy", NULL)
+    : "plugin-dummy"
+    ;
+  relocprefix = make_relative_prefix (dummyplugin, 
+				      cpp_EXEC_PREFIX,
+				      cpp_PREFIX);
+  plugdirname = concat (relocprefix, "plugin", NULL);
+  /* The plugdirname is never freed. */
+  memset (&dirst, 0, sizeof(dirst));
+  /* Sanity checks: the plugin directory should exist and be a directory! */
+  if (stat (plugdirname, &dirst))
+    fatal_error ("cannot stat the plugin directory %s - %m", plugdirname);
+  if (!S_ISDIR (dirst.st_mode)) 
+    fatal_error ("%s should be the plugin directory, but is not a directory.", 
+		 plugdirname);
+  return plugdirname;
+}
Index: gcc-trunk-bstarynk/gcc/Makefile.in
===================================================================
--- gcc-trunk-bstarynk/gcc/Makefile.in	(revision 154643)
+++ gcc-trunk-bstarynk/gcc/Makefile.in	(working copy)
@@ -2728,7 +2728,8 @@ passes.o : passes.c $(CONFIG_H) $(SYSTEM_H) corety
    gt-passes.h $(DF_H) $(PREDICT_H) $(LTO_HEADER_H) $(LTO_SECTION_OUT_H)
 
 plugin.o : plugin.c $(PLUGIN_H) $(CONFIG_H) $(SYSTEM_H) coretypes.h \
-   $(TOPLEV_H) $(TREE_H) $(TREE_PASS_H) intl.h $(PLUGIN_VERSION_H) $(GGC_H)
+   $(TOPLEV_H) $(TREE_H) $(TREE_PASS_H) intl.h $(PLUGIN_VERSION_H) $(GGC_H) \
+   prefix.h cppdefault.h
 
 main.o : main.c $(CONFIG_H) $(SYSTEM_H) coretypes.h $(TM_H) $(TOPLEV_H)