[PATCH][LTO] Support -fno-use-linker-plugin with auto-loaded plugin

[Richard Biener]

BFD supports plugin auto-loading for plugins placed in 
/usr/lib/bfd-plugins (if you make it work for GNU LTO objects by
fixing PR14698).  If it does so then we claim LTO IR objects
via the plugin machinery even if -fno-use-linker-plugin is
specified (in that case the gcc driver won't pass a -plugin option
to ld already).  Thus the following patch makes the auto-load
plus -fno-use-linker-plugin combination work by failing at
plugin-load time if that option is in COLLECT_GCC_OPTIONS.

Built and tested on x86_64-unknown-linux-gnu.

Ok?

(I have to repeat myself that we have too many supported
LTO-modes-of-operation)

Thanks,
Richard.

2014-04-01  Richard Biener  <rguent...@suse.de>

        lto-plugin/
        * lto-plugin.c (onload): Fail to load if -fno-use-linker-plugin
        is set in COLLECT_GCC_OPTIONS.

Index: lto-plugin/lto-plugin.c
===================================================================
*** lto-plugin/lto-plugin.c     (revision 208978)
--- lto-plugin/lto-plugin.c     (working copy)
*************** onload (struct ld_plugin_tv *tv)
*** 1067,1071 ****
--- 1067,1078 ----
             "could not register the all_symbols_read callback");
      }
  
+   /* Support -fno-use-linker-plugin by failing to load the plugin
+      for the case where it is auto-loaded by BFD.  */
+   char *collect_gcc_options = getenv ("COLLECT_GCC_OPTIONS");
+   if (collect_gcc_options
+       && strstr (collect_gcc_options, "'-fno-use-linker-plugin'"))
+     return LDPS_ERR;
+ 
    return LDPS_OK;
  }