[PATCH] Use the LTO linker plugin by default

[Richard Biener]

On Thu, 13 Mar 2014, Rainer Orth wrote:

> Richard Biener <rguenther@suse.de> writes:
> 
> >> > So then if it succeeds to link to a shared libgcc_s then why
> >> > is it not able to find that later?  Maybe you miss setting
> >> > of a suitable LD_LIBRARY_PATH to pick up the runtime for
> >> > your host compiler?
> >> 
> >> For the same reason that we use -static-libstdc++ to avoid this issue
> >> for libstdc++.so.  I've always considered gcc's tendency to build
> >> binaries that don't run by default a major annoyance, all the weasel
> >> wording in the FAQ nonwithstanding.  I hope to finally do something
> >
> > True, but if your host compiler builds sth then it's the host
> > compiler installs business to make sure it can run ... (and thus
> > make the libgcc_s it links to available or only provide a static
> > libgcc_s).
> 
> Exactly my words.  But gcc provides zero help for that.  All proposed
> workarounds (having every user of gcc set LD_LIBRARY_PATH, messing
> around with ldconfig or equivalent, having every single compiler user
> provide -rpath/-R on his own) are usability or functionality nightmares
> one way or another: the first and second don't scale (imagine a large
> site with hundreds of machines and users), and the third imposes work on
> the user that the compiler can do best on its own.  This may be somewhat
> acceptable for single-user/single-system installations of knowledgable
> users, but otherwise it's just a bad joke.  The compiler has all the
> information when/how to pass -rpath/-R and should provide an option to
> do so.  And if a target has different multilibs, the user suddenly needs
> to no not only about $libdir, but about the various multilib (sub)dirs.
> Not what I consider user-friendly, and I've seen a large enough share of
> somewhat experienced users fail with that.

Ah, we've done that in the past for compilers with libs in
non-standard install locations ...

cat > $RPM_BUILD_ROOT%{libsubdir}/defaults.spec << EOF
*link:
+ %%{!m32:%%{!m64:-rpath=%{libsubdir}}} %%{m32:-rpath=%{libsubdir}/32} 
%%{m64:-rpath=%{libsubdir}/64}
EOF

together with the following (ISTR it was posted but never
approved / applied):

Index: gcc/gcc.c
===================================================================
--- gcc/gcc.c.orig	2012-11-28 10:36:38.000000000 +0100
+++ gcc/gcc.c	2012-12-11 12:30:30.053124280 +0100
@@ -260,6 +260,7 @@ static const char *replace_outfile_spec_
 static const char *remove_outfile_spec_function (int, const char **);
 static const char *version_compare_spec_function (int, const char **);
 static const char *include_spec_function (int, const char **);
+static const char *include_noerr_spec_function (int, const char **);
 static const char *find_file_spec_function (int, const char **);
 static const char *find_plugindir_spec_function (int, const char **);
 static const char *print_asm_header_spec_function (int, const char **);
@@ -1293,6 +1294,7 @@ static const struct spec_function static
   { "remove-outfile",		remove_outfile_spec_function },
   { "version-compare",		version_compare_spec_function },
   { "include",			include_spec_function },
+  { "include_noerr",            include_noerr_spec_function },
   { "find-file",		find_file_spec_function },
   { "find-plugindir",		find_plugindir_spec_function },
   { "print-asm-header",		print_asm_header_spec_function },
@@ -6382,6 +6384,8 @@ main (int argc, char **argv)
   if (access (specs_file, R_OK) == 0)
     read_specs (specs_file, true, false);
 
+  do_self_spec ("%:include_noerr(defaults.spec)%(default_spec)");
+
   /* Process any configure-time defaults specified for the command line
      options, via OPTION_DEFAULT_SPECS.  */
   for (i = 0; i < ARRAY_SIZE (option_default_specs); i++)
@@ -8271,6 +8275,21 @@ get_random_number (void)
   return ret ^ getpid();
 }
 
+static const char *
+include_noerr_spec_function (int argc, const char **argv)
+{
+  char *file;
+
+  if (argc != 1)
+    abort ();
+
+  file = find_a_file (&startfile_prefixes, argv[0], R_OK, 0);
+  if (file)
+    read_specs (file, FALSE, TRUE);
+
+  return NULL;
+}
+
 /* %:compare-debug-dump-opt spec function.  Save the last argument,
    expected to be the last -fdump-final-insns option, or generate a
    temporary.  */

> > For this particular case at least.
> >
> > Note that I'm not against linking against static libgcc_s for
> > lto-plugin.  The -static-libstdc++ we use is just because during
> > bootstrap picking up the correct libstdc++ was deemed too hard
> > to implement and thus the easy way out was -static-libstdc++.
> 
> So how should we go forward with this issue?  This bootstrap failure is
> a regression from all previous releases.  As I said, I'd rather not
> duplicate the -static-libgcc test from the toplevel, but would do so if
> all else fails.  Perhaps Paolo could weigh in as the build maintainer?

Yeah, I'd like a build maintainer to look over your first proposed patch
(workaround libtools nicyness).

Richard.