From http://sources.redhat.com/ml/binutils/2004-08/msg00190.html

Date: Tue, 17 Aug 2004 12:04:29 +0200

From: Jakub Jelinek <jakub at redhat dot com>

To: binutils at sources dot redhat dot com

Subject: [PATCH] Fix `defined in discarded section' errors when building ia64 gcc

Message-ID: <20040817100429.GL30497@sunsite.ms.mff.cuni.cz>

Reply-To: Jakub Jelinek <jakub at redhat dot com>

References: <20040817090201.GK30497@sunsite.ms.mff.cuni.cz>

In-Reply-To: <20040817090201 dot GK30497 at sunsite dot ms dot mff dot cuni dot cz>

On Tue, Aug 17, 2004 at 11:02:01AM +0200, Jakub Jelinek wrote:

> Current gcc 3.4.x (at least gcc-3_4-rhl-branch) doesn't build with CVS

> binutils (nor 2.15.91.0.2).

> The problem is that libstdc++.so linking fails with:

> `.gnu.linkonce.t._ZNSdD2Ev' referenced in section `.gnu.linkonce.ia64unw._ZNSdD2Ev' of .libs/sstream-inst.o: defined in discarded section `.gnu.linkonce.t._ZNSdD2Ev' of .libs/sstream-inst.o

> The problem is that both io-inst.s and sstream-inst.s have

> .gnu.linkonce.t._ZNSdD2Ev definition, but because io-inst.cc

> also instantiates some templates sstream-inst.cc doesn't instantiate,

> the inliner can do a better job in io-inst.cc.

> The result is that _ZNSdD2Ev in io-inst.cc is a leaf routine, while

> it is not in sstream-inst.cc (in assembly,

> _ZNSdD2Ev in io-inst.s starts with .prologue and no .save directives,

> while _ZNSdD2Ev] in sstream-inst.s has .prologue 12, 35 and some

> .save directives.

> IA-64 ABI allows leaf routines to have no unwind section at all,

> which means .gnu.linkonce.ia64unw._ZNSdD2Ev is not created in

> io-inst.o at all and as .gnu.linkonce.t._ZNSdD2Ev comes first

> and wins, .gnu.linkonce.ia64unw._ZNSdD2Ev in sstream.o suddenly

> references a discarded section.

> 

> Not sure what should be done here, but certainly the compiler

> isn't at fault here, it is a binutils problem.

> One fix could be to create empty .gnu.linkonce.ia64unw.* section

> in assembler, another special case ia64 unwind sections in the linker.

Here is a patch for the first possibility.

It certainly makes libstdc++.so to link and even the unwind info looks

good on brief skimming.

2004-08-17  Jakub Jelinek  <jakub@redhat.com>

	* config/tc-ia64.c (start_unwind_section): Add linkonce_empty

	argument, don't do anything if current section is not

	.gnu.linkonce.t.* and linkonce_empty is set.

	(generate_unwind_image, dot_endp): Adjust callers, call

	start_unwind_section (*, 1) if nothing will be put into the

	section.

--- binutils/gas/config/tc-ia64.c.jj	2004-07-30 11:42:24.000000000 +0200

+++ binutils/gas/config/tc-ia64.c	2004-08-17 13:45:04.288173205 +0200

@@ -1,5 +1,6 @@

 /* tc-ia64.c -- Assembler for the HP/Intel IA-64 architecture.

-   Copyright 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.

+   Copyright 1998, 1999, 2000, 2001, 2002, 2003, 2004

+   Free Software Foundation, Inc.

    Contributed by David Mosberger-Tang <davidm@hpl.hp.com>

    This file is part of GAS, the GNU Assembler.

@@ -3297,7 +3298,7 @@ static char *special_linkonce_name[] =

   };

 static void

-start_unwind_section (const segT text_seg, int sec_index)

+start_unwind_section (const segT text_seg, int sec_index, int linkonce_empty)

 {

   /*

     Use a slightly ugly scheme to derive the unwind section names from

@@ -3359,6 +3360,8 @@ start_unwind_section (const segT text_se

       prefix = special_linkonce_name [sec_index - SPECIAL_SECTION_UNWIND];

       suffix += sizeof (".gnu.linkonce.t.") - 1;

     }

+  else if (linkonce_empty)

+    return;

   prefix_len = strlen (prefix);

   suffix_len = strlen (suffix);

@@ -3444,7 +3447,7 @@ generate_unwind_image (const segT text_s

       expressionS exp;

       bfd_reloc_code_real_type reloc;

-      start_unwind_section (text_seg, SPECIAL_SECTION_UNWIND_INFO);

+      start_unwind_section (text_seg, SPECIAL_SECTION_UNWIND_INFO, 0);

       /* Make sure the section has 4 byte alignment for ILP32 and

 	 8 byte alignment for LP64.  */

@@ -3485,6 +3488,8 @@ generate_unwind_image (const segT text_s

 	  unwind.personality_routine = 0;

 	}

     }

+  else

+    start_unwind_section (text_seg, SPECIAL_SECTION_UNWIND_INFO, 1);

   free_saved_prologue_counts ();

   unwind.list = unwind.tail = unwind.current_entry = NULL;

@@ -4164,7 +4169,7 @@ dot_endp (dummy)

       subseg_set (md.last_text_seg, 0);

       unwind.proc_end = expr_build_dot ();

-      start_unwind_section (saved_seg, SPECIAL_SECTION_UNWIND);

+      start_unwind_section (saved_seg, SPECIAL_SECTION_UNWIND, 0);

       /* Make sure that section has 4 byte alignment for ILP32 and

          8 byte alignment for LP64.  */

@@ -4204,6 +4209,9 @@ dot_endp (dummy)

 			    bytes_per_address);

     }

+  else

+    start_unwind_section (saved_seg, SPECIAL_SECTION_UNWIND, 1);

+

   subseg_set (saved_seg, saved_subseg);

   /* Parse names of main and alternate entry points and set symbol sizes.  */

	Jakub