Re: Emit a warning when -z relro is unsupported

[Alan Modra <amodra@gmail.com>]

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I believe the ia64-linux glibc problem is triggered by a fairly simple
glibc build bug.  There is a linker bug too.

I was able to reproduce the problem, with
.IA_64.unwind__libc_freeres_fn being mapped to bfd_abs_section, which
is what happens when a section is discarded by a linker script.

On looking at glibc/shlib.lds I see toward the end:

  .gnu.attributes 0 : { KEEP (*(.gnu.attributes)) }
  /DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) *(.gnu.lto_/home/local/bin/../lib/gcc/ia64-linux/9.3.1/../../../../ia64-linux/bin/ld: warning: -z relro ignored
*) }
}

Uh oh, the script will discard all orphan sections due to *(*)
appearing.  (Yes there are some odd section match patterns before
that from the warning, but the final * gets everything.)

Now .IA_64.unwind__libc_freeres_fn is not an orphan, but it is
SHF_LINK_ORDER and __libc_freeres_fn is its linked-to section, and
that one is an orphan.  ldelf_before_place_orphans handles linked-to
sections, correctly discarding .IA_64.unwind__libc_freeres_fn but
failing to set SEC_EXCLUDE which would avoid the ldwrite.c assertion.

glibc patch attached

-- 
Alan Modra
Australia Development Lab, IBM

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From 3425515f19d47eb2e13180fe031d94a9c13ce39b Mon Sep 17 00:00:00 2001
From: Alan Modra <amodra@gmail.com>
Date: Wed, 29 Jul 2020 16:28:57 +0930
Subject: Don't mix linker error messages into edited scripts

	* Makerules (shlib.lds): Discard linker warning output.
	(format.lds): Likewise.

diff --git a/Makerules b/Makerules
index 341db86c7e..ef0fe67d9a 100644
--- a/Makerules
+++ b/Makerules
@@ -557,7 +557,7 @@ $(common-objpfx)shlib.lds: $(common-objpfx)config.make $(..)Makerules
 	$(LINK.o) -shared -Wl,-O1 \
 		  -nostdlib -nostartfiles \
 		  $(sysdep-LDFLAGS) $(rtld-LDFLAGS) $(LDFLAGS.so) \
-		  -Wl,--verbose 2>&1 | \
+		  -Wl,--verbose 2>/dev/null | \
 	  sed > $@T \
 	      -e '/^=========/,/^=========/!d;/^=========/d' \
 	      $(if $(filter yes,$(have-hash-style)), \
@@ -1073,7 +1073,7 @@ ifneq (unknown,$(output-format))
 else
 	$(LINK.o) -shared $(sysdep-LDFLAGS) $(rtld-LDFLAGS) \
 		  $(LDFLAGS.so) $(LDFLAGS-lib.so) \
-		  -x c /dev/null -o $@.so -Wl,--verbose -v 2>&1 \
+		  -x c /dev/null -o $@.so -Wl,--verbose -v 2>/dev/null \
 	| sed -n -f $< > $@.new
 	test -s $@.new
 	rm -f $@.so