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Re: libsigsegv on LinuxFromScratch


From: Bruno Haible
Subject: Re: libsigsegv on LinuxFromScratch
Date: Sun, 20 Sep 2020 01:47:45 +0200
User-agent: KMail/5.1.3 (Linux/4.4.0-189-generic; KDE/5.18.0; x86_64; ; )

Thanks Bruce for the details about the .la file.

> If ./configure is run with --prefix=/usr with both libsigsegv and 
> /usr/lib/libc.a are present, configure gives:
> 
> configure:10063: checking for libsigsegv
> configure:10086: gcc -o conftest -g -O2   conftest.c 
> /usr/lib/libsigsegv.so /usr/lib/libc.a  >&5
> configure:10086: $? = 0
> configure:10097: result: yes
> configure:10104: checking how to link with libsigsegv
> configure:10106: result: /usr/lib/libsigsegv.so /usr/lib/libc.a
> 
> Which causes grep to segfault immediately.

Whereas on an Ubuntu 16.04 system the effect is weird in a different sense:
the compilation fails with an error
  /usr/bin/ld: dynamic STT_GNU_IFUNC symbol `strcmp' with pointer equality in 
`/usr/lib/libc.a(strcmp.o)' can not be used when making an executable; 
recompile with -fPIE and relink with -pie
leading to
  checking for libsigsegv... no

> If I move all libtool .la files (I really dislike libtool) out of the 
> way

The .la file contains a comment

  # Please DO NOT delete this file!
  # It is necessary for linking the library.

but in fact all distros I know of don't distribute .la files. Go figure.

The patch below should fix it.


2020-09-19  Bruno Haible  <bruno@clisp.org>

        havelib: Avoid linking with libc.a on GNU systems.
        Reported by Bruce Dubbs <bruce.dubbs@gmail.com> in
        <https://lists.gnu.org/archive/html/grep-devel/2020-09/msg00052.html>.
        * m4/lib-link.m4 (AC_LIB_LINKFLAGS_BODY): When processing the
        dependency_libs value of a .la file, ignore '-lc' options on GNU
        systems.

diff --git a/m4/lib-link.m4 b/m4/lib-link.m4
index eecf70e..5ce1aa2 100644
--- a/m4/lib-link.m4
+++ b/m4/lib-link.m4
@@ -1,4 +1,4 @@
-# lib-link.m4 serial 31
+# lib-link.m4 serial 32
 dnl Copyright (C) 2001-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -631,7 +631,20 @@ AC_DEFUN([AC_LIB_LINKFLAGS_BODY],
                     ;;
                   -l*)
                     dnl Handle this in the next round.
-                    names_next_round="$names_next_round "`echo "X$dep" | sed 
-e 's/^X-l//'`
+                    dnl But on GNU systems, ignore -lc options, because
+                    dnl   - linking with libc is the default anyway,
+                    dnl   - linking with libc.a may produce an error
+                    dnl     "/usr/bin/ld: dynamic STT_GNU_IFUNC symbol 
`strcmp' with pointer equality in `/usr/lib/libc.a(strcmp.o)' can not be used 
when making an executable; recompile with -fPIE and relink with -pie"
+                    dnl     or may produce an executable that always crashes, 
see
+                    dnl     
<https://lists.gnu.org/archive/html/grep-devel/2020-09/msg00052.html>.
+                    dep=`echo "X$dep" | sed -e 's/^X-l//'`
+                    if test "X$dep" != Xc \
+                       || case $host_os in
+                            linux* | gnu* | k*bsd*-gnu) false ;;
+                            *)                          true ;;
+                          esac; then
+                      names_next_round="$names_next_round $dep"
+                    fi
                     ;;
                   *.la)
                     dnl Handle this in the next round. Throw away the .la's




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