Re: Bug report: bad check for ELF binary format

[Bruno Haible]

Hi,

comex wrote:
> From m4/lib-prefix.m4:
> 
> --
>   AC_CACHE_CHECK([for ELF binary format], [gl_cv_elf],
>     [AC_EGREP_CPP([Extensible Linking Format],
>        [#ifdef __ELF__
>         Extensible Linking Format
>         #endif
>        ],
>        [gl_cv_elf=yes],
>        [gl_cv_elf=no])
>      ])
>   if test $gl_cv_elf; then
> —
> 
> I believe this does not work as intended.  'test $gl_cv_elf' is equivalent to 
> 'test -n $gl_cv_elf', i.e. it tests whether the variable is nonempty.  Both 
> ‘yes’ and ‘no’ are nonempty, so the ‘if’ will always be taken.

Ouch, indeed. This probably breaks the whole 'havelib' module for platforms
such as macOS, AIX, HP-UX. Thanks for the report!!


2020-11-30  Bruno Haible  <bruno@clisp.org>

        havelib: Fix for non-ELF platforms (regression 2019-11-17).
        Reported by comex <comexk@gmail.com> in
        <https://lists.gnu.org/archive/html/bug-gnulib/2020-11/msg00188.html>.
        * m4/lib-prefix.m4 (AC_LIB_PREPARE_MULTILIB): On non-ELF platforms,
        don't expect an ELF header.

diff --git a/m4/lib-prefix.m4 b/m4/lib-prefix.m4
index c8a0b46..28bb3d3 100644
--- a/m4/lib-prefix.m4
+++ b/m4/lib-prefix.m4
@@ -1,4 +1,4 @@
-# lib-prefix.m4 serial 17
+# lib-prefix.m4 serial 18
 dnl Copyright (C) 2001-2005, 2008-2020 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -180,8 +180,8 @@ AC_DEFUN([AC_LIB_PREPARE_MULTILIB],
        ],
        [gl_cv_elf=yes],
        [gl_cv_elf=no])
-     ])
-  if test $gl_cv_elf; then
+    ])
+  if test $gl_cv_elf = yes; then
     # Extract the ELF class of a file (5th byte) in decimal.
     # Cf. 
https://en.wikipedia.org/wiki/Executable_and_Linkable_Format#File_header
     if od -A x < /dev/null >/dev/null 2>/dev/null; then