Re: lib-ignore: link error with Sun C++ compiler

[Bruno Haible]

Ralf Wildenhues wrote:
> > The reason is that the flag -Wl,-z,ignore is accepted by the C compiler 
> > (cc), but
> > leads to an error with the C++ compiler (CC).
> 
> Sun CC needs '-Qoption ld ' as prefix to linker flags (mind the trailing
> space) rather than '-Wl,'.

Thanks for this info.

So, a possible first step is to update the comments in lib-ignore.m4, like in
the proposed patch below.

But this does not fix the problem with coreutils, as long as it has some source
files in C++. I would therefore find it useful to change lib-ignore.m4 so that
it sets an AC_SUBSTed variable IGNORE_UNUSED_LIBS, and coreutils/Makefile.am
can then do
  AM_LDFLAGS = $(IGNORE_UNUSED_LIBS)

What do you think?

Bruno


2010-03-14  Bruno Haible  <address@hidden>

        * m4/lib-ignore.m4 (gl_IGNORE_UNUSED_LIBRARIES): Add comments.

--- m4/lib-ignore.m4.orig       Sun Mar 14 17:06:37 2010
+++ m4/lib-ignore.m4    Sun Mar 14 16:20:31 2010
@@ -9,6 +9,30 @@
 
 AC_DEFUN([gl_IGNORE_UNUSED_LIBRARIES],
 [
+  # Determines the option to be passed to the C compiler, so that it
+  # omits unused libraries.
+  # Example (on Solaris):
+  # $ cc foo.c -lnsl; ldd ./a.out
+  #         libnsl.so.1 =>   /lib/libnsl.so.1
+  #         libc.so.1 =>     /lib/libc.so.1
+  #         libmp.so.2 =>    /lib/libmp.so.2
+  #         libmd.so.1 =>    /lib/libmd.so.1
+  #         libscf.so.1 =>   /lib/libscf.so.1
+  #         libdoor.so.1 =>  /lib/libdoor.so.1
+  #         libuutil.so.1 =>         /lib/libuutil.so.1
+  #         libgen.so.1 =>   /lib/libgen.so.1
+  #         libm.so.2 =>     /lib/libm.so.2
+  # $ cc foo.c -lnsl -Wl,-z,ignore; ldd ./a.out
+  #         libc.so.1 =>     /lib/libc.so.1
+  #         libm.so.2 =>     /lib/libm.so.2
+
+  # Note that the options works only for the C compiler, not for the C++
+  # compiler:
+  # - Sun C likes '-Wl,-z,ignore'. '-Qoption ld -z,ignore' is not accepted.
+  #   '-z ignore' is accepted but has no effect.
+  # - Sun C++ likes '-Qoption ld -z,ignore'. '-Wl,-z,ignore' is not accepted.
+  #   '-z ignore' is accepted but has no effect.
+
   AC_CACHE_CHECK([for flag to ignore unused libraries],
     [gl_cv_ignore_unused_libraries],
     [gl_cv_ignore_unused_libraries=none
@@ -21,7 +45,7 @@
      # to forestall problems with linkers that have -z, -i, -g, -n, etc. flags.
      # GCC + binutils likes '-Wl,--as-needed'.
      # GCC + Solaris ld likes '-Wl,-z,ignore'.
-     # Sun C likes '-z ignore'.
+     # Sun C likes '-Wl,-z,ignore'. '-z ignore' is accepted but has no effect.
      # Don't try bare '--as-needed'; nothing likes it and the HP-UX 11.11
      # native cc issues annoying warnings and then ignores it,
      # which would cause us to incorrectly conclude that it worked.
@@ -38,6 +62,8 @@
      done
      LIBS=$gl_saved_libs])
 
+  # Note that adding this options to LDFLAGS unconditionally does not work in
+  # projects that are partially in C++.
   test "$gl_cv_ignore_unused_libraries" != none &&
     LDFLAGS="$LDFLAGS $gl_cv_ignore_unused_libraries"
 ])