Checking for -rdynamic flag in gcc/configure

Checking for -rdynamic flag in gcc/configure

[Steve Ellcey]

I have a question about the check for -rdynamic in gcc/configure.
What we have in configure.ac is:

  # Check -rdynamic
  LDFLAGS="$LDFLAGS -rdynamic"
  AC_MSG_CHECKING([for -rdynamic])
  AC_TRY_LINK([],[return 0;],
    [AC_MSG_RESULT([yes]); have_rdynamic=yes],
    [AC_MSG_RESULT([no])])
  if test x"$have_rdynamic" = x"yes" ; then
    pluginlibs="-rdynamic"
  fi

The problem I have is that on HP-UX this test will set have_rdynamic
to yes even though the HP linker doesn't understand the option.
The AC_TRY_LINK works because the linker prints a warning message
about not understanding -rdynamic but still runs and creates an
object file.  Thus the configure script thinks the HP linker does
know about the -rdynamic flag and continues to use it (resulting
in more warnings during the GCC build).

Any ideas on how to address this?

Steve Ellcey
sje@cup.hp.com

Re: Checking for -rdynamic flag in gcc/configure

[Ian Lance Taylor]

Steve Ellcey <sje@cup.hp.com> writes:

> I have a question about the check for -rdynamic in gcc/configure.
> What we have in configure.ac is:
>
>   # Check -rdynamic
>   LDFLAGS="$LDFLAGS -rdynamic"
>   AC_MSG_CHECKING([for -rdynamic])
>   AC_TRY_LINK([],[return 0;],
>     [AC_MSG_RESULT([yes]); have_rdynamic=yes],
>     [AC_MSG_RESULT([no])])
>   if test x"$have_rdynamic" = x"yes" ; then
>     pluginlibs="-rdynamic"
>   fi
>
> The problem I have is that on HP-UX this test will set have_rdynamic
> to yes even though the HP linker doesn't understand the option.
> The AC_TRY_LINK works because the linker prints a warning message
> about not understanding -rdynamic but still runs and creates an
> object file.  Thus the configure script thinks the HP linker does
> know about the -rdynamic flag and continues to use it (resulting
> in more warnings during the GCC build).
>
> Any ideas on how to address this?

Link a small program with -rdynamic, one which defines a globally
visible function which is not called.  Run objdump -T and see if you can
see that symbol in the output.

If you follow this path you must do the in_tree_ld/ld_ver dance so that
cross-compilers continue to work.

Or, run ld --help and look for --export-dynamic.

Ian

Re: Checking for -rdynamic flag in gcc/configure

[Joseph S. Myers]

On Fri, 28 Aug 2009, Ian Lance Taylor wrote:

> Link a small program with -rdynamic, one which defines a globally
> visible function which is not called.  Run objdump -T and see if you can
> see that symbol in the output.
> 
> If you follow this path you must do the in_tree_ld/ld_ver dance so that
> cross-compilers continue to work.

This is testing properties of the *host* linker (build-x-host in the 
Canadian cross case), so in-tree tools (which will be built as 
host-x-target) are irrelevant, and you can always assume that the host 
tools are already installed (of course you need to make sure you use the 
correct objdump, not that for build or target).

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: Checking for -rdynamic flag in gcc/configure

[Ian Lance Taylor]

"Joseph S. Myers" <joseph@codesourcery.com> writes:

> On Fri, 28 Aug 2009, Ian Lance Taylor wrote:
>
>> Link a small program with -rdynamic, one which defines a globally
>> visible function which is not called.  Run objdump -T and see if you can
>> see that symbol in the output.
>> 
>> If you follow this path you must do the in_tree_ld/ld_ver dance so that
>> cross-compilers continue to work.
>
> This is testing properties of the *host* linker (build-x-host in the 
> Canadian cross case), so in-tree tools (which will be built as 
> host-x-target) are irrelevant, and you can always assume that the host 
> tools are already installed (of course you need to make sure you use the 
> correct objdump, not that for build or target).

Ah, you're quite right, sorry.

Ian