Re: [PATCH] Use libunwind library when linking g++

[Steve Ellcey <sje at cup dot hp dot com>]

Here is a new version of my libunwind patch in response to Richard's
comments.  I will send a seperate mail for the libjava change so I can
send it to the java-patches mailing list as well as gcc-patches.

I changed CONFIG_LIBUNWIND_EXCEPTIONS to USE_LIBUNWIND_EXCEPTIONS and
removed by change to config.in.  I got errors when I tried to regenerate
config.in with autoheader until I added a change to acconfig.h.  I don't
know if this is right or not, acconfig.h has no comments about being
generated by a tool but other things set in configure.in don't seem to
be listed here.  Am I missing something?  Or perhaps using the wrong
version of autoheader (I used 2.13).  I included my change to acconfig.h
in this patch.

> From: Richard Henderson <rth@redhat.com>
>
> The patch doesn't control the generation of libgcc_eh.
> What's going to happen when both libgcc_eh and libunwind
> appear on the same link line?  Are we absolutely certain
> that libunwind is a superset of libgcc_eh and so having
> the both cannot result in multiply defined symbols?

Well, I am pretty sure that my libunwind is a superset of libgcc_eh.  I
don't know if there is anyway to ensure that in general.  It might be
nice if the use of --enable-libunwind-exceptions turned off the use of
libgcc_eh.  I am not sure how to do that though, I looked at init_spec
and init_gcc_specs and it looks pretty convoluted.  I am setting
LIBGCC_SPEC for my platform (IA64 HP-UX) and I think that that is
"accidently" preventing libgcc_eh.a from ever being added to my link
line.

It seems a little odd to me that even if I specify LIBGCC_SPEC the
functions init_spec/init_gcc_specs still mangles what I set it to.  This
makes it harder to tell GCC not to use libgcc_eh but it seems
intentional.

Steve Ellcey
sje@cup.hp.com


2002-06-13  Steve Ellcey  <sje@cup.hp.com>
	* gcc/configure.in (USE_UNWIND_EXCEPTIONS): Add support to set
	USE_UNWIND_EXCEPTIONS if --enable-libunwind-exceptions is set.
	* gcc/configure: Regenerate
	* gcc/config.in: Regenerate
	* gcc/acconfig.h (USE_UNWIND_EXCEPTIONS): Set to undef by default.


*** gcc.orig/gcc/configure.in	Thu Jun 13 10:37:30 2002
--- gcc/gcc/configure.in	Thu Jun 13 10:56:07 2002
*************** AC_ARG_ENABLE(sjlj-exceptions,
*** 2337,2342 ****
--- 2337,2351 ----
  AC_DEFINE_UNQUOTED(CONFIG_SJLJ_EXCEPTIONS, $sjlj,
    [Define 0/1 to force the choice for exception handling model.])])
  
+ # Use libunwind based exception handling.
+ AC_ARG_ENABLE(libunwind-exceptions,
+ [  --enable-libunwind-exceptions  force use libunwind for exceptions],
+ use_libunwind_exceptions=$enableval,
+ use_libunwind_exceptions=no)
+ if test x"$use_libunwind_exceptions" = xyes; then
+    AC_DEFINE(USE_LIBUNWIND_EXCEPTIONS, 1)
+ fi
+ 
  # Make empty files to contain the specs and options for each language.
  # Then add #include lines to for a compiler that has specs and/or options.
  
*** gcc.orig/gcc/acconfig.h	Thu Jun 13 10:37:39 2002
--- gcc/gcc/acconfig.h	Thu Jun 13 10:54:58 2002
***************
*** 29,34 ****
--- 29,37 ----
  /* Define if cpp should also search $prefix/include.  */
  #undef PREFIX_INCLUDE_DIR
  
+ /* Define if gcc should use -lunwind.  */
+ #undef USE_LIBUNWIND_EXCEPTIONS
+ 
  @BOTTOM@
  
  /* Bison unconditionally undefines `const' if neither `__STDC__' nor