[Bug bootstrap/64919] bootstrap failure of gcc-4.9.2 on ia64-hpux in libgcc

["jvb at cyberscience dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64919

John Buddery <jvb at cyberscience dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |jvb at cyberscience dot com

--- Comment #6 from John Buddery <jvb at cyberscience dot com> ---
I had this issue as well, and here is the solution I used in case anyone is
still interested. I believe it is caused by an HP-UX linker bug, the same one
described by this comment and workaround  in config/ia64/hpux.h:

  /* The HP-UX linker has a bug that causes calls from functions in
   .text.unlikely to functions in .text to cause a segfault.  Until
   it is fixed, prevent code from being put into .text.unlikely or
   .text.hot.  */

  #define TARGET_ASM_FUNCTION_SECTION ia64_hpux_function_section

While this workaround is sufficient for C code, unfortunately g++ can use
multiple text sections for various different reasons when compiling c++ code
(lookup Vague Linkage for details).

This means g++ is broken on HP ia64, and gcc 4.8.0 build using g++, which is
why the bootstrap now fails.

The workaround I applied was to add the line:

   #undef MAKE_DECL_ONE_ONLY

to gcc/config/ia64/hpux.h, below the lines I referenced above. This seems to
prevent gcc from using .linkonce.t sections, and keeps the HP-UX linker happy.
I've no idea if this is the correct solution, but it does produce a working
g++.

Unfortunately just applying this edit you your 4.9.2 sources and building isn't
good enough, because it's your existing broken g++ which does the stage1 build. 

As far as I can tell all g++ versions available for download are broken, so you
have to first download and build 4.7.4 or earlier, applying the same 
gcc/config/ia64/hpux.h as above. This version builds with gcc, not g++, so the
bootstrap isn't a problem. Once you have a fixed 4.7.4 g++, you can then use
that to bootstrap 4.9.2 - after again apply the hpux.h edit to the 4.9.2
sources.

In my case when building 4.9.2 I also had to disable libgomp, but I think
that's a different issue.

Of course a much better solution to all this would be to get a fixed HP linker;
but I can't even tell if any of the HP patches help as they don't seem to make
these fixes generally available.