Re: Bootstrap failures on ia64 (was Re: Readiness of tree-ssa)

[Jim Wilson <wilson at specifixinc dot com>]

Richard Guenther wrote:
> Ah, ok.  But shouldn't detect configure this problem and disable support
> for libunwind then?

We tried that.  We couldn't get it to work.

>  Also the mentioned --disable-libunwind-exceptions
> workaround is not documented in install.texi, instead there is a note
> for ia64 which reads "If you are using the optional libunwind library,

It is optional in the sense that gcc will work without it.  However, 
since libunwind is better than gcc's builtin unwinder, it is used by 
default if it exists.

> then you must use libunwind 0.96 or later." which suggests, I have to
> enable this manually, not fix a wrong configure guess with
> --disable-libunwind-exceptions.

It would be reasonable to modify the documentation to mention this 
configure option.  Would you like to suggest some wording?

There are no known OS releases that ship any version of libunwind before 
0.96 so it was believed that this would not be a serious inconvenience 
for anyone.  You are the first to report the conflict with the Intel 
compiler.  This is unfortunate.  We may have to do something to address 
this problem if updating the documentation is not enough.

Incidentally, the change to require 0.96 was done at the request of the 
libunwind author (and linux kernel maintainer) David Mosberger, because 
he believed the advantages of requiring 0.96 outweighed the disadvantages.

> !    AC_CHECK_LIB(unwind, _Unwind_Resume_or_Rethrow, use_libunwind_default=yes, use_libunwind_default=no)

We already tried that.  It doesn't work.  This uses the currently 
installed compiler to link a testcase with libunwind.  If the currently 
installed compiler is working, then it will provide a copy of 
_Unwind_Resume_or_Rethrow if libunwind does not have it, and thus this 
test always succeeds making it useless.

We can make this work if we directly run nm on the library instead of 
doing a link first.  However, that begs the question of how to find the 
library if we don't run the linker, and I don't know how to solve that 
problem.
--
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com