[build] Move gthr to toplevel libgcc

[Rainer Orth]

John David Anglin <dave.anglin@nrc-cnrc.gc.ca> writes:

>> I haven't moved two macros used in gthr*.h yet: GTHREAD_USE_WEAK and
>> SUPPORTS_WEAK.  This seems to warrant a separate followup patch, but for
>> the record I report my findings:
>>
>> * GTHREAD_USE_WEAK must be defined explicitly.  It needs to be poisoned
>>  in system.h after the move.  Right now, only a few targets defined a
>>  non-default value:
>>
>>  darwin.h		#define GTHREAD_USE_WEAK 0
>>  i386/cygwin.h		#define GTHREAD_USE_WEAK 0
>>
>>  ia64/hpux.h		#define GTHREAD_USE_WEAK 0
>>  pa/pa64-hpux.h	#define GTHREAD_USE_WEAK 0
>>  pa/som.h		#define GTHREAD_USE_WEAK 0
>>
>>  The last 3 could be handled in a new hpux-lib.h, but perhaps this
>>  isn't necessary if ax_sys_weak_alias.m4 works.
>
> I'm not sure this is possible in general on HP-UX.

Do you suggest that support for weak definitions (undefined weak) cannot
be detected by a configure test on HP-UX?

>> * SUPPORTS_WEAK is probably best detected with autoconf.  We have
>>  libgfortran/acinclude.m4 (LIBGFOR_GTHREAD_WEAK), but should probably
>>  go for m4/ax_sys_weak_alias.m4 from the autoconf-archive instead.  If
>>  we're lucky, that macro can detect support for weak definitions and
>>  replace both SUPPORTS_WEAK and GTHREAD_USE_WEAK.
>
> There are multiple meanings for SUPPORTS_WEAK.  Within the compiler,
> SUPPORTS_WEAK implies that multiple definitions of code and data symbols
> are possible.  At the moment, there is no need for undefined weak or weak
> aliases.  The situation is different in the gthr* headers and compiled code
> such as libgfortran.

I was only talking about autoconfiguring the equivalent of SUPPORTS_WEAK
&& GTHREAD_USE_WEAK in the target libraries that need it.  There will be
no change in gcc/config, of course.

> On PA HP-UX, the compiler "weak" support is implemented using COMDAT
> and secondary definitions.  Neither of these support undefined weak.

The latter is also missing on Tru64 UNIX, so I'm working on such a
platform myself and have introduced gthr-posix.c to deal with it.

	Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University