On 27/12/2005, at 1:49 AM, Jakub Jelinek wrote:
On Mon, Dec 26, 2005 at 11:34:16PM -0800, Geoff Keating wrote:We've had Real Problems with this feature since it was introduced. I expect it'll take at least another two or three months before it settles down and starts to work on most targets; that's only to be expected for such a far-reaching change to GCC's capabilities.It works just fine on ELF targets on gcc-4_1-branch, where you haven'tapplied your set of changes (as well as in the 4.0, 3.4 and 3.2 backportsAlex did).
I'm not sure what "just fine" definition you're using here. I don't think you can say it's been extensively tested, and I'm fairly sure I can find a bunch of bugs in it. I have already filed one as <http:// gcc.gnu.org/bugzilla/show_bug.cgi?id=25140>; I understand that also occurs on ELF targets. I don't believe it's been tested with IMA (and obviously the TREE_PUBLIC stuff is an issue there, because IMA will honour TREE_PUBLIC even if varasm.c won't). I don't know what kind of debugging output is produced, and don't think anyone has tested that. You can probably do really strange things with it and C+ + templates. Probably there are other interactions with GCC features that I haven't thought of yet.
I also note that GCC supports targets that do not have ELF, and on some of those targets the testcases fail in 4.1, which surely doesn't count as 'just fine' by anyone's definition. I see this happens on HPUX, <http://gcc.gnu.org/ml/gcc-testresults/2005-12/msg01442.html>; it also happens on Darwin. I don't see any AIX results either way.
I would describe the version on the 4.1 branch as a hack that's to work only for libgfortran on ELF targets, and that's OK; but that version is not ready for general use. I'd like to see such a general- use feature available in 4.2, and that means working our way through the issues.
More importantly, it is very wrong if GCC 4.1 and 4.2 weakrefs are
incompatible in their user visible part (trunk requires
static __typeof (bar) foo __attribute__ ((weakref ("bar")))
while 4.1 requires
extern __typeof (bar) foo __attribute__ ((weakref ("bar")))
).
IMHO this needs to be resolved before GCC 4.1 is released, so very
soon.
I agree that it would be desirable if 4.1 and 4.2 had a consistent syntax for this feature.
Either someone needs to investigate all TREE_PUBLIC checks in whole GCCand backport trunk changes to 4.1; I'd say this is pretty dangerous.
I think that you're assuming that if TREE_PUBLIC is set to true, then no investigation is necessary, everything will 'just work'. It's pretty clear that is not the case; it is just that a different collection of things will break. It's not like someone investigated all the TREE_PUBLIC checks in GCC before committing the feature in the first place.
Or the trunk change needs to be reverted. Or perhaps 4.1 could keep
the static __typeof (bar) ... syntax, but internally set TREE_PUBLIC
in those cases (this will need some changes if we want to allow say
static __typeof (bar) foo;
...
static __typeof (bar) foo __attribute__ ((weakref ("bar")));
or
static __typeof (bar) foo __attribute__ ((weakref ("bar")));
...
static __typeof (bar) foo;
but I don't think they really need to be allowed).
Clearly the safest thing to do is for 4.1 to back out the change that introduced it, and say that this is a 4.2-only feature. If it is made to work on all platforms that libgfortran supports, maybe you could keep it but say that in 4.1 it's for internal libgfortran use only; perhaps you could rename the attribute to, say, __internal_weakref for 4.1, so that users don't get confused.
smime.p7s
Description: S/MIME cryptographic signature
