From: ak@muc.de
To: Jason Merrill <jason@cygnus.com>
Cc: ak@muc.de, egcs@cygnus.com
Subject: Re: C++ name mangling, old and new versions?
Date: Thu, 05 Mar 1998 15:33:00 -0000 [thread overview]
Message-ID: <19980305060218.21443@fred.muc.de> (raw)
In-Reply-To: <u9ogzlix36.fsf@yorick.cygnus.com>
On Thu, Mar 05, 1998 at 05:24:29AM +0100, Jason Merrill wrote:
> >>>>> ak <ak@muc.de> writes:
>
> > On Thu, Mar 05, 1998 at 04:37:33AM +0100, Jason Merrill wrote:
> >> >>>>> Andi Kleen <ak@muc.de> writes:
> >>
> >> > I had good look with -fno-rtti -fno-exceptions together with a 2.7.2
> >> > compiled Qt. The vtable layout is different when RTTI is enabled, so
> >> > egcs protects against mistakes by encoding that in the mangled name.
> >>
> >> Both those statements are false for -fno-rtti, though they are true of
> >> -fvtable-thunks.
>
> > You mean the mangling is only changed (between -frtti/no-rtti) when
> > vtable-thunks is enabled? If this is true how is the typeinfo encoded
> > then when vtable-thunks is not enabled?
>
> No. -frtti has no effect on vtable layout or mangling, ever.
> -fvtable-thunks changes vtable layout and mangling.
>
> If -fno-rtti, the RTTI entry in the vtable is set to zero, but the layout
> is the same.
I see. I didn't know that 2.7.2 already had a reserved vtable entry for
the rtti function(1), therefore the confusion. The original point still holds -
a 2.7.2 compiled shared library Qt doesn't link with a egcs program (even
though Qt doesn't use RTTI) unless -fno-exceptions -fno-rtti is specified.
It complains about missing "Class type_info function" (that is probably the
RTTI entry you were refering to), and missing RTTI (__rtti_class) and
exceptions function from the runtime library. I don't know why -fno-rtti/
-fno-exceptions makes a difference for the runtime library.
-Andi
(1) Thanks to rth for the pointer.
next prev parent reply other threads:[~1998-03-05 15:33 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
1998-03-04 6:10 T. Huld
1998-03-04 12:45 ` Martin von Loewis
1998-03-04 19:27 ` Andi Kleen
[not found] ` <k2n2f5vms1.fsf.cygnus.egcs@zero.aec.at>
1998-03-04 19:38 ` Jason Merrill
1998-03-04 20:12 ` ak
1998-03-04 20:25 ` Jason Merrill
1998-03-05 15:33 ` ak [this message]
1998-03-05 15:33 ` Jason Merrill
1998-03-05 0:18 ` Martin von Loewis
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