Sender: nate AT cartsys DOT com
Message-ID: <375C565E.B33A7060@cartsys.com>
Date: Mon, 07 Jun 1999 16:31:42 -0700
From: Nate Eldredge <nate AT cartsys DOT com>
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To: djgpp-workers AT delorie DOT com
Subject: Re: egcs-19990602 (gcc-2.95 prerelease) binaries for testing
References: <B0000089571 AT stargate DOT astr DOT lu DOT lv> <99060717171200 DOT 00403 AT hal>
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Reply-To: djgpp-workers AT delorie DOT com

Andris Pavenis wrote:
> 
> On Mon, 07 Jun 1999, pavenis AT lanet DOT lv wrote:
> >       compiler generates code which access class member
> >       via wrong address (result is SIGSEGV for me). Below is
> >       some test data I got (I simply copied this from rhide watch
> >       window and added some comments)
> >
> >  this: (TEphApp *) 0x240f20
> >  App: (TEphApp *) 0x240f20
> >  &slrcfg: (LoadedConfigFile *) 0x240f84
> >  &App->slrcfg: (LoadedConfigFile *) 0x240f84
> >  &satinfo: (LoadedConfigFile *) 0x240fa5             - false address
> >        (but this address is used both when I call satinfo.foo() and
> >       App->satinfo.foo() (name changed) from member function)
> >  &(App->satinfo): (LoadedConfigFile *) 0x240fa8   - right value (I can
> >       get contents here)
> >
> > I have this problem in rather big application (TVision + different
> > other stuff, TEphApp is derived from TApplication such stuff as
> > virtual base classes etc is present) only.
> >
> > I tried to reproduce this problem in a simple test example but didn't
> > succeed. Perhaps I'll check the same sometime under Linux as this
> > app can be built (and it should normally work) also under Linux.
> >
> 
> I reproduced the same thing with egcs-19990601 (I updated gcc 2.95
> branch with CVS then) under Linux (kernel 2.2.9, glibc-2.1.1).
> As I don't have good test example to send then perhaps I'll retry the same
> with later snapshots. Perhaps it would be worth to try also with
> gcc-2.96 tree to see whether something changes.

I don't fully understand all the issues involved, but I understand
recent EGCS releases (since 1.1.2) do some special optimizations
regarding something called aliasing.  (As you can tell, I haven't done
my homework :)  This is said to break a lot of extant code.  (The Linux
kernel folks, for instance, are having a lot of trouble.)  There is an
option to turn it off; you might try that and see if it helps.

-- 

Nate Eldredge
nate AT cartsys DOT com