Date: Thu, 2 Sep 1999 21:09:26 +0200 From: Juergen Lock <nox@jelal.kn-bremen.de> To: Ulrich Weigand <weigand@informatik.uni-erlangen.de> Cc: nox@jelal.kn-bremen.de, wine-devel@winehq.com, luoqi@watermarkgroup.com, freebsd-emulation@FreeBSD.ORG Subject: Re: wine signal handlers lose %fs on FreeBSD Message-ID: <19990902210926.B5073@saturn.kn-bremen.de> In-Reply-To: <199909021218.OAA21251@faui11.informatik.uni-erlangen.de> References: <199909021218.OAA21251@faui11.informatik.uni-erlangen.de>
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On Thu, Sep 02, 1999 at 02:18:21PM +0200, Ulrich Weigand wrote:
>
> Luoqi Chen <luoqi@watermarkgroup.com> wrote:
>
(That was me actually:)
> > > Here's a strange one: Sometimes apparently wine's signal handlers receive
> > > %fs messed up (zeroed actually) and therefore crash/hang on FreeBSD
> > > (3.2-stable, wine current-cvs). Patch this and watch for
> > > `warn:seh:EXC_SaveContext teb=0xsomewhere teb_sel=something, fs=0, gs=foo'
> > > messages, teb_sel is what fs really should have been (and what is loaded
> > > back there after the message, so the program actually continues too.)
>
> Well, this problem would seem to be caused by Wine.
*DOH!*
> The problem is
> that while any Wine signal handler is running, %fs needs to be loaded
> with the value %fs had in the code that was interrupted by the signal
> *if that code is 32-bit*. If *16-bit* code was interrupted, however,
> %fs needs to be loaded with the value had at the time the switch from
> 32-bit to 16-bit took place (this value was saved at the time) ...
>
> The reason for this is that Wine, like 32-bit Windows, uses the %fs
> register to identify the current thread. On 16-bit Windows, however,
> %fs has no special meaning and is freely used by apps ...
>
> To achieve this, Wine calls a macro HANDLER_INIT() at the start of
> every signal handler which is supposed to set %fs correctly. This is
> defined as follows:
>
> #ifdef FS_sig
> #include "syslevel.h"
> #define HANDLER_INIT() \
> do { int fs = IS_SELECTOR_SYSTEM(CS_sig(HANDLER_CONTEXT)) ? \
> FS_sig(HANDLER_CONTEXT) : SYSLEVEL_Win16CurrentTeb; \
> if (!fs) fs = SYSLEVEL_EmergencyTeb; \
> SET_FS(fs); } while (0)
> #else
> #define HANDLER_INIT() /* nothing */
> #endif
>
> The problem is that the second case (which is active only if FS_sig
> is undefined, meaning that the sigcontext structure doesn't contain
> the %fs value, like on FreeBSD) is clearly wrong. Try changing this to
>
> #define HANDLER_INIT() \
> do { int fs; GET_FS(fs); fs &= 0xffff; \
> if (!IS_SELECTOR_SYSTEM(CS_sig(HANDLER_CONTEXT))) \
> fs = SYSLEVEL_Win16CurrentTeb; \
> if (!fs) fs = SYSLEVEL_EmergencyTeb; \
> SET_FS(fs); } while (0) \
>
Heh. I did search the wine sources for SET_FS but seems i forgot its
includes! Yes, looks like this is the real fix (after removing the last \)
Thank you for restoring my confidence in FreeBSD's kernel... :)
> > I took a brief look at the exception code, it probably would not work
> > under 4.0-current because the kernel uses %fs and signal handlers are
> > called with a default %fs value (the same as the default %ds). You might
> > need to restore %fs from the value in sigcontext at beginning of your
> > signal handlers (yes, fs in sigcontext is set for 4.0-current. Regarding
> > this, we could change the kernel, both -current and -stable, so that fs/gs
> > are always saved in sigcontext when the signal is delivered, and restored
> > during the signal trampoline, hence a consistent interface to application
> > authors). Alternatively, we could change the kernel to call signal handlers
> > with the original fs.
>
> Well, Wine can work with both ways, as long as there is way to find
> out what method the OS uses! What should we use as a check?
True, there needs to be some way to find out whether the fs/gs in the
sigcontext struct are for real or not...
Regards,
--
Juergen Lock <nox.foo@jelal.kn-bremen.de>
(remove dot foo from address to reply)
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