Re: -mregparm=3 (was Re: [PATCH] i386 do_machine_check() is redundant.

[Daniel Jacobowitz <dan@debian.org>]

On Mon, Sep 29, 2003 at 11:36:06PM +0200, Mikulas Patocka wrote:
> 
> 
> On Mon, 29 Sep 2003, Daniel Jacobowitz wrote:
> 
> > On Mon, Sep 29, 2003 at 10:20:45PM +0200, Mikulas Patocka wrote:
> > > > > > Use machine_check_vector in the entry code instead.
> > > > >
> > > > > This is wrong. You just lost the "asmlinkage" thing, which means that it
> > > > > breaks when asmlinkage matters.
> > > > >
> > > > > And yes, asmlinkage _can_ matter, even on x86. It disasbles regparm, for
> > > > > one thing, so it makes a huge difference if the kernel is compiled with
> > > > > -mregparm=3 (which used to work, and which I'd love to do, but gcc has
> > > > > often been a tad fragile).
> > > >
> > > > gcc 3.2 and later are supposed to be ok (eg during 3.2 development a
> > > > long standing bug with regparm was fixed and now is believed to work)...
> > > > since our makefiles check gcc version already... this can be made gcc
> > > > version dependent as well for sure..
> > >
> > > They are still buggy. gcc 3.3.1 miscompiles itself with -mregparm=3
> > > (without -O or -O2 it works). (I am too lazy to spend several days trying
> > > to find exactly which function in gcc was miscompiled, maybe I do it one
> > > day). gcc 2.95.3 compiles gcc 3.3.1 with -mregparm=3 -O2 correctly.
> > > gcc 3.4 doesn't seem to be better.
> > >
> > > gcc 2.7.2.3 has totally broken -mregparm=3, even quite simple programs
> > > fail.
> >
> > You can't build GCC with -mregparm=3.  It changes the interface to
> > system functions.  So unless your libc happened to be built with
> > -mregparm=3, and extensively hacked to expect arguments in registers to
> > the assembly stubs, it can't work.
> 
> Of course I linked it with libc compiled with regparm=3.

Did you also hack all the syscall wrappers and hand-coded assembly
routines?  For instance, mmap won't work.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer