cvs commit: src/sys/i386/i386 trap.c

[Don Lewis]

On 27 Jul, John Baldwin wrote:
> On Friday 27 July 2007 06:42:20 am Don Lewis wrote:
>> On 13 Jun, John Baldwin wrote:
>> > jhb         2007-06-13 22:37:48 UTC
>> > 
>> >   FreeBSD src repository
>> > 
>> >   Modified files:
>> >     sys/i386/i386        trap.c 
>> >   Log:
>> >   Don't clobber tf_err with the eva from a page fault as the page fault
>> >   address is saved in ksi_addr already.
>> >   
>> >   PR:             i386/101379
>> >   Submitted by:   Tijl Coosemans : tijl ulyssis org
>> >   
>> >   Revision  Changes    Path
>> >   1.306     +0 -3      src/sys/i386/i386/trap.c
>> 
>> This change appears to have broken the garbage collector in
>> ports/lang/pm3-base, which means that cvsup no longer works on -CURRENT.
>> The garbage collector uses the old sigvec() interface, and counts on
>> getting the fault address from the sc_err field in struct sigcontext,
>> which is copied from tf_err.
>> 
>> The Modula-3 source code for the handler and the sigvec() call is in
>> pm3-1.1.15/libs/m3core/src/runtime/FreeBSD4/RTHeapDep.m3 under the port
>> work directory. Since Modula-3 compiler uses this code, the compiler is
>> bootstrapped from a version of this file that has already been
>> translated to i386 assembly language. The latter lives in
>> pm3-1.1.15/boot-FreeBSD4/m3core/FreeBSD4/RTHeapDep.ms.
>> 
>> Modifying the assembly code to convert it to use sigaction() and to pull
>> the fault address out of the siginfo structure is left as an exercise
>> for someone more masochistic than me.
> 
> Assuming wine doesn't use sigvec() this should work.  I noticed while looking 
> at this that ddb's backtrace had some special handling that assumes tf_err == 
> faulting address as well. :-/

Cute!

> Index: machdep.c
> ===================================================================
> RCS file: /usr/cvs/src/sys/i386/i386/machdep.c,v
> retrieving revision 1.657
> diff -u -r1.657 machdep.c
> --- machdep.c   6 Jun 2007 07:35:07 -0000       1.657
> +++ machdep.c   27 Jul 2007 12:17:22 -0000
> @@ -352,7 +352,12 @@
>         sf.sf_siginfo.si_sc.sc_pc = regs->tf_eip;
>         sf.sf_siginfo.si_sc.sc_ps = regs->tf_eflags;
>         sf.sf_siginfo.si_sc.sc_trapno = regs->tf_trapno;
> -       sf.sf_siginfo.si_sc.sc_err = regs->tf_err;
> +
> +       /*
> +        * XXX: Some old binaries using sigvec() such as cvsup depend
> +        * on this.
> +        */
> +       sf.sf_siginfo.si_sc.sc_err = (register_t)ksi->ksi_addr;
> 
>         /*
>          * If we're a vm86 process, we want to save the segment registers.


I was considering something like this as well, but I was able to come up
with a simple, two line change to the pm3 bootstrap assembly code to get
it to use the "undocumented 4th arg", sf_addr that is a member of the
struct sigframe* in sys/i386/include/sigframe.h.  This appears to be
portable all the way back to RELENG_4, and probably earlier, and also
looks like it should work in i386 mode on amd64.

With this change to the bootstrap code, the pm3 build gets a lot
farther.  It blows up pretty badly when it tries to build the compiler
with GCC 4.2, but I worked around that by hacking the build to use GCC
3.4 from ports.

The next problem is that it rebuilds the runtime code from Module-3
source and blows up when it tries to use the signal handler compiled
from the unmodified Modula-3 source.  I started working on a patch for
that, which turns out to be a bit more tedious than I thought, because
the code uses a mixture of sigvec() and sigaction() and assumes that the
handlers are compatible.


Your patch might be worthwhile from the POLA standpoint.  Would similar
changes need to be made to freebsd4_sendsig() and sendsig()?