Re: [OpenBIOS] PATCH: Implement Forth source debugger for OpenBIOS

[Laurent Vivier]

> Laurent Vivier wrote:
> > > In the meantime, I've looked again at the v2 patch I posted and I still 
> > > can't work out why the debugging output by printk() doesn't appear on a 
> > > VNC display for Qemu SPARC64, while it appears fine when Qemu SPARC64 is 
> > > invoked in -nographic mode. Can anyone shed any light on this?
> >
> > Because "printk()" are sent to serial and must use only for debug purpose.
> > You must use forth words like "emit" or "type" to send characters to
>
> display. For instance, look at "modules/cmdline.c":
> > static void
> > emit( int ch )
> > {
> >         PUSH( ch );
> >         fword("emit");
> > }
> >
> > static int
> > emit_str( const char *str )
> > {
> >         int n = 0;
> >         while( *str ) {
> >                 n++;
> >                 emit( *str++ );
> >         }
> >         return n;
> > }
>
> Yeah, I did consider that this might be the case but it still doesn't 
> seem to make sense looking at the code. The source for the forth emit 
> word can be found in kernel/forth.c:
>
> /*
> emit       ( char --  )
>
> */
>
> static void emit(void)
> {
> #ifndef FCOMPILER
>         cell tmp = POP();
>         putchar(tmp);
> #else
>         (void) POP();
> #endif
> }
>
> while for SPARC64 the source for printk() can be found in 
> arch/sparc64/lib.c:
>
> /* Format a string and print it on the screen, just like the libc
> function printf.
>
> */
> int printk( const char *fmt, ... )
> {
>         char *p, buf[512];
>         va_list args;
>         int i;
>     va_start(args, fmt);
>     i = vsnprintf(buf, sizeof(buf), fmt, args);
>     va_end(args);
>
>     for( p=buf; *p; p++ )
>             putchar(*p);
>     return i;
>
> }
>
> Both of these use putchar() in order to write characters out to the 
> console, and yet one of them works in a graphical terminal and one of 
> them doesn't...

But "emit" is redefined later to "io-emit" which use "stdout" which can be serial or graphic:

0- arch/ppc/qemu/start.S:_entry (this is the bootstrap)

...
    bl      entry
    ...

1- arch/ppc/qemu/init.c:entry()

...
    initialize_forth();
    ...

2- arch/ppc/qemu/kernel.c:initialize_forth()

...
    PUSH_xt( bind_noname_func(arch_of_init) );
    fword("PREPOST-initializer");

PC = (ucell)findword("initialize-of");
    ...

3- forth/system/main.fs:initialize-of

...
    install-console
    ...

4- forth/admin/iocontrol.fs:install-console

...
    ['] io-emit to emit
    ...

where io-emit is:

: io-emit ( char -- )
  io-out-char c!
  io-out-char 1 " write" stdout @ $call-method drop
;

And stdout is defined in arch/ppc/qemu/init.c:arch_of_init() (see 2- )

Regards,
Laurent

PATCH: Implement Forth source debugger for OpenBIOS

[Mark Cave-Ayland]

Laurent Vivier wrote:

(lots cut)
> 4- forth/admin/iocontrol.fs:install-console
> ...
> ['] io-emit to emit
> ...
>
> where io-emit is:
>
> : io-emit ( char -- )
>   io-out-char c!
>   io-out-char 1 " write" stdout @ $call-method drop
> ;
>
> And stdout is defined in arch/ppc/qemu/init.c:arch_of_init() (see 2- )

Thank you - now I see that the defer word "emit" is not set to execute 
the C function emit, which is what was confusing me.

Here's a proof-of-concept v3 patch which bounces off the forth 
trampoline in order to perform console output which seems to work for me 
on SPARC64 with VNC - please can you check it works for you?

Note this patch isn't ready to be applied yet, since I haven't had 
enough time to implement a patch to ensure that there is no speed 
penalty when debug mode is disabled.

Many thanks,

Mark.