oskit-mach: gdb_break_stub() confusion

["B. Douglas Hilton" <doug.hilton@engineer.com>]

I am trying to follow Igor's instruction at this
web page -> http://hurd.dyndns.org/oskit-boot.txt

First off, the patch doesn't compile properly. There
are conflicting types between the prototype and the
function.

Here is the patch:
> --- gdb-stub.diff ---
> Index: kern/syscall_sw.c
> ===================================================================
> RCS file: /cvs/gnumach/kern/syscall_sw.c,v
> retrieving revision 1.1.1.1.2.2
> diff -u -r1.1.1.1.2.2 syscall_sw.c
> --- kern/syscall_sw.c	2001/04/05 06:52:47	1.1.1.1.2.2
> +++ kern/syscall_sw.c	2001/07/30 21:45:14
> @@ -98,6 +98,8 @@
>  extern kern_return_t	syscall_fipc_recv();
>  #endif /* FIPC */
>  
> +/*XXX*/extern kern_return_t gdb_break_stub ();
> +
>  mach_trap_t	mach_trap_table[] = {
>  	MACH_TRAP(kern_invalid, 0),		/* 0 */		/* Unix */
>  	MACH_TRAP(kern_invalid, 0),		/* 1 */		/* Unix */
> @@ -283,7 +285,14 @@
>  	MACH_TRAP(kern_invalid, 0),		/* 126 */
>  	MACH_TRAP(kern_invalid, 0),		/* 127 */
>  	MACH_TRAP(kern_invalid, 0),		/* 128 */
> -	MACH_TRAP(kern_invalid, 0),		/* 129 */
> +	MACH_TRAP(gdb_break_stub, 1),		/* 129 */
>  };
>  
> +volatile int gdb_break_stub (void *addr) /*XXX*/
> +{<
> br>+	void *dummy;
> +	dummy = addr;
> +	return 0;
> +}
> +
>  int	mach_trap_count = (sizeof(mach_trap_table) / sizeof(mach_trap_table[0]));
> --- end ---
>   
>
And here is the resulting error from Make:
> gcc -O -g -DOSKIT_MACH=1 -DMACH -DMACH_KERNEL -DKERNEL
> -DCONTINUATIONS 
>       -DHAVE_CONFIG_H -D__ELF__=1 -Di386=1 -DAT386=1 -I../i386/i386at
> -I../i386/i386 
>       -I../i386/include -I../i386/include/mach/sa -I../i386/bogus -I../i386
> -I. -I.. 
>       -I../include -I../bogus -I../kern -I../device  -c -o syscall_sw.o
> ../kern/syscall_sw.c
>       ../kern/syscall_sw.c:292: conflicting types for `gdb_break_stub'
>       ../kern/syscall_sw.c:101: previous declaration of `gdb_break_stub'
>       make: *** [syscall_sw.o] Error 1
>       
Now, when I modified the source like this:
> /*XXX*/ /* extern kern_return_t gdb_break_stub (); */
> extern kern_return_t gdb_break_stub(void *addr);
>
> ... and ...
>
> /* volatile int gdb_break_stub (void *addr) */ /*XXX*/
> extern kern_return_t gdb_break_stub(void *addr)
> {
>     void *dummy;
>     dummy = *addr;
>     return 0;
> }
>         
Then it compiled ok, but I don't know if this is right or not. Should
it be "volatile int" or should it be "extern kern_return_t" ? Apparently
it cannot be both. Also, why is it an "extern" since the function is right
there in the same file, does this perhaps coerce the compiler to
assign it a huge pointer for external linkage reasons?
        
Ant then finally, there is this: gdb-break.c
> When starting an oskit-mach debug session with GDB set a break poit at
> `gdb_break_stub'. Then use this program to invoke the system call when
> desired:
>
> --- gdb-break.c ---
> /* Compile with: gcc -o gdb-break gdb-break.c gdb-break-stub.S */
>
> #include <mach.h>
>
> #include <stdio.h>
> #include <string.h>
>
> extern int gdb_break_stub (void *addr);
>
> int main () {
> 	kern_return_t err;
>
> 	err = gdb_break_stub (&main);
> 	printf ("result from syscall: %s\n", strerror(err));
>
> 	return 0;
> }
> --- end ---
> --- gdb-break-stub.S ---
> #include <mach/syscall_sw.h>
>
> kernel_trap(gdb_break_stub,-129,1)
> --- end ---
>           
          
First of all, I don't have a <mach.h> anywhere on my system.
The
sources for oskit-mach don't seem to install one when one does
a "make install-headers". Granted I can symlink /gnu/include/mach.h
to /usr/i386-gnu/include but should I? I am very wary of linking
"real" Hurd headers into my cross-compiler /usr/i386-gnu/include
directory.
          
Secondly, how do I run this program on the remote hppa machine?
How is it used anyways? I get the idea about putting a system call
into oskit-mach, but I can't see in my gdb manual any info on calling
an external program while remote debugging.
          
Is there a better way to call the trap?
          
Thanks,
- Doug