From: "Amit S. Kale" <amitkale@emsyssoft.com>
Organization: EmSysSoft
To: Matt Mackall <mpm@selenic.com>, George Anzinger <george@mvista.com>
Subject: Re: kgdb cleanups
Date: Mon, 12 Jan 2004 19:23:26 +0530
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Regarding pluggable iterfaces -
The version I have lets a user to choose the interface by supplying 
appropriate command line. (e.g. kgdbwait kgdb8250=... or kgdbwait 
kgdbeth=...) It supports an arbitrary number of interfaces. The kgdb core 
itself is independent of an interface. All interfaces are defined by a 
structure described below. An interface registers itself with kgdb core by 
assigning this structure to pointer kgdb_serial.

struct kgdb_serial {
	int chunksize;
	int (*read_char)(void);
	void (*write_char)(int);
	void (*flush)(void);
	int (*hook)(void);
	void (*begin_session)(void);
	void (*end_session)(void);
};

Where chunksize is maximum chunksize an interface can handle.

read_char and write_char are derived from getDebugChar and putDebugChar
flush flushes written characters. Flush control is given to kgdb core so that 
it can ensure that #checksum doesn't split.

begin_session and end_session inform an interface about a gdb communication 
session. (Haven't decided about console packets to gdb yet)

hook is interface initialization. It can return errors. This allows kgdb core 
to probe the interface for availability at multiple points. Because of this, 
there can be multiple debugger entry points
1. At very begining of start_kernel -> Only an 8250 interface with early boot 
enabled can respond to hook call.
2. After smp initialization -> An 8250 interface without an early boot can 
respond to this.
3. An ethernet interface can itself call debugger_entry to enter debugger 
after it's brought up from userland.

Other interfaces can come up at (1) or (2)

On Monday 12 Jan 2004 12:19 pm, Matt Mackall wrote:
> On Sun, Jan 11, 2004 at 09:41:57PM -0800, George Anzinger wrote:
> > For the internal kgdb stuff I have created kdgb_local.h which I intended
> > to be local to the workings of kgdb and not to contain anything a user
> > would need.
>
> Agreed, I just haven't touched it since you last mentioned it.
>
> > >+struct kgdb_hook {
> > >+	char *sendbuf;
> > >+	int maxsend;
> >
> > I don't see the need of maxsend, or sendbuff, for that matter, as kgdb
> > uses it now (for the eth code) it is redundant, in that the eth putchar
> > also does the same thing as is being done in the kgdb_stub.c code.  I
> > think this should be removed from the stub and the limit in the ethcode
> > relied upon.
>
> Fair enough.
>
> > > void
> > > putDebugChar(int c)
> > > {
> > >-	if (!kgdboe) {
> > >-		tty_putDebugChar(c);
> > >-	} else {
> > >-		eth_putDebugChar(c);
> > >-	}
> > >+	if (kh)
> > >+		kh->putchar(c);
> > > }
> >
> > I was thinking that this might read something like:
> >          if (xxx[kh].putchar(c))
> >                 xxx[kh].putchar(c);
> >
> > One might further want to do something like:
> >          if (!xxx[kh].putchar(c))
> >                 kh = 0;
> >
> > In otherwords, an array (xxx must, of course, be renamed) of stuct
> > kgdb_hook (which name should also be changed to relate to I/O,
> > kgdb_IO_hook, for example). Then reserve entry 0 for the rs232 I/O code.
>
> Dunno about that. Probably should work more like the console code,
> whoever registers first wins. Early boot will probably be the
> exclusive province of serial for a while yet, but designing it in is
> probably short-sighted.
>
> >  An alternate possibility is an array of pointer to struct kgdb_hook
> > which allows one to define the struct contents as below and to build the
> > array, all at compile/link time.  A legal entry MUST define get and put,
> > but why not define them all, using dummy functions for the ones that make
> > no sense in a particular interface.
>
> Throwing all the stubs in a special section could work well too. Then
> we could add an avail() function so that early boot debugging could
> discover if each one was available. The serial code could use this to
> kickstart itself while the eth code could test a local initialized
> flag and say "not a chance". Which gives us all the architecture to
> throw in other trivial interfaces (parallel, bus-snoopers, etc.).

-- 
Amit Kale
EmSysSoft (http://www.emsyssoft.com)
KGDB: Linux Kernel Source Level Debugger (http://kgdb.sourceforge.net)

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