On Wed, Feb 10, 2021 at 01:11:28PM +0100, Maciej W. Rozycki wrote:

On Wed, 10 Feb 2021, Daniel Thompson wrote:

quoted

quoted

 Wrapping the relevant parts of this file into #ifdef MIPS_FP_SUPPORT 
would be as easy though and would qualify as a proper fix given that we 
have no XML description support for the MIPS target (so we need to supply 
the inexistent registers in the protocol; or maybe we can return NULL in 
`dbg_get_reg' to get them padded out in the RSP packet, I haven't checked 
if generic KGDB code supports this feature).

Returning NULL should be fine.

The generic code will cope OK. The values in the f.p. registers may
act a little odd if gdb uses a 'G' packet to set them to non-zero values
(since kgdb will cache the values gdb sent it) but the developer
operating the debugger will probably figure out what is going on without
too much pain.

 Ack, thanks!

 NB if GDB sees a register padded out (FAOD it means all-x's rather than a 
hex string placed throughout the respective slot) in a `g' packet, then it 
will mark the register internally as "unavailable" and present it to the 
receiver of the information as such rather than giving any specific value.  
I don't remember offhand what the syntax for the `G' packet is in that 
case; possibly GDB just sends all-zeros, and in any case you can't make 
GDB write any specific value to such a register via any user
interface.

kgdb doesn't track register validity and adding would be a fairly big
change. Everything internally (including some of the interactions with
arch code) is based on updating a binary shadow of register state which
is only bin2hex'ed just before transmitting a packet.

It will simply default them to zero and update them on a 'G' packet.

 The way the unavailability is shown depends on the interface used, i.e. 
it will be different between the `info all-registers'/`info register $reg' 
commands, and the `p $reg' command (or any expression involving `$reg'), 
and the MI interface.  But in any case it will be unambiguous.

I guess this probably does create a technical protocol violation since
kgdb will reject per-register read/write for register that its report
says are zero rather then invalid.


Daniel.