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