On 2019-11-14 13:11, David Hildenbrand wrote:
On 14.11.19 12:57, Pierre Morel wrote:
On 2019-11-14 11:28, David Hildenbrand wrote:
Am 14.11.2019 um 11:11 schrieb Pierre Morel <pmorel@xxxxxxxxxxxxx>:
On 2019-11-13 17:12, Janosch Frank wrote:
On 11/13/19 1:23 PM, Pierre Morel wrote:
If we use multiple source of interrupts, for exemple, using SCLP
console
to print information while using I/O interrupts or during
exceptions, we
need to have a re-entrant register saving interruption handling.
Instead of saving at a static place, let's save the base
registers on
the stack.
Note that we keep the static register saving that we need for the
RESET
tests.
We also care to give the handlers a pointer to the save registers in
case the handler needs it (fixup_pgm_int needs the old psw address).
So you're still ignoring the FPRs...
I disassembled a test and looked at all stds and it looks like printf
and related functions use them. Wouldn't we overwrite test FPRs if
printing in a handler?
If printf uses the FPRs in my opinion we should modify the
compilation options for the library.
What is the reason for printf and related functions to use floating
point?
Register spilling. This can and will be done.
Hum, can you please clarify?
AFAIK register spilling is for a compiler, to use memory if it has not
enough registers.
Not strictly memory. If the compiler needs more GPRS, it can
save/restore GPRS to FPRS.
Any function the compiler generates is free to use the FPRS..
So your answer is for the my first sentence, meaning yes register
spilling will be done
or
do you mean register spilling is the reason why the compiler use FPRs
and it must be done so?
Confused by both options :D The compiler might generate code that uses
the FPRS although no floating point instructions are in use. That's
why we have to enable the AFP control and properly take care of FPRS
being used.
The compiler has the -msoft-float switch to avoid using the floating
point instructions and registers, so it is our decision.
Saving the FP registers on exceptions is not very efficient, we loose
time on each interrupt, not sure that we win it back by using FPregs to
as Regs backup.
Usually a system at low level uses some enter_fpu, leave_fpu routine to
enter critical sections using FPU instead of losing time on each
interruptions.
We can think about this, in between I do as you recomand and save the
FPregs too.
Best regards,
Pierre
--
Pierre Morel
IBM Lab Boeblingen
