Microblaze libgloss and gdb simulator

[Mike Frysinger]

On 24 Apr 2021 01:02, Mike Frysinger via Gdb wrote:
> On 22 Apr 2021 21:19, Mike Frysinger via Gdb wrote:
> > On 22 Apr 2021 19:55, Joel Sherrill wrote:
> > > On Thu, Apr 22, 2021, 7:27 PM Mike Frysinger wrote:
> > > > ignoring that, the microblaze sim doesn't have syscall support hooked up.
> > > > so it's only a CPU simulator atm.
> > > 
> > > So it has no output whatsoever? Does it get used for anything?
> > 
> > afaict, correct.  the most basic sims just do CPU level stuff and then have
> > their state inspected, or communicate pass/fail via exit status or abort.
> > this behavior actually isn't that rare ... it's where most sims start.
> > 
> > > We are resurrecting some old work that I did for a Microblaze port. I did
> > > write an inbyte() and outbyte() which would normally come from the xil
> > > library. But I don't have any idea how I figured out there was a uart at a
> > > particular address. I swear I had it working to print then but now it
> > > faults after the first instruction.
> > > 
> > > Is there any known good executable for it? Even just seeing it operate with
> > > a linked executable that had a crt0 and did something would be helpful at
> > > this point.
> > 
> > ftr, i've never worked on microblaze.  i'm just reading the code and poking
> > the toolchain :).
> > 
> > getting i/o (or maybe just o) support into the sim shouldn't be terribly hard.
> > we could even do the normal libgloss syscalls.  the important things we need to
> > know are:
> > * how does outbyte work ?  is it writing to MMIO UARTs, or something else ?
> > * is there an interrupt or exception or specific insn that microblaze uses to
> >   trigger the hypervisor/monitor/whatever ?  if so, should be possible to wire
> >   that up in the microblaze port.  my reading of libgloss/microblaze/ isn't
> >   picking out anything interesting, but i'm by no means an expert here.
> > 
> > if you can figure out those bits, happy to help on the sim side.
> 
> here's wiring up the syscall path, but it's unclear whether we should do this
> without changes landing in libgloss first.

Michael: what do you think of wiring up the libgloss syscalls for microblaze
via the brki insn ?  is there any prior art in this space for microblaze ?
i wouldn't want to try an allocate syscall space that's already used.
-mike

> --- a/sim/common/gennltvals.py
> +++ b/sim/common/gennltvals.py
> @@ -66,6 +66,7 @@ TARGETS = {
>      'm32c',
>      'm32r',
>      'mcore',
> +    'microblaze',
>      'mn10200',
>      'mn10300',
>      'moxie',
> --- a/sim/common/nltvals.def
> +++ b/sim/common/nltvals.def
> @@ -484,6 +484,37 @@
>  /* end mcore sys target macros */
>  #endif
>  #endif
> +#ifdef NL_TARGET_microblaze
> +#ifdef sys_defs
> +/* from syscall.h */
> +/* begin microblaze sys target macros */
> + { "SYS_argc", 22 },
> + { "SYS_argn", 24 },
> + { "SYS_argnlen", 23 },
> + { "SYS_argv", 13 },
> + { "SYS_argvlen", 12 },
> + { "SYS_chdir", 14 },
> + { "SYS_chmod", 16 },
> + { "SYS_close", 3 },
> + { "SYS_exit", 1 },
> + { "SYS_fstat", 10 },
> + { "SYS_getpid", 8 },
> + { "SYS_gettimeofday", 19 },
> + { "SYS_kill", 9 },
> + { "SYS_link", 21 },
> + { "SYS_lseek", 6 },
> + { "SYS_open", 2 },
> + { "SYS_read", 4 },
> + { "SYS_reconfig", 25 },
> + { "SYS_stat", 15 },
> + { "SYS_time", 18 },
> + { "SYS_times", 20 },
> + { "SYS_unlink", 7 },
> + { "SYS_utime", 17 },
> + { "SYS_write", 5 },
> +/* end microblaze sys target macros */
> +#endif
> +#endif
>  #ifdef NL_TARGET_mn10200
>  #ifdef sys_defs
>  /* from syscall.h */
> --- a/sim/microblaze/Makefile.in
> +++ b/sim/microblaze/Makefile.in
> @@ -15,6 +15,9 @@
>  # You should have received a copy of the GNU General Public License
>  # along with this program.  If not, see <http://www.gnu.org/licenses/>.
>  
> +# This selects the bfin newlib/libgloss syscall definitions.
> +NL_TARGET = -DNL_TARGET_microblaze
> +
>  ## COMMON_PRE_CONFIG_FRAG
>  
>  SIM_OBJS = \
> diff --git a/sim/microblaze/interp.c b/sim/microblaze/interp.c
> index 2bd067c6dc51..ed29d020efbc 100644
> --- a/sim/microblaze/interp.c
> +++ b/sim/microblaze/interp.c
> @@ -28,6 +28,7 @@
>  
>  #include "sim-main.h"
>  #include "sim-options.h"
> +#include "sim-syscall.h"
>  
>  #include "microblaze-dis.h"
>  
> @@ -162,11 +163,14 @@ sim_engine_run (SIM_DESC sd,
>        delay_slot_enable = 0;
>        branch_taken = 0;
>        if (op == microblaze_brk)
> -	sim_engine_halt (sd, NULL, NULL, NULL_CIA, sim_stopped, SIM_SIGTRAP);
> +	{
> +	  sim_engine_halt (sd, NULL, NULL, NULL_CIA, sim_stopped, SIM_SIGTRAP);
> +	}
>        else if (inst == MICROBLAZE_HALT_INST)
>  	{
>  	  insts += 1;
>  	  bonus_cycles++;
> +	  TRACE_INSN (cpu, "HALT (%i)", RETREG);
>  	  sim_engine_halt (sd, NULL, NULL, NULL_CIA, sim_exited, RETREG);
>  	}
>        else
> @@ -175,6 +179,7 @@ sim_engine_run (SIM_DESC sd,
>  	    {
>  #define INSTRUCTION(NAME, OPCODE, TYPE, ACTION)		\
>  	    case NAME:					\
> +	      TRACE_INSN (cpu, #NAME);			\
>  	      ACTION;					\
>  	      break;
>  #include "microblaze.isa"
> @@ -284,8 +289,18 @@ sim_engine_run (SIM_DESC sd,
>  		    IMM_ENABLE = 0;
>  	        }
>  	      else
> -		/* no delay slot: increment cycle count */
> -		bonus_cycles++;
> +		{
> +		  if (op == brki)
> +		    {
> +		      RETREG = sim_syscall (cpu, CPU.regs[12], CPU.regs[5],
> +					    CPU.regs[6], CPU.regs[7],
> +					    CPU.regs[8]);
> +		      PC = RD + INST_SIZE;
> +		    }
> +
> +		  /* no delay slot: increment cycle count */
> +		  bonus_cycles++;
> +		}
>  	    }
>  	}
>  
> --- a/sim/microblaze/microblaze.isa
> +++ b/sim/microblaze/microblaze.isa
> @@ -110,6 +110,7 @@ INSTRUCTION(addi,
>  	    INST_TYPE_RD_RA_IMM,
>              CARRY = C_calc(RA, IMM, 0);
>  	    RD = RA + IMM;
> +	    TRACE_REGISTER (cpu, "r%i = r%i + %i", rd, ra, IMM);
>  	    C_wr(CARRY);
>  	    PC += INST_SIZE)
>  
> --- a/sim/testsuite/microblaze/pass.s
> +++ b/sim/testsuite/microblaze/pass.s
> @@ -1,6 +1,5 @@
>  # check that the sim doesn't die immediately.
>  # mach: microblaze
> -# output:
>  
>  .include "testutils.inc"
>  
> --- a/sim/testsuite/microblaze/testutils.inc
> +++ b/sim/testsuite/microblaze/testutils.inc
> @@ -1,5 +1,12 @@
> +# MACRO: system_call
> +# Make a libgloss/Linux system call
> +	.macro system_call nr:req
> +	addi r12, r0, \nr;
> +	brki r14, 8;
> +	.endm
> +
>  # MACRO: exit
> -	.macro exit nr
> +	.macro exit nr:req
>  	addi r3, r0, \nr;
>  	bri 0;
>  	.endm
> @@ -7,6 +14,7 @@
>  # MACRO: pass
>  # Write 'pass' to stdout and quit
>  	.macro pass
> +	write 1, 1f, 5
>  	exit 0
>  	.data
>  	1: .asciz "pass\n"
> @@ -15,6 +23,7 @@
>  # MACRO: fail
>  # Write 'fail' to stdout and quit
>  	.macro fail
> +	write 1, 1f, 5
>  	exit 1
>  	.data
>  	1: .asciz "fail\n"
> @@ -27,3 +36,12 @@
>  .global _start
>  _start:
>  	.endm
> +
> +# MACRO: write
> +# Just like the write() C function; uses system calls
> +	.macro write fd:req, buf:req, count:req
> +	addi r5, r0, \fd;
> +	addi r6, r0, \buf;
> +	addi r7, r0, \count;
> +	system_call 5
> +	.endm