dummy_rocc is a naive built-in RoCC accelerator example in RISCV tools, where several custom0 instructions are defined. After setup dummy_rocc (either on Spike ISA simulator or on Rocket-FPGA, differently), we use dummy_rocc_test -- a user program testcase to verify the correctness of the dummy_rocc accelerator. We have two ways to run dummy_rocc_test, either on pk (proxy kernel) or on Linux.
I once setup dummy_rocc on Spike ISA simulator, the dummy_rocc_test worked well either on pk or on Linux.
Now I replace Spike with Rocket-FPGA on Zedboard. While the execution on pk succeeds:
root@zynq:~# ./fesvr-zynq pk /nfs/copy_to_rootfs/work/dummy_rocc_test
begin
after asm code
load x into accumulator 2 (funct=0)
read it back into z (funct=1) to verify it
accumulate 456 into it (funct=3)
verify it
do it all again, but initialize acc2 via memory this time (funct=2)
do it all again, but initialize acc2 via memory this time (funct=2)
do it all again, but initialize acc2 via memory this time (funct=2)
success!
the execution on Linux fails:
./fesvr-zynq +disk=/nfs/root.bin bbl /nfs/fpga-zynq/zedboard/fpga-images-zedboard/riscv/vmlinux
..................................Booting RISC-V Linux.........................................
/ # ./work/dummy_rocc_test
begin
after asm code
[ 0.400000] dummy_rocc_test[23]: unhandled signal 4 code 0x30001 at 0x0000000000800500 in ]
[ 0.400000] CPU: 0 PID: 23 Comm: dummy_rocc_test Not tainted 3.14.33-g043bb5d #1
[ 0.400000] task: ffffffff8fa3f500 ti: ffffffff8fb76000 task.ti: ffffffff8fb76000
[ 0.400000] sepc: 0000000000800500 ra : 00000000008004fc sp : 0000003fff943c70
[ 0.400000] gp : 0000000000882198 tp : 0000000000884700 t0 : 0000000000000000
[ 0.400000] t1 : 000000000080adc8 t2 : 8101010101010100 s0 : 0000003fff943ca0
[ 0.400000] s1 : 0000000000800d5c a0 : 000000000000000f a1 : 0000002000002000
[ 0.400000] a2 : 000000000000000f a3 : 000000000085cee8 a4 : 0000000000000001
[ 0.400000] a5 : 000000000000007b a6 : 0000000000000008 a7 : 0000000000000040
[ 0.400000] s2 : 0000000000000000 s3 : 00000000008a2668 s4 : 00000000008d8d98
[ 0.400000] s5 : 00000000008d7770 s6 : 0000000000000008 s7 : 00000000008d6000
[ 0.400000] s8 : 00000000008d8d60 s9 : 0000000000000000 s10: 00000000008a32b8
[ 0.400000] s11: ffffffffffffffff t3 : 000000000000000b t4 : 000000006ffffdff
[ 0.400000] t5 : 000000000000000a t6 : 000000006ffffeff
[ 0.400000] sstatus: 8000000000003008 sbadaddr: 0000000000800500 scause: 0000000000000002
Illegal instruction
A screenshot shows that the "signal 4" is caused by a custom0 instruction. readelf screenshot of dummy_rocc_test
So my problem is "How come Linux kernel interferes the execution of RISC-V custom0 instruction on Zedboard? "
The source code of dummy_rocc_test is provided as reference:
// The following is a RISC-V program to test the functionality of the
// dummy RoCC accelerator.
// Compile with riscv64-unknown-elf-gcc dummy_rocc_test.c
// Run with spike --extension=dummy_rocc pk a.out
#include <assert.h>
#include <stdio.h>
#include <stdint.h>
int main() {
printf("begin\n");
uint64_t x = 123, y = 456, z = 0;
// load x into accumulator 2 (funct=0)
// asm code
asm volatile ("addi a1, a1, 2");
/// printf again
printf("after asm code\n");
asm volatile ("custom0 x0, %0, 2, 0" : : "r"(x));
printf("load x into accumulator 2 (funct=0)\n");
// read it back into z (funct=1) to verify it
asm volatile ("custom0 %0, x0, 2, 1" : "=r"(z));
printf("read it back into z (funct=1) to verify it\n");
assert(z == x);
// accumulate 456 into it (funct=3)
asm volatile ("custom0 x0, %0, 2, 3" : : "r"(y));
printf("accumulate 456 into it (funct=3)\n");
// verify it
asm volatile ("custom0 %0, x0, 2, 1" : "=r"(z));
printf("verify it\n");
assert(z == x+y);
// do it all again, but initialize acc2 via memory this time (funct=2)
asm volatile ("custom0 x0, %0, 2, 2" : : "r"(&x));
printf("do it all again, but initialize acc2 via memory this time (funct=2)\n");
asm volatile ("custom0 x0, %0, 2, 3" : : "r"(y));
printf("do it all again, but initialize acc2 via memory this time (funct=2)\n");
asm volatile ("custom0 %0, x0, 2, 1" : "=r"(z));
printf("do it all again, but initialize acc2 via memory this time (funct=2)\n");
assert(z == x+y);
printf("success!\n");
}