Spike executed wrongly when GDB controlled it in single-step mode

[zhenbohu]

Hi,

When I try to use Spike to run with GDB for single-step mode, I found the execution sequence is not expected, and one instruction is lost.

If I run spike with the isa-test rv32uc-p-rvc (from the riscv-tests/isa directory), I can see the instruction trace is like this:

core 0: 0xffffffff800000b0 (0x34129073) csrw mepc, t0
core 0: 0xffffffff800000b4 (0xf1402573) csrr a0, mhartid
core 0: 0xffffffff800000b8 (0x30200073) mret
core 0: 0x00000000800000bc (0x00200e13) li t3, 2 //<---------------------------------------> This instruction
core 0: 0xffffffff800000c0 (0x29a00593) li a1, 666
core 0: 0xffffffff800000c4 (0x00100613) li a2, 1

But when I run this test with GDB in single-step-mode, I can see the trace is like this:
0x800000ac in reset_vector ()
(gdb) ni
0x800000b0 in reset_vector ()
(gdb) ni
0x800000b4 in reset_vector ()
(gdb) ni
0x800000b8 in reset_vector ()
(gdb) ni
0x800000c0 in reset_vector ()//<------------------> We can see after the 0x800000b8, the next instruction here is 0x800000c0. This should not happen, the original 800000bc instruction is lost.
(gdb) ni
0x800000c4 in reset_vector ()
(gdb)

I guess this should be a bug, so report it here.

Thanks
Bob