UVM_ERROR reporter [CORE_TRACER 992]

While running malloc (maybe lots of),

float ****kernel_C0;
kernel_C0 = (float****)malloc(KERNEL_NUM_C * sizeof(float***));
    for (int l = 0; l < KERNEL_NUM_C; l++) {
        kernel_C0[l] = (float***)malloc(DEPTH_C * sizeof(float**));
        for (int k = 0; k < DEPTH_C; k++) {
            kernel_C0[l][k] = (float**)malloc(KERNEL_SIZE_5 * sizeof(float*));
            for (int i = 0; i < KERNEL_SIZE_5; i++) {
                kernel_C0[l][k][i] = (float*)malloc(KERNEL_SIZE_5 * sizeof(float));
        }
    }
}
    for (int l = 0; l < KERNEL_NUM_C; l++){
        for (int k = 0; k < DEPTH_C; k++){
            for (int i = 0; i < KERNEL_SIZE_5; i++) {
                for (int j = 0; j < KERNEL_SIZE_5; j++) {
                    kernel_C0[l][k][i][j] = 1;
                }
            }
        }
    }

float ***out_cnn_C0;
out_cnn_C0 = (float ***)malloc(KERNEL_NUM_C * sizeof(float **));
for (int k = 0; k < KERNEL_NUM_C; k++) {
    out_cnn_C0[k] = (float **)malloc(IMG_SIZE_C0 * sizeof(float *));
    for (int i = 0; i < IMG_SIZE_C0; i++) {
        out_cnn_C0[k][i] = (float *)malloc(IMG_SIZE_C0 * sizeof(float));
    }
}
for (int k = 0; k < KERNEL_NUM_C; k++){
    for (int i = 0; i < IMG_SIZE_C0; i++) {
        for (int j = 0; j < IMG_SIZE_C0; j++) {
            out_cnn_C0[k][i][j] = 0;
        }
    }
}

following errors occured during make run

# 106265212ns: Illegal instruction (core 0) at PC 0x00000000:
# UVM_ERROR /root/pulpissimo/.bender/git/checkouts/cv32e40p-703290f15a6e8974/bhv/cv32e40p_tracer.sv(525) @ 106266948ns: reporter [CORE_TRACER
992] EX: Reg WR 44:0x00000000 but no active EX instruction
# 106270765ns: Illegal instruction (core 0) at PC 0x00000000:
# UVM_ERROR /root/pulpissimo/.bender/git/checkouts/cv32e40p-703290f15a6e8974/bhv/cv32e40p_tracer.sv(525) @ 106272501ns: reporter [CORE_TRACER
992] EX: Reg WR 44:0x00000000 but no active EX instruction
# 106276317ns: Illegal instruction (core 0) at PC 0x00000000:
# UVM_ERROR /root/pulpissimo/.bender/git/checkouts/cv32e40p-703290f15a6e8974/bhv/cv32e40p_tracer.sv(525) @ 106278054ns: reporter [CORE_TRACER
992] EX: Reg WR 44:0x00000000 but no active EX instruction
# 106281870ns: Illegal instruction (core 0) at PC 0x00000000:
# UVM_ERROR /root/pulpissimo/.bender/git/checkouts/cv32e40p-703290f15a6e8974/bhv/cv32e40p_tracer.sv(525) @ 106283607ns: reporter [CORE_TRACER
992] EX: Reg WR 44:0x00000000 but no active EX instruction
# 106287423ns: Illegal instruction (core 0) at PC 0x00000000:
# UVM_ERROR /root/pulpissimo/.bender/git/checkouts/cv32e40p-703290f15a6e8974/bhv/cv32e40p_tracer.sv(525) @ 106289159ns: reporter [CORE_TRACER
992] EX: Reg WR 44:0x00000000 but no active EX instruction
# 106292976ns: Illegal instruction (core 0) at PC 0x00000000:
# UVM_ERROR /root/pulpissimo/.bender/git/checkouts/cv32e40p-703290f15a6e8974/bhv/cv32e40p_tracer.sv(525) @ 106294712ns: reporter [CORE_TRACER
992] EX: Reg WR 44:0x00000000 but no active EX instruction
# 106298529ns: Illegal instruction (core 0) at PC 0x00000000:
# UVM_ERROR /root/pulpissimo/.bender/git/checkouts/cv32e40p-703290f15a6e8974/bhv/cv32e40p_tracer.sv(525) @ 106300265ns: reporter [CORE_TRACER
992] EX: Reg WR 44:0x00000000 but no active EX instruction
# 106304081ns: Illegal instruction (core 0) at PC 0x00000000:
# UVM_ERROR /root/pulpissimo/.bender/git/checkouts/cv32e40p-703290f15a6e8974/bhv/cv32e40p_tracer.sv(525) @ 106305818ns: reporter [CORE_TRACER
992] EX: Reg WR 44:0x00000000 but no active EX instruction
# 106309634ns: Illegal instruction (core 0) at PC 0x00000000:
# UVM_ERROR /root/pulpissimo/.bender/git/checkouts/cv32e40p-703290f15a6e8974/bhv/cv32e40p_tracer.sv(525) @ 106311371ns: reporter [CORE_TRACER
992] EX: Reg WR 44:0x00000000 but no active EX instruction

What will be the reason of the error? Is it occured by busy memory?

pulp-platform / pulpissimo

UVM_ERROR reporter [CORE_TRACER 992] #421