If I just copy your swapu16 function into my code (and it looks very similar to mine) the result continues to be the same (error). Here is a gist with python and c-components of my program https://gist.github.com/ibaldin/716d70d490b44e05d15db59ee983c0c0 Looking at the BPF byte code print out from BCC (below) something strange is indeed going on that I think Yonghong alluded to. The last instruction is r2 = *(u16*)(r1 + 8), and r1 is invalid. R1 is initially set, but then for some reason becomes invalid: 50: (2d) if r4 > r2 goto pc+35 R1=pkt(id=2,off=0,r=2),aux_off_align=2 R2=pkt_end R3=pkt(id=1,off=0,r=20),aux_off_align=2 R4=pkt(id=2,off=2,r=2),aux_off_align=2 R5=inv56,min_value=22,max_value=142,min_align=2,aux_off_align=2 R10=fp 51: (57) r1 &= 65535 52: (15) if r1 == 0x0 goto pc+33 R1=inv,min_value=0,max_value=65535,min_align=1,aux_off_align=2 R2=pkt_end R3=pkt(id=1,off=0,r=20),aux_off_align=2 R4=pkt(id=2,off=2,r=2),aux_off_align=2 R5=inv56,min_value=22,max_value=14 —— FULL TEXT OF BPF PROGRAM BYTECODE ——— 0: (61) r2 = *(u32 *)(r1 +4) 1: (61) r1 = *(u32 *)(r1 +0) 2: (bf) r3 = r1 3: (07) r3 += 14 4: (2d) if r3 > r2 goto pc+81 R1=pkt(id=0,off=0,r=14) R2=pkt_end R3=pkt(id=0,off=14,r=14) R10=fp 5: (71) r3 = *(u8 *)(r1 +12) 6: (71) r4 = *(u8 *)(r1 +13) 7: (67) r4 <<= 8 8: (4f) r4 |= r3 9: (15) if r4 == 0xa888 goto pc+2 R1=pkt(id=0,off=0,r=14) R2=pkt_end R3=inv56 R4=inv R10=fp 10: (b7) r3 = 14 11: (55) if r4 != 0x81 goto pc+4 R1=pkt(id=0,off=0,r=14) R2=pkt_end R3=imm14,min_value=14,max_value=14,min_align=2 R4=inv,min_value=129,max_value=129 R10=fp 12: (b7) r3 = 18 13: (bf) r5 = r1 14: (07) r5 += 18 15: (2d) if r5 > r2 goto pc+70 R1=pkt(id=0,off=0,r=18) R2=pkt_end R3=imm18,min_value=18,max_value=18,min_align=2 R4=inv,min_value=129,max_value=129 R5=pkt(id=0,off=18,r=18) R10=fp 16: (15) if r4 == 0xa888 goto pc+1 R1=pkt(id=0,off=0,r=18) R2=pkt_end R3=imm18,min_value=18,max_value=18,min_align=2 R4=inv,min_value=129,max_value=129 R5=pkt(id=0,off=18,r=18) R10=fp 17: (55) if r4 != 0x81 goto pc+4 R1=pkt(id=0,off=0,r=18) R2=pkt_end R3=imm18,min_value=18,max_value=18,min_align=2 R4=inv,min_value=129,max_value=129 R5=pkt(id=0,off=18,r=18) R10=fp 18: (07) r3 += 4 19: (bf) r5 = r1 20: (0f) r5 += r3 21: (2d) if r5 > r2 goto pc+64 R1=pkt(id=0,off=0,r=22) R2=pkt_end R3=imm22,min_value=22,max_value=22,min_align=2 R4=inv,min_value=129,max_value=129 R5=pkt(id=0,off=22,r=22) R10=fp 22: (55) if r4 != 0x8 goto pc+63 R1=pkt(id=0,off=0,r=22) R2=pkt_end R3=imm22,min_value=22,max_value=22,min_align=2 R4=inv,min_value=8,max_value=8 R5=pkt(id=0,off=22,r=22) R10=fp 23: (bf) r4 = r1 24: (0f) r4 += r3 25: (15) if r4 == 0x0 goto pc+60 R1=pkt(id=0,off=0,r=22) R2=pkt_end R3=imm22,min_value=22,max_value=22,min_align=2 R4=pkt(id=0,off=22,r=22) R5=pkt(id=0,off=22,r=22) R10=fp 26: (bf) r5 = r4 27: (07) r5 += 20 28: (2d) if r5 > r2 goto pc+57 R1=pkt(id=0,off=0,r=42) R2=pkt_end R3=imm22,min_value=22,max_value=22,min_align=2 R4=pkt(id=0,off=22,r=42) R5=pkt(id=0,off=42,r=42) R10=fp 29: (71) r4 = *(u8 *)(r4 +9) 30: (55) if r4 != 0x6 goto pc+55 R1=pkt(id=0,off=0,r=42) R2=pkt_end R3=imm22,min_value=22,max_value=22,min_align=2 R4=inv56,min_value=6,max_value=6 R5=pkt(id=0,off=42,r=42) R10=fp 31: (bf) r4 = r1 32: (0f) r4 += r3 33: (71) r4 = *(u8 *)(r4 +0) 34: (57) r4 &= 15 35: (67) r4 <<= 2 36: (0f) r4 += r3 37: (bf) r3 = r1 38: (0f) r3 += r4 39: (15) if r3 == 0x0 goto pc+46 R1=pkt(id=0,off=0,r=42) R2=pkt_end R3=pkt(id=1,off=0,r=0),aux_off_align=2 R4=inv57,min_value=22,max_value=82,min_align=2 R5=pkt(id=0,off=42,r=42) R10=fp 40: (bf) r5 = r3 41: (07) r5 += 20 42: (2d) if r5 > r2 goto pc+43 R1=pkt(id=0,off=0,r=42) R2=pkt_end R3=pkt(id=1,off=0,r=20),aux_off_align=2 R4=inv57,min_value=22,max_value=82,min_align=2 R5=pkt(id=1,off=20,r=20),aux_off_align=2 R10=fp 43: (69) r5 = *(u16 *)(r3 +12) 44: (77) r5 >>= 2 45: (57) r5 &= 60 46: (0f) r5 += r4 47: (0f) r1 += r5 48: (bf) r4 = r1 49: (07) r4 += 2 50: (2d) if r4 > r2 goto pc+35 R1=pkt(id=2,off=0,r=2),aux_off_align=2 R2=pkt_end R3=pkt(id=1,off=0,r=20),aux_off_align=2 R4=pkt(id=2,off=2,r=2),aux_off_align=2 R5=inv56,min_value=22,max_value=142,min_align=2,aux_off_align=2 R10=fp 51: (57) r1 &= 65535 52: (15) if r1 == 0x0 goto pc+33 R1=inv,min_value=0,max_value=65535,min_align=1,aux_off_align=2 R2=pkt_end R3=pkt(id=1,off=0,r=20),aux_off_align=2 R4=pkt(id=2,off=2,r=2),aux_off_align=2 R5=inv56,min_value=22,max_value=142,min_align=2,aux_off_align=2 R10=fp 53: (b7) r5 = 0 54: (bf) r0 = r1 55: (07) r0 += 6 56: (b7) r4 = 0 57: (2d) if r0 > r2 goto pc+9 R0=inv,min_value=6,max_value=65541,min_align=1,aux_off_align=2 R1=inv,min_value=0,max_value=65535,min_align=1,aux_off_align=2 R2=pkt_end R3=pkt(id=1,off=0,r=20),aux_off_align=2 R4=imm0,min_value=0,max_value=0,min_align=2147483648,aux_off_align=2 R5=imm0,min_value=0,max_value=0,min_align=2147483648,aux_off_align=2 R10=fp 58: (bf) r0 = r1 59: (07) r0 += 10 60: (b7) r4 = 0 61: (2d) if r0 > r2 goto pc+5 R0=inv,min_value=10,max_value=65545,min_align=1,aux_off_align=2 R1=inv,min_value=0,max_value=65535,min_align=1,aux_off_align=2 R2=pkt_end R3=pkt(id=1,off=0,r=20),aux_off_align=2 R4=imm0,min_value=0,max_value=0,min_align=2147483648,aux_off_align=2 R5=imm0,min_value=0,max_value=0,min_align=2147483648,aux_off_align=2 R10=fp 62: (69) r2 = *(u16 *)(r1 +8) R1 invalid mem access 'inv' -ilya Ilya Baldin
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