Yonghong Song wrote: > When do experiments with llvm (disabling instcombine and > simplifyCFG), I hit the following error with test_seg6_loop.o. > > ; R1=pkt(id=0,off=0,r=48,imm=0), R7=pkt(id=0,off=40,r=48,imm=0) > w2 = w7 > ; R2_w=inv(id=0,umax_value=4294967295,var_off=(0x0; 0xffffffff)) > w2 -= w1 > R2 32-bit pointer arithmetic prohibited > > The corresponding source code is: > uint32_t srh_off > // srh and skb->data are all packet pointers > srh_off = (char *)srh - (char *)(long)skb->data; > > The verifier does not support 32-bit pointer/scalar arithmetic. > > Without my llvm change, the code looks like > > ; R3=pkt(id=0,off=40,r=48,imm=0), R8=pkt(id=0,off=0,r=48,imm=0) > w3 -= w8 > ; R3_w=inv(id=0) > > This is explicitly allowed in verifier if both registers are > pointers and the opcode is BPF_SUB. > > To fix this problem, I changed the verifier to allow > 32-bit pointer/scaler BPF_SUB operations. > > At the source level, the issue could be workarounded with > inline asm or changing "uint32_t srh_off" to "uint64_t srh_off". > But I feel that verifier change might be the right thing to do. > > Signed-off-by: Yonghong Song <yhs@xxxxxx> > --- Agreed we have same logic in 64-bit case so LGTM. Acked-by: John Fastabend <john.fastabend@xxxxxxxxx>
