6c6935419e
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@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: John Fastabend <john.fastabend@gmail.com> Link: https://lore.kernel.org/bpf/20200618234631.3321118-1-yhs@fb.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.