netlink_delinearize: zero shift removal

Remove shifts-by-0.  These can occur after binop postprocessing
has adjusted the RHS value to account for a mask operation.

Example: frag frag-off @s4

Is internally represented via:

  [ exthdr load ipv6 2b @ 44 + 2 => reg 1 ]
  [ bitwise reg 1 = ( reg 1 & 0x0000f8ff ) ^ 0x00000000 ]
  [ bitwise reg 1 = ( reg 1 >> 0x00000003 ) ]
  [ lookup reg 1 set s ]

First binop masks out unwanted parts of the 16-bit field.
Second binop needs to left-shift so that lookups in the set will work.

When decoding, the first binop is removed after the exthdr load
has been adjusted accordingly.  Constant propagation adjusts the
shift-value to 0 on removal.  This change then gets rid of the
shift-by-0 entirely.

After this change, 'frag frag-off @s4' input is shown as-is.

Signed-off-by: Florian Westphal <fw@strlen.de>

0 files changed, 0 insertions, 0 deletions