7d134041a8
The encoding for this new variant is based on BPF_X format. "imm" field was
0 only, now it could be 1 which means doing zero extension unconditionally
.code = BPF_ALU | BPF_MOV | BPF_X
.dst_reg = DST
.src_reg = SRC
.imm = 1
We use this new form for doing zero extension for which verifier will
guarantee SRC == DST.
Implications on JIT back-ends when doing code-gen for
BPF_ALU | BPF_MOV | BPF_X:
1. No change if hardware already does zero extension unconditionally for
sub-register write.
2. Otherwise, when seeing imm == 1, just generate insns to clear high
32-bit. No need to generate insns for the move because when imm == 1,
dst_reg is the same as src_reg at the moment.
Interpreter doesn't need change as well. It is doing unconditionally zero
extension for mov32 already.
One helper macro BPF_ZEXT_REG is added to help creating zero extension
insn using this new mov32 variant.
One helper function insn_is_zext is added for checking one insn is an
zero extension on dst. This will be widely used by a few JIT back-ends in
later patches in this set.
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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.