From: Jakub Kicinski
> Sent: 19 October 2017 23:46
> The eBPF instruction permitting to load double words (8 bytes) into a
> register need 8-byte long "immediate" field, and thus occupy twice the
> space of other instructions. bpftool was aware of this and would
> increment the instruction counter only once on meeting such instruction,
> but it would only print the first four bytes of the immediate value to
> load. Make it able to dump the whole 16 byte-long double instruction
> instead (as would `llvm-objdump -d <program>`).
Guess why most modern instruction sets use a 'load high' instruction
to generate big constants...
Interestingly, is there anything special in the rest of the
second instruction in order to make it an identifiable no-op?
...
> diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
> index 355c14325622..57edbea2fbe8 100644
> --- a/tools/bpf/bpftool/prog.c
> +++ b/tools/bpf/bpftool/prog.c
> @@ -313,20 +313,29 @@ static void print_insn(struct bpf_verifier_env *env,
> const char *fmt, ...)
> static void dump_xlated(void *buf, unsigned int len, bool opcodes)
> {
> struct bpf_insn *insn = buf;
> + bool double_insn = false;
> unsigned int i;
>
> for (i = 0; i < len / sizeof(*insn); i++) {
> + if (double_insn) {
> + double_insn = false;
> + continue;
> + }
Why not just:
for (i = 0; i < len / sizeof(*insn); i += 1 + double_insn) {
...
David
