On Wed, Oct 11, 2023 at 11:27:22PM +0800, Leon Hwang wrote:
> For next commit to reuse emit_nops(), move emit_nops() before
> emit_prologue().
>
> By the way, change memcpy(prog, x86_nops[5], X86_PATCH_SIZE) to
> emit_nops(&prog, X86_PATCH_SIZE).
I find the subject of the commit a bit bogus. Could you change it to
something like:
use emit_nops() to produce nop5 instead memcpy'ing x86_nops[5]
I also feel that you should be consistent and address other spots that are
the same as the one that you are touching in emit_prologue() - there are
two more from what i see.
>
> Signed-off-by: Leon Hwang <hffilwlqm@xxxxxxxxx>
> ---
> arch/x86/net/bpf_jit_comp.c | 41 ++++++++++++++++++-------------------
> 1 file changed, 20 insertions(+), 21 deletions(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 8c10d9abc2394..c2a0465d37da4 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -304,6 +304,25 @@ static void pop_callee_regs(u8 **pprog, bool *callee_regs_used)
> *pprog = prog;
> }
>
> +static void emit_nops(u8 **pprog, int len)
> +{
> + u8 *prog = *pprog;
> + int i, noplen;
> +
> + while (len > 0) {
> + noplen = len;
> +
> + if (noplen > ASM_NOP_MAX)
> + noplen = ASM_NOP_MAX;
> +
> + for (i = 0; i < noplen; i++)
> + EMIT1(x86_nops[noplen][i]);
> + len -= noplen;
> + }
> +
> + *pprog = prog;
> +}
> +
> /*
> * Emit x86-64 prologue code for BPF program.
> * bpf_tail_call helper will skip the first X86_TAIL_CALL_OFFSET bytes
> @@ -319,8 +338,7 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf,
> * but let's waste 5 bytes for now and optimize later
> */
> EMIT_ENDBR();
> - memcpy(prog, x86_nops[5], X86_PATCH_SIZE);
> - prog += X86_PATCH_SIZE;
> + emit_nops(&prog, X86_PATCH_SIZE);
> if (!ebpf_from_cbpf) {
> if (tail_call_reachable && !is_subprog)
> /* When it's the entry of the whole tailcall context,
> @@ -989,25 +1007,6 @@ static void detect_reg_usage(struct bpf_insn *insn, int insn_cnt,
> }
> }
>
> -static void emit_nops(u8 **pprog, int len)
> -{
> - u8 *prog = *pprog;
> - int i, noplen;
> -
> - while (len > 0) {
> - noplen = len;
> -
> - if (noplen > ASM_NOP_MAX)
> - noplen = ASM_NOP_MAX;
> -
> - for (i = 0; i < noplen; i++)
> - EMIT1(x86_nops[noplen][i]);
> - len -= noplen;
> - }
> -
> - *pprog = prog;
> -}
> -
> /* emit the 3-byte VEX prefix
> *
> * r: same as rex.r, extra bit for ModRM reg field
> --
> 2.41.0
>
