netdev - Re: [PATCH v2 bpf-next 11/17] bpf: Reserver space for BPF trampoline in BPF programs

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Date:   Thu, 7 Nov 2019 21:03:32 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>, x86@...nel.org,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 11/17] bpf: Reserver space for BPF trampoline
 in BPF programs

On Wed, Nov 6, 2019 at 9:48 PM Alexei Starovoitov <ast@...nel.org> wrote:
>
> BPF trampoline can be made to work with existing 5 bytes of BPF program
> prologue, but let's add 5 bytes of NOPs to the beginning of every JITed BPF
> program to make BPF trampoline job easier. They can be removed in the future.
>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>

>  arch/x86/net/bpf_jit_comp.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 44169e8bffc0..260f61276f18 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -206,7 +206,7 @@ struct jit_context {
>  /* number of bytes emit_call() needs to generate call instruction */
>  #define X86_CALL_SIZE          5
>
> -#define PROLOGUE_SIZE          20
> +#define PROLOGUE_SIZE          25

nit: define as 20 + X86_CALL_SIZE ?

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