linux-kernel - Re: [PATCH 3/9] x86/bpf: Move epilogue generation to a dedicated function

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Message-ID: <A753FBC1-3781-4A47-B0AD-A4300C552F7B@fb.com>
Date:   Thu, 13 Jun 2019 18:57:10 +0000
From:   Song Liu <songliubraving@...com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
CC:     X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Kairui Song <kasong@...hat.com>
Subject: Re: [PATCH 3/9] x86/bpf: Move epilogue generation to a dedicated
 function



> On Jun 13, 2019, at 6:21 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> 
> Improve code readability by moving the BPF JIT function epilogue
> generation code to a dedicated emit_epilogue() function, analagous to
> the existing emit_prologue() function.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
> arch/x86/net/bpf_jit_comp.c | 37 ++++++++++++++++++++++++-------------
> 1 file changed, 24 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 32bfab4e21eb..da8c988b0f0f 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -240,6 +240,28 @@ static void emit_prologue(u8 **pprog, u32 stack_depth, bool ebpf_from_cbpf)
> 	*pprog = prog;
> }
> 
> +static void emit_epilogue(u8 **pprog)
> +{
> +	u8 *prog = *pprog;
> +	int cnt = 0;
> +
> +	/* mov rbx, qword ptr [rbp+0] */
> +	EMIT4(0x48, 0x8B, 0x5D, 0);
> +	/* mov r13, qword ptr [rbp+8] */
> +	EMIT4(0x4C, 0x8B, 0x6D, 8);
> +	/* mov r14, qword ptr [rbp+16] */
> +	EMIT4(0x4C, 0x8B, 0x75, 16);
> +	/* mov r15, qword ptr [rbp+24] */
> +	EMIT4(0x4C, 0x8B, 0x7D, 24);

Shall we update these comments to AT&T syntax? 

Thanks,
Song

> +
> +	/* add rbp, AUX_STACK_SPACE */
> +	EMIT4(0x48, 0x83, 0xC5, AUX_STACK_SPACE);
> +	EMIT1(0xC9); /* leave */
> +	EMIT1(0xC3); /* ret */
> +
> +	*pprog = prog;
> +}
> +
> /*
>  * Generate the following code:
>  *
> @@ -1036,19 +1058,8 @@ xadd:			if (is_imm8(insn->off))
> 			seen_exit = true;
> 			/* Update cleanup_addr */
> 			ctx->cleanup_addr = proglen;
> -			/* mov rbx, qword ptr [rbp+0] */
> -			EMIT4(0x48, 0x8B, 0x5D, 0);
> -			/* mov r13, qword ptr [rbp+8] */
> -			EMIT4(0x4C, 0x8B, 0x6D, 8);
> -			/* mov r14, qword ptr [rbp+16] */
> -			EMIT4(0x4C, 0x8B, 0x75, 16);
> -			/* mov r15, qword ptr [rbp+24] */
> -			EMIT4(0x4C, 0x8B, 0x7D, 24);
> -
> -			/* add rbp, AUX_STACK_SPACE */
> -			EMIT4(0x48, 0x83, 0xC5, AUX_STACK_SPACE);
> -			EMIT1(0xC9); /* leave */
> -			EMIT1(0xC3); /* ret */
> +
> +			emit_epilogue(&prog);
> 			break;
> 
> 		default:
> -- 
> 2.20.1
>