[PATCH bpf-next v2 2/2] bpf, arm64: calculate offset as byte-offset for bpf line info

[Martin KaFai Lau]

On Tue, Jan 25, 2022 at 06:57:07PM +0800, Hou Tao wrote:
> insn_to_jit_off passed to bpf_prog_fill_jited_linfo() is calculated
> in instruction granularity instead of bytes granularity, but bpf
> line info requires byte offset, so fixing it by calculating offset
> as byte-offset.
> 
> Signed-off-by: Hou Tao <houtao1 at huawei.com>
> ---
>  arch/arm64/net/bpf_jit_comp.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> index 6a83f3070985..7b94e0c5e134 100644
> --- a/arch/arm64/net/bpf_jit_comp.c
> +++ b/arch/arm64/net/bpf_jit_comp.c
> @@ -152,10 +152,12 @@ static inline int bpf2a64_offset(int bpf_insn, int off,
>  	bpf_insn++;
>  	/*
>  	 * Whereas arm64 branch instructions encode the offset
> -	 * from the branch itself, so we must subtract 1 from the
> +	 * from the branch itself, so we must subtract 4 from the
>  	 * instruction offset.
>  	 */
> -	return ctx->offset[bpf_insn + off] - (ctx->offset[bpf_insn] - 1);
> +	return (ctx->offset[bpf_insn + off] -
> +		(ctx->offset[bpf_insn] - AARCH64_INSN_SIZE)) /
> +		AARCH64_INSN_SIZE;
Is it another bug fix? It does not seem to be related
to the change described in the commit message.

>  }
>  
>  static void jit_fill_hole(void *area, unsigned int size)
> @@ -946,13 +948,14 @@ static int build_body(struct jit_ctx *ctx, bool extra_pass)
>  		const struct bpf_insn *insn = &prog->insnsi[i];
>  		int ret;
>  
> +		/* BPF line info needs byte-offset instead of insn-offset */
>  		if (ctx->image == NULL)
> -			ctx->offset[i] = ctx->idx;
> +			ctx->offset[i] = ctx->idx * AARCH64_INSN_SIZE;
>  		ret = build_insn(insn, ctx, extra_pass);
>  		if (ret > 0) {
>  			i++;
>  			if (ctx->image == NULL)
> -				ctx->offset[i] = ctx->idx;
> +				ctx->offset[i] = ctx->idx * AARCH64_INSN_SIZE;
>  			continue;
>  		}
>  		if (ret)
> @@ -964,7 +967,7 @@ static int build_body(struct jit_ctx *ctx, bool extra_pass)
>  	 * instruction (end of program)
>  	 */
>  	if (ctx->image == NULL)
> -		ctx->offset[i] = ctx->idx;
> +		ctx->offset[i] = ctx->idx * AARCH64_INSN_SIZE;
Changes in this function makes sense.