linux-kernel - Re: [PATCH bpf-next v4 2/3] bpf: btf: add btf print functionality

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Date:   Wed, 11 Jul 2018 22:18:19 +0100
From:   Okash Khawaja <osk@...com>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Yonghong Song <yhs@...com>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <kernel-team@...com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v4 2/3] bpf: btf: add btf print functionality

On Wed, Jul 11, 2018 at 12:10:15PM -0700, Jakub Kicinski wrote:
> Thank you for all the changes made so far.
> 
> On Tue, 10 Jul 2018 20:21:10 -0700, Okash Khawaja wrote:
> > --- /dev/null
> > +++ b/tools/bpf/bpftool/btf_dumper.c
> > @@ -0,0 +1,248 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (c) 2018 Facebook */
> > +
> > +#include <linux/btf.h>
> > +#include <linux/err.h>
> > +#include <stdio.h> /* for (FILE *) used by json_writer */
> > +#include <linux/bitops.h>
> > +#include <string.h>
> > +#include <ctype.h>
> 
> Again, please sort the headers the way I suggested.  Otherwise as the
> list of includes grows it's hard to know what's already there.
> 
> > +#include "btf.h"
> > +#include "json_writer.h"
> > +#include "main.h"
> > +
> > +#define BITS_PER_BYTE_MASK (BITS_PER_BYTE - 1)
> > +#define BITS_PER_BYTE_MASKED(bits) ((bits) & BITS_PER_BYTE_MASK)
> > +#define BITS_ROUNDDOWN_BYTES(bits) ((bits) >> 3)
> > +#define BITS_ROUNDUP_BYTES(bits) \
> > +	(BITS_ROUNDDOWN_BYTES(bits) + !!BITS_PER_BYTE_MASKED(bits))
> > +
> > +static int btf_dumper_do_type(const struct btf_dumper *d, __u32 type_id,
> > +			      __u8 bit_offset, const void *data);
> > +
> > +static void btf_dumper_ptr(const void *data, json_writer_t *jw,
> > +			   bool is_plain_text)
> > +{
> > +	if (is_plain_text)
> > +		jsonw_printf(jw, "%p", *((unsigned long *)data));
> > +	else
> > +		jsonw_printf(jw, "%u", *((unsigned long *)data));
> 
> Again, please drop the extraneous parens. 
> 
> > +}
> > +
> 
> > +static void btf_dumper_int_bits(__u32 int_type, __u8 bit_offset,
> > +				const void *data, json_writer_t *jw,
> > +				bool is_plain_text)
> > +{
> > +	int left_shift_bits, right_shift_bits;
> > +	int nr_bits = BTF_INT_BITS(int_type);
> > +	int total_bits_offset;
> > +	int bytes_to_copy;
> > +	int bits_to_copy;
> > +	__u64 print_num;
> > +
> > +	total_bits_offset = bit_offset + BTF_INT_OFFSET(int_type);
> > +	data += BITS_ROUNDDOWN_BYTES(total_bits_offset);
> > +	bit_offset = BITS_PER_BYTE_MASKED(total_bits_offset);
> > +	bits_to_copy = bit_offset + nr_bits;
> > +	bytes_to_copy = BITS_ROUNDUP_BYTES(bits_to_copy);
> > +
> > +	print_num = 0;
> > +	memcpy(&print_num, data, bytes_to_copy);
> > +#ifdef __BIG_ENDIAN_BITFIELD
> > +	left_shift_bits = bit_offset;
> > +#else
> > +	left_shift_bits = 64 - bits_to_copy;
> > +#endif
> > +	right_shift_bits = 64 - nr_bits;
> 
> Please include <asm/byteorder.h> as I suggested to you previously.
> This is dead code right now, look:
Sorry, should have checked ifndef case. Will fix. Thanks.

> 
> $ git diff
> diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
> index c64465094b92..045add07b721 100644
> --- a/tools/bpf/bpftool/btf_dumper.c
> +++ b/tools/bpf/bpftool/btf_dumper.c
> @@ -91,7 +91,8 @@ static void btf_dumper_int_bits(__u32 int_type, __u8 bit_offset,
>  
>         print_num = 0;
>         memcpy(&print_num, data, bytes_to_copy);
> -#ifdef __BIG_ENDIAN_BITFIELD
> +#ifndef __LITTLE_ENDIAN_BITFIELD
> +#error "abc"
>         left_shift_bits = bit_offset;
>  #else
>         left_shift_bits = 64 - bits_to_copy;
> 
> $ make -C tools/bpf/bpftool/ CC=gcc-8
> make: Entering directory '/home/jkicinski/devel/linux/tools/bpf/bpftool'
>   CC       btf_dumper.o
> btf_dumper.c: In function ‘btf_dumper_int_bits’:
> btf_dumper.c:95:2: error: #error "abc"
>  #error "abc"
>   ^~~~~
> Makefile:96: recipe for target 'btf_dumper.o' failed
> make: *** [btf_dumper.o] Error 1
> make: Leaving directory '/home/jkicinski/devel/linux/tools/bpf/bpftool'