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

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Message-ID: <20180711212049.GB4102@w1t1fb>
Date:   Wed, 11 Jul 2018 22:20:49 +0100
From:   Okash Khawaja <osk@...com>
To:     Daniel Borkmann <daniel@...earbox.net>
CC:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        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 10:08:35PM +0200, Daniel Borkmann wrote:
> On 07/11/2018 09:10 PM, 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:
> > 
> > $ 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'
> 
> You could also easily test this on s390x (big endian) through a LinuxONE
> test instance, this is how I usually test changes related to their JIT.
Thanks. I've been using MIPS qemu set up. This will definitely help.

> 
> Thanks,
> Daniel