linux-kernel - Re: [PATCH RFC v2 bpf-next 5/9] selftests/bpf: Add read

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Message-ID: <ZAiShb3hVRlnGam0@krava>
Date:   Wed, 8 Mar 2023 14:49:57 +0100
From:   Jiri Olsa <olsajiri@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Hao Luo <haoluo@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Matthew Wilcox <willy@...radead.org>, bpf@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Namhyung Kim <namhyung@...il.com>
Subject: Re: [PATCH RFC v2 bpf-next 5/9] selftests/bpf: Add read_buildid
 function

On Tue, Mar 07, 2023 at 05:22:51PM -0800, Andrii Nakryiko wrote:
> On Tue, Feb 28, 2023 at 1:33 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > Adding read_build_id function that parses out build id from
> > specified binary.
> >
> > It will replace extract_build_id and also be used in following
> > changes.
> >
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  tools/testing/selftests/bpf/trace_helpers.c | 98 +++++++++++++++++++++
> >  tools/testing/selftests/bpf/trace_helpers.h |  5 ++
> >  2 files changed, 103 insertions(+)
> >
> > diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
> > index 09a16a77bae4..c10e16626cd3 100644
> > --- a/tools/testing/selftests/bpf/trace_helpers.c
> > +++ b/tools/testing/selftests/bpf/trace_helpers.c
> > @@ -11,6 +11,9 @@
> >  #include <linux/perf_event.h>
> >  #include <sys/mman.h>
> >  #include "trace_helpers.h"
> > +#include <linux/limits.h>
> > +#include <libelf.h>
> > +#include <gelf.h>
> >
> >  #define DEBUGFS "/sys/kernel/debug/tracing/"
> >
> > @@ -230,3 +233,98 @@ ssize_t get_rel_offset(uintptr_t addr)
> >         fclose(f);
> >         return -EINVAL;
> >  }
> > +
> > +static int
> > +parse_build_id_buf(const void *note_start, Elf32_Word note_size,
> > +                  char *build_id)
> > +{
> > +       Elf32_Word note_offs = 0, new_offs;
> > +
> > +       while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
> > +               Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
> > +
> > +               if (nhdr->n_type == 3 &&
> > +                   nhdr->n_namesz == sizeof("GNU") &&
> > +                   !strcmp((char *)(nhdr + 1), "GNU") &&
> > +                   nhdr->n_descsz > 0 &&
> > +                   nhdr->n_descsz <= BPF_BUILD_ID_SIZE) {
> > +                       memcpy(build_id, note_start + note_offs +
> > +                              ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
> > +                              nhdr->n_descsz);
> > +                       memset(build_id + nhdr->n_descsz, 0,
> > +                              BPF_BUILD_ID_SIZE - nhdr->n_descsz);
> 
> I won't count :) but if something fits within 100 characters, please
> keep it on single line

copy&paste from kernel code ;-) I'll reformat that

SNIP

> > diff --git a/tools/testing/selftests/bpf/trace_helpers.h b/tools/testing/selftests/bpf/trace_helpers.h
> > index 53efde0e2998..50b2cc498ba7 100644
> > --- a/tools/testing/selftests/bpf/trace_helpers.h
> > +++ b/tools/testing/selftests/bpf/trace_helpers.h
> > @@ -4,6 +4,9 @@
> >
> >  #include <bpf/libbpf.h>
> >
> > +#define ALIGN(x, a)            __ALIGN_MASK(x, (typeof(x))(a)-1)
> > +#define __ALIGN_MASK(x, mask)  (((x)+(mask))&~(mask))
> 
> nit: I know these are macros, but why would you first use __ALIGN_MASK
> and then #define it? swap them?

same reason as above, I'll swap that

thanks,
jirka