linux-kernel - Re: ANNOUNCE: pahole v1.20 (gcc11 DWARF5's default, lots of ELF sections, BTF)

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Date:   Mon, 8 Feb 2021 13:36:43 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     dwarves@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        bpf@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>,
        Jan Engelhardt <jengelh@...i.de>,
        Domenico Andreoli <cavok@...ian.org>,
        Matthias Schwarzott <zzam@...too.org>,
        Andrii Nakryiko <andriin@...com>, Yonghong Song <yhs@...com>,
        Mark Wieelard <mjw@...hat.com>,
        Paul Moore <paul@...l-moore.com>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        Daniel P. Berrangé <berrange@...hat.com>,
        Tom Stellard <tstellar@...hat.com>
Subject: Re: ANNOUNCE: pahole v1.20 (gcc11 DWARF5's default, lots of ELF
 sections, BTF)

On Mon, Feb 8, 2021 at 1:32 PM Arnaldo Carvalho de Melo
<arnaldo.melo@...il.com> wrote:
>
> Em Mon, Feb 08, 2021 at 03:44:54AM +0100, Sedat Dilek escreveu:
> > On Thu, Feb 4, 2021 at 11:07 PM Arnaldo Carvalho de Melo
> > <arnaldo.melo@...il.com> wrote:
> > >
> > > Hi,
> > >
> > >         The v1.20 release of pahole and its friends is out, mostly
> > > addressing problems related to gcc 11 defaulting to DWARF5 for -g,
> > > available at the usual places:
> > >
> > > Main git repo:
> > >
> > >    git://git.kernel.org/pub/scm/devel/pahole/pahole.git
> > >
> > > Mirror git repo:
> > >
> > >    https://github.com/acmel/dwarves.git
> > >
> > > tarball + gpg signature:
> > >
> > >    https://fedorapeople.org/~acme/dwarves/dwarves-1.20.tar.xz
> > >    https://fedorapeople.org/~acme/dwarves/dwarves-1.20.tar.bz2
> > >    https://fedorapeople.org/~acme/dwarves/dwarves-1.20.tar.sign
> > >
> >
> > FYI:
> > Debian now ships dwarves package version 1.20-1 in unstable.
> >
> > Just a small nit to this release and its tagging:
> >
> > You did:
> > commit 0d415f68c468b77c5bf8e71965cd08c6efd25fc4 ("pahole: Prep 1.20")
> >
> > Is this new?
> >
> > The release before:
> > commit dd15aa4b0a6421295cbb7c3913429142fef8abe0 ("dwarves: Prep v1.19")
>
> Its minor but intentional, pahole is by far the most well known tool in
> dwarves, so using that name more frequently (the git repo is pahole.git
> , for instance) may help more quickly associate with the tool needed for
> BTF encoding, data analysis, etc. And since its not about only DWARF,
> perhaps transitioning to using 'pahole' more widely is interesting.
>

I am fine with that, Arnaldo.
The Git tree is called "pahole" Git, so that makes sense to me.

- Sedat -

> - Arnaldo
>
> > - Sedat -
> >
> > > Best Regards,
> > >
> > >  - Arnaldo
> > >
> > > v1.20:
> > >
> > > BTF encoder:
> > >
> > >   - Improve ELF error reporting using elf_errmsg(elf_errno()).
> > >
> > >   - Improve objcopy error handling.
> > >
> > >   - Fix handling of 'restrict' qualifier, that was being treated as a 'const'.
> > >
> > >   - Support SHN_XINDEX in st_shndx symbol indexes, to handle ELF objects with
> > >     more than 65534 sections, for instance, which happens with kernels built
> > >     with 'KCFLAGS="-ffunction-sections -fdata-sections", Other cases may
> > >     include when using FG-ASLR, LTO.
> > >
> > >   - Cope with functions without a name, as seen sometimes when building kernel
> > >     images with some versions of clang, when a SEGFAULT was taking place.
> > >
> > >   - Fix BTF variable generation for kernel modules, not skipping variables at
> > >     offset zero.
> > >
> > >   - Fix address size to match what is in the ELF file being processed, to fix using
> > >     a 64-bit pahole binary to generate BTF for a 32-bit vmlinux image.
> > >
> > >   - Use kernel module ftrace addresses when finding which functions to encode,
> > >     which increases the number of functions encoded.
> > >
> > > libbpf:
> > >
> > >   - Allow use of packaged version, for distros wanting to dynamically link with
> > >     the system's libbpf package instead of using the libbpf git submodule shipped
> > >     in pahole's source code.
> > >
> > > DWARF loader:
> > >
> > >   - Support DW_AT_data_bit_offset
> > >
> > >     This appeared in DWARF4 but is supported only in gcc's -gdwarf-5,
> > >     support it in a way that makes the output be the same for both cases.
> > >
> > >       $ gcc -gdwarf-5 -c examples/dwarf5/bf.c
> > >       $ pahole bf.o
> > >       struct pea {
> > >             long int                   a:1;                  /*     0: 0  8 */
> > >             long int                   b:1;                  /*     0: 1  8 */
> > >             long int                   c:1;                  /*     0: 2  8 */
> > >
> > >             /* XXX 29 bits hole, try to pack */
> > >             /* Bitfield combined with next fields */
> > >
> > >             int                        after_bitfield;       /*     4     4 */
> > >
> > >             /* size: 8, cachelines: 1, members: 4 */
> > >             /* sum members: 4 */
> > >             /* sum bitfield members: 3 bits, bit holes: 1, sum bit holes: 29 bits */
> > >             /* last cacheline: 8 bytes */
> > >       };
> > >
> > >   - DW_FORM_implicit_const in attr_numeric() and attr_offset()
> > >
> > >   - Support DW_TAG_GNU_call_site, its the standardized rename of the previously supported
> > >     DW_TAG_GNU_call_site.
> > >
> > > build:
> > >
> > >     - Fix compilation on 32-bit architectures.
> > >
> > > Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
>
> --
>
> - Arnaldo