Dwarves Archive on lore.kernel.org
 help / color / Atom feed
From: Lorenz Bauer <lmb-lDpJ742SOEtZroRs9YW3xA@public.gmane.org>
To: bpf <bpf-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Cc: kernel-team <kernel-team-lDpJ742SOEtZroRs9YW3xA@public.gmane.org>
Subject: pahole generates invalid BTF for code compiled with recent clang
Date: Wed, 24 Jun 2020 12:05:50 +0100
Message-ID: <CACAyw9-cinpz=U+8tjV-GMWuth71jrOYLQ05Q7_c34TCeMJxMg@mail.gmail.com> (raw)


If pahole -J is used on an ELF that has BTF info from clang, it
produces an invalid
output. This is because pahole rewrites the .BTF section (which
includes a new string
table) but it doesn't touch .BTF.ext at all.

To demonstrate, on a recent check out of bpf-next:
    $ cp connect4_prog.o connect4_pahole.o
    $ pahole -J connect4_pahole.o
    $ llvm-objcopy-10 --dump-section .BTF=pahole-btf.bin
--dump-section .BTF.ext=pahole-btf-ext.bin connect4_pahole.o
    $ llvm-objcopy-10 --dump-section .BTF=btf.bin --dump-section
.BTF.ext=btf-ext.bin connect4_prog.o
    $ sha1sum *.bin
    1b5c7407dd9fd13f969931d32f6b864849e66a68  btf.bin
    4c43efcc86d3cd908ddc77c15fc4a35af38d842b  btf-ext.bin
    2a60767a3a037de66a8d963110601769fa0f198e  pahole-btf.bin
    4c43efcc86d3cd908ddc77c15fc4a35af38d842b  pahole-btf-ext.bin

This problem crops up when compiling old kernels like 4.19 which have
an extra pahole
build step with clang-10.

I think a possible fix is to strip .BTF.ext if .BTF is rewritten.


Lorenz Bauer  |  Systems Engineer
6th Floor, County Hall/The Riverside Building, SE1 7PB, UK


             reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-24 11:05 Lorenz Bauer [this message]
     [not found] ` <CACAyw9-cinpz=U+8tjV-GMWuth71jrOYLQ05Q7_c34TCeMJxMg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-06-24 16:06   ` Arnaldo Carvalho de Melo
     [not found]     ` <20200624160659.GA20203-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2020-06-24 16:22       ` Lorenz Bauer
     [not found]         ` <CACAyw9-zLLDJ4vXo7jGS_XoYsiiv4c5NmUCjCnAf0eZBXU3dVA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-06-24 17:23           ` Arnaldo Carvalho de Melo
2020-06-24 17:05       ` Yonghong Song
2020-06-24 17:41   ` Andrii Nakryiko
     [not found]     ` <CAEf4BzbSc-wykq1_62CQwtszO+76rkudz_B=GkzE6ZheMUAusw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-06-24 17:57       ` Arnaldo Carvalho de Melo
     [not found]         ` <20200624175754.GD20203-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2020-06-24 18:40           ` Andrii Nakryiko
     [not found]             ` <CAEf4BzY8b71tE5B4rw5sfy=xajtgqUGHVaoHNf_YzVtQ9aLCBg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-06-24 18:57               ` Arnaldo Carvalho de Melo
     [not found]                 ` <20200624185737.GA25807-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2020-06-24 19:06                   ` Andrii Nakryiko
     [not found]                     ` <CAEf4Bza=ZT1yZvoJNMK72pYm6VGwGp22detc7kgC_24OBt4-FA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-06-24 19:11                       ` Arnaldo Carvalho de Melo
     [not found]                         ` <20200624191159.GB25807-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2020-06-24 19:25                           ` Andrii Nakryiko
2020-06-25  9:25       ` Lorenz Bauer
     [not found]         ` <CACAyw98ojwGjQm+Xk+_-B8Ah-hEt-Tgv_LQ1BdH4yBLYgVwpiA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-06-25 16:56           ` Andrii Nakryiko
     [not found]             ` <CAEf4BzYjge6fijFadwuuHf-vr2VUqneT5b0k-GgQSkLMTj=UAA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-06-30 15:52               ` Lorenz Bauer

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CACAyw9-cinpz=U+8tjV-GMWuth71jrOYLQ05Q7_c34TCeMJxMg@mail.gmail.com' \
    --to=lmb-ldpj742soetzrors9yw3xa@public.gmane.org \
    --cc=bpf-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
    --cc=dwarves-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
    --cc=kernel-team-lDpJ742SOEtZroRs9YW3xA@public.gmane.org \


* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Dwarves Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/dwarves/0 dwarves/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 dwarves dwarves/ https://lore.kernel.org/dwarves \
	public-inbox-index dwarves

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone https://public-inbox.org/public-inbox.git