From: Sam Ravnborg <sam@ravnborg.org>
To: Paul Walmsley <paul.walmsley@sifive.com>
Cc: linux-kernel@vger.kernel.org,
Russell King <linux@armlinux.org.uk>,
Jim Wilson <jimw@sifive.com>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Michal Marek <michal.lkml@markovi.net>,
linux-kbuild@vger.kernel.org, Paul Walmsley <paul@pwsan.com>
Subject: Re: [PATCH v2 2/2] modpost: skip ELF local symbols by default during section mismatch check
Date: Fri, 16 Nov 2018 20:52:03 +0100 [thread overview]
Message-ID: <20181116195203.GB15240@ravnborg.org> (raw)
In-Reply-To: <20181115005602.30746-3-paul.walmsley@sifive.com>
On Wed, Nov 14, 2018 at 04:56:02PM -0800, Paul Walmsley wrote:
> During development of a serial console driver with a gcc 8.2.0
> toolchain for RISC-V, the following modpost warning appeared:
>
> ----
> WARNING: vmlinux.o(.data+0x19b10): Section mismatch in reference from the variable .LANCHOR1 to the function .init.text:sifive_serial_console_setup()
> The variable .LANCHOR1 references
> the function __init sifive_serial_console_setup()
> If the reference is valid then annotate the
> variable with __init* or __refdata (see linux/init.h) or name the variable:
> *_template, *_timer, *_sht, *_ops, *_probe, *_probe_one, *_console
> ----
>
> ".LANCHOR1" is an ELF local symbol, automatically created by gcc's section
> anchor generation code:
>
> https://gcc.gnu.org/onlinedocs/gccint/Anchored-Addresses.html
>
> https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/varasm.c;h=cd9591a45617464946dcf9a126dde277d9de9804;hb=9fb89fa845c1b2e0a18d85ada0b077c84508ab78#l7473
>
> This was verified by compiling the kernel with -fno-section-anchors.
> The serial driver code idiom triggering the warning is standard serial
> driver practice, and one that has a specific whitelist inclusion in
> modpost.c.
>
> I'm neither a modpost nor an ELF expert, but naively, it doesn't seem
> useful for modpost to report section mismatch warnings caused by ELF
> local symbols by default. Local symbols have compiler-generated
> names, and thus bypass modpost's whitelisting algorithm, which relies
> on the presence of a non-autogenerated symbol name. This increases
> the likelihood that false positive warnings will be generated (as in
> the above case).
>
> Thus, disable section mismatch reporting on ELF local symbols. The
> rationale here is similar to that of commit 2e3a10a1551d ("ARM: avoid
> ARM binutils leaking ELF local symbols") and of similar code already
> present in modpost.c:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/mod/modpost.c?h=v4.19-rc4&id=7876320f88802b22d4e2daf7eb027dd14175a0f8#n1256
>
> This second version of the patch drops the option to keep section
> mismatch warnings for local sections, based on feedback from Sam
> Ravnborg <sam@ravnborg.org>; and clarifies that these warnings
> appear with gcc 8.2.0.
>
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Jim Wilson <jimw@sifive.com>
> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
> Cc: Michal Marek <michal.lkml@markovi.net>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: linux-kbuild@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
> Signed-off-by: Paul Walmsley <paul@pwsan.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
next prev parent reply other threads:[~2018-11-16 19:52 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-15 0:56 [PATCH v2 0/2] modpost: skip section mismatch warnings on ELF local symbols by default Paul Walmsley
2018-11-15 0:56 ` [PATCH v2 1/2] modpost: drop unused command line switches Paul Walmsley
2018-11-16 19:51 ` Sam Ravnborg
2018-11-21 6:14 ` Masahiro Yamada
2018-11-15 0:56 ` [PATCH v2 2/2] modpost: skip ELF local symbols by default during section mismatch check Paul Walmsley
2018-11-16 19:52 ` Sam Ravnborg [this message]
2018-11-21 6:13 ` Masahiro Yamada
2018-11-21 17:52 ` Paul Walmsley
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:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20181116195203.GB15240@ravnborg.org \
--to=sam@ravnborg.org \
--cc=jimw@sifive.com \
--cc=linux-kbuild@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@armlinux.org.uk \
--cc=michal.lkml@markovi.net \
--cc=paul.walmsley@sifive.com \
--cc=paul@pwsan.com \
--cc=yamada.masahiro@socionext.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).