linux-kernel - Re: [PATCH v3] scripts/link-vmlinux.sh: Add alias to duplicate symbols for kallsyms

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Date:   Mon, 11 Sep 2023 16:21:10 +0200
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     "Alessandro Carminati (Red Hat)" <alessandro.carminati@...il.com>
CC:     Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...nel.org>,
        "Josh Poimboeuf" <jpoimboe@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "Luis Chamberlain" <mcgrof@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Nick Alcock <nick.alcock@...cle.com>,
        Kris Van Hees <kris.van.hees@...cle.com>,
        Eugene Loh <eugene.loh@...cle.com>,
        "Francis Laniel" <flaniel@...ux.microsoft.com>,
        Viktor Malik <vmalik@...hat.com>,
        <linux-kbuild@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-trace-kernel@...r.kernel.org>,
        <live-patching@...r.kernel.org>
Subject: Re: [PATCH v3] scripts/link-vmlinux.sh: Add alias to duplicate
 symbols for kallsyms

From: Alessandro Carminati (Red Hat) <alessandro.carminati@...il.com>
Date: Mon, 28 Aug 2023 08:04:23 +0000

> From: Alessandro Carminati <alessandro.carminati@...il.com>
> 
> It is not uncommon for drivers or modules related to similar peripherals
> to have symbols with the exact same name.

[...]

> Changes from v2:
> - Alias tags are created by querying DWARF information from the vmlinux.
> - The filename + line number is normalized and appended to the original name.
> - The tag begins with '@' to indicate the symbol source.
> - Not a change, but worth mentioning, since the alias is added to the existing
>   list, the old duplicated name is preserved, and the livepatch way of dealing
>   with duplicates is maintained.
> - Acknowledging the existence of scenarios where inlined functions declared in
>   header files may result in multiple copies due to compiler behavior, though
>    it is not actionable as it does not pose an operational issue.
> - Highlighting a single exception where the same name refers to different
>   functions: the case of "compat_binfmt_elf.c," which directly includes
>   "binfmt_elf.c" producing identical function copies in two separate
>   modules.

Oh, I thought you managed to handle this in v3 since you didn't reply in
the previous thread...

> 
> sample from new v3
> 
>  ~ # cat /proc/kallsyms | grep gic_mask_irq
>  ffffd0b03c04dae4 t gic_mask_irq
>  ffffd0b03c04dae4 t gic_mask_irq@...ivers_irqchip_irq-gic_c_167
>  ffffd0b03c050960 t gic_mask_irq
>  ffffd0b03c050960 t gic_mask_irq@...ivers_irqchip_irq-gic-v3_c_404

BTW, why normalize them? Why not just

gic_mask_irq@...vers/irqchip/...

Aaaaand why line number? Line numbers break reproducible builds and also
would make it harder to refer to a particular symbol by its path and
name since we also have to pass its line number which may change once
you add a debug print there, for example.
OTOH there can't be 2 symbols with the same name within one file, so
just path + name would be enough. Or not?

(sorry if some of this was already discussed previously)

[...]

Thanks,
Olek