linux-kernel - Re: [PATCH] depmod: create and use System.map.no

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Date:   Fri, 4 Oct 2019 11:25:33 -0700
From:   Lucas De Marchi <lucas.de.marchi@...il.com>
To:     Matthias Maennich <maennich@...gle.com>
Cc:     lkml <linux-kernel@...r.kernel.org>, kernel-team@...roid.com,
        Stefan Wahren <stefan.wahren@...e.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Jessica Yu <jeyu@...nel.org>,
        Martijn Coenen <maco@...roid.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-modules <linux-modules@...r.kernel.org>
Subject: Re: [PATCH] depmod: create and use System.map.no_namespaces

On Fri, Oct 4, 2019 at 2:57 AM Matthias Maennich <maennich@...gle.com> wrote:
>
> depmod in its current version is not aware of symbol namespace in
> ksymtab entries introduced with 8651ec01daed ("module: add support for
> symbol namespaces."). They have the form
>
>   __ksymtab_NAMESPACE.symbol_name
>
> A fix for kmod's depmod has been proposed [1]. In order to support older
> versions of depmod as well, create a System.map.no_namespaces during
> scripts/depmod.sh that has the pre-namespaces format. That way users do
> not immediately upgrade the userspace tool.
>
> [1] https://lore.kernel.org/linux-modules/20191004094136.166621-1-maennich@google.com/
>
> Reported-by: Stefan Wahren <stefan.wahren@...e.com>
> Fixes: 8651ec01daed ("module: add support for symbol namespaces.")
> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Cc: Lucas De Marchi <lucas.de.marchi@...il.com>
> Cc: Jessica Yu <jeyu@...nel.org>
> Cc: Martijn Coenen <maco@...roid.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: linux-modules@...r.kernel.org
> Signed-off-by: Matthias Maennich <maennich@...gle.com>
> ---
>
> Please note this depends on the new ksymtab entry format proposed in
> https://lore.kernel.org/lkml/20191003075826.7478-2-yamada.masahiro@socionext.com/

I don't really agree with that thought, more below.

>
> That is likely to be merged soon as well as it fixes problems in 5.4-rc*, hence
> this patch depends on it.
>
> Cheers,
> Matthias
>
>  .gitignore        | 1 +
>  scripts/depmod.sh | 8 +++++++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/.gitignore b/.gitignore
> index 70580bdd352c..5ed58a7cb433 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -59,6 +59,7 @@ modules.order
>  /vmlinux-gdb.py
>  /vmlinuz
>  /System.map
> +/System.map.no_namespaces
>  /Module.markers
>  /modules.builtin.modinfo
>
> diff --git a/scripts/depmod.sh b/scripts/depmod.sh
> index e083bcae343f..602e1af072c7 100755
> --- a/scripts/depmod.sh
> +++ b/scripts/depmod.sh
> @@ -39,7 +39,13 @@ if $depmod_hack_needed; then
>         KERNELRELEASE=99.98.$KERNELRELEASE
>  fi
>
> -set -- -ae -F System.map
> +# Older versions of depmod do not support symbol namespaces in ksymtab entries,
> +# hence create an alternative System.map with namespace patched out to use for
> +# depmod. I.e. transform entries as follows:
> +#    __ksymtab_NAMESPACE.symbol_name -> __ksymtab_symbol_name
> +sed 's/__ksymtab_.*\./__ksymtab_/' System.map > System.map.no_namespaces

So people with old kmod will have to know they need to pass
System.map.no_namespaces rather than the usual
System.map. Also, distros will need to be update to also copy the new
file to the kernel package (or upgrade/patch kmod).

I'd rather maintain the current format and fix the bug that patch is
fixing. The namespace
in the end IMO is just a small annoyance with a reason to  exist.

Lucas De Marchi

> +
> +set -- -ae -F System.map.no_namespaces
>  if test -n "$INSTALL_MOD_PATH"; then
>         set -- "$@" -b "$INSTALL_MOD_PATH"
>  fi
> --
> 2.23.0.581.g78d2f28ef7-goog
>


-- 
Lucas De Marchi