linux-kernel - Re: [PATCH v2] kbuild: add CONFIG_VMLINUX

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Date:   Fri, 5 Mar 2021 22:50:49 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Jonathan Corbet <corbet@....net>,
        Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH v2] kbuild: add CONFIG_VMLINUX_MAP expert option

On Fri, Mar 5, 2021 at 6:27 PM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
>
> It can be quite useful to have ld emit a link map file, in order to
> debug or verify that special sections end up where they are supposed
> to, and to see what LD_DEAD_CODE_DATA_ELIMINATION manages to get rid
> of.
>
> The only reason I'm not just adding this unconditionally is that the
> .map file can be rather large (several MB), and that's a waste of
> space when one isn't interested in these things. Also make it depend
> on CONFIG_EXPERT.
>
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> ---

Applied to linux-kbuild.
Thanks.




>  .gitignore              |  1 +
>  Documentation/dontdiff  |  1 +
>  lib/Kconfig.debug       | 10 ++++++++++
>  scripts/link-vmlinux.sh |  8 ++++++++
>  4 files changed, 20 insertions(+)
>
> diff --git a/.gitignore b/.gitignore
> index 3af66272d6f1..3adea59847ce 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -59,6 +59,7 @@ modules.order
>  /linux
>  /vmlinux
>  /vmlinux.32
> +/vmlinux.map
>  /vmlinux.symvers
>  /vmlinux-gdb.py
>  /vmlinuz
> diff --git a/Documentation/dontdiff b/Documentation/dontdiff
> index e361fc95ca29..ac42ad8d430d 100644
> --- a/Documentation/dontdiff
> +++ b/Documentation/dontdiff
> @@ -252,6 +252,7 @@ vmlinux-*
>  vmlinux.aout
>  vmlinux.bin.all
>  vmlinux.lds
> +vmlinux.map
>  vmlinux.symvers
>  vmlinuz
>  voffset.h
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5ea0c1773b0a..663c1cd5018c 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -412,6 +412,16 @@ config VMLINUX_VALIDATION
>         depends on STACK_VALIDATION && DEBUG_ENTRY && !PARAVIRT
>         default y
>
> +config VMLINUX_MAP
> +       bool "Generate vmlinux.map file when linking"
> +       depends on EXPERT
> +       help
> +         Selecting this option will pass "-Map=vmlinux.map" to ld
> +         when linking vmlinux. That file can be useful for verifying
> +         and debugging magic section games, and for seeing which
> +         pieces of code get eliminated with
> +         CONFIG_LD_DEAD_CODE_DATA_ELIMINATION.
> +
>  config DEBUG_FORCE_WEAK_PER_CPU
>         bool "Force weak per-cpu definitions"
>         depends on DEBUG_KERNEL
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 3b261b0f74f0..855fd4e6f03e 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -155,6 +155,7 @@ vmlinux_link()
>         local output=${1}
>         local objects
>         local strip_debug
> +       local map_option
>
>         info LD ${output}
>
> @@ -166,6 +167,10 @@ vmlinux_link()
>                 strip_debug=-Wl,--strip-debug
>         fi
>
> +       if [ -n "${CONFIG_VMLINUX_MAP}" ]; then
> +               map_option="-Map=${output}.map"
> +       fi
> +
>         if [ "${SRCARCH}" != "um" ]; then
>                 if [ -n "${CONFIG_LTO_CLANG}" ]; then
>                         # Use vmlinux.o instead of performing the slow LTO
> @@ -187,6 +192,7 @@ vmlinux_link()
>                 ${LD} ${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux}      \
>                         ${strip_debug#-Wl,}                     \
>                         -o ${output}                            \
> +                       ${map_option}                           \
>                         -T ${lds} ${objects}
>         else
>                 objects="-Wl,--whole-archive                    \
> @@ -200,6 +206,7 @@ vmlinux_link()
>                 ${CC} ${CFLAGS_vmlinux}                         \
>                         ${strip_debug}                          \
>                         -o ${output}                            \
> +                       ${map_option:+-Wl,${map_option}}        \
>                         -Wl,-T,${lds}                           \
>                         ${objects}                              \
>                         -lutil -lrt -lpthread
> @@ -303,6 +310,7 @@ cleanup()
>         rm -f .tmp_vmlinux*
>         rm -f System.map
>         rm -f vmlinux
> +       rm -f vmlinux.map
>         rm -f vmlinux.o
>  }
>
> --
> 2.29.2
>


--
Best Regards
Masahiro Yamada