linux-kernel - Re: [PATCH] kbuild: Try up to eight kallsyms link passes

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Message-ID: <20200922032903.GA222779@roeck-us.net>
Date:   Mon, 21 Sep 2020 20:29:03 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH] kbuild: Try up to eight kallsyms link passes

On Thu, Sep 10, 2020 at 08:32:04AM -0700, Guenter Roeck wrote:
> Since v5.8, powerpc:allmodconfig often fails to build with the following
> error message.
> 
> 	Inconsistent kallsyms data
> 	Try make KALLSYMS_EXTRA_PASS=1 as a workaround
> 
> Setting KALLSYMS_EXTRA_PASS=1 does not help. As it turns out, the build
> currently needs up to four link passes to succeed.
> 
> Similar problems have been observed over time for other architectures.
> 
> Make the number of link passes dynamic to solve the problem. Try up to
> eight passes before giving up. If KALLSYMS_EXTRA_PASS is set, add one
> additional pass after succeeding.
> 
> Suggested-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>

I still see a build failure for powerpc:allmodconfig due to this problem.

Feedback/comments/thoughts ? Does anyone have a better idea ?

Thanks,
Guenter

> ---
>  scripts/link-vmlinux.sh | 31 +++++++++++++++++++------------
>  1 file changed, 19 insertions(+), 12 deletions(-)
> 
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index e6e2d9e5ff48..72abdee0e649 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -316,11 +316,10 @@ if [ -n "${CONFIG_KALLSYMS}" ]; then
>  	#     From here, we generate a correct .tmp_kallsyms2.o
>  	# 3)  That link may have expanded the kernel image enough that
>  	#     more linker branch stubs / trampolines had to be added, which
> -	#     introduces new names, which further expands kallsyms. Do another
> -	#     pass if that is the case. In theory it's possible this results
> -	#     in even more stubs, but unlikely.
> -	#     KALLSYMS_EXTRA_PASS=1 may also used to debug or work around
> -	#     other bugs.
> +	#     introduces new names, which further expands kallsyms. Try up
> +	#     to eight passes to handle that situation before giving up.
> +	#     KALLSYMS_EXTRA_PASS=1 may be used to add an extra step
> +	#     for debugging or to work around other bugs.
>  	# 4)  The correct ${kallsymso} is linked into the final vmlinux.
>  	#
>  	# a)  Verify that the System.map from vmlinux matches the map from
> @@ -329,13 +328,21 @@ if [ -n "${CONFIG_KALLSYMS}" ]; then
>  	kallsyms_step 1
>  	kallsyms_step 2
>  
> -	# step 3
> -	size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso_prev})
> -	size2=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
> -
> -	if [ $size1 -ne $size2 ] || [ -n "${KALLSYMS_EXTRA_PASS}" ]; then
> -		kallsyms_step 3
> -	fi
> +	# step n
> +	step=3
> +	while [ $step -le 8 ]; do
> +		size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso_prev})
> +		size2=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
> +
> +		if [ $size1 -eq $size2 ]; then
> +			if [ -z "${KALLSYMS_EXTRA_PASS}" ]; then
> +				break
> +			fi
> +			KALLSYMS_EXTRA_PASS=""
> +		fi
> +		kallsyms_step $step
> +		step="$(expr $step + 1)"
> +	done
>  fi
>  
>  vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
> -- 
> 2.17.1
>