From 1518c633df78185f5cbd7322b52ef06358febac3 Mon Sep 17 00:00:00 2001 From: Quentin Perret Date: Fri, 28 Feb 2020 17:20:13 +0000 Subject: [PATCH] kbuild: allow symbol whitelisting with TRIM_UNUSED_KSYMS CONFIG_TRIM_UNUSED_KSYMS currently removes all unused exported symbols from ksymtab. This works really well when using in-tree drivers, but cannot be used in its current form if some of them are out-of-tree. Indeed, even if the list of symbols required by out-of-tree drivers is known at compile time, the only solution today to guarantee these don't get trimmed is to set CONFIG_TRIM_UNUSED_KSYMS=n. This not only wastes space, but also makes it difficult to control the ABI usable by vendor modules in distribution kernels such as Android. Being able to control the kernel ABI surface is particularly useful to ship a unique Generic Kernel Image (GKI) for all vendors, which is a first step in the direction of getting all vendors to contribute their code upstream. As such, attempt to improve the situation by enabling users to specify a symbol 'whitelist' at compile time. Any symbol specified in this whitelist will be kept exported when CONFIG_TRIM_UNUSED_KSYMS is set, even if it has no in-tree user. The whitelist is defined as a simple text file, listing symbols, one per line. Acked-by: Jessica Yu Acked-by: Nicolas Pitre Tested-by: Matthias Maennich Reviewed-by: Matthias Maennich Signed-off-by: Quentin Perret Signed-off-by: Masahiro Yamada --- init/Kconfig | 13 +++++++++++++ scripts/adjust_autoksyms.sh | 12 ++++++++++++ 2 files changed, 25 insertions(+) diff --git a/init/Kconfig b/init/Kconfig index 240c1ed15c69..9f2f10cfb097 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -2207,6 +2207,19 @@ config TRIM_UNUSED_KSYMS If unsure, or if you need to build out-of-tree modules, say N. +config UNUSED_KSYMS_WHITELIST + string "Whitelist of symbols to keep in ksymtab" + depends on TRIM_UNUSED_KSYMS + help + By default, all unused exported symbols will be un-exported from the + build when TRIM_UNUSED_KSYMS is selected. + + UNUSED_KSYMS_WHITELIST allows to whitelist symbols that must be kept + exported at all times, even in absence of in-tree users. The value to + set here is the path to a text file containing the list of symbols, + one per line. The path can be absolute, or relative to the kernel + source tree. + endif # MODULES config MODULES_TREE_LOOKUP diff --git a/scripts/adjust_autoksyms.sh b/scripts/adjust_autoksyms.sh index a904bf1f5e67..212ba45595d3 100755 --- a/scripts/adjust_autoksyms.sh +++ b/scripts/adjust_autoksyms.sh @@ -38,6 +38,17 @@ esac # We need access to CONFIG_ symbols . include/config/auto.conf +ksym_wl=/dev/null +if [ -n "$CONFIG_UNUSED_KSYMS_WHITELIST" ]; then + # Use 'eval' to expand the whitelist path and check if it is relative + eval ksym_wl="$CONFIG_UNUSED_KSYMS_WHITELIST" + [ "${ksym_wl}" != "${ksym_wl#/}" ] || ksym_wl="$abs_srctree/$ksym_wl" + if [ ! -f "$ksym_wl" ] || [ ! -r "$ksym_wl" ]; then + echo "ERROR: '$ksym_wl' whitelist file not found" >&2 + exit 1 + fi +fi + # Generate a new ksym list file with symbols needed by the current # set of modules. cat > "$new_ksyms_file" << EOT @@ -48,6 +59,7 @@ cat > "$new_ksyms_file" << EOT EOT sed 's/ko$/mod/' modules.order | xargs -n1 sed -n -e '2{s/ /\n/g;/^$/!p;}' -- | +cat - "$ksym_wl" | sort -u | sed -e 's/\(.*\)/#define __KSYM_\1 1/' >> "$new_ksyms_file"