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Automatically detecting compiler & linker used by kernel #298

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Automatically detecting compiler & linker used by kernel #298

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a4d904f
Automatically detecting CC & LD used by kernel
xuzhen Jan 24, 2023
111ae83
Fix test script for kernel compiled by clang
xuzhen Jan 24, 2023
0841cb0
Add clang test workflow
xuzhen Jan 25, 2023
7f44fd9
Fix printf errors caused by leading zeros
xuzhen Feb 6, 2023
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163 changes: 127 additions & 36 deletions dkms.in
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Original file line number Diff line number Diff line change
Expand Up @@ -593,23 +593,6 @@ read_conf()
[[ ! $make_command ]] && make_command="make -C $kernel_source_dir M=$dkms_tree/$module/$module_version/build"
[[ ! $clean ]] && clean="make -C $kernel_source_dir M=$dkms_tree/$module/$module_version/build clean"

# Check if clang was used to compile or lld was used to link the kernel.
if [[ -e $kernel_source_dir/vmlinux ]]; then
if readelf -p .comment $kernel_source_dir/vmlinux | grep -q clang; then
make_command="${make_command} CC=clang"
fi
if readelf -p .comment $kernel_source_dir/vmlinux | grep -q LLD; then
make_command="${make_command} LD=ld.lld"
fi
elif [[ -e "${kernel_config}" ]]; then
if grep -q CONFIG_CC_IS_CLANG=y "${kernel_config}"; then
make_command="${make_command} CC=clang"
fi
if grep -q CONFIG_LD_IS_LLD=y "${kernel_config}"; then
make_command="${make_command} LD=ld.lld"
fi
fi

# Set patch_array (including kernel specific patches)
count=0
for ((index=0; index < ${#PATCH[@]}; index++)); do
Expand Down Expand Up @@ -833,6 +816,90 @@ run_build_script() {
fi
}

# helper functions for getting cc/ld used by kernel
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Do you mind adding a bit more context here;
Create an array of candidates, first one having the complete version suffixed and strip numbers until we find a match.

detect_toolchain_version() {
# $1 = program name, e.g. gcc, ld.lld
# $2 = major version
# $3 = minor version
# $4 = patch version, optional
local -a filenames
if [[ "$4" ]]; then
filenames+=( "$1-$(printf "%d.%d.%d" "$2" "$3" "$4")" )
fi
filenames+=(
"$1-$(printf "%d.%d" "$2" "$3")"
"$1-$(printf "%d" "$2")"
"$1"
)
for f in "${filenames[@]}"; do
if command -V "$f" &>/dev/null; then
echo "$f"
return 0
fi
done
return 1
}
detect_toolchain_from_text() {
# $1 = program version text, contains x.y.z
# $2 = program name, e.g. gcc, clang
local patterns=(
's/^.*\b([0-9]+\.[0-9]+\.[0-9]+).*$/\1/p'
)
local -a ver
for p in "${patterns[@]}"; do
readarray -d '.' -t ver <<< "$(echo "$1" | sed -En "$p")"
if [[ "$ver" ]]; then
if detect_toolchain_version "$2" ${ver[0]} ${ver[1]} ${ver[2]}; then
return 0
fi
fi
done
return 1
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@evelikov evelikov Mar 12, 2023 •
edited
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Do we need to read the binary, if the KCONFIG is always available?

Edit: since we always add a KCONFIG in the tests, the codepath is not covered in CI. So let's drop this, if the existing code does not work then we can worry about it.

}
detect_toolchain_from_kconfig() {
# $1 = program name in kconfig, e.g. GCC, CLANG, LD, LLD
# $2 = program name, e.g. gcc, clang, ld.bfd, ld.lld
local ver_full="$(grep "^CONFIG_$1_VERSION=" "${kernel_config}" | cut -f2 -d= )"
if [[ -z "${ver_full}" ]] || [[ "${ver_full}" = 0 ]]; then
return 1
fi
local ver_major="${ver_full:0: -4}"
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Let's add a couple of examples for illustration purposes - one GCC and one CLANG. For example my system has CONFIG_GCC_VERSION=60300
Looking at the code below - seems like ver_patch is always set so one can drop the explicit check if [[ "$4" ]] in detect_toolchain_version, right?

local ver_minor="${ver_full: -4:2}"
local ver_patch="${ver_full: -2}"
detect_toolchain_version "$2" "${ver_major}" "${ver_minor}" "${ver_patch}"
return $?
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The trailing return $? should not be needed.

}
detect_toolchain_from_cc_version_text() {
# since kernel 5.8
local text="$(grep "^CONFIG_CC_VERSION_TEXT=" "${kernel_config}" | cut -f2 -d= )"
if [[ -z "$text" ]]; then
return 1
fi
if echo "$text" | grep -q gcc; then
detect_toolchain_from_text "$text" "gcc"
return $?
elif echo "$text" | grep -q clang; then
detect_toolchain_from_text "$text" "clang"
return $?
fi
return 1
}
detect_toolchain_from_vmlinux() {
# $1 = string in vmlinux .comment section, e.g. clang, LLD
# $2 = program name, e.g. clang, ld.lld
local vmlinux="${kernel_source_dir}/vmlinux"
if [[ ! -f "$vmlinux" ]]; then
return 1
fi
local text="$(readelf -p .comment "$vmlinux" 2>/dev/null | grep "$1" 2>/dev/null)"
if [[ -z "$text" ]]; then
return 1
fi
detect_toolchain_from_text "$text" "$2"
return $?
}


# Register a DKMS-ified source tree with DKMS.
# This function is smart enough to register the module if we
# passed a source tree or a tarball instead of relying on the source tree
Expand Down Expand Up @@ -1040,22 +1107,52 @@ prepare_build()
$"Check $build_dir for more information."
done

if [[ -e "${kernel_config}" ]]; then
if grep -q 'CONFIG_CC_IS_CLANG=y' "${kernel_config}"; then
local cc=clang
if command -v "$cc" >/dev/null; then
export CC="$cc"
export KERNEL_CC="$cc"
# Detect CC and LD used by kernel
if ! grep -qE '(^|\s)CC=' <<< "${make_command}"; then
# No CC specified within MAKE in dkms.conf
if [[ -e "${kernel_config}" ]]; then
if grep -q '^CONFIG_CC_IS_GCC=y' "${kernel_config}"; then
# Since kernel 4.18
KERNEL_CC="$(detect_toolchain_from_kconfig GCC gcc)"
elif grep -q '^CONFIG_CC_IS_CLANG=y' "${kernel_config}"; then
# Since kernel 4.18
KERNEL_CC="$(detect_toolchain_from_kconfig CLANG clang)"
elif [[ -f "$kernel_source_dir/.kernelvariables" ]]; then
# Debian specific
KERNEL_CC="$(echo -e "show-%:\n\t@echo \$(\$*)\ninclude $kernel_source_dir/.kernelvariables" | make -f - show-CC)"
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In my testing, detect_toolchain_from_kconfig works correctly and this kernelvariables workaround could be dropped. Not a big deal if you want to keep it, but in practise it's untested and never used.

else
KERNEL_CC="$(detect_toolchain_from_cc_version_text)"
fi
fi

if grep -q 'CONFIG_LD_IS_LLD=y' "${kernel_config}"; then
local ld=ld.lld
if command -v "$ld" >/dev/null; then
export LD="$ld"
export KERNEL_LD="$ld"
if [[ -z "$KERNEL_CC" ]]; then
KERNEL_CC="$(detect_toolchain_from_vmlinux GCC gcc || \
detect_toolchain_from_vmlinux clang clang)"
fi
if [[ "$KERNEL_CC" ]]; then
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@evelikov evelikov Mar 12, 2023 •
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Since KERNEL_CC and KERNEL_LD are local, so let's use local KERNEL_CC... in this function.

Both variables were exported with #294, although searching through the Debian patches/tooling does not indicate why. So I suspect keeping them local is fine.

Wires got shorted - zfs is the one needing the exports. Although it can/will use CC/LD, which we explicit export for that purpose.

make_command="${make_command} CC=${KERNEL_CC}"
# the pre_build script may need these, e.g. zfs-dkms
export CC="${KERNEL_CC}" KERNEL_CC
fi
fi
if ! grep -qE '(^|\s)LD=' <<< "${make_command}"; then
# No LD specified within MAKE in dkms.conf
if [[ -e "${kernel_config}" ]]; then
if grep -q '^CONFIG_LD_IS_LLD=y' "${kernel_config}"; then
# Since kernel 5.8
KERNEL_LD="$(detect_toolchain_from_kconfig LLD ld.lld)"
elif grep -q '^CONFIG_LD_IS_BFD=y' "${kernel_config}"; then
# Since kernel 5.14
KERNEL_LD="$(detect_toolchain_from_kconfig LD ld.bfd)"
fi
fi
if [[ -z "$KERNEL_LD" ]]; then
KERNEL_LD="$(detect_toolchain_from_vmlinux LLD ld.lld)"
fi
if [[ "$KERNEL_LD" ]]; then
make_command="${make_command} LD=${KERNEL_LD}"
# the pre_build script may need these, e.g. zfs-dkms
export LD="${KERNEL_LD}" KERNEL_LD
fi
fi

# Run the pre_build script
Expand All @@ -1073,12 +1170,6 @@ actual_build()
echo $""
echo $"Building module:"

if [ -f "$kernel_source_dir/.kernelvariables" ]; then
export CC=$(echo -e "show-%:\n\t@echo \$(\$*)\ninclude $kernel_source_dir/.kernelvariables" | make -f - show-CC)
else
unset CC
fi

invoke_command "$clean" "Cleaning build area" background
echo $"DKMS make.log for $module-$module_version for kernel $kernelver ($arch)" >> "$build_log"
date >> "$build_log"
Expand Down Expand Up @@ -2304,7 +2395,7 @@ PATH="$PATH:/usr/lib/dkms"
umask 022

# Unset environment variables that may interfere with the build
unset CC CXX CFLAGS CXXFLAGS LDFLAGS
unset CC CXX LD CFLAGS CXXFLAGS LDFLAGS KERNEL_CC KERNEL_LD
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AFAICT KERNEL_CC KERNEL_LD are only local, so I would drop them from here.


# Set important variables
current_kernel=$(uname -r)
Expand Down