Use Fat LTO with Clang
Currently, when the clang toolchain is used, we use the brp-llvm-compile-lto-to-elf script to post-process any shipped object files or static libraries to convert the LLVM bitcode they contain into ELF object code. With LLVM 18, Clang has introduced support for fat LTO objects (https://llvm.org/docs/FatLTO.html), which work essentially the same way as with GCC: If `-ffat-lto-objects` is passed, then the objects will contain both the ELF code, as well as the LLVM bitcode in a special section. This redhat-rpm-config change enables the use of fat LTO and drops the brp-llvm-compile-lto-to-elf script. Instead, the brp-strip-lto script used by GCC also strips the LLVM section name now. Resolves: RHEL-87637
This commit is contained in:
Nikita Popov
Tom Stellard
parent
9c66b68329
commit
308a854b33
@ -1,54 +0,0 @@
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#!/usr/bin/bash -eu
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if [ -z "$RPM_BUILD_ROOT" ] || [ "$RPM_BUILD_ROOT" = "/" ]; then
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exit 0
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fi
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CLANG_FLAGS=$@
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NCPUS=${RPM_BUILD_NCPUS:-1}
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check_convert_bitcode () {
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local file_name=$(realpath ${1})
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local file_type=$(file ${file_name})
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shift
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CLANG_FLAGS="$@"
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if [[ "${file_type}" == *"LLVM IR bitcode"* ]]; then
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# Check the output of llvm-strings for the command line, which is in the LLVM bitcode because
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# we pass -frecord-gcc-switches.
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# Check for a line that has "-flto" after (or without) "-fno-lto".
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llvm-strings ${file_name} | while read line ; do
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flto=$(echo $line | grep -o -b -e -flto | tail -n 1 | cut -d : -f 1)
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fnolto=$(echo $line | grep -o -b -e -fno-lto | tail -n 1 | cut -d : -f 1)
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if test -n "$flto" && { test -z "$fnolto" || test "$flto" -gt "$fnolto"; } ; then
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echo "Compiling LLVM bitcode file ${file_name}."
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clang ${CLANG_FLAGS} -fno-lto -Wno-unused-command-line-argument \
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-x ir ${file_name} -c -o ${file_name}
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break
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fi
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done
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elif [[ "${file_type}" == *"current ar archive"* ]]; then
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echo "Unpacking ar archive ${file_name} to check for LLVM bitcode components."
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# create archive stage for objects
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local archive_stage=$(mktemp -d)
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local archive=${file_name}
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pushd ${archive_stage}
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ar x ${archive}
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for archived_file in $(find -not -type d); do
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check_convert_bitcode ${archived_file} ${CLANG_FLAGS}
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echo "Repacking ${archived_file} into ${archive}."
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ar r ${archive} ${archived_file}
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done
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popd
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fi
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}
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echo "Checking for LLVM bitcode artifacts"
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export -f check_convert_bitcode
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# Deduplicate by device:inode to avoid processing hardlinks in parallel.
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find "$RPM_BUILD_ROOT" -type f -name "*.[ao]" -printf "%D:%i %p\n" | \
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awk '!seen[$1]++' | cut -d" " -f2- | \
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xargs -d"\n" -r -n1 -P$NCPUS sh -c "check_convert_bitcode \$@ $CLANG_FLAGS" ARG0
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@ -14,4 +14,5 @@ esac
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# Strip ELF binaries
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find "$RPM_BUILD_ROOT" -type f -name '*.[ao]' \! -regex "$RPM_BUILD_ROOT/*usr/lib/debug.*" -print0 | \
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eu-elfclassify --not-program --not-library --not-linux-kernel-module --stdin0 --print0 | xargs -0 -r -P$NCPUS -n32 sh -c "$STRIP -p -R .gnu.lto_* -R .gnu.debuglto_* -N __gnu_lto_v1 \"\$@\"" ARG0
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eu-elfclassify --not-program --not-library --not-linux-kernel-module --stdin0 --print0 | \
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xargs -0 -r -P$NCPUS -n32 sh -c "$STRIP -p -R .gnu.lto_* -R .gnu.debuglto_* -R .llvm.lto -N __gnu_lto_v1 \"\$@\"" ARG0
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4
macros
4
macros
@ -233,7 +233,6 @@ print(result)
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# __brp_mangle_shebangs_exclude_from_file - file from which to get files to ignore
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%__brp_mangle_shebangs /usr/lib/rpm/redhat/brp-mangle-shebangs %{?__brp_mangle_shebangs_exclude:--shebangs "%{?__brp_mangle_shebangs_exclude}"} %{?__brp_mangle_shebangs_exclude_file:--shebangs-from "%{__brp_mangle_shebangs_exclude_file}"} %{?__brp_mangle_shebangs_exclude_from:--files "%{?__brp_mangle_shebangs_exclude_from}"} %{?__brp_mangle_shebangs_exclude_from_file:--files-from "%{__brp_mangle_shebangs_exclude_from_file}"}
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%__brp_llvm_compile_lto_elf /usr/lib/rpm/redhat/brp-llvm-compile-lto-elf %{build_cflags} %{build_ldflags}
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%__os_install_post \
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%{?__brp_ldconfig} \
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@ -251,7 +250,6 @@ print(result)
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%{nil}
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%__spec_install_post\
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%[ "%{toolchain}" == "clang" ? "%{?__brp_llvm_compile_lto_elf}" : "%{nil}" ] \
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%{?__debug_package:%{__debug_install_post}}\
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%{__arch_install_post}\
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%{__os_install_post}\
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@ -328,7 +326,7 @@ print(result)
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# way we can detect installing an unusable .o/.a file. This is on the TODO
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# list for F34.
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%_gcc_lto_cflags -flto=auto -ffat-lto-objects
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%_clang_lto_cflags -flto=thin
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%_clang_lto_cflags -flto=thin -ffat-lto-objects
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%_lto_cflags %{expand:%%{_%{toolchain}_lto_cflags}}
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%_general_options -O2 %{?_lto_cflags} -fexceptions -g -grecord-gcc-switches -pipe
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@ -6,7 +6,7 @@
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Summary: Red Hat specific rpm configuration files
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Name: redhat-rpm-config
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Version: 209
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Version: 210
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Release: 1%{?dist}
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# No version specified.
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License: GPL+
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@ -60,9 +60,6 @@ Source202: brp-python-bytecompile
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# https://github.com/fedora-python/marshalparser
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Source203: brp-fix-pyc-reproducibility
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# for converting llvm LTO bitcode objects into ELF
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Source204: brp-llvm-compile-lto-elf
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# Dependency generator scripts (deprecated)
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Source300: find-provides
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Source304: find-requires
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@ -128,10 +125,6 @@ Requires: %{_bindir}/grep
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Requires: %{_bindir}/sed
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Requires: %{_bindir}/xargs
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# for brp-llvm-compile-lto-elf
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Requires: (llvm if clang)
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Requires: (gawk if clang)
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# -fstack-clash-protection and -fcf-protection require GCC 8.
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Conflicts: gcc < 8.0.1-0.22
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@ -255,6 +248,9 @@ install -p -m 644 -t %{buildroot}%{_rpmluadir}/fedora/srpm forge.lua
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%doc buildflags.md
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%changelog
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* Mon Jun 02 2025 Nikita Popov <npopov@redhat.com> - 210-1
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- Use Fat LTO with Clang
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* Wed Dec 11 2024 Mikolaj Izdebski <mizdebsk@redhat.com> - 209-1
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- Add java_arches macro
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