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Fix building with clang and lld #13046

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Peter-Levine
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Explicitly pass CC and LD when building modules to prevent kbuild from defaulting to gcc and ld.bfd.

Motivation and Context

Fixes 10107

Description

When building sys-fs/zfs-kmod-9999 on Gentoo Linux, configure fails with:

configure: error: 
        *** Unable to build an empty module.

config.log shows:

configure:16388: clang -c -march=native -O2 -pipe -Werror -Wbool-compare  conftest.c >&5
error: unknown warning option '-Wbool-compare' [-Werror,-Wunknown-warning-option]

build/conftest/build.log shows:

make: Entering directory '/usr/src/linux-5.16.3-gentoo'
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: clang version 13.0.0
  You are using:           x86_64-pc-linux-gnu-gcc (Gentoo Hardened 11.2.1_p20220115 p4) 11.2.1 20220115
  CC [M]  /var/tmp/portage/sys-fs/zfs-kmod-9999/work/zfs-kmod-9999/build/conftest/conftest.o
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-Qunused-arguments’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-mretpoline-external-thunk’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-mno-global-merge’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-ftrivial-auto-var-init=zero’
make[1]: *** [scripts/Makefile.build:287: /var/tmp/portage/sys-fs/zfs-kmod-9999/work/zfs-kmod-9999/build/conftest/conftest.o] Error 1
make[1]: Target '__build' not remade because of errors.
make: *** [Makefile:1846: /var/tmp/portage/sys-fs/zfs-kmod-9999/work/zfs-kmod-9999/build/conftest] Error 2
make: Target 'modules' not remade because of errors.
make: Leaving directory '/usr/src/linux-5.16.3-gentoo'

The offending code is from config/kernel.m4:

dnl #
dnl # ZFS_LINUX_COMPILE
dnl #
dnl # $1 - build dir
dnl # $2 - test command
dnl # $3 - pass command
dnl # $4 - fail command
dnl # $5 - set KBUILD_MODPOST_NOFINAL='yes'
dnl # $6 - set KBUILD_MODPOST_WARN='yes'
dnl #
dnl # Used internally by ZFS_LINUX_TEST_{COMPILE,MODPOST}
dnl #
AC_DEFUN([ZFS_LINUX_COMPILE], [
	AC_TRY_COMMAND([
	    KBUILD_MODPOST_NOFINAL="$5" KBUILD_MODPOST_WARN="$6"
	    make modules -k -j$TEST_JOBS -C $LINUX_OBJ $ARCH_UM
	    M=$PWD/$1 >$1/build.log 2>&1])
	AS_IF([AC_TRY_COMMAND([$2])], [$3], [$4])
])

kbuild doesn't parse CC, LD, et al., from the environment but expects the to be explicitly passed to make.

Similarly, the build fails to compile, with

x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-Qunused-arguments’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-Qunused-arguments’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-Qunused-arguments’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-mretpoline-external-thunk’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-mretpoline-external-thunk’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-mretpoline-external-thunk’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-mno-global-merge’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-mno-global-merge’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-mno-global-merge’
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-ftrivial-auto-var-init=zero’
make[5]: *** [scripts/Makefile.build:287: /var/tmp/portage/sys-fs/zfs-kmod-9999/work/zfs-kmod-9999/module/avl/avl.o] Error 1
make[4]: *** [scripts/Makefile.build:549: /var/tmp/portage/sys-fs/zfs-kmod-9999/work/zfs-kmod-9999/module/avl] Error 2
make[4]: *** Waiting for unfinished jobs....
x86_64-pc-linux-gnu-gcc: error: unrecognized command-line option ‘-ftrivial-auto-var-init=zero’
make[5]: *** [scripts/Makefile.build:287: /var/tmp/portage/sys-fs/zfs-kmod-9999/work/zfs-kmod-9999/module/spl/../os/linux/spl/spl-atomic.o] Error 1
make[4]: *** [scripts/Makefile.build:549: /var/tmp/portage/sys-fs/zfs-kmod-9999/work/zfs-kmod-9999/module/spl] Error 2

The offending code is from module/Makefile.in:

modules-Linux:
	list='$(SUBDIR_TARGETS)'; for td in $$list; do $(MAKE) -C $$td; done
	$(MAKE) -C @LINUX_OBJ@ M="$$PWD" @KERNEL_MAKE@ CONFIG_ZFS=m modules

Again, this is resolved by explicitly passing CC and LD.

How Has This Been Tested?

Tested using /etc/portage/patches/sys-fs/zfs-kmod-9999/zfs-kmod-9999-clang.patch:

--- a/config/kernel.m4
+++ b/config/kernel.m4
@@ -604,7 +604,7 @@
 	AC_TRY_COMMAND([
 	    KBUILD_MODPOST_NOFINAL="$5" KBUILD_MODPOST_WARN="$6"
 	    make modules -k -j$TEST_JOBS -C $LINUX_OBJ $ARCH_UM
-	    M=$PWD/$1 >$1/build.log 2>&1])
+	    CC="$CC" LD="$LD" M=$PWD/$1 >$1/build.log 2>&1])
 	AS_IF([AC_TRY_COMMAND([$2])], [$3], [$4])
 ])

and /etc/portage/patches/sys-fs/zfs-kmod-9999/zfs-kmod-9999-clang2.patch:

--- zfs-kmod-9999/module/Makefile.in.old	2022-01-30 01:51:53.977190277 -0500
+++ zfs-kmod-9999/module/Makefile.in	2022-01-30 02:19:35.827239919 -0500
@@ -52,7 +52,7 @@
 
 modules-Linux:
 	list='$(SUBDIR_TARGETS)'; for td in $$list; do $(MAKE) -C $$td; done
-	$(MAKE) -C @LINUX_OBJ@ M="$$PWD" @KERNEL_MAKE@ CONFIG_ZFS=m modules
+	$(MAKE) -C @LINUX_OBJ@ CC="$(CC)" LD="$(LD)" M="$$PWD" @KERNEL_MAKE@ CONFIG_ZFS=m modules
 
 modules-FreeBSD:
 	+$(FMAKE)

then ebuild /var/db/repos/local/sys-fs/zfs-kmod/zfs-kmod-9999.ebuild merge

Types of changes

  • Bug fix (non-breaking change which fixes an issue)
  • New feature (non-breaking change which adds functionality)
  • Performance enhancement (non-breaking change which improves efficiency)
  • Code cleanup (non-breaking change which makes code smaller or more readable)
  • Breaking change (fix or feature that would cause existing functionality to change)
  • Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
  • Documentation (a change to man pages or other documentation)

Checklist:

szubersk
szubersk suggested changes Jan 31, 2022
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@behlendorf behlendorf added the Status: Code Review Needed Ready for review and testing label Feb 2, 2022
szubersk
szubersk suggested changes Feb 3, 2022
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szubersk commented Feb 3, 2022

Good change overall! This patch will help experimenting with clang builds on Linux.

Peter-Levine
Peter-Levine commented Feb 4, 2022
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OK. Works on my end with both gcc/ld.bfd and clang/ld.lld when building against a kernel built with the same toolchain.

szubersk
szubersk reviewed Feb 4, 2022
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@behlendorf behlendorf added Status: Accepted Ready to integrate (reviewed, tested) and removed Status: Code Review Needed Ready for review and testing labels Feb 4, 2022
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szubersk commented Feb 7, 2022 •
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@Peter-Levine I just tried out this patch with 5.15.21 LLVM=1 built kernel. What bothers me is that while make works fine, make pkg-kmod doesn't. KERNEL_* variables are not injected into rpmbuild and GCC is still enforced there: the build fails.
It's still worth it to include this PR in master branch as it unblocks people down the stream. Clang-compiled modules cannot be used for ZTS yet, though.

@behlendorf
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@Peter-Levine would you also mind rebasing this PR on the latest version of the master branch, then force updating the PR. This should get us a cleaner CI run to make sure all is well before merging it.

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szubersk commented Feb 8, 2022 •
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@Peter-Levine Please consider incorporating szubersk@d21dba8 into this PR. I just tested that commit and compilation passes for clang-built 5.15.21 kernel.

@Peter-Levine
Add support for $KERNEL_{CC,LD,LLVM} variables
842c932 
Currently, $(CC), $(LD), and $(LLVM) variables aren't passed to kbuild
while building modules.  This causes modules to build with the default
GNU GCC toolchain and prevents experimenting with other toolchains such
as CLANG/LLVM.  It can also lead to build failure if the CFLAGS/LDFLAGS
passed are incompatible with gcc/ld.

Pass $KERNEL_CC, $KERNEL_LD, and $KERNEL_LLVM as $(CC), $(LD), and
$(LLVM), respectively, to kbuild for each that is defined in the
environment.  This should take care of the majority of alternative
toolchain use cases.

Signed-off-by: Peter Levine <plevine457@gmail.com>
@Peter-Levine
propagate KERNEL_* to *.spec
450e1dd 
Authored by: Damian Szuberski <szuberskidamian@gmail.com>
Signed-off-by: Peter Levine <plevine457@gmail.com>
@Peter-Levine
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@szubersk PR is incorporated.
@behlendorf Rebased and pushed.

@behlendorf behlendorf closed this in b66140c Feb 9, 2022
behlendorf pushed a commit that referenced this pull request Feb 9, 2022
@szubersk @behlendorf
Propagate KERNEL_* to *.spec
4eea717 
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Authored-by: Damian Szuberski <szuberskidamian@gmail.com>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes #13046
@szubersk
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szubersk commented Feb 13, 2022 •
edited
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Fix #10107
Fix #10267

tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Feb 15, 2022
@Peter-Levine @tonyhutter
Add support for $KERNEL_{CC,LD,LLVM} variables
7e2877d 
Currently, $(CC), $(LD), and $(LLVM) variables aren't passed to kbuild
while building modules.  This causes modules to build with the default
GNU GCC toolchain and prevents experimenting with other toolchains such
as CLANG/LLVM.  It can also lead to build failure if the CFLAGS/LDFLAGS
passed are incompatible with gcc/ld.

Pass $KERNEL_CC, $KERNEL_LD, and $KERNEL_LLVM as $(CC), $(LD), and
$(LLVM), respectively, to kbuild for each that is defined in the
environment.  This should take care of the majority of alternative
toolchain use cases.

Reviewed-by: Damian Szuberski <szuberskidamian@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes openzfs#13046
tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Feb 15, 2022
@szubersk @tonyhutter
Propagate KERNEL_* to *.spec
10ec129 
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Authored-by: Damian Szuberski <szuberskidamian@gmail.com>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes openzfs#13046
tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Feb 16, 2022
@Peter-Levine @tonyhutter
Add support for $KERNEL_{CC,LD,LLVM} variables
f62ce3e 
Currently, $(CC), $(LD), and $(LLVM) variables aren't passed to kbuild
while building modules.  This causes modules to build with the default
GNU GCC toolchain and prevents experimenting with other toolchains such
as CLANG/LLVM.  It can also lead to build failure if the CFLAGS/LDFLAGS
passed are incompatible with gcc/ld.

Pass $KERNEL_CC, $KERNEL_LD, and $KERNEL_LLVM as $(CC), $(LD), and
$(LLVM), respectively, to kbuild for each that is defined in the
environment.  This should take care of the majority of alternative
toolchain use cases.

Reviewed-by: Damian Szuberski <szuberskidamian@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes openzfs#13046
tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Feb 16, 2022
@szubersk @tonyhutter
Propagate KERNEL_* to *.spec
7adb87f 
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Authored-by: Damian Szuberski <szuberskidamian@gmail.com>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes openzfs#13046
tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Feb 17, 2022
@Peter-Levine @tonyhutter
Add support for $KERNEL_{CC,LD,LLVM} variables
c7fcf00 
Currently, $(CC), $(LD), and $(LLVM) variables aren't passed to kbuild
while building modules.  This causes modules to build with the default
GNU GCC toolchain and prevents experimenting with other toolchains such
as CLANG/LLVM.  It can also lead to build failure if the CFLAGS/LDFLAGS
passed are incompatible with gcc/ld.

Pass $KERNEL_CC, $KERNEL_LD, and $KERNEL_LLVM as $(CC), $(LD), and
$(LLVM), respectively, to kbuild for each that is defined in the
environment.  This should take care of the majority of alternative
toolchain use cases.

Reviewed-by: Damian Szuberski <szuberskidamian@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes openzfs#13046
tonyhutter pushed a commit to tonyhutter/zfs that referenced this pull request Feb 17, 2022
@szubersk @tonyhutter
Propagate KERNEL_* to *.spec
2681f8a 
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Authored-by: Damian Szuberski <szuberskidamian@gmail.com>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes openzfs#13046
gentoo-bot pushed a commit to gentoo/gentoo that referenced this pull request Mar 11, 2022
@thesamesam
sys-fs/zfs-kmod: add Clang logic
7b55c82 
The needed patch made its way upstream but we need
a small amount of logic in the ebuild to accommodate
it fully.

Bug: openzfs/zfs#13046
Closes: https://bugs.gentoo.org/814194
Thanks-to: Peter Levine <plevine457@gmail.com>
Signed-off-by: Sam James <sam@gentoo.org>
nicman23 pushed a commit to nicman23/zfs that referenced this pull request Aug 22, 2022
@Peter-Levine @nicman23
Add support for $KERNEL_{CC,LD,LLVM} variables
cdb858e 
Currently, $(CC), $(LD), and $(LLVM) variables aren't passed to kbuild
while building modules.  This causes modules to build with the default
GNU GCC toolchain and prevents experimenting with other toolchains such
as CLANG/LLVM.  It can also lead to build failure if the CFLAGS/LDFLAGS
passed are incompatible with gcc/ld.

Pass $KERNEL_CC, $KERNEL_LD, and $KERNEL_LLVM as $(CC), $(LD), and
$(LLVM), respectively, to kbuild for each that is defined in the
environment.  This should take care of the majority of alternative
toolchain use cases.

Reviewed-by: Damian Szuberski <szuberskidamian@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes openzfs#13046
nicman23 pushed a commit to nicman23/zfs that referenced this pull request Aug 22, 2022
@szubersk @nicman23
Propagate KERNEL_* to *.spec
3ef0097 
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Authored-by: Damian Szuberski <szuberskidamian@gmail.com>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes openzfs#13046
nicman23 pushed a commit to nicman23/zfs that referenced this pull request Aug 22, 2022
@Peter-Levine @nicman23
Add support for $KERNEL_{CC,LD,LLVM} variables
9cbc5a8 
Currently, $(CC), $(LD), and $(LLVM) variables aren't passed to kbuild
while building modules.  This causes modules to build with the default
GNU GCC toolchain and prevents experimenting with other toolchains such
as CLANG/LLVM.  It can also lead to build failure if the CFLAGS/LDFLAGS
passed are incompatible with gcc/ld.

Pass $KERNEL_CC, $KERNEL_LD, and $KERNEL_LLVM as $(CC), $(LD), and
$(LLVM), respectively, to kbuild for each that is defined in the
environment.  This should take care of the majority of alternative
toolchain use cases.

Reviewed-by: Damian Szuberski <szuberskidamian@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes openzfs#13046
nicman23 pushed a commit to nicman23/zfs that referenced this pull request Aug 22, 2022
@szubersk @nicman23
Propagate KERNEL_* to *.spec
2d58776 
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Authored-by: Damian Szuberski <szuberskidamian@gmail.com>
Signed-off-by: Peter Levine <plevine457@gmail.com>
Closes openzfs#13046
gentoo-repo-qa-bot pushed a commit to gentoo-mirror/linux-be that referenced this pull request Jul 2, 2023
@thesamesam
sys-fs/zfs-kmod: add Clang logic
bab69b6 
The needed patch made its way upstream but we need
a small amount of logic in the ebuild to accommodate
it fully.

Bug: openzfs/zfs#13046
Closes: https://bugs.gentoo.org/814194
Thanks-to: Peter Levine <plevine457@gmail.com>
Signed-off-by: Sam James <sam@gentoo.org>
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@behlendorf behlendorf behlendorf approved these changes

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