On 04/05/2022 17:11, Alexey Kardashevskiy wrote:
On 5/4/22 07:21, Nick Desaulniers wrote:On Thu, Apr 28, 2022 at 11:46 PM Alexey Kardashevskiy <a...@ozlabs.ru> wrote:This enables LTO_CLANG builds on POWER with the upstream version of LLVM. LTO optimizes the output vmlinux binary and this may affect the FTP alternative section if alt branches use "bc" (Branch Conditional) which is limited by 16 bit offsets. This shows up in errors like:ld.lld: error: InputSection too large for range extension thunk vmlinux.o:(__ftr_alt_97+0xF0)This works around the issue by replacing "bc" in FTR_SECTION_ELSE with "b" which allows 26 bit offsets. This catches the problem instructions in vmlinux.o before it LTO'ed: $ objdump -d -M raw -j __ftr_alt_97 vmlinux.o | egrep '\S+\s*\<bc\>' 30: 00 00 82 40 bc 4,eq,30 <__ftr_alt_97+0x30> f0: 00 00 82 40 bc 4,eq,f0 <__ftr_alt_97+0xf0> This allows LTO builds for ppc64le_defconfig plus LTO options. Note that DYNAMIC_FTRACE/FUNCTION_TRACER is not supported by LTO builds but this is not POWERPC-specific.$ ARCH=powerpc make LLVM=1 -j72 ppc64le_defconfig $ ARCH=powerpc make LLVM=1 -j72 menuconfig <disable FTRACE, enable LTO_CLANG_THIN> $ ARCH=powerpc make LLVM=1 -j72 ... VDSO64L arch/powerpc/kernel/vdso/vdso64.so.dbg /usr/bin/powerpc64le-linux-gnu-ld: /android0/llvm-project/llvm/build/bin/../lib/LLVMgold.so: error loading plugin: /android0/llvm-project/llvm/build/bin/../lib/LLVMgold.so: cannot open shared object file: No such file or directory clang-15: error: linker command failed with exit code 1 (use -v to see invocation) make[1]: *** [arch/powerpc/kernel/vdso/Makefile:67: arch/powerpc/kernel/vdso/vdso64.so.dbg] Error 1 Looks like LLD isn't being invoked correctly to link the vdso. Probably need to revisit https://lore.kernel.org/lkml/20200901222523.1941988-1-ndesaulni...@google.com/ How were you working around this issue? Perhaps you built clang to default to LLD? (there's a cmake option for that)I was not. Just did clean build like this: mkdir ~/pbuild/llvm/llvm-lto-latest-cleanbuild cd ~/pbuild/llvm/llvm-lto-latest-cleanbuildCC='clang' CXX='clang++' cmake -G Ninja -DLLVM_ENABLE_PROJECTS="clang;lld" -DLLVM_TARGETS_TO_BUILD=PowerPC ~/p/llvm/llvm-latest/llvm/ -DLLVM_ENABLE_LTO=ON -DLLVM_ENABLE_LLD=ON -DLLVM_BINUTILS_INCDIR=/usr/include -DCMAKE_BUILD_TYPE=Releaseninja -j 50 It builds fine:[fstn1-p1 ~/p/kernels-llvm/llvm]$ find /home/aik/pbuild/llvm/llvm-lto-latest-cleanbuild/ -iname LLVMgold.so -exec ls -l {} \; -rwxrwxr-x 1 aik aik 39032840 May 4 13:06 /home/aik/pbuild/llvm/llvm-lto-latest-cleanbuild/lib/LLVMgold.soand then in the kernel tree:PATH=/home/aik/pbuild/llvm/llvm-lto-latest-cleanbuild/bin:$PATH make -j64 O=/home/aik/pbuild/kernels-llvm/llvm-wip-llvm-latest-lto-full-cleanbuild/ ARCH=powerpc LLVM_IAS=1 CC=clang LLVM=1 ppc64le_defconfigthen enabled LTO in that .config and then just built "vmlinux":[fstn1-p1 ~/p/kernels-llvm/llvm]$ ls -l /home/aik/pbuild/kernels-llvm/llvm-wip-llvm-latest-lto-full-cleanbuild/vmlinux -rwxrwxr-x 1 aik aik 48145272 May 4 17:00 /home/aik/pbuild/kernels-llvm/llvm-wip-llvm-latest-lto-full-cleanbuild/vmlinuxwhich boots under qemu, the kernel version is:Preparing to boot Linux version 5.18.0-rc2_0bb153baeff0_a+fstn1 (aik@fstn1-p1) (clang version 15.0.0 (https://github.com/llvm/llvm-proje ct.git e29dc0c6fde284e7f05aa5f45b05c629c9fad295), LLD 15.0.0) #1 SMP Wed May 4 16:54:16 AEST 2022Before I got to this point, I did many unspeakable things to that build system so may be it is screwed in some way but I cannot pinpoint it.The installed clang/lld is 12.0.0-3ubuntu1~21.04.2 and -DLLVM_ENABLE_LLD=ON from cmake is to accelerate rebuilding of LLVM (for bisecting). I'll try without it now, just takes ages to complete.
And I just did. clang built with gcc simply crashes while building kernel's scripts/basic/fixdep :-D
I may have to file a bug against clang now :-/
Perhaps for now I should just send: ``` diff --git a/arch/powerpc/kernel/vdso/Makefile b/arch/powerpc/kernel/vdso/Makefile index 954974287ee7..8762e6513683 100644 --- a/arch/powerpc/kernel/vdso/Makefile +++ b/arch/powerpc/kernel/vdso/Makefile @@ -55,6 +55,11 @@ AS32FLAGS := -D__VDSO32__ -s CC64FLAGS := -Wl,-soname=linux-vdso64.so.1 AS64FLAGS := -D__VDSO64__ -s +ifneq ($(LLVM),) +CC32FLAGS += -fuse-ld=lld +CC64FLAGS += -fuse-ld=lld +endif + targets += vdso32.lds CPPFLAGS_vdso32.lds += -P -C -Upowerpc targets += vdso64.lds ```Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> --- Note 1: This is further development of https://lore.kernel.org/all/20220211023125.1790960-1-...@ozlabs.ru/T/ Note 2: CONFIG_ZSTD_COMPRESS and CONFIG_ZSTD_DECOMPRESS must be both "m" or "y" or it won't link. For details: https://lore.kernel.org/lkml/20220428043850.1706973-1-...@ozlabs.ru/T/Yeah, I just hit this: ``` LTO vmlinux.o LLVM ERROR: Function Import: link error: linking module flags 'Code Model': IDs have conflicting values in 'lib/built-in.a(entropy_common.o at 5782)' and 'lib/built-in.a(zstd_decompress_block.o at 6202)' PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace. LLVM ERROR: Failed to rename temporary file .thinlto-cache/Thin-96f93f.tmp.o to .thinlto-cache/llvmcache-A5B351EA452D46A86980E29C78B7260673348AAF: No such file or directory scripts/link-vmlinux.sh: line 76: 1240312 Aborted ${LD} ${KBUILD_LDFLAGS} -r -o ${1} ${lds} ${objects} make: *** [Makefile:1158: vmlinux] Error 134 ``` These two configs aren't easily modified in menuconfig. Perhaps you could find the concise set of configs that need to be disabled for this to be buildable? At least so others can test more easily, or even so we can update Kconfig checks.I have posted v2: https://lore.kernel.org/lkml/20220429053329.2278740-1-...@ozlabs.ru/T/ with this one, the ppc64 defconfigs should just work.--- arch/powerpc/Kconfig | 2 ++ arch/powerpc/kernel/exceptions-64s.S | 4 +++- arch/powerpc/lib/copyuser_64.S | 3 ++- arch/powerpc/lib/feature-fixups-test.S | 3 +-- arch/powerpc/lib/memcpy_64.S | 3 ++- 5 files changed, 10 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 174edabb74fa..e2c7b5c1d0a6 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -158,6 +158,8 @@ config PPC select ARCH_WANT_IRQS_OFF_ACTIVATE_MM select ARCH_WANT_LD_ORPHAN_WARN select ARCH_WEAK_RELEASE_ACQUIRE + select ARCH_SUPPORTS_LTO_CLANG + select ARCH_SUPPORTS_LTO_CLANG_THIN select BINFMT_ELF select BUILDTIME_TABLE_SORT select CLONE_BACKWARDSdiff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.Sindex b66dd6f775a4..5b783bd51260 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -476,9 +476,11 @@ DEFINE_FIXED_SYMBOL(\name\()_common_real, text) .if IHSRR_IF_HVMODE BEGIN_FTR_SECTION bne masked_Hinterrupt + b 4f FTR_SECTION_ELSE - bne masked_interruptALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)+ bne masked_interrupt +4: .elseif IHSRR bne masked_Hinterrupt .elsediff --git a/arch/powerpc/lib/copyuser_64.S b/arch/powerpc/lib/copyuser_64.Sindex db8719a14846..d07f95eebc65 100644 --- a/arch/powerpc/lib/copyuser_64.S +++ b/arch/powerpc/lib/copyuser_64.S @@ -75,10 +75,11 @@ _GLOBAL(__copy_tofrom_user_base) * set is Power6. */ test_feature = (SELFTEST_CASE == 1) + beq .Ldst_aligned BEGIN_FTR_SECTION nop FTR_SECTION_ELSE - bne .Ldst_unaligned + b .Ldst_unaligned ALT_FTR_SECTION_END(CPU_FTR_UNALIGNED_LD_STD | CPU_FTR_CP_USE_DCBTZ, \ CPU_FTR_UNALIGNED_LD_STD) .Ldst_aligned:diff --git a/arch/powerpc/lib/feature-fixups-test.S b/arch/powerpc/lib/feature-fixups-test.Sindex 480172fbd024..2751e42a9fd7 100644 --- a/arch/powerpc/lib/feature-fixups-test.S +++ b/arch/powerpc/lib/feature-fixups-test.S @@ -145,7 +145,6 @@ BEGIN_FTR_SECTION FTR_SECTION_ELSE 2: or 2,2,2 PPC_LCMPI r3,1 - beq 3f blt 2b b 3f b 1b @@ -160,10 +159,10 @@ globl(ftr_fixup_test6_expected) 1: or 1,1,1 2: or 2,2,2 PPC_LCMPI r3,1 - beq 3f blt 2b b 3f b 1b + nop 3: or 1,1,1 or 2,2,2 or 3,3,3 diff --git a/arch/powerpc/lib/memcpy_64.S b/arch/powerpc/lib/memcpy_64.S index 016c91e958d8..286c7e2d0883 100644 --- a/arch/powerpc/lib/memcpy_64.S +++ b/arch/powerpc/lib/memcpy_64.S @@ -50,10 +50,11 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_VMX_COPY)At the time of writing the only CPU that has this combination of bitsset is Power6. */ test_feature = (SELFTEST_CASE == 1) + beq .ldst_aligned BEGIN_FTR_SECTION nop FTR_SECTION_ELSE - bne .Ldst_unaligned + b .Ldst_unaligned ALT_FTR_SECTION_END(CPU_FTR_UNALIGNED_LD_STD | CPU_FTR_CP_USE_DCBTZ, \ CPU_FTR_UNALIGNED_LD_STD) .Ldst_aligned: -- 2.30.2
-- Alexey
