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. 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/ --- 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_BACKWARDS diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index 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_interrupt ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206) + bne masked_interrupt +4: .elseif IHSRR bne masked_Hinterrupt .else diff --git a/arch/powerpc/lib/copyuser_64.S b/arch/powerpc/lib/copyuser_64.S index 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.S index 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 bits 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: -- 2.30.2
