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-cleanbuild
CC='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=Release
ninja -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.so
and then in the kernel tree:
PATH=/home/aik/pbuild/llvm/llvm-lto-latest-cleanbuild/bin:$PATH make
-j64
O=/home/aik/pbuild/kernels-llvm/llvm-wip-llvm-latest-lto-full-cleanbuild/
ARCH=powerpc LLVM_IAS=1 CC=clang LLVM=1 ppc64le_defconfig
then enabled LTO in that .config and then just built "vmlinux":
[fstn1-p1 ~/p/kernels-llvm/llvm]$ 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/vmlinux
which 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 2022
Before 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.
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_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
