Re: [PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

[Nicolas Pitre]

On Fri, 2 Feb 2018, Arnd Bergmann wrote:

> On Fri, Feb 2, 2018 at 9:38 PM, Nicolas Pitre  
> wrote:
> > On Fri, 2 Feb 2018, Arnd Bergmann wrote:
> >
> >> Do you have a git tree with other changes for LTO on ARM? I'd
> >> like to try that as well.
> >
> > I currently have only 2 other patches.
> >
> > You need commit 75fea300d73a that just hit mainline (you may cherry-pick
> > it easily if necessary).
> 
> Ok, I apparently have that already by basing on today's linux-next.

OK. linux-next has had it for quite a while.

> > Then the following:
> >
> > - >8
> > Subject: [PATCH] HACK: enable LTO on ARM
> >
> > Without the ${KBUILD_VMLINUX_LIBS} move the build fails with missing
> > memcpy all over the place. Didn't figure it out yet.
> 
> Added that now as well, thanks! I'll see what comes out of it.

I forgot: you'll need to hack your toolchain a bit too.

Here's the script I created to remember about the issue:

- >8
#!/bin/bash

# work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78353

GCC_ROOT=/opt/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabihf

set -e
set -x

cd $GCC_ROOT//arm-linux-gnueabihf/bin
[ -e fat-as ] && exit 1
mv as fat-as
cat > as << EOF
#!/bin/bash
exec -a "\$0" "\$(dirname "\$0")/fat-as" -mimplicit-it=always "\$@"
EOF
chmod +x as
8< -

> Have you tried arm64 already? I suppose I could do the same change 
> there and see what happens.

No, didn't try arm64.


Nicolas

Re: [PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

[Nicolas Pitre]

On Fri, 2 Feb 2018, Arnd Bergmann wrote:

> On Fri, Feb 2, 2018 at 9:38 PM, Nicolas Pitre  
> wrote:
> > On Fri, 2 Feb 2018, Arnd Bergmann wrote:
> >
> >> Do you have a git tree with other changes for LTO on ARM? I'd
> >> like to try that as well.
> >
> > I currently have only 2 other patches.
> >
> > You need commit 75fea300d73a that just hit mainline (you may cherry-pick
> > it easily if necessary).
> 
> Ok, I apparently have that already by basing on today's linux-next.

OK. linux-next has had it for quite a while.

> > Then the following:
> >
> > - >8
> > Subject: [PATCH] HACK: enable LTO on ARM
> >
> > Without the ${KBUILD_VMLINUX_LIBS} move the build fails with missing
> > memcpy all over the place. Didn't figure it out yet.
> 
> Added that now as well, thanks! I'll see what comes out of it.

I forgot: you'll need to hack your toolchain a bit too.

Here's the script I created to remember about the issue:

- >8
#!/bin/bash

# work around https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78353

GCC_ROOT=/opt/gcc-linaro-6.3.1-2017.05-x86_64_arm-linux-gnueabihf

set -e
set -x

cd $GCC_ROOT//arm-linux-gnueabihf/bin
[ -e fat-as ] && exit 1
mv as fat-as
cat > as << EOF
#!/bin/bash
exec -a "\$0" "\$(dirname "\$0")/fat-as" -mimplicit-it=always "\$@"
EOF
chmod +x as
8< -

> Have you tried arm64 already? I suppose I could do the same change 
> there and see what happens.

No, didn't try arm64.


Nicolas

Re: [PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

[Arnd Bergmann]

On Fri, Feb 2, 2018 at 9:38 PM, Nicolas Pitre  wrote:
> On Fri, 2 Feb 2018, Arnd Bergmann wrote:
>
>> Do you have a git tree with other changes for LTO on ARM? I'd
>> like to try that as well.
>
> I currently have only 2 other patches.
>
> You need commit 75fea300d73a that just hit mainline (you may cherry-pick
> it easily if necessary).

Ok, I apparently have that already by basing on today's linux-next.

> Then the following:
>
> - >8
> Subject: [PATCH] HACK: enable LTO on ARM
>
> Without the ${KBUILD_VMLINUX_LIBS} move the build fails with missing
> memcpy all over the place. Didn't figure it out yet.

Added that now as well, thanks! I'll see what comes out of it. Have you
tried arm64 already? I suppose I could do the same change there and
see what happens.

  Arnd

Re: [PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

[Arnd Bergmann]

On Fri, Feb 2, 2018 at 9:38 PM, Nicolas Pitre  wrote:
> On Fri, 2 Feb 2018, Arnd Bergmann wrote:
>
>> Do you have a git tree with other changes for LTO on ARM? I'd
>> like to try that as well.
>
> I currently have only 2 other patches.
>
> You need commit 75fea300d73a that just hit mainline (you may cherry-pick
> it easily if necessary).

Ok, I apparently have that already by basing on today's linux-next.

> Then the following:
>
> - >8
> Subject: [PATCH] HACK: enable LTO on ARM
>
> Without the ${KBUILD_VMLINUX_LIBS} move the build fails with missing
> memcpy all over the place. Didn't figure it out yet.

Added that now as well, thanks! I'll see what comes out of it. Have you
tried arm64 already? I suppose I could do the same change there and
see what happens.

  Arnd

Re: [PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

[Nicolas Pitre]

On Fri, 2 Feb 2018, Arnd Bergmann wrote:

> Do you have a git tree with other changes for LTO on ARM? I'd
> like to try that as well.

I currently have only 2 other patches.

You need commit 75fea300d73a that just hit mainline (you may cherry-pick 
it easily if necessary).

Then the following:

- >8
Subject: [PATCH] HACK: enable LTO on ARM

Without the ${KBUILD_VMLINUX_LIBS} move the build fails with missing
memcpy all over the place. Didn't figure it out yet.

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 4382315005..84450843ed 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -17,6 +17,7 @@ config ARM
select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
select ARCH_SUPPORTS_ATOMIC_RMW
+   select ARCH_SUPPORTS_LTO
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF
select ARCH_WANT_IPC_PARSE_VERSION
@@ -101,6 +102,7 @@ config ARM
select PERF_USE_VMALLOC
select RTC_LIB
select SYS_SUPPORTS_APM_EMULATION
+   select THIN_ARCHIVES if LTO
# Above selects are sorted alphabetically; please add new ones
# according to that.  Thanks.
help
diff --git a/arch/arm/boot/compressed/Makefile 
b/arch/arm/boot/compressed/Makefile
index 45a6b9b7af..39ac0a9639 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -97,7 +97,7 @@ targets   := vmlinux vmlinux.lds piggy_data piggy.o \
 clean-files += piggy_data lib1funcs.S ashldi3.S bswapsdi2.S \
$(libfdt) $(libfdt_hdrs) hyp-stub.S
 
-KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
+KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING $(DISABLE_LTO)
 
 ifeq ($(CONFIG_FUNCTION_TRACER),y)
 ORIG_CFLAGS := $(KBUILD_CFLAGS)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 964b2ee855..0774a87788 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -99,9 +99,9 @@ vmlinux_link()
if [ -n "${CONFIG_THIN_ARCHIVES}" ]; then
objects="--whole-archive\
built-in.o  \
+   ${KBUILD_VMLINUX_LIBS}  \
--no-whole-archive  \
--start-group   \
-   ${KBUILD_VMLINUX_LIBS}  \
--end-group \
${1}"
else






> 
>Arnd
> 

Re: [PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

[Nicolas Pitre]

On Fri, 2 Feb 2018, Arnd Bergmann wrote:

> Do you have a git tree with other changes for LTO on ARM? I'd
> like to try that as well.

I currently have only 2 other patches.

You need commit 75fea300d73a that just hit mainline (you may cherry-pick 
it easily if necessary).

Then the following:

- >8
Subject: [PATCH] HACK: enable LTO on ARM

Without the ${KBUILD_VMLINUX_LIBS} move the build fails with missing
memcpy all over the place. Didn't figure it out yet.

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 4382315005..84450843ed 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -17,6 +17,7 @@ config ARM
select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
select ARCH_SUPPORTS_ATOMIC_RMW
+   select ARCH_SUPPORTS_LTO
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF
select ARCH_WANT_IPC_PARSE_VERSION
@@ -101,6 +102,7 @@ config ARM
select PERF_USE_VMALLOC
select RTC_LIB
select SYS_SUPPORTS_APM_EMULATION
+   select THIN_ARCHIVES if LTO
# Above selects are sorted alphabetically; please add new ones
# according to that.  Thanks.
help
diff --git a/arch/arm/boot/compressed/Makefile 
b/arch/arm/boot/compressed/Makefile
index 45a6b9b7af..39ac0a9639 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -97,7 +97,7 @@ targets   := vmlinux vmlinux.lds piggy_data piggy.o \
 clean-files += piggy_data lib1funcs.S ashldi3.S bswapsdi2.S \
$(libfdt) $(libfdt_hdrs) hyp-stub.S
 
-KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
+KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING $(DISABLE_LTO)
 
 ifeq ($(CONFIG_FUNCTION_TRACER),y)
 ORIG_CFLAGS := $(KBUILD_CFLAGS)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 964b2ee855..0774a87788 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -99,9 +99,9 @@ vmlinux_link()
if [ -n "${CONFIG_THIN_ARCHIVES}" ]; then
objects="--whole-archive\
built-in.o  \
+   ${KBUILD_VMLINUX_LIBS}  \
--no-whole-archive  \
--start-group   \
-   ${KBUILD_VMLINUX_LIBS}  \
--end-group \
${1}"
else






> 
>Arnd
> 

Re: [PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

[Arnd Bergmann]

On Fri, Feb 2, 2018 at 7:41 PM, Nicolas Pitre  wrote:
> On Fri, 2 Feb 2018, Arnd Bergmann wrote:
>
>> Building randconfig kernels with a biarch compiler fails with LTO
>> when the final link uses a different target architecture compared
>> to the earlier compilation stages.
>>
>> Setting -m32 or -m64 in ${LDFINAL} solves this problem, though my
>> feeling is that there is a better way to do this. There might also
>> be other from KBUILD_CFLAGS that we may need in LDFINAL.
>
> On ARM I had the same problem as it requires explicit arch flags. I
> therefore used this patch:

> -exec $CC $ARGS
> +case "${KBUILD_VERBOSE}" in
> +*1*)
> +   set -x
> +   ;;
> +esac
> +
> +exec $CC $KBUILD_CFLAGS $ARGS

Ah, right, that's much simpler. I'll put that in my test tree now and
will see if it works on x86.

Do you have a git tree with other changes for LTO on ARM? I'd
like to try that as well.

   Arnd

Re: [PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

[Arnd Bergmann]

On Fri, Feb 2, 2018 at 7:41 PM, Nicolas Pitre  wrote:
> On Fri, 2 Feb 2018, Arnd Bergmann wrote:
>
>> Building randconfig kernels with a biarch compiler fails with LTO
>> when the final link uses a different target architecture compared
>> to the earlier compilation stages.
>>
>> Setting -m32 or -m64 in ${LDFINAL} solves this problem, though my
>> feeling is that there is a better way to do this. There might also
>> be other from KBUILD_CFLAGS that we may need in LDFINAL.
>
> On ARM I had the same problem as it requires explicit arch flags. I
> therefore used this patch:

> -exec $CC $ARGS
> +case "${KBUILD_VERBOSE}" in
> +*1*)
> +   set -x
> +   ;;
> +esac
> +
> +exec $CC $KBUILD_CFLAGS $ARGS

Ah, right, that's much simpler. I'll put that in my test tree now and
will see if it works on x86.

Do you have a git tree with other changes for LTO on ARM? I'd
like to try that as well.

   Arnd

Re: [PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

[Nicolas Pitre]

On Fri, 2 Feb 2018, Arnd Bergmann wrote:

> Building randconfig kernels with a biarch compiler fails with LTO
> when the final link uses a different target architecture compared
> to the earlier compilation stages.
> 
> Setting -m32 or -m64 in ${LDFINAL} solves this problem, though my
> feeling is that there is a better way to do this. There might also
> be other from KBUILD_CFLAGS that we may need in LDFINAL.

On ARM I had the same problem as it requires explicit arch flags. I 
therefore used this patch:

- >8
Subject: [PATCH] LTO: scripts/gcc-ld: LTO on ARM needs arch specific gcc flags

Otherwise the final link where code generation happens produces code
for the wrong ISA when the default CPU configured into gcc is not the
one we need.

Also display the actual command when invoked with "make V=1".

Signed-off-by: Nicolas Pitre 

diff --git a/scripts/gcc-ld b/scripts/gcc-ld
index d95dd0be38..fa53be2a34 100755
--- a/scripts/gcc-ld
+++ b/scripts/gcc-ld
@@ -27,4 +27,10 @@ while [ "$1" != "" ] ; do
shift
 done
 
-exec $CC $ARGS
+case "${KBUILD_VERBOSE}" in
+*1*)
+   set -x
+   ;;
+esac
+
+exec $CC $KBUILD_CFLAGS $ARGS

Re: [PATCH 7/7] Kbuild: lto: pass -m32/-m64 to to LDFINAL

[Nicolas Pitre]

On Fri, 2 Feb 2018, Arnd Bergmann wrote:

> Building randconfig kernels with a biarch compiler fails with LTO
> when the final link uses a different target architecture compared
> to the earlier compilation stages.
> 
> Setting -m32 or -m64 in ${LDFINAL} solves this problem, though my
> feeling is that there is a better way to do this. There might also
> be other from KBUILD_CFLAGS that we may need in LDFINAL.

On ARM I had the same problem as it requires explicit arch flags. I 
therefore used this patch:

- >8
Subject: [PATCH] LTO: scripts/gcc-ld: LTO on ARM needs arch specific gcc flags

Otherwise the final link where code generation happens produces code
for the wrong ISA when the default CPU configured into gcc is not the
one we need.

Also display the actual command when invoked with "make V=1".

Signed-off-by: Nicolas Pitre 

diff --git a/scripts/gcc-ld b/scripts/gcc-ld
index d95dd0be38..fa53be2a34 100755
--- a/scripts/gcc-ld
+++ b/scripts/gcc-ld
@@ -27,4 +27,10 @@ while [ "$1" != "" ] ; do
shift
 done
 
-exec $CC $ARGS
+case "${KBUILD_VERBOSE}" in
+*1*)
+   set -x
+   ;;
+esac
+
+exec $CC $KBUILD_CFLAGS $ARGS