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toolchain: add link-time-optimization support

PATCH Superseded Peter Kümmel 3 participants 5 messages Mar 4, 2015 – Mar 6, 2015

v1 of 2 Superseded Latest is v2 →

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Peter Kümmel

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#0 lore raw

PATCH 1/1 toolchain: add link-time-optimization support

GCC's link-time-optimization could be enabled by the flag '-flto'. With LTO enabled, ar and runlib must be called with an argument which triggers the usage of a LTO plugin.
GCC provides wrappers for ar and ranlib which implicitly pass the LTO arguments to ar/ranlib. This way existing Makefiles don't need to be changed for LTO support when these wrappers around ar and ranlib are used. Also the LTO and plugin support must be enabled in the host's binutils.

Signed-off-by Peter K?mmel <[email protected]>
---
 package/binutils/binutils.mk                       | 4 ++++
 package/gcc/Config.in.host                         | 7 +++++++
 package/gcc/gcc.mk                                 | 4 ++++
 toolchain/toolchain-external/toolchain-external.mk | 8 ++++++++
 4 files changed, 23 insertions(+)
package/binutils/binutils.mk +4 -0
index 9e99253..daa8c45 100644
@@ -96,5 +96,9 @@ BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH
 HOST_BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH
 endif
 
+ifeq ($(BR2_GCC_ENABLE_LTO),y)
+HOST_BINUTILS_CONF_OPTS += --enable-plugins --enable-lto
+endif
+
 $(eval $(autotools-package))
 $(eval $(host-autotools-package))
package/gcc/Config.in.host +7 -0
index dd61f51..3c83579 100644
@@ -116,6 +116,13 @@ config BR2_GCC_ENABLE_TLS
 	  Enable the compiler to generate code for accessing
 	  thread local storage variables
 
+config BR2_GCC_ENABLE_LTO
+	bool "Enable compiler link-time-optimization support"
+	depends on !BR2_GCC_VERSION_4_2_2_AVR32_2_1_5
+	help
+	  Since version 4.5 GCC supports lto. Build GCC with lto support enabled.
+	  Needed when -flto should be used.
+
 config BR2_GCC_ENABLE_OPENMP
 	bool "Enable compiler OpenMP support"
 	depends on !BR2_PTHREADS_NONE && !BR2_arc && !BR2_microblaze
package/gcc/gcc.mk +4 -0
index ffac15c..b5d2ddb 100644
@@ -132,6 +132,10 @@ else
 HOST_GCC_COMMON_CONF_OPTS += --disable-tls
 endif
 
+ifeq ($(BR2_GCC_ENABLE_LTO),y)
+HOST_GCC_COMMON_CONF_OPTS += --enable-plugins --enable-lto
+endif
+
 ifeq ($(BR2_GCC_ENABLE_LIBMUDFLAP),y)
 HOST_GCC_COMMON_CONF_OPTS += --enable-libmudflap
 else
toolchain/toolchain-external/toolchain-external.mk +8 -0
index ab73f9a..d7a8499 100644
@@ -656,12 +656,20 @@ endif
 # Build toolchain wrapper for preprocessor, C and C++ compiler and setup
 # symlinks for everything else. Skip gdb symlink when we are building our
 # own gdb to prevent two gdb's in output/host/usr/bin.
+# When the link-time-optimazation flag '-flto' is used, then the compiler
+# and binutils have to support lto. ar/ranlib needs to be called with the
+# lto plugin. The wrappers *-gcc-ar and *-gcc-ranlib provided by GCC could
+# be used as drop-ins for ar/runlib when Makefiles are used which do not
+# pass the lto arguments.
 define TOOLCHAIN_EXTERNAL_INSTALL_WRAPPER
 	$(Q)$(call MESSAGE,"Building ext-toolchain wrapper")
 	mkdir -p $(HOST_DIR)/usr/bin; cd $(HOST_DIR)/usr/bin; \
 	for i in $(TOOLCHAIN_EXTERNAL_CROSS)*; do \
 		base=$${i##*/}; \
 		case "$$base" in \
+		*-ar|*-ranlib|*-nm) \
+			ln -sf $$(echo $$i | sed 's%^$(HOST_DIR)%../..%') .; \
+			;; \
 		*cc|*cc-*|*++|*++-*|*cpp) \
 			ln -sf ext-toolchain-wrapper $$base; \
 			;; \
Signature · 1 line
2.3.0
author
#1 lore raw

PATCH 1/1 toolchain: add link-time-optimization support

This patch is an update of the reviewed patch:

     http://patchwork.ozlabs.org/patch/423082

Hope it is enough to get committed.

BTW, how do I add comments in patchwork.

Am 04.03.2015 um 15:35 schrieb Peter K?mmel:

Quoted 89 lines

GCC's link-time-optimization could be enabled by the flag '-flto'. With LTO enabled, ar and runlib must be called with an argument which triggers the usage of a LTO plugin.
GCC provides wrappers for ar and ranlib which implicitly pass the LTO arguments to ar/ranlib. This way existing Makefiles don't need to be changed for LTO support when these wrappers around ar and ranlib are used. Also the LTO and plugin support must be enabled in the host's binutils.

Signed-off-by Peter K?mmel <[email protected]>
---
  package/binutils/binutils.mk                       | 4 ++++
  package/gcc/Config.in.host                         | 7 +++++++
  package/gcc/gcc.mk                                 | 4 ++++
  toolchain/toolchain-external/toolchain-external.mk | 8 ++++++++
  4 files changed, 23 insertions(+)
package/binutils/binutils.mk +4 -0
index 9e99253..daa8c45 100644
@@ -96,5 +96,9 @@ BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH
  HOST_BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH
  endif
 
+ifeq ($(BR2_GCC_ENABLE_LTO),y)
+HOST_BINUTILS_CONF_OPTS += --enable-plugins --enable-lto
+endif
+
  $(eval $(autotools-package))
  $(eval $(host-autotools-package))
package/gcc/Config.in.host +7 -0
index dd61f51..3c83579 100644
@@ -116,6 +116,13 @@ config BR2_GCC_ENABLE_TLS
  	  Enable the compiler to generate code for accessing
  	  thread local storage variables
 
+config BR2_GCC_ENABLE_LTO
+	bool "Enable compiler link-time-optimization support"
+	depends on !BR2_GCC_VERSION_4_2_2_AVR32_2_1_5
+	help
+	  Since version 4.5 GCC supports lto. Build GCC with lto support enabled.
+	  Needed when -flto should be used.
+
  config BR2_GCC_ENABLE_OPENMP
  	bool "Enable compiler OpenMP support"
  	depends on !BR2_PTHREADS_NONE && !BR2_arc && !BR2_microblaze
package/gcc/gcc.mk +4 -0
index ffac15c..b5d2ddb 100644
@@ -132,6 +132,10 @@ else
  HOST_GCC_COMMON_CONF_OPTS += --disable-tls
  endif
 
+ifeq ($(BR2_GCC_ENABLE_LTO),y)
+HOST_GCC_COMMON_CONF_OPTS += --enable-plugins --enable-lto
+endif
+
  ifeq ($(BR2_GCC_ENABLE_LIBMUDFLAP),y)
  HOST_GCC_COMMON_CONF_OPTS += --enable-libmudflap
  else
toolchain/toolchain-external/toolchain-external.mk +8 -0
index ab73f9a..d7a8499 100644
@@ -656,12 +656,20 @@ endif
  # Build toolchain wrapper for preprocessor, C and C++ compiler and setup
  # symlinks for everything else. Skip gdb symlink when we are building our
  # own gdb to prevent two gdb's in output/host/usr/bin.
+# When the link-time-optimazation flag '-flto' is used, then the compiler
+# and binutils have to support lto. ar/ranlib needs to be called with the
+# lto plugin. The wrappers *-gcc-ar and *-gcc-ranlib provided by GCC could
+# be used as drop-ins for ar/runlib when Makefiles are used which do not
+# pass the lto arguments.
  define TOOLCHAIN_EXTERNAL_INSTALL_WRAPPER
  	$(Q)$(call MESSAGE,"Building ext-toolchain wrapper")
  	mkdir -p $(HOST_DIR)/usr/bin; cd $(HOST_DIR)/usr/bin; \
  	for i in $(TOOLCHAIN_EXTERNAL_CROSS)*; do \
  		base=$${i##*/}; \
  		case "$$base" in \
+		*-ar|*-ranlib|*-nm) \
+			ln -sf $$(echo $$i | sed 's%^$(HOST_DIR)%../..%') .; \
+			;; \
  		*cc|*cc-*|*++|*++-*|*cpp) \
  			ln -sf ext-toolchain-wrapper $$base; \
  			;; \
#2 lore raw

PATCH 1/1 toolchain: add link-time-optimization support

Dear Peter K?mmel,

Quoted 5 lines · Peter K?mmel

This patch is an update of the reviewed patch:

     http://patchwork.ozlabs.org/patch/423082

Hope it is enough to get committed.

Thanks for this update.

Quoted 1 line

BTW, how do I add comments in patchwork.

You don't add comments in patchwork, you reply to a patch by mail, and it gets tracked by patchwork. What do you want to do exactly?

Best regarzds,

Thomas

Signature · 3 lines
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
#3 lore raw

PATCH 1/1 toolchain: add link-time-optimization support

In reply to Peter Kümmel

Hi Peter,

On 04/03/15 15:35, Peter K?mmel wrote:

I would start the commit log with mentioning that LTO is not used by default.

Quoted 2 lines

GCC's link-time-optimization could be enabled by the flag '-flto'. With LTO enabled, ar and runlib must be called with an argument which

runlib -> ranlib

Quoted 5 lines

triggers the usage of a LTO plugin.
GCC provides wrappers for ar and ranlib which implicitly pass the LTO arguments to ar/ranlib. This way existing Makefiles don't need to be changed for LTO support when these wrappers around ar and ranlib are used. Also the LTO and plugin support must be enabled in the host's binutils.

This part should mention explicitly that it applies to the external toolchains.

Example of an (IMHO) improved commit message:

Quoted 1 line
Quoted 1 line
Quoted 1 line

Add a new option BR2_GCC_ENABLE_LTO that builds gcc and binutils with LTO support.

Individual packages still have to enable LTO explicitly by passing '-flto' to GCC, which passes it on to the linker. This option does not add that flag globally. Some packages detect if the compiler supports LTO and enable the flag if it does.

To support LTO, ar and ranlib must be called with an argument which triggers the usage of the LTO plugin. Since GCC doesn't call these tools itself, it instead provides wrappers for ar and ranlib that pass the LTO arguments. This way existing Makefiles don't need to be changed for LTO support. However, these wrappers are called <tuple>-gcc-ar which matches the pattern to link to the buildroot wrapper in the external toolchain logic. So the external toolchain logic is updated to provide the correct symlink.
<<<

Quoted 2 lines
Signed-off-by Peter K?mmel <[email protected]>

Can you add a patch changelog in the future? Look at other patches on the list
to see how it is done.

Also, put the version number of the patch in the subject. You can easily do
this using 'git format-patch -v5' (or for older git versions 'git format-patch --subject-prefix="PATCH v5"')

Quoted 26 lines
---
 package/binutils/binutils.mk                       | 4 ++++
 package/gcc/Config.in.host                         | 7 +++++++
 package/gcc/gcc.mk                                 | 4 ++++
 toolchain/toolchain-external/toolchain-external.mk | 8 ++++++++
 4 files changed, 23 insertions(+)
package/binutils/binutils.mk +4 -0
index 9e99253..daa8c45 100644
@@ -96,5 +96,9 @@ BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH
 HOST_BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH
 endif
 
+ifeq ($(BR2_GCC_ENABLE_LTO),y)
+HOST_BINUTILS_CONF_OPTS += --enable-plugins --enable-lto
+endif
+
 $(eval $(autotools-package))
 $(eval $(host-autotools-package))
package/gcc/Config.in.host +0 -0
index dd61f51..3c83579 100644

package/gcc/Config.in.host config BR2_GCC_ENABLE_TLS · line 123

Quoted 8 lines
package/gcc/Config.in.host +5 -0
@@ -116,6 +116,13 @@ config BR2_GCC_ENABLE_TLS
 	  Enable the compiler to generate code for accessing
 	  thread local storage variables
 
+config BR2_GCC_ENABLE_LTO
+	bool "Enable compiler link-time-optimization support"
+	depends on !BR2_GCC_VERSION_4_2_2_AVR32_2_1_5
+	help
+	  Since version 4.5 GCC supports lto. Build GCC with lto support enabled.

This line should be wrapped. And perhaps an improved help text would be:

Since version 4.5, GCC supports link-time optimization (LTO). Select this option to turn on LTO support in GCC.

Quoted 32 lines
package/gcc/Config.in.host +2 -0
+	  Needed when -flto should be used.
+
 config BR2_GCC_ENABLE_OPENMP
 	bool "Enable compiler OpenMP support"
 	depends on !BR2_PTHREADS_NONE && !BR2_arc && !BR2_microblaze
package/gcc/gcc.mk +4 -0
index ffac15c..b5d2ddb 100644
@@ -132,6 +132,10 @@ else
 HOST_GCC_COMMON_CONF_OPTS += --disable-tls
 endif
 
+ifeq ($(BR2_GCC_ENABLE_LTO),y)
+HOST_GCC_COMMON_CONF_OPTS += --enable-plugins --enable-lto
+endif
+
 ifeq ($(BR2_GCC_ENABLE_LIBMUDFLAP),y)
 HOST_GCC_COMMON_CONF_OPTS += --enable-libmudflap
 else
toolchain/toolchain-external/toolchain-external.mk +4 -0
index ab73f9a..d7a8499 100644
@@ -656,12 +656,20 @@ endif
 # Build toolchain wrapper for preprocessor, C and C++ compiler and setup
 # symlinks for everything else. Skip gdb symlink when we are building our
 # own gdb to prevent two gdb's in output/host/usr/bin.
+# When the link-time-optimazation flag '-flto' is used, then the compiler
+# and binutils have to support lto. ar/ranlib needs to be called with the
+# lto plugin. The wrappers *-gcc-ar and *-gcc-ranlib provided by GCC could
+# be used as drop-ins for ar/runlib when Makefiles are used which do not

toolchain/toolchain-external/toolchain-external.mk endif · line 672

Quoted 10 lines
toolchain/toolchain-external/toolchain-external.mk +4 -0
+# pass the lto arguments.
 define TOOLCHAIN_EXTERNAL_INSTALL_WRAPPER
 	$(Q)$(call MESSAGE,"Building ext-toolchain wrapper")
 	mkdir -p $(HOST_DIR)/usr/bin; cd $(HOST_DIR)/usr/bin; \
 	for i in $(TOOLCHAIN_EXTERNAL_CROSS)*; do \
 		base=$${i##*/}; \
 		case "$$base" in \
+		*-ar|*-ranlib|*-nm) \
+			ln -sf $$(echo $$i | sed 's%^$(HOST_DIR)%../..%') .; \
+			;; \

This part could actually be a separate patch, since it fixes a problem that is
exists even if we don't support LTO in buildroot. However, since this patch is already in good shape, (just some text changes), it's not really necessary for me to still split it.

Quoted 4 lines
toolchain/toolchain-external/toolchain-external.mk +0 -0
 		*cc|*cc-*|*++|*++-*|*cpp) \
 			ln -sf ext-toolchain-wrapper $$base; \
 			;; \
Signature · 6 lines
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium           BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint:  7CB5 E4CC 6C2E EFD4 6E3D A754 F963 ECAB 2450 2F1F
author
#4 lore raw

PATCH 1/1 toolchain: add link-time-optimization support

Thanks Arnout, I send an updated patch with your changes.

Am 05.03.2015 um 22:41 schrieb Arnout Vandecappelle:

Quoted 143 lines

Hi Peter,

On 04/03/15 15:35, Peter K?mmel wrote:

I would start the commit log with mentioning that LTO is not used by default.

Quoted 2 lines

GCC's link-time-optimization could be enabled by the flag '-flto'. With LTO enabled, ar and runlib must be called with an argument which

runlib -> ranlib

Quoted 5 lines

triggers the usage of a LTO plugin.
GCC provides wrappers for ar and ranlib which implicitly pass the LTO arguments to ar/ranlib. This way existing Makefiles don't need to be changed for LTO support when these wrappers around ar and ranlib are used. Also the LTO and plugin support must be enabled in the host's binutils.

This part should mention explicitly that it applies to the external toolchains.

Example of an (IMHO) improved commit message:

Quoted 1 line
Quoted 1 line
Quoted 1 line

Add a new option BR2_GCC_ENABLE_LTO that builds gcc and binutils with LTO support.

Individual packages still have to enable LTO explicitly by passing '-flto' to GCC, which passes it on to the linker. This option does not add that flag globally. Some packages detect if the compiler supports LTO and enable the flag if it does.

To support LTO, ar and ranlib must be called with an argument which triggers the usage of the LTO plugin. Since GCC doesn't call these tools itself, it instead provides wrappers for ar and ranlib that pass the LTO arguments. This way existing Makefiles don't need to be changed for LTO support. However, these wrappers are called <tuple>-gcc-ar which matches the pattern to link to the buildroot wrapper in the external toolchain logic. So the external toolchain logic is updated to provide the correct symlink.
<<<

Quoted 2 lines
Signed-off-by Peter K?mmel <[email protected]>

Can you add a patch changelog in the future? Look at other patches on the list
to see how it is done.

Also, put the version number of the patch in the subject. You can easily do
this using 'git format-patch -v5' (or for older git versions 'git format-patch --subject-prefix="PATCH v5"')

Quoted 26 lines
---
  package/binutils/binutils.mk                       | 4 ++++
  package/gcc/Config.in.host                         | 7 +++++++
  package/gcc/gcc.mk                                 | 4 ++++
  toolchain/toolchain-external/toolchain-external.mk | 8 ++++++++
  4 files changed, 23 insertions(+)
package/binutils/binutils.mk +4 -0
index 9e99253..daa8c45 100644
@@ -96,5 +96,9 @@ BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH
  HOST_BINUTILS_PRE_PATCH_HOOKS += BINUTILS_XTENSA_PRE_PATCH
  endif
 
+ifeq ($(BR2_GCC_ENABLE_LTO),y)
+HOST_BINUTILS_CONF_OPTS += --enable-plugins --enable-lto
+endif
+
  $(eval $(autotools-package))
  $(eval $(host-autotools-package))
package/gcc/Config.in.host +0 -0
index dd61f51..3c83579 100644

package/gcc/Config.in.host config BR2_GCC_ENABLE_TLS · line 123

Quoted 8 lines
package/gcc/Config.in.host +5 -0
@@ -116,6 +116,13 @@ config BR2_GCC_ENABLE_TLS
  	  Enable the compiler to generate code for accessing
  	  thread local storage variables
 
+config BR2_GCC_ENABLE_LTO
+	bool "Enable compiler link-time-optimization support"
+	depends on !BR2_GCC_VERSION_4_2_2_AVR32_2_1_5
+	help
+	  Since version 4.5 GCC supports lto. Build GCC with lto support enabled.

This line should be wrapped. And perhaps an improved help text would be:

Since version 4.5, GCC supports link-time optimization (LTO). Select this option to turn on LTO support in GCC.

Quoted 32 lines
package/gcc/Config.in.host +2 -0
+	  Needed when -flto should be used.
+
  config BR2_GCC_ENABLE_OPENMP
  	bool "Enable compiler OpenMP support"
  	depends on !BR2_PTHREADS_NONE && !BR2_arc && !BR2_microblaze
package/gcc/gcc.mk +4 -0
index ffac15c..b5d2ddb 100644
@@ -132,6 +132,10 @@ else
  HOST_GCC_COMMON_CONF_OPTS += --disable-tls
  endif
 
+ifeq ($(BR2_GCC_ENABLE_LTO),y)
+HOST_GCC_COMMON_CONF_OPTS += --enable-plugins --enable-lto
+endif
+
  ifeq ($(BR2_GCC_ENABLE_LIBMUDFLAP),y)
  HOST_GCC_COMMON_CONF_OPTS += --enable-libmudflap
  else
toolchain/toolchain-external/toolchain-external.mk +4 -0
index ab73f9a..d7a8499 100644
@@ -656,12 +656,20 @@ endif
  # Build toolchain wrapper for preprocessor, C and C++ compiler and setup
  # symlinks for everything else. Skip gdb symlink when we are building our
  # own gdb to prevent two gdb's in output/host/usr/bin.
+# When the link-time-optimazation flag '-flto' is used, then the compiler
+# and binutils have to support lto. ar/ranlib needs to be called with the
+# lto plugin. The wrappers *-gcc-ar and *-gcc-ranlib provided by GCC could
+# be used as drop-ins for ar/runlib when Makefiles are used which do not

toolchain/toolchain-external/toolchain-external.mk endif · line 672

Quoted 10 lines
toolchain/toolchain-external/toolchain-external.mk +4 -0
+# pass the lto arguments.
  define TOOLCHAIN_EXTERNAL_INSTALL_WRAPPER
  	$(Q)$(call MESSAGE,"Building ext-toolchain wrapper")
  	mkdir -p $(HOST_DIR)/usr/bin; cd $(HOST_DIR)/usr/bin; \
  	for i in $(TOOLCHAIN_EXTERNAL_CROSS)*; do \
  		base=$${i##*/}; \
  		case "$$base" in \
+		*-ar|*-ranlib|*-nm) \
+			ln -sf $$(echo $$i | sed 's%^$(HOST_DIR)%../..%') .; \
+			;; \

This part could actually be a separate patch, since it fixes a problem that is
exists even if we don't support LTO in buildroot. However, since this patch is already in good shape, (just some text changes), it's not really necessary for me to still split it.

Quoted 4 lines
toolchain/toolchain-external/toolchain-external.mk +0 -0
  		*cc|*cc-*|*++|*++-*|*cpp) \
  			ln -sf ext-toolchain-wrapper $$base; \
  			;; \