* [RFC PATCH] powerpc/Makefile: Add option to build with gold
@ 2016-08-12 11:30 Michael Ellerman
2016-08-12 14:30 ` Nicholas Piggin
0 siblings, 1 reply; 2+ messages in thread
From: Michael Ellerman @ 2016-08-12 11:30 UTC (permalink / raw)
To: linuxppc-dev; +Cc: anton
This adds a Kconfig option which can be turned on to enable use of the
gold linker. It depends on DEBUG_KERNEL to hopefully hide it from users
who don't really care about it, and also !COMPILE_TEST so that it will
be turned off for allyes/modconfig builds.
In the wrapper script we currently always use ${CROSS}ld, so instead
make that the default if ${LD} isn't already set. When we're called as
part of a normal build ${LD} will be set, but if the wrapper is called
separately we will fall back to ${CROSS}ld as before.
With this enabled I have successfully built a ppc64[le]_defconfig using
a toolchain which only has ld.gold.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
arch/powerpc/Kconfig.debug | 7 +++++++
arch/powerpc/Makefile | 4 ++++
arch/powerpc/boot/wrapper | 4 +++-
3 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 63292f64b25a..c63ec2bb08ae 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -19,6 +19,13 @@ config PPC_WERROR
depends on !PPC_DISABLE_WERROR
default y
+config PPC_USE_GOLD
+ bool "Build with the gold linker"
+ depends on DEBUG_KERNEL && !COMPILE_TEST
+ default n
+ Build the kernel with the ld.gold linker, rather than ld.bfd.
+ If you don't know what this means say N.
+
config PRINT_STACK_DEPTH
int "Stack depth to print" if DEBUG_KERNEL
default 64
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 1934707bf321..005c63fd8be1 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -65,6 +65,10 @@ endif
UTS_MACHINE := $(OLDARCH)
+ifdef CONFIG_PPC_USE_GOLD
+LD := $(LD).gold
+endif
+
ifeq ($(CONFIG_CPU_LITTLE_ENDIAN),y)
override LD += -EL
override CROSS32AS += -mlittle-endian
diff --git a/arch/powerpc/boot/wrapper b/arch/powerpc/boot/wrapper
index 6681ec3625c9..00f13d18fd6f 100755
--- a/arch/powerpc/boot/wrapper
+++ b/arch/powerpc/boot/wrapper
@@ -140,6 +140,8 @@ while [ "$#" -gt 0 ]; do
shift
done
+LD=${LD:-${CROSS}ld}
+
if [ -n "$dts" ]; then
if [ ! -r "$dts" -a -r "$object/dts/$dts" ]; then
dts="$object/dts/$dts"
@@ -417,7 +419,7 @@ if [ "$platform" != "miboot" ]; then
if [ -n "$link_address" ] ; then
text_start="-Ttext $link_address"
fi
- ${CROSS}ld -m $format -T $lds $text_start $pie -o "$ofile" \
+ ${LD} -m $format -T $lds $text_start $pie -o "$ofile" \
$platformo $tmp $object/wrapper.a
rm $tmp
fi
--
2.7.4
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [RFC PATCH] powerpc/Makefile: Add option to build with gold
2016-08-12 11:30 [RFC PATCH] powerpc/Makefile: Add option to build with gold Michael Ellerman
@ 2016-08-12 14:30 ` Nicholas Piggin
0 siblings, 0 replies; 2+ messages in thread
From: Nicholas Piggin @ 2016-08-12 14:30 UTC (permalink / raw)
To: Michael Ellerman; +Cc: linuxppc-dev, anton, Alan Modra
On Fri, 12 Aug 2016 21:30:21 +1000
Michael Ellerman <mpe@ellerman.id.au> wrote:
> This adds a Kconfig option which can be turned on to enable use of the
> gold linker. It depends on DEBUG_KERNEL to hopefully hide it from users
> who don't really care about it, and also !COMPILE_TEST so that it will
> be turned off for allyes/modconfig builds.
>
> In the wrapper script we currently always use ${CROSS}ld, so instead
> make that the default if ${LD} isn't already set. When we're called as
> part of a normal build ${LD} will be set, but if the wrapper is called
> separately we will fall back to ${CROSS}ld as before.
>
> With this enabled I have successfully built a ppc64[le]_defconfig using
> a toolchain which only has ld.gold.
Nice. Out of curiosity, I ran some testing.
On allyesconfig with sfr's thin archives patch and --gc-sections,
ld.gold is about 10% faster than ld.bfd. About 11 seconds vs 12. A lot
of that is in utf8 conversions from "fnmatch" it's using to match
section names though. Setting LANG=C brings it down to 8 seconds and
helps ld.bfd a tiny bit but not much. So that's a pretty good win.
Threading still has some crashes.
ld.gold creates a larger executable though. It seems to be creating a
lot more branch stubs (19000 vs 6500 for ld.bfd).
I should keep in mind we link the kernel about 4 times every build
before complain too much about linker performance to the binutils guys.
I wonder if we couldn't objcopy the kallsyms onto the end of the image
to avoid that relinking.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2016-08-12 11:30 [RFC PATCH] powerpc/Makefile: Add option to build with gold Michael Ellerman
2016-08-12 14:30 ` Nicholas Piggin
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