Commit 8c50b72a authored by Torsten Duwe's avatar Torsten Duwe Committed by Michael Ellerman
Browse files

powerpc/ftrace: Add Kconfig & Make glue for mprofile-kernel 



Firstly we add logic to Kconfig to allow a user to choose if they want
mprofile-kernel. This has to be user-selectable because only some
current toolchains support it. If we enabled it unconditionally we would
prevent some users from building the kernel entirely.

Arguably it would be nice if we could detect if mprofile-kernel was
available, and use it then. However that would violate the principle of
least surprise because a user having choosen options such as live
patching, would then see them quietly disabled at build time.

We also make the user selectable option negative, ie. it disables when
selected, so that allyesconfig continues to build on old toolchains.

Once we've decided we do want to use mprofile-kernel, we then add a
script which checks it actually works. That is because there are
versions of gcc that accept the flag but don't generate correct code.

Due to the way kconfig works, we can't error out when we detect a
non-working toolchain. If we did a user would never be able to modify
their config and run oldconfig - because the check would block oldconfig
from running. Instead we emit a warning and add a bogus flag to CFLAGS
so that the build will fail.

Signed-off-by: default avatarTorsten Duwe <duwe@suse.de>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 15308664

arch/powerpc/Kconfig

+19 −0
Original line number Diff line number Diff line
@@ -94,6 +94,7 @@ config PPC 
	select OF_RESERVED_MEM

	select HAVE_FTRACE_MCOUNT_RECORD

	select HAVE_DYNAMIC_FTRACE

	select HAVE_DYNAMIC_FTRACE_WITH_REGS if MPROFILE_KERNEL

	select HAVE_FUNCTION_TRACER

	select HAVE_FUNCTION_GRAPH_TRACER

	select SYSCTL_EXCEPTION_TRACE
@@ -373,6 +374,24 @@ config PPC_TRANSACTIONAL_MEM 
       ---help---

         Support user-mode Transactional Memory on POWERPC.



config DISABLE_MPROFILE_KERNEL

	bool "Disable use of mprofile-kernel for kernel tracing"

	depends on PPC64 && CPU_LITTLE_ENDIAN

	default y

	help

	  Selecting this options disables use of the mprofile-kernel ABI for

	  kernel tracing. That will cause options such as live patching

	  (CONFIG_LIVEPATCH) which depend on CONFIG_DYNAMIC_FTRACE_WITH_REGS to

	  be disabled also.



	  If you have a toolchain which supports mprofile-kernel, then you can

	  enable this. Otherwise leave it disabled. If you're not sure, say

	  "N".



config MPROFILE_KERNEL

	depends on PPC64 && CPU_LITTLE_ENDIAN

	def_bool !DISABLE_MPROFILE_KERNEL



config IOMMU_HELPER

	def_bool PPC64

arch/powerpc/Makefile

+15 −0
Original line number Diff line number Diff line
@@ -133,6 +133,21 @@ else 
CFLAGS-$(CONFIG_GENERIC_CPU) += -mcpu=powerpc64

endif



ifdef CONFIG_MPROFILE_KERNEL

    ifeq ($(shell $(srctree)/arch/powerpc/scripts/gcc-check-mprofile-kernel.sh $(CC) -I$(srctree)/include -D__KERNEL__),OK)

        CC_FLAGS_FTRACE := -pg -mprofile-kernel

        KBUILD_CPPFLAGS += -DCC_USING_MPROFILE_KERNEL

    else

        # If the user asked for mprofile-kernel but the toolchain doesn't

        # support it, emit a warning and deliberately break the build later

        # with mprofile-kernel-not-supported. We would prefer to make this an

        # error right here, but then the user would never be able to run

        # oldconfig to change their configuration.

        $(warning Compiler does not support mprofile-kernel, set CONFIG_DISABLE_MPROFILE_KERNEL)

        CC_FLAGS_FTRACE := -mprofile-kernel-not-supported

    endif

endif



CFLAGS-$(CONFIG_CELL_CPU) += $(call cc-option,-mcpu=cell)

CFLAGS-$(CONFIG_POWER4_CPU) += $(call cc-option,-mcpu=power4)

CFLAGS-$(CONFIG_POWER5_CPU) += $(call cc-option,-mcpu=power5)

arch/powerpc/scripts/gcc-check-mprofile-kernel.sh

0 → 100755
+23 −0
Original line number Diff line number Diff line 
#!/bin/bash



set -e

set -o pipefail



# To debug, uncomment the following line

# set -x



# Test whether the compile option -mprofile-kernel exists and generates

# profiling code (ie. a call to _mcount()).

echo "int func() { return 0; }" | \

    $* -S -x c -O2 -p -mprofile-kernel - -o - 2> /dev/null | \

    grep -q "_mcount"



# Test whether the notrace attribute correctly suppresses calls to _mcount().



echo -e "#include <linux/compiler.h>\nnotrace int func() { return 0; }" | \

    $* -S -x c -O2 -p -mprofile-kernel - -o - 2> /dev/null | \

    grep -q "_mcount" && \

    exit 1



echo "OK"

exit 0

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