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

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
......@@ -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
......
......@@ -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)
......
#!/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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