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Reply-To: sedat.dilek@gmail.com
From:   Sedat Dilek <sedat.dilek@gmail.com>
Date:   Mon, 11 Jan 2021 09:42:12 +0100
Message-ID: <CA+icZUXs5w+dWrTUAF-fzYfeAzsZLjBL=kKE7URUqc-dyPEdCA@mail.gmail.com>
Subject: Re: [PATCH] pgo: add clang's Profile Guided Optimization infrastructure
To:     Bill Wendling <morbo@google.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Masahiro Yamada <masahiroy@kernel.org>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kbuild@vger.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@googlegroups.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Sami Tolvanen <samitolvanen@google.com>
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On Mon, Jan 11, 2021 at 9:39 AM Sedat Dilek <sedat.dilek@gmail.com> wrote:
>
> On Mon, Jan 11, 2021 at 9:18 AM 'Bill Wendling' via Clang Built Linux
> <clang-built-linux@googlegroups.com> wrote:
> >
> > From: Sami Tolvanen <samitolvanen@google.com>
> >
> > Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> > profile, the kernel is instrumented with PGO counters, a representative
> > workload is run, and the raw profile data is collected from
> > /sys/kernel/debug/pgo/profraw.
> >
> > The raw profile data must be processed by clang's "llvm-profdata" tool before
> > it can be used during recompilation:
> >
> >   $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> >   $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> >
> > Multiple raw profiles may be merged during this step.
> >
> > The data can be used either by the compiler if LTO isn't enabled:
> >
> >     ... -fprofile-use=vmlinux.profdata ...
> >
> > or by LLD if LTO is enabled:
> >
> >     ... -lto-cs-profile-file=vmlinux.profdata ...
> >
> > This initial submission is restricted to x86, as that's the platform we know
> > works. This restriction can be lifted once other platforms have been verified
> > to work with PGO.
> >
> > Note that this method of profiling the kernel is clang-native and isn't
> > compatible with clang's gcov support in kernel/gcov.
> >
> > [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> >
>
> Hi Bill and Sami,
>
> I have seen the pull-request in the CBL issue tracker and had some
> questions in mind.
>
> Good you send this.
>
> First of all, I like to fetch any development stuff easily from a Git
> repository.
> Can you offer this, please?
> What is the base for your work?
> I hope this is (fresh released) Linux v5.11-rc3.
>
> I myself had some experiences with a PGO + ThinLTO optimized LLVM
> toolchain built with the help of tc-build.
> Here it takes very long to build it.
>
> This means I have some profile-data archived.
> Can I use it?
>
> Is an own PGO + ThinLTO optimized LLVM toolchain pre-requirement for
> this or not?

When I recall correctly such an optimized LLVM toolchain saved here
40% of build-time.
So, I am highly interested in reducing my build-time.

- Sedat -

> That is one of my important questions.
>
> Thanks for your work.
>
> Regards,
> - Sedat -
>
> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > Co-developed-by: Bill Wendling <morbo@google.com>
> > Signed-off-by: Bill Wendling <morbo@google.com>
> > ---
> >  Documentation/dev-tools/index.rst     |   1 +
> >  Documentation/dev-tools/pgo.rst       | 127 +++++++++
> >  MAINTAINERS                           |   9 +
> >  Makefile                              |   3 +
> >  arch/Kconfig                          |   1 +
> >  arch/arm/boot/bootp/Makefile          |   1 +
> >  arch/arm/boot/compressed/Makefile     |   1 +
> >  arch/arm/vdso/Makefile                |   3 +-
> >  arch/arm64/kernel/vdso/Makefile       |   3 +-
> >  arch/arm64/kvm/hyp/nvhe/Makefile      |   1 +
> >  arch/mips/boot/compressed/Makefile    |   1 +
> >  arch/mips/vdso/Makefile               |   1 +
> >  arch/nds32/kernel/vdso/Makefile       |   4 +-
> >  arch/parisc/boot/compressed/Makefile  |   1 +
> >  arch/powerpc/kernel/Makefile          |   6 +-
> >  arch/powerpc/kernel/trace/Makefile    |   3 +-
> >  arch/powerpc/kernel/vdso32/Makefile   |   1 +
> >  arch/powerpc/kernel/vdso64/Makefile   |   1 +
> >  arch/powerpc/kexec/Makefile           |   3 +-
> >  arch/powerpc/xmon/Makefile            |   1 +
> >  arch/riscv/kernel/vdso/Makefile       |   3 +-
> >  arch/s390/boot/Makefile               |   1 +
> >  arch/s390/boot/compressed/Makefile    |   1 +
> >  arch/s390/kernel/Makefile             |   1 +
> >  arch/s390/kernel/vdso64/Makefile      |   3 +-
> >  arch/s390/purgatory/Makefile          |   1 +
> >  arch/sh/boot/compressed/Makefile      |   1 +
> >  arch/sh/mm/Makefile                   |   1 +
> >  arch/sparc/vdso/Makefile              |   1 +
> >  arch/x86/Kconfig                      |   1 +
> >  arch/x86/boot/Makefile                |   1 +
> >  arch/x86/boot/compressed/Makefile     |   1 +
> >  arch/x86/entry/vdso/Makefile          |   1 +
> >  arch/x86/kernel/vmlinux.lds.S         |   2 +
> >  arch/x86/platform/efi/Makefile        |   1 +
> >  arch/x86/purgatory/Makefile           |   1 +
> >  arch/x86/realmode/rm/Makefile         |   1 +
> >  arch/x86/um/vdso/Makefile             |   1 +
> >  drivers/firmware/efi/libstub/Makefile |   1 +
> >  drivers/s390/char/Makefile            |   1 +
> >  include/asm-generic/vmlinux.lds.h     |  44 +++
> >  kernel/Makefile                       |   1 +
> >  kernel/pgo/Kconfig                    |  34 +++
> >  kernel/pgo/Makefile                   |   5 +
> >  kernel/pgo/fs.c                       | 382 ++++++++++++++++++++++++++
> >  kernel/pgo/instrument.c               | 147 ++++++++++
> >  kernel/pgo/pgo.h                      | 206 ++++++++++++++
> >  scripts/Makefile.lib                  |  10 +
> >  48 files changed, 1017 insertions(+), 9 deletions(-)
> >  create mode 100644 Documentation/dev-tools/pgo.rst
> >  create mode 100644 kernel/pgo/Kconfig
> >  create mode 100644 kernel/pgo/Makefile
> >  create mode 100644 kernel/pgo/fs.c
> >  create mode 100644 kernel/pgo/instrument.c
> >  create mode 100644 kernel/pgo/pgo.h
> >
> > diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
> > index f7809c7b1ba9e..8d6418e858062 100644
> > --- a/Documentation/dev-tools/index.rst
> > +++ b/Documentation/dev-tools/index.rst
> > @@ -26,6 +26,7 @@ whole; patches welcome!
> >     kgdb
> >     kselftest
> >     kunit/index
> > +   pgo
> >
> >
> >  .. only::  subproject and html
> > diff --git a/Documentation/dev-tools/pgo.rst b/Documentation/dev-tools/pgo.rst
> > new file mode 100644
> > index 0000000000000..2ed7f549b20ef
> > --- /dev/null
> > +++ b/Documentation/dev-tools/pgo.rst
> > @@ -0,0 +1,127 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +===============================
> > +Using PGO with the Linux kernel
> > +===============================
> > +
> > +Clang's profiling kernel support (PGO_) enables profiling of the Linux kernel
> > +when building with Clang. The profiling data is exported via the ``pgo``
> > +debugfs directory.
> > +
> > +.. _PGO: https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> > +
> > +
> > +Preparation
> > +===========
> > +
> > +Configure the kernel with:
> > +
> > +.. code-block:: make
> > +
> > +   CONFIG_DEBUG_FS=y
> > +   CONFIG_PGO_CLANG=y
> > +
> > +Note that kernels compiled with profiling flags will be significantly larger
> > +and run slower.
> > +
> > +Profiling data will only become accessible once debugfs has been mounted:
> > +
> > +.. code-block:: sh
> > +
> > +   mount -t debugfs none /sys/kernel/debug
> > +
> > +
> > +Customization
> > +=============
> > +
> > +You can enable or disable profiling for individual file and directories by
> > +adding a line similar to the following to the respective kernel Makefile:
> > +
> > +- For a single file (e.g. main.o)
> > +
> > +  .. code-block:: make
> > +
> > +     PGO_PROFILE_main.o := y
> > +
> > +- For all files in one directory
> > +
> > +  .. code-block:: make
> > +
> > +     PGO_PROFILE := y
> > +
> > +To exclude files from being profiled use
> > +
> > +  .. code-block:: make
> > +
> > +     PGO_PROFILE_main.o := n
> > +
> > +and
> > +
> > +  .. code-block:: make
> > +
> > +     PGO_PROFILE := n
> > +
> > +Only files which are linked to the main kernel image or are compiled as kernel
> > +modules are supported by this mechanism.
> > +
> > +
> > +Files
> > +=====
> > +
> > +The PGO kernel support creates the following files in debugfs:
> > +
> > +``/sys/kernel/debug/pgo``
> > +       Parent directory for all PGO-related files.
> > +
> > +``/sys/kernel/debug/pgo/reset``
> > +       Global reset file: resets all coverage data to zero when written to.
> > +
> > +``/sys/kernel/debug/profraw``
> > +       The raw PGO data that must be processed with ``llvm_profdata``.
> > +
> > +
> > +Workflow
> > +========
> > +
> > +The PGO kernel can be run on the host or test machines. The data though should
> > +be analyzed with Clang's tools from the same Clang version as the kernel was
> > +compiled. Clang's tolerant of version skew, but it's easier to use the same
> > +Clang version.
> > +
> > +The profiling data is useful for optimizing the kernel, analyzing coverage,
> > +etc. Clang offers tools to perform these tasks.
> > +
> > +Here is an example workflow for profiling an instrumented kernel with PGO and
> > +using the result to optimize the kernel:
> > +
> > +1) Install the kernel on the TEST machine.
> > +
> > +2) Reset the data counters right before running the load tests
> > +
> > +   .. code-block:: sh
> > +
> > +      echo 1 > /sys/kernel/debug/pgo/reset
> > +
> > +3) Run the load tests.
> > +
> > +4) Collect the raw profile data
> > +
> > +   .. code-block:: sh
> > +
> > +      cp -a /sys/kernel/debug/pgo/profraw /tmp/vmlinux.profraw
> > +
> > +5) (Optional) Download the raw profile data to the HOST machine.
> > +
> > +6) Process the raw profile data
> > +
> > +   .. code-block:: sh
> > +
> > +      llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > +
> > +   Note that multiple raw profile data files can be merged during this step.
> > +
> > +7) Rebuild the kernel using the profile data (PGO disabled)
> > +
> > +   .. code-block:: sh
> > +
> > +      make ... KCLAGS=-fprofile-use=vmlinux.profdata
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 6390491b07e51..7a98bdaab9861 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -13955,6 +13955,15 @@ S:     Maintained
> >  F:     include/linux/personality.h
> >  F:     include/uapi/linux/personality.h
> >
> > +PGO BASED KERNEL PROFILING
> > +M:     Sami Tolvanen <samitolvanen@google.com>
> > +M:     Bill Wendling <wcw@google.com>
> > +R:     Nathan Chancellor <natechancellor@gmail.com>
> > +R:     Nick Desaulniers <ndesaulniers@google.com>
> > +S:     Supported
> > +F:     Documentation/dev-tools/pgo.rst
> > +F:     kernel/pgo
> > +
> >  PHOENIX RC FLIGHT CONTROLLER ADAPTER
> >  M:     Marcus Folkesson <marcus.folkesson@gmail.com>
> >  L:     linux-input@vger.kernel.org
> > diff --git a/Makefile b/Makefile
> > index 8b2c3f88ee5ea..4f42957c78134 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -659,6 +659,9 @@ endif # KBUILD_EXTMOD
> >  # Defaults to vmlinux, but the arch makefile usually adds further targets
> >  all: vmlinux
> >
> > +CFLAGS_PGO_CLANG := -fprofile-generate
> > +export CFLAGS_PGO_CLANG
> > +
> >  CFLAGS_GCOV    := -fprofile-arcs -ftest-coverage \
> >         $(call cc-option,-fno-tree-loop-im) \
> >         $(call cc-disable-warning,maybe-uninitialized,)
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 78c6f05b10f91..a7a6ab7d204dc 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -1106,6 +1106,7 @@ config ARCH_SUPPORTS_DEBUG_PAGEALLOC
> >         bool
> >
> >  source "kernel/gcov/Kconfig"
> > +source "kernel/pgo/Kconfig"
> >
> >  source "scripts/gcc-plugins/Kconfig"
> >
> > diff --git a/arch/arm/boot/bootp/Makefile b/arch/arm/boot/bootp/Makefile
> > index 981a8d03f064c..523bd58df0a4b 100644
> > --- a/arch/arm/boot/bootp/Makefile
> > +++ b/arch/arm/boot/bootp/Makefile
> > @@ -7,6 +7,7 @@
> >  #
> >
> >  GCOV_PROFILE   := n
> > +PGO_PROFILE    := n
> >
> >  LDFLAGS_bootp  := --no-undefined -X \
> >                  --defsym initrd_phys=$(INITRD_PHYS) \
> > diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> > index fb521efcc6c20..5fd0fd85fc0e5 100644
> > --- a/arch/arm/boot/compressed/Makefile
> > +++ b/arch/arm/boot/compressed/Makefile
> > @@ -24,6 +24,7 @@ OBJS          += hyp-stub.o
> >  endif
> >
> >  GCOV_PROFILE           := n
> > +PGO_PROFILE            := n
> >  KASAN_SANITIZE         := n
> >
> >  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> > diff --git a/arch/arm/vdso/Makefile b/arch/arm/vdso/Makefile
> > index b558bee0e1f6b..11f6ce4b48b56 100644
> > --- a/arch/arm/vdso/Makefile
> > +++ b/arch/arm/vdso/Makefile
> > @@ -36,8 +36,9 @@ else
> >  CFLAGS_vgettimeofday.o = -O2 -include $(c-gettimeofday-y)
> >  endif
> >
> > -# Disable gcov profiling for VDSO code
> > +# Disable gcov and PGO profiling for VDSO code
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> >  KCOV_INSTRUMENT := n
> > diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> > index cd9c3fa25902f..d48fc0df07020 100644
> > --- a/arch/arm64/kernel/vdso/Makefile
> > +++ b/arch/arm64/kernel/vdso/Makefile
> > @@ -41,8 +41,9 @@ ifneq ($(c-gettimeofday-y),)
> >    CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
> >  endif
> >
> > -# Disable gcov profiling for VDSO code
> > +# Disable gcov and PGO profiling for VDSO code
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  obj-y += vdso.o
> >  targets += vdso.lds
> > diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> > index 1f1e351c5fe2b..ad128ecdbfbdf 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> > +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> > @@ -60,6 +60,7 @@ KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_FTRACE) $(CC_FLAGS_SCS), $(KBUILD_CFLAG
> >  # compiler instrumentation that inserts callbacks or checks into the code may
> >  # cause crashes. Just disable it.
> >  GCOV_PROFILE   := n
> > +PGO_PROFILE    := n
> >  KASAN_SANITIZE := n
> >  UBSAN_SANITIZE := n
> >  KCOV_INSTRUMENT        := n
> > diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile
> > index 47cd9dc7454af..0855ea12f2c7f 100644
> > --- a/arch/mips/boot/compressed/Makefile
> > +++ b/arch/mips/boot/compressed/Makefile
> > @@ -37,6 +37,7 @@ KBUILD_AFLAGS := $(KBUILD_AFLAGS) -D__ASSEMBLY__ \
> >  # Prevents link failures: __sanitizer_cov_trace_pc() is not linked in.
> >  KCOV_INSTRUMENT                := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  # decompressor objects (linked with vmlinuz)
> >  vmlinuzobjs-y := $(obj)/head.o $(obj)/decompress.o $(obj)/string.o
> > diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> > index 5810cc12bc1d9..d7eb64de35eae 100644
> > --- a/arch/mips/vdso/Makefile
> > +++ b/arch/mips/vdso/Makefile
> > @@ -66,6 +66,7 @@ ldflags-y := -Bsymbolic --no-undefined -soname=linux-vdso.so.1 \
> >  CFLAGS_REMOVE_vdso.o = -pg
> >
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >  KCOV_INSTRUMENT := n
> >
> > diff --git a/arch/nds32/kernel/vdso/Makefile b/arch/nds32/kernel/vdso/Makefile
> > index 55df25ef00578..f2b53ee2124b7 100644
> > --- a/arch/nds32/kernel/vdso/Makefile
> > +++ b/arch/nds32/kernel/vdso/Makefile
> > @@ -15,9 +15,9 @@ obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
> >  ccflags-y := -shared -fno-common -fno-builtin -nostdlib -fPIC -Wl,-shared -g \
> >         -Wl,-soname=linux-vdso.so.1 -Wl,--hash-style=sysv
> >
> > -# Disable gcov profiling for VDSO code
> > +# Disable gcov and PGO profiling for VDSO code
> >  GCOV_PROFILE := n
> > -
> > +PGO_PROFILE := n
> >
> >  obj-y += vdso.o
> >  targets += vdso.lds
> > diff --git a/arch/parisc/boot/compressed/Makefile b/arch/parisc/boot/compressed/Makefile
> > index dff4536875305..5cf93a67f7da7 100644
> > --- a/arch/parisc/boot/compressed/Makefile
> > +++ b/arch/parisc/boot/compressed/Makefile
> > @@ -7,6 +7,7 @@
> >
> >  KCOV_INSTRUMENT := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >
> >  targets := vmlinux.lds vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2
> > diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> > index fe2ef598e2ead..c642c046660d7 100644
> > --- a/arch/powerpc/kernel/Makefile
> > +++ b/arch/powerpc/kernel/Makefile
> > @@ -153,17 +153,21 @@ endif
> >  obj-$(CONFIG_PPC_SECURE_BOOT)  += secure_boot.o ima_arch.o secvar-ops.o
> >  obj-$(CONFIG_PPC_SECVAR_SYSFS) += secvar-sysfs.o
> >
> > -# Disable GCOV, KCOV & sanitizers in odd or sensitive code
> > +# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
> >  GCOV_PROFILE_prom_init.o := n
> > +PGO_PROFILE_prom_init.o := n
> >  KCOV_INSTRUMENT_prom_init.o := n
> >  UBSAN_SANITIZE_prom_init.o := n
> >  GCOV_PROFILE_kprobes.o := n
> > +PGO_PROFILE_kprobes.o := n
> >  KCOV_INSTRUMENT_kprobes.o := n
> >  UBSAN_SANITIZE_kprobes.o := n
> >  GCOV_PROFILE_kprobes-ftrace.o := n
> > +PGO_PROFILE_kprobes-ftrace.o := n
> >  KCOV_INSTRUMENT_kprobes-ftrace.o := n
> >  UBSAN_SANITIZE_kprobes-ftrace.o := n
> >  GCOV_PROFILE_syscall_64.o := n
> > +PGO_PROFILE_syscall_64.o := n
> >  KCOV_INSTRUMENT_syscall_64.o := n
> >  UBSAN_SANITIZE_syscall_64.o := n
> >  UBSAN_SANITIZE_vdso.o := n
> > diff --git a/arch/powerpc/kernel/trace/Makefile b/arch/powerpc/kernel/trace/Makefile
> > index 858503775c583..7d72ae7d4f8c6 100644
> > --- a/arch/powerpc/kernel/trace/Makefile
> > +++ b/arch/powerpc/kernel/trace/Makefile
> > @@ -23,7 +23,8 @@ obj-$(CONFIG_TRACING)                 += trace_clock.o
> >  obj-$(CONFIG_PPC64)                    += $(obj64-y)
> >  obj-$(CONFIG_PPC32)                    += $(obj32-y)
> >
> > -# Disable GCOV, KCOV & sanitizers in odd or sensitive code
> > +# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
> >  GCOV_PROFILE_ftrace.o := n
> > +PGO_PROFILE_ftrace.o := n
> >  KCOV_INSTRUMENT_ftrace.o := n
> >  UBSAN_SANITIZE_ftrace.o := n
> > diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
> > index 9cb6f524854b9..655e159975a04 100644
> > --- a/arch/powerpc/kernel/vdso32/Makefile
> > +++ b/arch/powerpc/kernel/vdso32/Makefile
> > @@ -34,6 +34,7 @@ targets := $(obj-vdso32) vdso32.so.dbg
> >  obj-vdso32 := $(addprefix $(obj)/, $(obj-vdso32))
> >
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  KCOV_INSTRUMENT := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> > diff --git a/arch/powerpc/kernel/vdso64/Makefile b/arch/powerpc/kernel/vdso64/Makefile
> > index bf363ff371521..12c286f5afc16 100644
> > --- a/arch/powerpc/kernel/vdso64/Makefile
> > +++ b/arch/powerpc/kernel/vdso64/Makefile
> > @@ -21,6 +21,7 @@ targets := $(obj-vdso64) vdso64.so.dbg
> >  obj-vdso64 := $(addprefix $(obj)/, $(obj-vdso64))
> >
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  KCOV_INSTRUMENT := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> > diff --git a/arch/powerpc/kexec/Makefile b/arch/powerpc/kexec/Makefile
> > index 4aff6846c7726..1c7f65e3cb969 100644
> > --- a/arch/powerpc/kexec/Makefile
> > +++ b/arch/powerpc/kexec/Makefile
> > @@ -16,7 +16,8 @@ endif
> >  endif
> >
> >
> > -# Disable GCOV, KCOV & sanitizers in odd or sensitive code
> > +# Disable GCOV, PGO, KCOV & sanitizers in odd or sensitive code
> >  GCOV_PROFILE_core_$(BITS).o := n
> > +PGO_PROFILE_core_$(BITS).o := n
> >  KCOV_INSTRUMENT_core_$(BITS).o := n
> >  UBSAN_SANITIZE_core_$(BITS).o := n
> > diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
> > index eb25d7554ffd1..7aff80d18b44b 100644
> > --- a/arch/powerpc/xmon/Makefile
> > +++ b/arch/powerpc/xmon/Makefile
> > @@ -2,6 +2,7 @@
> >  # Makefile for xmon
> >
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  KCOV_INSTRUMENT := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> > diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
> > index 0cfd6da784f84..882340dc3c647 100644
> > --- a/arch/riscv/kernel/vdso/Makefile
> > +++ b/arch/riscv/kernel/vdso/Makefile
> > @@ -32,8 +32,9 @@ CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
> >  # Disable -pg to prevent insert call site
> >  CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
> >
> > -# Disable gcov profiling for VDSO code
> > +# Disable gcov and PGO profiling for VDSO code
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  KCOV_INSTRUMENT := n
> >
> >  # Force dependency
> > diff --git a/arch/s390/boot/Makefile b/arch/s390/boot/Makefile
> > index 41a64b8dce252..bee4a32040e79 100644
> > --- a/arch/s390/boot/Makefile
> > +++ b/arch/s390/boot/Makefile
> > @@ -5,6 +5,7 @@
> >
> >  KCOV_INSTRUMENT := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> >
> > diff --git a/arch/s390/boot/compressed/Makefile b/arch/s390/boot/compressed/Makefile
> > index de18dab518bb6..c3ab883e8425a 100644
> > --- a/arch/s390/boot/compressed/Makefile
> > +++ b/arch/s390/boot/compressed/Makefile
> > @@ -7,6 +7,7 @@
> >
> >  KCOV_INSTRUMENT := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> >
> > diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
> > index dd73b7f074237..bd857aacad794 100644
> > --- a/arch/s390/kernel/Makefile
> > +++ b/arch/s390/kernel/Makefile
> > @@ -14,6 +14,7 @@ CFLAGS_REMOVE_early.o         = $(CC_FLAGS_FTRACE)
> >  endif
> >
> >  GCOV_PROFILE_early.o           := n
> > +PGO_PROFILE_early.o            := n
> >  KCOV_INSTRUMENT_early.o                := n
> >  UBSAN_SANITIZE_early.o         := n
> >  KASAN_SANITIZE_ipl.o           := n
> > diff --git a/arch/s390/kernel/vdso64/Makefile b/arch/s390/kernel/vdso64/Makefile
> > index a6e0fb6b91d6c..d7c43b7c1db96 100644
> > --- a/arch/s390/kernel/vdso64/Makefile
> > +++ b/arch/s390/kernel/vdso64/Makefile
> > @@ -35,8 +35,9 @@ obj-y += vdso64_wrapper.o
> >  targets += vdso64.lds
> >  CPPFLAGS_vdso64.lds += -P -C -U$(ARCH)
> >
> > -# Disable gcov profiling, ubsan and kasan for VDSO code
> > +# Disable gcov and PGO profiling, ubsan and kasan for VDSO code
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> >
> > diff --git a/arch/s390/purgatory/Makefile b/arch/s390/purgatory/Makefile
> > index c57f8c40e9926..9aef584e98466 100644
> > --- a/arch/s390/purgatory/Makefile
> > +++ b/arch/s390/purgatory/Makefile
> > @@ -17,6 +17,7 @@ $(obj)/mem.o: $(srctree)/arch/s390/lib/mem.S FORCE
> >
> >  KCOV_INSTRUMENT := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >  KASAN_SANITIZE := n
> >
> > diff --git a/arch/sh/boot/compressed/Makefile b/arch/sh/boot/compressed/Makefile
> > index 589d2d8a573db..ae19aeeb3964c 100644
> > --- a/arch/sh/boot/compressed/Makefile
> > +++ b/arch/sh/boot/compressed/Makefile
> > @@ -13,6 +13,7 @@ targets               := vmlinux vmlinux.bin vmlinux.bin.gz \
> >  OBJECTS = $(obj)/head_32.o $(obj)/misc.o $(obj)/cache.o
> >
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  #
> >  # IMAGE_OFFSET is the load offset of the compression loader
> > diff --git a/arch/sh/mm/Makefile b/arch/sh/mm/Makefile
> > index f69ddc70b1465..ea2782c631f43 100644
> > --- a/arch/sh/mm/Makefile
> > +++ b/arch/sh/mm/Makefile
> > @@ -43,3 +43,4 @@ obj-$(CONFIG_UNCACHED_MAPPING)        += uncached.o
> >  obj-$(CONFIG_HAVE_SRAM_POOL)   += sram.o
> >
> >  GCOV_PROFILE_pmb.o := n
> > +PGO_PROFILE_pmb.o := n
> > diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> > index c5e1545bc5cf9..ab5f3783fe199 100644
> > --- a/arch/sparc/vdso/Makefile
> > +++ b/arch/sparc/vdso/Makefile
> > @@ -115,6 +115,7 @@ quiet_cmd_vdso = VDSO    $@
> >
> >  VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 -Bsymbolic
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  #
> >  # Install the unstripped copies of vdso*.so.  If our toolchain supports
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 7b6dd10b162ac..a751b4f8f6645 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -95,6 +95,7 @@ config X86
> >         select ARCH_SUPPORTS_DEBUG_PAGEALLOC
> >         select ARCH_SUPPORTS_NUMA_BALANCING     if X86_64
> >         select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP       if NR_CPUS <= 4096
> > +       select ARCH_SUPPORTS_PGO_CLANG          if X86_64
> >         select ARCH_USE_BUILTIN_BSWAP
> >         select ARCH_USE_QUEUED_RWLOCKS
> >         select ARCH_USE_QUEUED_SPINLOCKS
> > diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
> > index fe605205b4ce2..383853e32f673 100644
> > --- a/arch/x86/boot/Makefile
> > +++ b/arch/x86/boot/Makefile
> > @@ -71,6 +71,7 @@ KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> >  KBUILD_CFLAGS  += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
> >  KBUILD_CFLAGS  += -fno-asynchronous-unwind-tables
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> >
> >  $(obj)/bzImage: asflags-y  := $(SVGA_MODE)
> > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> > index e0bc3988c3faa..ed12ab65f6065 100644
> > --- a/arch/x86/boot/compressed/Makefile
> > +++ b/arch/x86/boot/compressed/Makefile
> > @@ -54,6 +54,7 @@ CFLAGS_sev-es.o += -I$(objtree)/arch/x86/lib/
> >
> >  KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE :=n
> >
> >  KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
> > diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> > index 02e3e42f380bd..26e2b3af0145c 100644
> > --- a/arch/x86/entry/vdso/Makefile
> > +++ b/arch/x86/entry/vdso/Makefile
> > @@ -179,6 +179,7 @@ quiet_cmd_vdso = VDSO    $@
> >  VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 \
> >         $(call ld-option, --eh-frame-hdr) -Bsymbolic
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  quiet_cmd_vdso_and_check = VDSO    $@
> >        cmd_vdso_and_check = $(cmd_vdso); $(cmd_vdso_check)
> > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> > index efd9e9ea17f25..f6cab2316c46a 100644
> > --- a/arch/x86/kernel/vmlinux.lds.S
> > +++ b/arch/x86/kernel/vmlinux.lds.S
> > @@ -184,6 +184,8 @@ SECTIONS
> >
> >         BUG_TABLE
> >
> > +       PGO_CLANG_DATA
> > +
> >         ORC_UNWIND_TABLE
> >
> >         . = ALIGN(PAGE_SIZE);
> > diff --git a/arch/x86/platform/efi/Makefile b/arch/x86/platform/efi/Makefile
> > index 84b09c230cbd5..5f22b31446ad4 100644
> > --- a/arch/x86/platform/efi/Makefile
> > +++ b/arch/x86/platform/efi/Makefile
> > @@ -2,6 +2,7 @@
> >  OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
> >  KASAN_SANITIZE := n
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  obj-$(CONFIG_EFI)              += quirks.o efi.o efi_$(BITS).o efi_stub_$(BITS).o
> >  obj-$(CONFIG_EFI_MIXED)                += efi_thunk_$(BITS).o
> > diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> > index 95ea17a9d20cb..36f20e99da0bc 100644
> > --- a/arch/x86/purgatory/Makefile
> > +++ b/arch/x86/purgatory/Makefile
> > @@ -23,6 +23,7 @@ targets += purgatory.ro purgatory.chk
> >
> >  # Sanitizer, etc. runtimes are unavailable and cannot be linked here.
> >  GCOV_PROFILE   := n
> > +PGO_PROFILE    := n
> >  KASAN_SANITIZE := n
> >  UBSAN_SANITIZE := n
> >  KCSAN_SANITIZE := n
> > diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
> > index 83f1b6a56449f..21797192f958f 100644
> > --- a/arch/x86/realmode/rm/Makefile
> > +++ b/arch/x86/realmode/rm/Makefile
> > @@ -76,4 +76,5 @@ KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP -D_WAKEUP \
> >  KBUILD_AFLAGS  := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> >  KBUILD_CFLAGS  += -fno-asynchronous-unwind-tables
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >  UBSAN_SANITIZE := n
> > diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
> > index 5943387e3f357..54f5768f58530 100644
> > --- a/arch/x86/um/vdso/Makefile
> > +++ b/arch/x86/um/vdso/Makefile
> > @@ -64,6 +64,7 @@ quiet_cmd_vdso = VDSO    $@
> >
> >  VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv
> >  GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> >  #
> >  # Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
> > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> > index 8a94388e38b33..2d81623b33f29 100644
> > --- a/drivers/firmware/efi/libstub/Makefile
> > +++ b/drivers/firmware/efi/libstub/Makefile
> > @@ -40,6 +40,7 @@ KBUILD_CFLAGS                 := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
> >  KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
> >
> >  GCOV_PROFILE                   := n
> > +PGO_PROFILE                    := n
> >  # Sanitizer runtimes are unavailable and cannot be linked here.
> >  KASAN_SANITIZE                 := n
> >  KCSAN_SANITIZE                 := n
> > diff --git a/drivers/s390/char/Makefile b/drivers/s390/char/Makefile
> > index c6fdb81a068a6..bf6c5db5da1fc 100644
> > --- a/drivers/s390/char/Makefile
> > +++ b/drivers/s390/char/Makefile
> > @@ -9,6 +9,7 @@ CFLAGS_REMOVE_sclp_early_core.o = $(CC_FLAGS_FTRACE)
> >  endif
> >
> >  GCOV_PROFILE_sclp_early_core.o         := n
> > +PGO_PROFILE_sclp_early_core.o          := n
> >  KCOV_INSTRUMENT_sclp_early_core.o      := n
> >  UBSAN_SANITIZE_sclp_early_core.o       := n
> >  KASAN_SANITIZE_sclp_early_core.o       := n
> > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> > index b2b3d81b1535a..3a591bb18c5fb 100644
> > --- a/include/asm-generic/vmlinux.lds.h
> > +++ b/include/asm-generic/vmlinux.lds.h
> > @@ -316,6 +316,49 @@
> >  #define THERMAL_TABLE(name)
> >  #endif
> >
> > +#ifdef CONFIG_PGO_CLANG
> > +#define PGO_CLANG_DATA                                                 \
> > +       __llvm_prf_data : AT(ADDR(__llvm_prf_data) - LOAD_OFFSET) {     \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_start = .;                                   \
> > +               __llvm_prf_data_start = .;                              \
> > +               KEEP(*(__llvm_prf_data))                                \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_data_end = .;                                \
> > +       }                                                               \
> > +       __llvm_prf_cnts : AT(ADDR(__llvm_prf_cnts) - LOAD_OFFSET) {     \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_cnts_start = .;                              \
> > +               KEEP(*(__llvm_prf_cnts))                                \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_cnts_end = .;                                \
> > +       }                                                               \
> > +       __llvm_prf_names : AT(ADDR(__llvm_prf_names) - LOAD_OFFSET) {   \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_names_start = .;                             \
> > +               KEEP(*(__llvm_prf_names))                               \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_names_end = .;                               \
> > +               . = ALIGN(8);                                           \
> > +       }                                                               \
> > +       __llvm_prf_vals : AT(ADDR(__llvm_prf_vals) - LOAD_OFFSET) {     \
> > +               __llvm_prf_vals_start = .;                              \
> > +               KEEP(*(__llvm_prf_vals))                                \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_vals_end = .;                                \
> > +               . = ALIGN(8);                                           \
> > +       }                                                               \
> > +       __llvm_prf_vnds : AT(ADDR(__llvm_prf_vnds) - LOAD_OFFSET) {     \
> > +               __llvm_prf_vnds_start = .;                              \
> > +               KEEP(*(__llvm_prf_vnds))                                \
> > +               . = ALIGN(8);                                           \
> > +               __llvm_prf_vnds_end = .;                                \
> > +               __llvm_prf_end = .;                                     \
> > +       }
> > +#else
> > +#define PGO_CLANG_DATA
> > +#endif
> > +
> >  #define KERNEL_DTB()                                                   \
> >         STRUCT_ALIGN();                                                 \
> >         __dtb_start = .;                                                \
> > @@ -1125,6 +1168,7 @@
> >                 CONSTRUCTORS                                            \
> >         }                                                               \
> >         BUG_TABLE                                                       \
> > +       PGO_CLANG_DATA
> >
> >  #define INIT_TEXT_SECTION(inittext_align)                              \
> >         . = ALIGN(inittext_align);                                      \
> > diff --git a/kernel/Makefile b/kernel/Makefile
> > index aa7368c7eabf3..0b34ca228ba46 100644
> > --- a/kernel/Makefile
> > +++ b/kernel/Makefile
> > @@ -111,6 +111,7 @@ obj-$(CONFIG_BPF) += bpf/
> >  obj-$(CONFIG_KCSAN) += kcsan/
> >  obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o
> >  obj-$(CONFIG_HAVE_STATIC_CALL_INLINE) += static_call.o
> > +obj-$(CONFIG_PGO_CLANG) += pgo/
> >
> >  obj-$(CONFIG_PERF_EVENTS) += events/
> >
> > diff --git a/kernel/pgo/Kconfig b/kernel/pgo/Kconfig
> > new file mode 100644
> > index 0000000000000..318d36bb3d106
> > --- /dev/null
> > +++ b/kernel/pgo/Kconfig
> > @@ -0,0 +1,34 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +menu "Profile Guided Optimization (PGO) (EXPERIMENTAL)"
> > +
> > +config ARCH_SUPPORTS_PGO_CLANG
> > +       bool
> > +
> > +config PGO_CLANG
> > +       bool "Enable clang's PGO-based kernel profiling"
> > +       depends on DEBUG_FS
> > +       depends on ARCH_SUPPORTS_PGO_CLANG
> > +       help
> > +         This option enables clang's PGO (Profile Guided Optimization) based
> > +         code profiling to better optimize the kernel.
> > +
> > +         If unsure, say N.
> > +
> > +         Run a representative workload for your application on a kernel
> > +         compiled with this option and download the raw profile file from
> > +         /sys/kernel/debug/pgo/profraw. This file needs to be processed with
> > +         llvm-profdata. It may be merged with other collected raw profiles.
> > +
> > +         Copy the resulting profile file into vmlinux.profdata, and enable
> > +         KCFLAGS=-fprofile-use=vmlinux.profdata to produce an optimized
> > +         kernel.
> > +
> > +         Note that a kernel compiled with profiling flags will be
> > +         significatnly larger and run slower. Also be sure to exclude files
> > +         from profiling which are not linked to the kernel image to prevent
> > +         linker errors.
> > +
> > +         Note that the debugfs filesystem has to be mounted to access
> > +         profiling data.
> > +
> > +endmenu
> > diff --git a/kernel/pgo/Makefile b/kernel/pgo/Makefile
> > new file mode 100644
> > index 0000000000000..41e27cefd9a47
> > --- /dev/null
> > +++ b/kernel/pgo/Makefile
> > @@ -0,0 +1,5 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +GCOV_PROFILE   := n
> > +PGO_PROFILE    := n
> > +
> > +obj-y  += fs.o instrument.o
> > diff --git a/kernel/pgo/fs.c b/kernel/pgo/fs.c
> > new file mode 100644
> > index 0000000000000..790a8df037bfc
> > --- /dev/null
> > +++ b/kernel/pgo/fs.c
> > @@ -0,0 +1,382 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 Google, Inc.
> > + *
> > + * Author:
> > + *     Sami Tolvanen <samitolvanen@google.com>
> > + *
> > + * This software is licensed under the terms of the GNU General Public
> > + * License version 2, as published by the Free Software Foundation, and
> > + * may be copied, distributed, and modified under those terms.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + */
> > +
> > +#define pr_fmt(fmt)    "pgo: " fmt
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/debugfs.h>
> > +#include <linux/fs.h>
> > +#include <linux/module.h>
> > +#include <linux/slab.h>
> > +#include <linux/vmalloc.h>
> > +#include "pgo.h"
> > +
> > +static struct dentry *directory;
> > +
> > +struct prf_private_data {
> > +       void *buffer;
> > +       unsigned long size;
> > +};
> > +
> > +/*
> > + * Raw profile data format:
> > + *
> > + *     - llvm_prf_header
> > + *     - __llvm_prf_data
> > + *     - __llvm_prf_cnts
> > + *     - __llvm_prf_names
> > + *     - zero padding to 8 bytes
> > + *     - for each llvm_prf_data in __llvm_prf_data:
> > + *             - llvm_prf_value_data
> > + *                     - llvm_prf_value_record + site count array
> > + *                             - llvm_prf_value_node_data
> > + *                             ...
> > + *                     ...
> > + *             ...
> > + */
> > +
> > +static void prf_fill_header(void **buffer)
> > +{
> > +       struct llvm_prf_header *header = *(struct llvm_prf_header **)buffer;
> > +
> > +       header->magic = LLVM_PRF_MAGIC;
> > +       header->version = LLVM_PRF_VARIANT_MASK_IR | LLVM_PRF_VERSION;
> > +       header->data_size = prf_data_count();
> > +       header->padding_bytes_before_counters = 0;
> > +       header->counters_size = prf_cnts_count();
> > +       header->padding_bytes_after_counters = 0;
> > +       header->names_size = prf_names_count();
> > +       header->counters_delta = (u64)__llvm_prf_cnts_start;
> > +       header->names_delta = (u64)__llvm_prf_names_start;
> > +       header->value_kind_last = LLVM_PRF_IPVK_LAST;
> > +
> > +       *buffer += sizeof(*header);
> > +}
> > +
> > +/*
> > + * Copy the source into the buffer, incrementing the pointer into buffer in the
> > + * process.
> > + */
> > +static void prf_copy_to_buffer(void **buffer, void *src, unsigned long size)
> > +{
> > +       memcpy(*buffer, src, size);
> > +       *buffer += size;
> > +}
> > +
> > +static u32 __prf_get_value_size(struct llvm_prf_data *p, u32 *value_kinds)
> > +{
> > +       struct llvm_prf_value_node **nodes =
> > +               (struct llvm_prf_value_node **)p->values;
> > +       u32 kinds = 0;
> > +       u32 size = 0;
> > +       unsigned int kind;
> > +       unsigned int n;
> > +       unsigned int s = 0;
> > +
> > +       for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
> > +               unsigned int sites = p->num_value_sites[kind];
> > +
> > +               if (!sites)
> > +                       continue;
> > +
> > +               /* Record + site count array */
> > +               size += prf_get_value_record_size(sites);
> > +               kinds++;
> > +
> > +               if (!nodes)
> > +                       continue;
> > +
> > +               for (n = 0; n < sites; n++) {
> > +                       u32 count = 0;
> > +                       struct llvm_prf_value_node *site = nodes[s + n];
> > +
> > +                       while (site && ++count <= U8_MAX)
> > +                               site = site->next;
> > +
> > +                       size += count *
> > +                               sizeof(struct llvm_prf_value_node_data);
> > +               }
> > +
> > +               s += sites;
> > +       }
> > +
> > +       if (size)
> > +               size += sizeof(struct llvm_prf_value_data);
> > +
> > +       if (value_kinds)
> > +               *value_kinds = kinds;
> > +
> > +       return size;
> > +}
> > +
> > +static u32 prf_get_value_size(void)
> > +{
> > +       u32 size = 0;
> > +       struct llvm_prf_data *p;
> > +
> > +       for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
> > +               size += __prf_get_value_size(p, NULL);
> > +
> > +       return size;
> > +}
> > +
> > +/* Serialize the profiling's value. */
> > +static void prf_serialize_value(struct llvm_prf_data *p, void **buffer)
> > +{
> > +       struct llvm_prf_value_data header;
> > +       struct llvm_prf_value_node **nodes =
> > +               (struct llvm_prf_value_node **)p->values;
> > +       unsigned int kind;
> > +       unsigned int n;
> > +       unsigned int s = 0;
> > +
> > +       header.total_size = __prf_get_value_size(p, &header.num_value_kinds);
> > +
> > +       if (!header.num_value_kinds)
> > +               /* Nothing to write. */
> > +               return;
> > +
> > +       prf_copy_to_buffer(buffer, &header, sizeof(header));
> > +
> > +       for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
> > +               struct llvm_prf_value_record *record;
> > +               u8 *counts;
> > +               unsigned int sites = p->num_value_sites[kind];
> > +
> > +               if (!sites)
> > +                       continue;
> > +
> > +               /* Profiling value record. */
> > +               record = *(struct llvm_prf_value_record **)buffer;
> > +               *buffer += prf_get_value_record_header_size();
> > +
> > +               record->kind = kind;
> > +               record->num_value_sites = sites;
> > +
> > +               /* Site count array. */
> > +               counts = *(u8 **)buffer;
> > +               *buffer += prf_get_value_record_site_count_size(sites);
> > +
> > +               /*
> > +                * If we don't have nodes, we can skip updating the site count
> > +                * array, because the buffer is zero filled.
> > +                */
> > +               if (!nodes)
> > +                       continue;
> > +
> > +               for (n = 0; n < sites; n++) {
> > +                       u32 count = 0;
> > +                       struct llvm_prf_value_node *site = nodes[s + n];
> > +
> > +                       while (site && ++count <= U8_MAX) {
> > +                               prf_copy_to_buffer(buffer, site,
> > +                                                  sizeof(struct llvm_prf_value_node_data));
> > +                               site = site->next;
> > +                       }
> > +
> > +                       counts[n] = (u8)count;
> > +               }
> > +
> > +               s += sites;
> > +       }
> > +}
> > +
> > +static void prf_serialize_values(void **buffer)
> > +{
> > +       struct llvm_prf_data *p;
> > +
> > +       for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
> > +               prf_serialize_value(p, buffer);
> > +}
> > +
> > +static inline unsigned long prf_get_padding(unsigned long size)
> > +{
> > +       return 8 - (size % 8);
> > +}
> > +
> > +static unsigned long prf_buffer_size(void)
> > +{
> > +       return sizeof(struct llvm_prf_header) +
> > +                       prf_data_size() +
> > +                       prf_cnts_size() +
> > +                       prf_names_size() +
> > +                       prf_get_padding(prf_names_size()) +
> > +                       prf_get_value_size();
> > +}
> > +
> > +/* Serialize the profling data into a format LLVM's tools can understand. */
> > +static int prf_serialize(struct prf_private_data *p)
> > +{
> > +       int err = 0;
> > +       void *buffer;
> > +
> > +       p->size = prf_buffer_size();
> > +       p->buffer = vzalloc(p->size);
> > +
> > +       if (!p->buffer) {
> > +               err = -ENOMEM;
> > +               goto out;
> > +       }
> > +
> > +       buffer = p->buffer;
> > +
> > +       prf_fill_header(&buffer);
> > +       prf_copy_to_buffer(&buffer, __llvm_prf_data_start,  prf_data_size());
> > +       prf_copy_to_buffer(&buffer, __llvm_prf_cnts_start,  prf_cnts_size());
> > +       prf_copy_to_buffer(&buffer, __llvm_prf_names_start, prf_names_size());
> > +       buffer += prf_get_padding(prf_names_size());
> > +
> > +       prf_serialize_values(&buffer);
> > +
> > +out:
> > +       return err;
> > +}
> > +
> > +/* open() implementation for PGO. Creates a copy of the profiling data set. */
> > +static int prf_open(struct inode *inode, struct file *file)
> > +{
> > +       struct prf_private_data *data;
> > +       unsigned long flags;
> > +       int err;
> > +
> > +       data = kzalloc(sizeof(*data), GFP_KERNEL);
> > +       if (!data) {
> > +               err = -ENOMEM;
> > +               goto out;
> > +       }
> > +
> > +       flags = prf_lock();
> > +
> > +       err = prf_serialize(data);
> > +       if (err) {
> > +               kfree(data);
> > +               goto out_unlock;
> > +       }
> > +
> > +       file->private_data = data;
> > +
> > +out_unlock:
> > +       prf_unlock(flags);
> > +out:
> > +       return err;
> > +}
> > +
> > +/* read() implementation for PGO. */
> > +static ssize_t prf_read(struct file *file, char __user *buf, size_t count,
> > +                       loff_t *ppos)
> > +{
> > +       struct prf_private_data *data = file->private_data;
> > +
> > +       BUG_ON(!data);
> > +
> > +       return simple_read_from_buffer(buf, count, ppos, data->buffer,
> > +                                      data->size);
> > +}
> > +
> > +/* release() implementation for PGO. Release resources allocated by open(). */
> > +static int prf_release(struct inode *inode, struct file *file)
> > +{
> > +       struct prf_private_data *data = file->private_data;
> > +
> > +       if (data) {
> > +               vfree(data->buffer);
> > +               kfree(data);
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> > +static const struct file_operations prf_fops = {
> > +       .owner          = THIS_MODULE,
> > +       .open           = prf_open,
> > +       .read           = prf_read,
> > +       .llseek         = default_llseek,
> > +       .release        = prf_release
> > +};
> > +
> > +/* write() implementation for resetting PGO's profile data. */
> > +static ssize_t reset_write(struct file *file, const char __user *addr,
> > +                          size_t len, loff_t *pos)
> > +{
> > +       struct llvm_prf_data *data;
> > +
> > +       memset(__llvm_prf_cnts_start, 0, prf_cnts_size());
> > +
> > +       for (data = __llvm_prf_data_start; data < __llvm_prf_data_end; ++data) {
> > +               struct llvm_prf_value_node **vnodes;
> > +               u64 current_vsite_count;
> > +               u32 i;
> > +
> > +               if (!data->values)
> > +                       continue;
> > +
> > +               current_vsite_count = 0;
> > +               vnodes = (struct llvm_prf_value_node **)data->values;
> > +
> > +               for (i = LLVM_PRF_IPVK_FIRST; i <= LLVM_PRF_IPVK_LAST; ++i)
> > +                       current_vsite_count += data->num_value_sites[i];
> > +
> > +               for (i = 0; i < current_vsite_count; ++i) {
> > +                       struct llvm_prf_value_node *current_vnode = vnodes[i];
> > +
> > +                       while (current_vnode) {
> > +                               current_vnode->count = 0;
> > +                               current_vnode = current_vnode->next;
> > +                       }
> > +               }
> > +       }
> > +
> > +       return len;
> > +}
> > +
> > +static const struct file_operations prf_reset_fops = {
> > +       .owner          = THIS_MODULE,
> > +       .write          = reset_write,
> > +       .llseek         = noop_llseek,
> > +};
> > +
> > +/* Create debugfs entries. */
> > +static int __init pgo_init(void)
> > +{
> > +       directory = debugfs_create_dir("pgo", NULL);
> > +       if (!directory)
> > +               goto err_remove;
> > +
> > +       if (!debugfs_create_file("profraw", 0600, directory, NULL,
> > +                                &prf_fops))
> > +               goto err_remove;
> > +
> > +       if (!debugfs_create_file("reset", 0200, directory, NULL,
> > +                                &prf_reset_fops))
> > +               goto err_remove;
> > +
> > +       return 0;
> > +
> > +err_remove:
> > +       pr_err("initialization failed\n");
> > +       return -EIO;
> > +}
> > +
> > +/* Remove debufs entries. */
> > +static void __exit pgo_exit(void)
> > +{
> > +       debugfs_remove_recursive(directory);
> > +}
> > +
> > +module_init(pgo_init);
> > +module_exit(pgo_exit);
> > diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
> > new file mode 100644
> > index 0000000000000..d96b61a1cf712
> > --- /dev/null
> > +++ b/kernel/pgo/instrument.c
> > @@ -0,0 +1,147 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 Google, Inc.
> > + *
> > + * Author:
> > + *     Sami Tolvanen <samitolvanen@google.com>
> > + *
> > + * This software is licensed under the terms of the GNU General Public
> > + * License version 2, as published by the Free Software Foundation, and
> > + * may be copied, distributed, and modified under those terms.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + */
> > +
> > +#define pr_fmt(fmt)    "pgo: " fmt
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/export.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/types.h>
> > +#include "pgo.h"
> > +
> > +/* Lock guarding value node access and serialization. */
> > +static DEFINE_SPINLOCK(pgo_lock);
> > +static int current_node;
> > +
> > +unsigned long prf_lock(void)
> > +{
> > +       unsigned long flags;
> > +
> > +       spin_lock_irqsave(&pgo_lock, flags);
> > +
> > +       return flags;
> > +}
> > +
> > +void prf_unlock(unsigned long flags)
> > +{
> > +       spin_unlock_irqrestore(&pgo_lock, flags);
> > +}
> > +
> > +/*
> > + * Return a newly allocated profiling value node which contains the tracked
> > + * value by the value profiler.
> > + * Note: caller *must* hold pgo_lock.
> > + */
> > +static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
> > +                                                u32 index, u64 value)
> > +{
> > +       if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
> > +               return NULL; /* Out of nodes */
> > +
> > +       current_node++;
> > +
> > +       /* Make sure the node is entirely within the section */
> > +       if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
> > +           &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
> > +               return NULL;
> > +
> > +       return &__llvm_prf_vnds_start[current_node];
> > +}
> > +
> > +/*
> > + * Counts the number of times a target value is seen.
> > + *
> > + * Records the target value for the CounterIndex if not seen before. Otherwise,
> > + * increments the counter associated w/ the target value.
> > + */
> > +void __llvm_profile_instrument_target(u64 target_value, void *data, u32 index)
> > +{
> > +       struct llvm_prf_data *p = (struct llvm_prf_data *)data;
> > +       struct llvm_prf_value_node **counters;
> > +       struct llvm_prf_value_node *curr;
> > +       struct llvm_prf_value_node *min = NULL;
> > +       struct llvm_prf_value_node *prev = NULL;
> > +       u64 min_count = U64_MAX;
> > +       u8 values = 0;
> > +       unsigned long flags;
> > +
> > +       if (!p || !p->values)
> > +               return;
> > +
> > +       counters = (struct llvm_prf_value_node **)p->values;
> > +       curr = counters[index];
> > +
> > +       while (curr) {
> > +               if (target_value == curr->value) {
> > +                       curr->count++;
> > +                       return;
> > +               }
> > +
> > +               if (curr->count < min_count) {
> > +                       min_count = curr->count;
> > +                       min = curr;
> > +               }
> > +
> > +               prev = curr;
> > +               curr = curr->next;
> > +               values++;
> > +       }
> > +
> > +       if (values >= LLVM_PRF_MAX_NUM_VALS_PER_SITE) {
> > +               if (!min->count || !(--min->count)) {
> > +                       curr = min;
> > +                       curr->value = target_value;
> > +                       curr->count++;
> > +               }
> > +               return;
> > +       }
> > +
> > +       /* Lock when updating the value node structure. */
> > +       flags = prf_lock();
> > +
> > +       curr = allocate_node(p, index, target_value);
> > +       if (!curr)
> > +               goto out;
> > +
> > +       curr->value = target_value;
> > +       curr->count++;
> > +
> > +       if (!counters[index])
> > +               counters[index] = curr;
> > +       else if (prev && !prev->next)
> > +               prev->next = curr;
> > +
> > +out:
> > +       prf_unlock(flags);
> > +}
> > +EXPORT_SYMBOL(__llvm_profile_instrument_target);
> > +
> > +/* Counts the number of times a range of targets values are seen. */
> > +void __llvm_profile_instrument_range(u64 target_value, void *data,
> > +                                    u32 index, s64 precise_start,
> > +                                    s64 precise_last, s64 large_value)
> > +{
> > +       if (large_value != S64_MIN && (s64)target_value >= large_value)
> > +               target_value = large_value;
> > +       else if ((s64)target_value < precise_start ||
> > +                (s64)target_value > precise_last)
> > +               target_value = precise_last + 1;
> > +
> > +       __llvm_profile_instrument_target(target_value, data, index);
> > +}
> > +EXPORT_SYMBOL(__llvm_profile_instrument_range);
> > diff --git a/kernel/pgo/pgo.h b/kernel/pgo/pgo.h
> > new file mode 100644
> > index 0000000000000..df0aa278f28bd
> > --- /dev/null
> > +++ b/kernel/pgo/pgo.h
> > @@ -0,0 +1,206 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2019 Google, Inc.
> > + *
> > + * Author:
> > + *     Sami Tolvanen <samitolvanen@google.com>
> > + *
> > + * This software is licensed under the terms of the GNU General Public
> > + * License version 2, as published by the Free Software Foundation, and
> > + * may be copied, distributed, and modified under those terms.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + */
> > +
> > +#ifndef _PGO_H
> > +#define _PGO_H
> > +
> > +/*
> > + * Note: These internal LLVM definitions must match the compiler version.
> > + * See llvm/include/llvm/ProfileData/InstrProfData.inc in LLVM's source code.
> > + */
> > +
> > +#ifdef CONFIG_64BIT
> > +       #define LLVM_PRF_MAGIC          \
> > +               ((u64)255 << 56 |       \
> > +                (u64)'l' << 48 |       \
> > +                (u64)'p' << 40 |       \
> > +                (u64)'r' << 32 |       \
> > +                (u64)'o' << 24 |       \
> > +                (u64)'f' << 16 |       \
> > +                (u64)'r' << 8  |       \
> > +                (u64)129)
> > +#else
> > +       #define LLVM_PRF_MAGIC          \
> > +               ((u64)255 << 56 |       \
> > +                (u64)'l' << 48 |       \
> > +                (u64)'p' << 40 |       \
> > +                (u64)'r' << 32 |       \
> > +                (u64)'o' << 24 |       \
> > +                (u64)'f' << 16 |       \
> > +                (u64)'R' << 8  |       \
> > +                (u64)129)
> > +#endif
> > +
> > +#define LLVM_PRF_VERSION               5
> > +#define LLVM_PRF_DATA_ALIGN            8
> > +#define LLVM_PRF_IPVK_FIRST            0
> > +#define LLVM_PRF_IPVK_LAST             1
> > +#define LLVM_PRF_MAX_NUM_VALS_PER_SITE 16
> > +
> > +#define LLVM_PRF_VARIANT_MASK_IR       (0x1ull << 56)
> > +#define LLVM_PRF_VARIANT_MASK_CSIR     (0x1ull << 57)
> > +
> > +/**
> > + * struct llvm_prf_header - represents the raw profile header data structure.
> > + * @magic: the magic token for the file format.
> > + * @version: the version of the file format.
> > + * @data_size: the number of entries in the profile data section.
> > + * @padding_bytes_before_counters: the number of padding bytes before the
> > + *   counters.
> > + * @counters_size: the size in bytes of the LLVM profile section containing the
> > + *   counters.
> > + * @padding_bytes_after_counters: the number of padding bytes after the
> > + *   counters.
> > + * @names_size: the size in bytes of the LLVM profile section containing the
> > + *   counters' names.
> > + * @counters_delta: the beginning of the LLMV profile counters section.
> > + * @names_delta: the beginning of the LLMV profile names section.
> > + * @value_kind_last: the last profile value kind.
> > + */
> > +struct llvm_prf_header {
> > +       u64 magic;
> > +       u64 version;
> > +       u64 data_size;
> > +       u64 padding_bytes_before_counters;
> > +       u64 counters_size;
> > +       u64 padding_bytes_after_counters;
> > +       u64 names_size;
> > +       u64 counters_delta;
> > +       u64 names_delta;
> > +       u64 value_kind_last;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_data - represents the per-function control structure.
> > + * @name_ref: the reference to the function's name.
> > + * @func_hash: the hash value of the function.
> > + * @counter_ptr: a pointer to the profile counter.
> > + * @function_ptr: a pointer to the function.
> > + * @values: the profiling values associated with this function.
> > + * @num_counters: the number of counters in the function.
> > + * @num_value_sites: the number of value profile sites.
> > + */
> > +struct llvm_prf_data {
> > +       const u64 name_ref;
> > +       const u64 func_hash;
> > +       const void *counter_ptr;
> > +       const void *function_ptr;
> > +       void *values;
> > +       const u32 num_counters;
> > +       const u16 num_value_sites[LLVM_PRF_IPVK_LAST + 1];
> > +} __aligned(LLVM_PRF_DATA_ALIGN);
> > +
> > +/**
> > + * structure llvm_prf_value_node_data - represents the data part of the struct
> > + *   llvm_prf_value_node data structure.
> > + * @value: the value counters.
> > + * @count: the counters' count.
> > + */
> > +struct llvm_prf_value_node_data {
> > +       u64 value;
> > +       u64 count;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_value_node - represents an internal data structure used by
> > + *   the value profiler.
> > + * @value: the value counters.
> > + * @count: the counters' count.
> > + * @next: the next value node.
> > + */
> > +struct llvm_prf_value_node {
> > +       u64 value;
> > +       u64 count;
> > +       struct llvm_prf_value_node *next;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_value_data - represents the value profiling data in indexed
> > + *   format.
> > + * @total_size: the total size in bytes including this field.
> > + * @num_value_kinds: the number of value profile kinds that has value profile
> > + *   data.
> > + */
> > +struct llvm_prf_value_data {
> > +       u32 total_size;
> > +       u32 num_value_kinds;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_value_record - represents the on-disk layout of the value
> > + *   profile data of a particular kind for one function.
> > + * @kind: the kind of the value profile record.
> > + * @num_value_sites: the number of value profile sites.
> > + * @site_count_array: the first element of the array that stores the number
> > + *   of profiled values for each value site.
> > + */
> > +struct llvm_prf_value_record {
> > +       u32 kind;
> > +       u32 num_value_sites;
> > +       u8 site_count_array[];
> > +};
> > +
> > +#define prf_get_value_record_header_size()             \
> > +       offsetof(struct llvm_prf_value_record, site_count_array)
> > +#define prf_get_value_record_site_count_size(sites)    \
> > +       roundup((sites), 8)
> > +#define prf_get_value_record_size(sites)               \
> > +       (prf_get_value_record_header_size() +           \
> > +        prf_get_value_record_site_count_size((sites)))
> > +
> > +/* Data sections */
> > +extern struct llvm_prf_data __llvm_prf_data_start[];
> > +extern struct llvm_prf_data __llvm_prf_data_end[];
> > +
> > +extern u64 __llvm_prf_cnts_start[];
> > +extern u64 __llvm_prf_cnts_end[];
> > +
> > +extern char __llvm_prf_names_start[];
> > +extern char __llvm_prf_names_end[];
> > +
> > +extern struct llvm_prf_value_node __llvm_prf_vnds_start[];
> > +extern struct llvm_prf_value_node __llvm_prf_vnds_end[];
> > +
> > +/* Locking for vnodes */
> > +extern unsigned long prf_lock(void);
> > +extern void prf_unlock(unsigned long flags);
> > +
> > +#define __DEFINE_PRF_SIZE(s) \
> > +       static inline unsigned long prf_ ## s ## _size(void)            \
> > +       {                                                               \
> > +               unsigned long start =                                   \
> > +                       (unsigned long)__llvm_prf_ ## s ## _start;      \
> > +               unsigned long end =                                     \
> > +                       (unsigned long)__llvm_prf_ ## s ## _end;        \
> > +               return roundup(end - start,                             \
> > +                               sizeof(__llvm_prf_ ## s ## _start[0])); \
> > +       }                                                               \
> > +       static inline unsigned long prf_ ## s ## _count(void)           \
> > +       {                                                               \
> > +               return prf_ ## s ## _size() /                           \
> > +                       sizeof(__llvm_prf_ ## s ## _start[0]);          \
> > +       }
> > +
> > +__DEFINE_PRF_SIZE(data);
> > +__DEFINE_PRF_SIZE(cnts);
> > +__DEFINE_PRF_SIZE(names);
> > +__DEFINE_PRF_SIZE(vnds);
> > +
> > +#undef __DEFINE_PRF_SIZE
> > +
> > +#endif /* _PGO_H */
> > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > index 213677a5ed33e..9b218afb5cb87 100644
> > --- a/scripts/Makefile.lib
> > +++ b/scripts/Makefile.lib
> > @@ -143,6 +143,16 @@ _c_flags += $(if $(patsubst n%,, \
> >                 $(CFLAGS_GCOV))
> >  endif
> >
> > +#
> > +# Enable clang's PGO profiling flags for a file or directory depending on
> > +# variables PGO_PROFILE_obj.o and PGO_PROFILE.
> > +#
> > +ifeq ($(CONFIG_PGO_CLANG),y)
> > +_c_flags += $(if $(patsubst n%,, \
> > +               $(PGO_PROFILE_$(basetarget).o)$(PGO_PROFILE)y), \
> > +               $(CFLAGS_PGO_CLANG))
> > +endif
> > +
> >  #
> >  # Enable address sanitizer flags for kernel except some files or directories
> >  # we don't want to check (depends on variables KASAN_SANITIZE_obj.o, KASAN_SANITIZE)
> > --
> > 2.30.0.284.gd98b1dd5eaa7-goog
> >
> > --
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