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Date:   Fri, 22 Jan 2021 01:14:45 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Bill Wendling <morbo@...gle.com>
Cc:     Jonathan Corbet <corbet@....net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kbuild@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: Re: [PATCH v6] pgo: add clang's Profile Guided Optimization infrastructure

On Thu, Jan 21, 2021 at 9:25 AM 'Bill Wendling' via Clang Built Linux
<clang-built-linux@...glegroups.com> wrote:
>
> From: Sami Tolvanen <samitolvanen@...gle.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 now be used by the compiler:
>
>   $ make LLVM=1 KCFLAGS=-fprofile-use=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, unlike
> the clang support in kernel/gcov.
>
> [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
> Co-developed-by: Bill Wendling <morbo@...gle.com>
> Signed-off-by: Bill Wendling <morbo@...gle.com>
> Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>

Was this v6 compile-tested?

This breaks and errors like this:

  clang -Wp,-MMD,kernel/pgo/.fs.o.d -nostdinc -isystem
/opt/llvm-toolchain/lib/clang/11.1.0/include -I./arch/x86/include
-I./arch/x86/include/generated  -I./include -I
./arch/x86/include/uapi -I./arch/x86/include/generated/uapi
-I./include/uapi -I./include/generated/uapi -include
./include/linux/kconfig.h -include ./include/linux/com
piler_types.h -D__KERNEL__ -Qunused-arguments -fmacro-prefix-map=./=
-Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs
-fno-strict-aliasing -fno-common -fshort-wc
har -fno-PIE -Werror=implicit-function-declaration
-Werror=implicit-int -Werror=return-type -Wno-format-security
-std=gnu89 -Werror=unknown-warning-option -mno-sse -mn
o-mmx -mno-sse2 -mno-3dnow -mno-avx -m64 -mno-80387
-mstack-alignment=8 -mtune=generic -mno-red-zone -mcmodel=kernel
-Wno-sign-compare -fno-asynchronous-unwind-tables
-mretpoline-external-thunk -fno-delete-null-pointer-checks
-Wno-frame-address -Wno-address-of-packed-member -O2
-Wframe-larger-than=2048 -fstack-protector-strong -Wno-
format-invalid-specifier -Wno-gnu -mno-global-merge
-Wno-unused-const-variable -g -gdwarf-5 -g -gdwarf-5 -pg -mfentry
-DCC_USING_FENTRY -Wdeclaration-after-statement -
Wvla -Wno-pointer-sign -Wno-array-bounds -fno-strict-overflow
-fno-stack-check -Werror=date-time -Werror=incompatible-pointer-types
-fcf-protection=none -Wno-initializ
er-overrides -Wno-format -Wno-sign-compare -Wno-format-zero-length
-Wno-pointer-to-enum-cast
-Wno-tautological-constant-out-of-range-compare
-DKBUILD_MODFILE='"ker
nel/pgo/fs"' -DKBUILD_BASENAME='"fs"' -DKBUILD_MODNAME='"fs"' -c -o
kernel/pgo/fs.o kernel/pgo/fs.c
In file included from kernel/pgo/fs.c:27:
kernel/pgo/pgo.h:102:28: error: use of undeclared identifier
'LLVM_PRF_IPVK_LAST'
       const u16 num_value_sites[LLVM_PRF_IPVK_LAST + 1];
                                 ^
kernel/pgo/fs.c:70:28: error: use of undeclared identifier 'LLVM_PRF_IPVK_LAST'
       header->value_kind_last = LLVM_PRF_IPVK_LAST;
                                 ^
2 errors generated.
make[5]: *** [scripts/Makefile.build:279: kernel/pgo/fs.o] Error 1

- Sedat -

> ---
> v2: - Added "__llvm_profile_instrument_memop" based on Nathan Chancellor's
>       testing.
>     - Corrected documentation, re PGO flags when using LTO, based on Fangrui
>       Song's comments.
> v3: - Added change log section based on Sedat Dilek's comments.
> v4: - Remove non-x86 Makfile changes and se "hweight64" instead of using our
>       own popcount implementation, based on Nick Desaulniers's comment.
> v5: - Correct padding calculation, discovered by Nathan Chancellor.
> v6: - Add better documentation about the locking scheme and other things.
>     - Rename macros to better match the same macros in LLVM's source code.
> ---
>  Documentation/dev-tools/index.rst     |   1 +
>  Documentation/dev-tools/pgo.rst       | 127 +++++++++
>  MAINTAINERS                           |   9 +
>  Makefile                              |   3 +
>  arch/Kconfig                          |   1 +
>  arch/x86/Kconfig                      |   1 +
>  arch/x86/boot/Makefile                |   1 +
>  arch/x86/boot/compressed/Makefile     |   1 +
>  arch/x86/crypto/Makefile              |   4 +
>  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 +
>  include/asm-generic/vmlinux.lds.h     |  44 +++
>  kernel/Makefile                       |   1 +
>  kernel/pgo/Kconfig                    |  35 +++
>  kernel/pgo/Makefile                   |   5 +
>  kernel/pgo/fs.c                       | 389 ++++++++++++++++++++++++++
>  kernel/pgo/instrument.c               | 189 +++++++++++++
>  kernel/pgo/pgo.h                      | 203 ++++++++++++++
>  scripts/Makefile.lib                  |  10 +
>  24 files changed, 1032 insertions(+)
>  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 f7809c7b1ba9..8d6418e85806 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 000000000000..b7f11d8405b7
> --- /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 LLVM=1 KCFLAGS=-fprofile-use=vmlinux.profdata ...
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 00836f6452f0..13333026e140 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -13948,6 +13948,15 @@ S:     Maintained
>  F:     include/linux/personality.h
>  F:     include/uapi/linux/personality.h
>
> +PGO BASED KERNEL PROFILING
> +M:     Sami Tolvanen <samitolvanen@...gle.com>
> +M:     Bill Wendling <wcw@...gle.com>
> +R:     Nathan Chancellor <natechancellor@...il.com>
> +R:     Nick Desaulniers <ndesaulniers@...gle.com>
> +S:     Supported
> +F:     Documentation/dev-tools/pgo.rst
> +F:     kernel/pgo
> +
>  PHOENIX RC FLIGHT CONTROLLER ADAPTER
>  M:     Marcus Folkesson <marcus.folkesson@...il.com>
>  L:     linux-input@...r.kernel.org
> diff --git a/Makefile b/Makefile
> index b0e4767735dc..9339541f7cec 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 24862d15f3a3..f39d3991f6bf 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -1112,6 +1112,7 @@ config ARCH_SPLIT_ARG64
>            pairs of 32-bit arguments, select this option.
>
>  source "kernel/gcov/Kconfig"
> +source "kernel/pgo/Kconfig"
>
>  source "scripts/gcc-plugins/Kconfig"
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 21f851179ff0..36305ea61dc0 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -96,6 +96,7 @@ 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 fe605205b4ce..383853e32f67 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  := $(SVGA_MODE)
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index e0bc3988c3fa..ed12ab65f606 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -54,6 +54,7 @@ CFLAGS_sev-es.o += -I$(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/crypto/Makefile b/arch/x86/crypto/Makefile
> index a31de0c6ccde..5753aea7bcbd 100644
> --- a/arch/x86/crypto/Makefile
> +++ b/arch/x86/crypto/Makefile
> @@ -4,6 +4,10 @@
>
>  OBJECT_FILES_NON_STANDARD := y
>
> +# Disable PGO for curve25519-x86_64. With PGO enabled, clang runs out of
> +# registers for some of the functions.
> +PGO_PROFILE_curve25519-x86_64.o := n
> +
>  obj-$(CONFIG_CRYPTO_GLUE_HELPER_X86) += glue_helper.o
>
>  obj-$(CONFIG_CRYPTO_TWOFISH_586) += twofish-i586.o
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 02e3e42f380b..26e2b3af0145 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); $(cmd_vdso_check)
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index efd9e9ea17f2..f6cab2316c46 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -184,6 +184,8 @@ SECTIONS
>
>         BUG_TABLE
>
> +       PGO_CLANG_DATA
> +
>         ORC_UNWIND_TABLE
>
>         . = ALIGN(PAGE_SIZE);
> diff --git a/arch/x86/platform/efi/Makefile b/arch/x86/platform/efi/Makefile
> index 84b09c230cbd..5f22b31446ad 100644
> --- a/arch/x86/platform/efi/Makefile
> +++ b/arch/x86/platform/efi/Makefile
> @@ -2,6 +2,7 @@
>  OBJECT_FILES_NON_STANDARD_efi_thunk_$(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 95ea17a9d20c..36f20e99da0b 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 83f1b6a56449..21797192f958 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 5943387e3f35..54f5768f5853 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 8a94388e38b3..2d81623b33f2 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/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index b2b3d81b1535..3a591bb18c5f 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 aa7368c7eabf..0b34ca228ba4 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 000000000000..76a640b6cf6e
> --- /dev/null
> +++ b/kernel/pgo/Kconfig
> @@ -0,0 +1,35 @@
> +# 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
> +       depends on CC_IS_CLANG && CLANG_VERSION >= 120000
> +       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
> +         significantly 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 000000000000..41e27cefd9a4
> --- /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 000000000000..132ff2ab3feb
> --- /dev/null
> +++ b/kernel/pgo/fs.c
> @@ -0,0 +1,389 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 Google, Inc.
> + *
> + * Author:
> + *     Sami Tolvanen <samitolvanen@...gle.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;
> +
> +#ifdef CONFIG_64BIT
> +       header->magic = LLVM_INSTR_PROF_RAW_MAGIC_64;
> +#else
> +       header->magic = LLVM_INSTR_PROF_RAW_MAGIC_32;
> +#endif
> +       header->version = LLVM_VARIANT_MASK_IR_PROF | LLVM_INSTR_PROF_RAW_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 7 & (sizeof(u64) - size % sizeof(u64));
> +}
> +
> +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 profiling data into a format LLVM's tools can understand.
> + * Note: caller *must* hold pgo_lock.
> + */
> +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 (unlikely(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_INSTR_PROF_IPVK_FIRST; i <= LLVM_INSTR_PROF_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 debugfs 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 000000000000..62ff5cfce7b1
> --- /dev/null
> +++ b/kernel/pgo/instrument.c
> @@ -0,0 +1,189 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2019 Google, Inc.
> + *
> + * Author:
> + *     Sami Tolvanen <samitolvanen@...gle.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/bitops.h>
> +#include <linux/kernel.h>
> +#include <linux/export.h>
> +#include <linux/spinlock.h>
> +#include <linux/types.h>
> +#include "pgo.h"
> +
> +/*
> + * This lock guards both profile count updating and serialization of the
> + * profiling data. Keeping both of these activities separate via locking
> + * ensures that we don't try to serialize data that's only partially updated.
> + */
> +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 index 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);
> +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_INSTR_PROF_MAX_NUM_VAL_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);
> +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);
> +
> +static u64 inst_prof_get_range_rep_value(u64 value)
> +{
> +       if (value <= 8)
> +               /* The first ranges are individually tracked, use it as is. */
> +               return value;
> +       else if (value >= 513)
> +               /* The last range is mapped to its lowest value. */
> +               return 513;
> +       else if (hweight64(value) == 1)
> +               /* If it's a power of two, use it as is. */
> +               return value;
> +
> +       /* Otherwise, take to the previous power of two + 1. */
> +       return (1 << (64 - __builtin_clzll(value) - 1)) + 1;
> +}
> +
> +/*
> + * The target values are partitioned into multiple ranges. The range spec is
> + * defined in compiler-rt/include/profile/InstrProfData.inc.
> + */
> +void __llvm_profile_instrument_memop(u64 target_value, void *data,
> +                                    u32 counter_index);
> +void __llvm_profile_instrument_memop(u64 target_value, void *data,
> +                                    u32 counter_index)
> +{
> +       u64 rep_value;
> +
> +       /* Map the target value to the representative value of its range. */
> +       rep_value = inst_prof_get_range_rep_value(target_value);
> +       __llvm_profile_instrument_target(rep_value, data, counter_index);
> +}
> +EXPORT_SYMBOL(__llvm_profile_instrument_memop);
> diff --git a/kernel/pgo/pgo.h b/kernel/pgo/pgo.h
> new file mode 100644
> index 000000000000..0d33e07a0bf3
> --- /dev/null
> +++ b/kernel/pgo/pgo.h
> @@ -0,0 +1,203 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2019 Google, Inc.
> + *
> + * Author:
> + *     Sami Tolvanen <samitolvanen@...gle.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.
> + */
> +
> +#define LLVM_INSTR_PROF_RAW_MAGIC_64   \
> +               ((u64)255 << 56 |       \
> +                (u64)'l' << 48 |       \
> +                (u64)'p' << 40 |       \
> +                (u64)'r' << 32 |       \
> +                (u64)'o' << 24 |       \
> +                (u64)'f' << 16 |       \
> +                (u64)'r' << 8  |       \
> +                (u64)129)
> +#define LLVM_INSTR_PROF_RAW_MAGIC_32   \
> +               ((u64)255 << 56 |       \
> +                (u64)'l' << 48 |       \
> +                (u64)'p' << 40 |       \
> +                (u64)'r' << 32 |       \
> +                (u64)'o' << 24 |       \
> +                (u64)'f' << 16 |       \
> +                (u64)'R' << 8  |       \
> +                (u64)129)
> +
> +#define LLVM_INSTR_PROF_RAW_VERSION            5
> +#define LLVM_INSTR_PROF_DATA_ALIGNMENT         8
> +#define LLVM_INSTR_PROF_IPVK_FIRST             0
> +#define LLVM_INSTR_PROF_IPVK_LAST              1
> +#define LLVM_INSTR_PROF_MAX_NUM_VAL_PER_SITE   255
> +
> +#define LLVM_VARIANT_MASK_IR_PROF      (0x1ULL << 56)
> +#define LLVM_VARIANT_MASK_CSIR_PROF    (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_INSTR_PROF_DATA_ALIGNMENT);
> +
> +/**
> + * 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 213677a5ed33..9b218afb5cb8 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)
> --
> 2.30.0.296.g2bfb1c46d8-goog
>
> --
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