linux-kernel - Re: [PATCH 8/8] perf docs: Document building with Clang

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Message-ID: <CAP-5=fV45npmMUVGakzpB0XDMJ+WudiHoanBXzJtrX2442k-YA@mail.gmail.com>
Date: Thu, 25 Sep 2025 12:43:55 -0700
From: Ian Rogers <irogers@...gle.com>
To: Leo Yan <leo.yan@....com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Quentin Monnet <qmo@...nel.org>, 
	Andrii Nakryiko <andrii@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	James Clark <james.clark@...aro.org>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, llvm@...ts.linux.dev, bpf@...r.kernel.org
Subject: Re: [PATCH 8/8] perf docs: Document building with Clang

On Thu, Sep 25, 2025 at 3:27 AM Leo Yan <leo.yan@....com> wrote:
>
> Add example commands for building perf with Clang.
>
> Since recent Android NDK releases use Clang as the default compiler, a
> separate Android specific document is no longer needed; point to the
> general build documentation instead.
>
> Signed-off-by: Leo Yan <leo.yan@....com>
> ---
>  tools/perf/Documentation/Build.txt   | 18 ++++++++
>  tools/perf/Documentation/android.txt | 82 ++++--------------------------------
>  2 files changed, 26 insertions(+), 74 deletions(-)
>
> diff --git a/tools/perf/Documentation/Build.txt b/tools/perf/Documentation/Build.txt
> index 83dc87c662b63ecc17553a15cc15a6b8d6f01d83..3e4104e605ac0d7d30b4408ef413cf1f90b034c1 100644
> --- a/tools/perf/Documentation/Build.txt
> +++ b/tools/perf/Documentation/Build.txt
> @@ -99,3 +99,21 @@ configuration paths for cross building:
>  In this case, the variable PKG_CONFIG_SYSROOT_DIR can be used alongside the
>  variable PKG_CONFIG_LIBDIR or PKG_CONFIG_PATH to prepend the sysroot path to
>  the library paths for cross compilation.
> +
> +5) Build with clang
> +===================
> +By default, the makefile uses GCC as compiler. With specifying environment
> +variables HOSTCC, CC and CXX, it allows to build perf with clang.
> +
> +Using clang for native build:
> +
> +  $ HOSTCC=clang CC=clang CXX=clang++ make -C tools/perf
> +
> +Using clang for cross compilation:
> +
> +  $ HOSTCC=clang CC=clang CXX=clang++ \
> +    make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -C tools/perf \
> +    NO_LIBELF=1 NO_LIBTRACEEVENT=1 NO_JEVENTS=1

The three NO_-s here are going to cripple the build quite a lot, I
wonder if we can list package dependencies to install and failing that
use the NO_-s.

> +
> +In the example above, due to lack libelf, python and libtraceevent for
> +cross comiplation, disable the features accordingly.

nit: s/comiplation/compilation/

> diff --git a/tools/perf/Documentation/android.txt b/tools/perf/Documentation/android.txt
> index 24a59998fc91e814ad96f658d3481d88d798b60c..e65204cf2921f6bd8a79875784c5b3d5487ce05d 100644
> --- a/tools/perf/Documentation/android.txt
> +++ b/tools/perf/Documentation/android.txt
> @@ -1,78 +1,12 @@
>  How to compile perf for Android
> -=========================================
> +===============================
>
> -I. Set the Android NDK environment
> -------------------------------------------------
> +There have two ways to build perf and run it on Android.

nit: s/There have/There are/

Thanks for doing this series!
Ian

>
> -(a). Use the Android NDK
> -------------------------------------------------
> -1. You need to download and install the Android Native Development Kit (NDK).
> -Set the NDK variable to point to the path where you installed the NDK:
> -  export NDK=/path/to/android-ndk
> +- The first method is to build perf with static linking, please refer to
> +  Build.txt, section "4) Cross compilation" for how to build a static
> +  perf binary.
>
> -2. Set cross-compiling environment variables for NDK toolchain and sysroot.
> -For arm:
> -  export NDK_TOOLCHAIN=${NDK}/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-
> -  export NDK_SYSROOT=${NDK}/platforms/android-24/arch-arm
> -For x86:
> -  export NDK_TOOLCHAIN=${NDK}/toolchains/x86-4.9/prebuilt/linux-x86_64/bin/i686-linux-android-
> -  export NDK_SYSROOT=${NDK}/platforms/android-24/arch-x86
> -
> -This method is only tested for Android NDK versions Revision 11b and later.
> -perf uses some bionic enhancements that are not included in prior NDK versions.
> -You can use method (b) described below instead.
> -
> -(b). Use the Android source tree
> ------------------------------------------------
> -1. Download the master branch of the Android source tree.
> -Set the environment for the target you want using:
> -  source build/envsetup.sh
> -  lunch
> -
> -2. Build your own NDK sysroot to contain latest bionic changes and set the
> -NDK sysroot environment variable.
> -  cd ${ANDROID_BUILD_TOP}/ndk
> -For arm:
> -  ./build/tools/build-ndk-sysroot.sh --abi=arm
> -  export NDK_SYSROOT=${ANDROID_BUILD_TOP}/ndk/build/platforms/android-3/arch-arm
> -For x86:
> -  ./build/tools/build-ndk-sysroot.sh --abi=x86
> -  export NDK_SYSROOT=${ANDROID_BUILD_TOP}/ndk/build/platforms/android-3/arch-x86
> -
> -3. Set the NDK toolchain environment variable.
> -For arm:
> -  export NDK_TOOLCHAIN=${ANDROID_TOOLCHAIN}/arm-linux-androideabi-
> -For x86:
> -  export NDK_TOOLCHAIN=${ANDROID_TOOLCHAIN}/i686-linux-android-
> -
> -II. Compile perf for Android
> -------------------------------------------------
> -You need to run make with the NDK toolchain and sysroot defined above:
> -For arm:
> -  make WERROR=0 ARCH=arm CROSS_COMPILE=${NDK_TOOLCHAIN} EXTRA_CFLAGS="-pie --sysroot=${NDK_SYSROOT}"
> -For x86:
> -  make WERROR=0 ARCH=x86 CROSS_COMPILE=${NDK_TOOLCHAIN} EXTRA_CFLAGS="-pie --sysroot=${NDK_SYSROOT}"
> -
> -III. Install perf
> ------------------------------------------------
> -You need to connect to your Android device/emulator using adb.
> -Install perf using:
> -  adb push perf /data/perf
> -
> -If you also want to use perf-archive you need busybox tools for Android.
> -For installing perf-archive, you first need to replace #!/bin/bash with #!/system/bin/sh:
> -  sed 's/#!\/bin\/bash/#!\/system\/bin\/sh/g' perf-archive >> /tmp/perf-archive
> -  chmod +x /tmp/perf-archive
> -  adb push /tmp/perf-archive /data/perf-archive
> -
> -IV. Environment settings for running perf
> -------------------------------------------------
> -Some perf features need environment variables to run properly.
> -You need to set these before running perf on the target:
> -  adb shell
> -  # PERF_PAGER=cat
> -
> -IV. Run perf
> -------------------------------------------------
> -Run perf on your device/emulator to which you previously connected using adb:
> -  # ./data/perf
> +- The second method is to download Android NDK, then use the contained
> +  clang compiler for building perf. Please refer to Build.txt, section
> +  "5) Build with clang" for details.
>
> --
> 2.34.1
>