Re: [PATCH v9 1/4] Create source symlink in perf object dir

[Luca Ceresoli <luca.ceresoli@bootlin.com>]

Hello Andi,

+cc Yann and the Buildroot mailing list (see the end of this report).

On Wed,  7 Aug 2024 16:18:20 -0700
Andi Kleen <ak@linux.intel.com> wrote:

> Create a source symlink to the original source in the objdir.
> This is similar to what the main kernel build script does.
> 
> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> ---
>  tools/perf/Makefile.perf | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
> index 175e4c7898f0..d46892d8223b 100644
> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -163,6 +163,8 @@ ifneq ($(OUTPUT),)
>  # for flex/bison parsers.
>  VPATH += $(OUTPUT)
>  export VPATH
> +# create symlink to the original source
> +SOURCE := $(shell ln -sf $(srctree)/tools/perf $(OUTPUT)/source)

I found that since this patch got applied in 890a1961c812 (v6.12-rc1)
building perf fails silently in some cases.

The cases I have tested:
 - make <FLAGS> -C tools/perf                       -> OK
 - make <FLAGS> -C tools/perf O=/my/out/of/tree/dir -> OK
 - make <FLAGS> -C tools/perf O=tools/perf          -> fails

The failure in the third case is silent: make exits with a return value
of 0, but there is no perf executable created.

Even 'make <FLAGS> -C tools/perf install' exits returning 0, but no
executable is installed. However the following lines are output during
'make install', which are a sign of this issue happening:

  install: omitting directory '/home/murray/w/bootlin/linux/tools/perf/perf'
  ln: failed to access '/tmp/aaa/usr/bin/perf': No such file or directory

I realize 'O=tools/perf' is "useless" in the sense that the same result
would be obtained by not setting 'O' at all. However I also believe it
is expected that O=tools/perf should work equally to not setting 'O',
and as such there is a regression.

Also, right now the Buildroot embedded Linux build system builds perf
by always passing O=$(LINUX_DIR)/tools/perf/, thus it is currently
broken for kernels 6.12-rc1 and later.

Below is the test script I wrote to automate my testing. It is a bit
more complex than expected because it needs to hide a different bug,
which would otherwise mask the one being reported here. A slightly
different version of this script was used to automate 'git bisect'.

-------------------------8<-------------------------

#!/bin/sh

# Usage:
#   build-perf-report          Build with O=tools/perf
#   build-perf-report <DIR>    Build with O=<DIR>

set -eu

# Default to O=tools/perf
OUT_DIR=${1:-tools/perf}

echo "Output dir: ${OUT_DIR}"

# This is the toolchain I initially used to reproduce the issue:
# https://toolchains.bootlin.com/downloads/releases/toolchains/aarch64/tarballs/aarch64--glibc--stable-2024.02-1.tar.bz2
#
# However commenting the two lines for a native build is equally
# reproducing the problem on my x86_64 Ubuntu 22.04 host
export ARCH=arm64
export CROSS_COMPILE="ccache ${HOME}/x-tools/aarch64--glibc--stable-2024.02-1/bin/aarch64-linux-"

LINUX_MAKE_FLAGS="\
    GIT_DIR=. \
    KCFLAGS=-Wno-attribute-alias \
    WERROR=0 \
    REGENERATE_PARSERS=1 \
    DESTDIR=/tmp/aaa \
    prefix=/usr \
    NO_GTK2=1 \
    NO_LIBPERL=1 \
    NO_LIBPYTHON=1 \
    NO_LIBBIONIC=1 \
    NO_LIBTRACEEVENT=1 \
    NO_NEWT=1 \
    NO_SLANG=1 \
    NO_LIBAUDIT=1 \
    NO_LIBUNWIND=1 \
    NO_LIBNUMA=1 \
    NO_LIBELF=1 \
    NO_DWARF=1 \
    NO_DEMANGLE=1 \
    NO_LIBCRYPTO=1 \
    NO_ZLIB=1 \
    NO_LZMA=1 \
    -C tools/perf O=${OUT_DIR}
"

echo "Kernel version: $(git describe)"

# Revert (without committing) 13d675aea6cac5bb4619ef9e3fdd90129fe6d139
# which introduces a different build failure (fixed by a later commit)
# masking the issue being examined
git checkout -- .
git show 13d675aea6cac5bb4619ef9e3fdd90129fe6d139 | git apply || :

# Clean the DESTDIR
rm -fr /tmp/aaa/

git clean -xdfq
make defconfig

# If building out of tree, create an empty build dir
if [ ${OUT_DIR} != "tools/perf" ]; then
    rm -fr ${OUT_DIR}
    mkdir -p ${OUT_DIR}
fi

make ${LINUX_MAKE_FLAGS}
make ${LINUX_MAKE_FLAGS} install

# remove the fix added above
git checkout -- .

echo "-------------------------------------------------------"
echo "perf files in O (${OUT_DIR}):"
find ${OUT_DIR} -name perf -not -type d  | xargs file
echo "-------------------------------------------------------"
echo "perf executable in DESTDIR:"
find /tmp/aaa/ -name perf -not -type d | xargs file | grep 'executable'
echo "-------------------------------------------------------"

-------------------------8<-------------------------

Best regards,
Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com