On Tue, Jan 12, 2021 at 3:06 AM Nathan Chancellor
<natechancellor@xxxxxxxxx> wrote:
>
> After commit da5fb18225b4 ("bpf: Support pre-2.25-binutils objcopy for
> vmlinux BTF"), having CONFIG_DEBUG_INFO_BTF enabled but lacking a valid
> copy of pahole results in a kernel that will fully compile but fail to
> link. The user then has to either install pahole or disable
> CONFIG_DEBUG_INFO_BTF and rebuild the kernel but only after their build
> has failed, which could have been a significant amount of time depending
> on the hardware.
>
> Avoid a poor user experience and require pahole to be installed with an
> appropriate version to select and use CONFIG_DEBUG_INFO_BTF, which is
> standard for options that require a specific tools version.
>
> Suggested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
> Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx>
I am not sure if this is the right direction.
I used to believe moving any tool test to the Kconfig
was the right thing to do.
For example, I tried to move the libelf test to Kconfig,
and make STACK_VALIDATION depend on it.
https://patchwork.kernel.org/project/linux-kbuild/patch/1531186516-15764-1-git-send-email-yamada.masahiro@xxxxxxxxxxxxx/
It was rejected.
In my understanding, it is good to test target toolchains
in Kconfig (e.g. cc-option, ld-option, etc).
As for host tools, in contrast, it is better to _intentionally_
break the build in order to let users know that something needed is missing.
Then, they will install necessary tools or libraries.
It is just a one-time setup, in most cases,
just running 'apt install' or 'dnf install'.
Recently, a similar thing happened to GCC_PLUGINS
https://patchwork.kernel.org/project/linux-kbuild/patch/20201203125700.161354-1-masahiroy@xxxxxxxxxx/#23855673
Following this pattern, if a new pahole is not installed,
it might be better to break the build instead of hiding
the CONFIG option.
In my case, it is just a matter of 'apt install pahole'.
On some distributions, the bundled pahole is not new enough,
and people may end up with building pahole from the source code.
> ---
> MAINTAINERS | 1 +
> init/Kconfig | 4 ++++
> lib/Kconfig.debug | 6 ++----
> scripts/link-vmlinux.sh | 13 -------------
> scripts/pahole-version.sh | 16 ++++++++++++++++
> 5 files changed, 23 insertions(+), 17 deletions(-)
> create mode 100755 scripts/pahole-version.sh
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index b8db7637263a..6f6e24285a94 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -3282,6 +3282,7 @@ F: net/core/filter.c
> F: net/sched/act_bpf.c
> F: net/sched/cls_bpf.c
> F: samples/bpf/
> +F: scripts/pahole-version.sh
> F: tools/bpf/
> F: tools/lib/bpf/
> F: tools/testing/selftests/bpf/
> diff --git a/init/Kconfig b/init/Kconfig
> index b77c60f8b963..872c61b5d204 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -74,6 +74,10 @@ config TOOLS_SUPPORT_RELR
> config CC_HAS_ASM_INLINE
> def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
>
> +config PAHOLE_VERSION
> + int
> + default $(shell,$(srctree)/scripts/pahole-version.sh $(PAHOLE))
> +
> config CONSTRUCTORS
> bool
> depends on !UML
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 7937265ef879..70c446af9664 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -267,6 +267,7 @@ config DEBUG_INFO_DWARF4
>
> config DEBUG_INFO_BTF
> bool "Generate BTF typeinfo"
> + depends on PAHOLE_VERSION >= 116
> depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED
> depends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST
> help
> @@ -274,12 +275,9 @@ config DEBUG_INFO_BTF
> Turning this on expects presence of pahole tool, which will convert
> DWARF type info into equivalent deduplicated BTF type info.
>
> -config PAHOLE_HAS_SPLIT_BTF
> - def_bool $(success, test `$(PAHOLE) --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'` -ge "119")
> -
> config DEBUG_INFO_BTF_MODULES
> def_bool y
> - depends on DEBUG_INFO_BTF && MODULES && PAHOLE_HAS_SPLIT_BTF
> + depends on DEBUG_INFO_BTF && MODULES && PAHOLE_VERSION >= 119
> help
> Generate compact split BTF type information for kernel modules.
>
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index 6eded325c837..eef40fa9485d 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -139,19 +139,6 @@ vmlinux_link()
> # ${2} - file to dump raw BTF data into
> gen_btf()
> {
> - local pahole_ver
> -
> - if ! [ -x "$(command -v ${PAHOLE})" ]; then
> - echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available"
> - return 1
> - fi
> -
> - pahole_ver=$(${PAHOLE} --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/')
> - if [ "${pahole_ver}" -lt "116" ]; then
> - echo >&2 "BTF: ${1}: pahole version $(${PAHOLE} --version) is too old, need at least v1.16"
> - return 1
> - fi
> -
> vmlinux_link ${1}
>
> info "BTF" ${2}
> diff --git a/scripts/pahole-version.sh b/scripts/pahole-version.sh
> new file mode 100755
> index 000000000000..6de6f734a345
> --- /dev/null
> +++ b/scripts/pahole-version.sh
> @@ -0,0 +1,16 @@
> +#!/bin/sh
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Usage: $ ./scripts/pahole-version.sh pahole
> +#
> +# Print the pahole version as a three digit string
> +# such as `119' for pahole v1.19 etc.
> +
> +pahole="$*"
> +
> +if ! [ -x "$(command -v $pahole)" ]; then
> + echo 0
> + exit 1
> +fi
> +
> +$pahole --version | sed -E 's/v([0-9]+)\.([0-9]+)/\1\2/'
>
> base-commit: e22d7f05e445165e58feddb4e40cc9c0f94453bc
> --
> 2.30.0
>
--
Best Regards
Masahiro Yamada
