[PATCH v2 1/3] btf: remove redundant CONFIG_BPF test in scripts/link-vmlinux.sh

[PATCH v2 1/3] btf: remove redundant CONFIG_BPF test in scripts/link-vmlinux.sh

[Masahiro Yamada]

CONFIG_DEBUG_INFO_BTF depends on CONFIG_BPF_SYSCALL, which in turn
selects CONFIG_BPF.

When CONFIG_DEBUG_INFO_BTF=y, CONFIG_BPF=y is always met.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
---

(no changes since v1)

 scripts/link-vmlinux.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index bd196944e350..cfffc41e20ed 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -288,7 +288,7 @@ strip_debug=
 vmlinux_link vmlinux
 
 # fill in BTF IDs
-if is_enabled CONFIG_DEBUG_INFO_BTF && is_enabled CONFIG_BPF; then
+if is_enabled CONFIG_DEBUG_INFO_BTF; then
 	info BTFIDS vmlinux
 	${RESOLVE_BTFIDS} vmlinux
 fi
-- 
2.43.0

[PATCH v2 2/3] btf: move pahole check in scripts/link-vmlinux.sh to lib/Kconfig.debug

[Masahiro Yamada]

When DEBUG_INFO_DWARF5 is selected, pahole 1.21+ is required to enable
DEBUG_INFO_BTF.

When DEBUG_INFO_DWARF4 or DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT is selected,
DEBUG_INFO_BTF can be enabled without pahole installed, but a build error
will occur in scripts/link-vmlinux.sh:

    LD      .tmp_vmlinux1
  BTF: .tmp_vmlinux1: pahole (pahole) is not available
  Failed to generate BTF for vmlinux
  Try to disable CONFIG_DEBUG_INFO_BTF

We did not guard DEBUG_INFO_BTF by PAHOLE_VERSION when previously
discussed [1].

However, commit 613fe1692377 ("kbuild: Add CONFIG_PAHOLE_VERSION")
added CONFIG_PAHOLE_VERSION after all. Now several CONFIG options, as
well as the combination of DEBUG_INFO_BTF and DEBUG_INFO_DWARF5, are
guarded by PAHOLE_VERSION.

The remaining compile-time check in scripts/link-vmlinux.sh now appears
to be an awkward inconsistency.

This commit adopts Nathan's original work.

[1]: https://lore.kernel.org/lkml/20210111180609.713998-1-natechancellor@gmail.com/

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
---

Changes in v2:
  - Reword the help message per Alan

 lib/Kconfig.debug       |  6 ++++--
 scripts/link-vmlinux.sh | 12 ------------
 2 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 5e2f30921cb2..bdf822bc1bab 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -379,13 +379,15 @@ config DEBUG_INFO_BTF
 	depends on !DEBUG_INFO_SPLIT && !DEBUG_INFO_REDUCED
 	depends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST
 	depends on BPF_SYSCALL
+	depends on PAHOLE_VERSION >= 116
 	depends on !DEBUG_INFO_DWARF5 || PAHOLE_VERSION >= 121
 	# pahole uses elfutils, which does not have support for Hexagon relocations
 	depends on !HEXAGON
 	help
 	  Generate deduplicated BTF type information from DWARF debug info.
-	  Turning this on expects presence of pahole tool, which will convert
-	  DWARF type info into equivalent deduplicated BTF type info.
+	  Turning this on requires pahole v1.16 or later (v1.21 or later to
+	  support DWARF 5), which will convert DWARF type info into equivalent
+	  deduplicated BTF type info.
 
 config PAHOLE_HAS_SPLIT_BTF
 	def_bool PAHOLE_VERSION >= 119
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index cfffc41e20ed..53bd4b727e21 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -111,20 +111,8 @@ vmlinux_link()
 # ${1} - vmlinux image
 gen_btf()
 {
-	local pahole_ver
 	local btf_data=${1}.btf.o
 
-	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
-
 	info BTF "${btf_data}"
 	LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
 
-- 
2.43.0

[PATCH v2 3/3] btf: require pahole 1.21+ for DEBUG_INFO_BTF with default DWARF version

[Masahiro Yamada]

As described in commit 42d9b379e3e1 ("lib/Kconfig.debug: Allow BTF +
DWARF5 with pahole 1.21+"), the combination of CONFIG_DEBUG_INFO_BTF
and CONFIG_DEBUG_INFO_DWARF5 requires pahole 1.21+.

GCC 11+ and Clang 14+ default to DWARF 5 when the -g flag is passed.
For the same reason, the combination of CONFIG_DEBUG_INFO_BTF and
CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT is also likely to require
pahole 1.21+ these days. (At least, it is uncertain whether the actual
requirement is pahole 1.16+ or 1.21+.)

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
---

(no changes since v1)

 lib/Kconfig.debug | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index bdf822bc1bab..e24c4caaa067 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -380,7 +380,7 @@ config DEBUG_INFO_BTF
 	depends on !GCC_PLUGIN_RANDSTRUCT || COMPILE_TEST
 	depends on BPF_SYSCALL
 	depends on PAHOLE_VERSION >= 116
-	depends on !DEBUG_INFO_DWARF5 || PAHOLE_VERSION >= 121
+	depends on DEBUG_INFO_DWARF4 || PAHOLE_VERSION >= 121
 	# pahole uses elfutils, which does not have support for Hexagon relocations
 	depends on !HEXAGON
 	help
-- 
2.43.0

Re: [PATCH v2 1/3] btf: remove redundant CONFIG_BPF test in scripts/link-vmlinux.sh

[Andrii Nakryiko]

On Fri, Sep 13, 2024 at 10:38 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> CONFIG_DEBUG_INFO_BTF depends on CONFIG_BPF_SYSCALL, which in turn
> selects CONFIG_BPF.
>
> When CONFIG_DEBUG_INFO_BTF=y, CONFIG_BPF=y is always met.
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> ---
>

Masahiro,

Are you planning to take this through your tree, or you'd prefer us
routing it through bpf-next?

> (no changes since v1)
>
>  scripts/link-vmlinux.sh | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
> index bd196944e350..cfffc41e20ed 100755
> --- a/scripts/link-vmlinux.sh
> +++ b/scripts/link-vmlinux.sh
> @@ -288,7 +288,7 @@ strip_debug=
>  vmlinux_link vmlinux
>
>  # fill in BTF IDs
> -if is_enabled CONFIG_DEBUG_INFO_BTF && is_enabled CONFIG_BPF; then
> +if is_enabled CONFIG_DEBUG_INFO_BTF; then
>         info BTFIDS vmlinux
>         ${RESOLVE_BTFIDS} vmlinux
>  fi
> --
> 2.43.0
>

Re: [PATCH v2 1/3] btf: remove redundant CONFIG_BPF test in scripts/link-vmlinux.sh

[Masahiro Yamada]

On Sat, Sep 14, 2024 at 7:26 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Fri, Sep 13, 2024 at 10:38 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > CONFIG_DEBUG_INFO_BTF depends on CONFIG_BPF_SYSCALL, which in turn
> > selects CONFIG_BPF.
> >
> > When CONFIG_DEBUG_INFO_BTF=y, CONFIG_BPF=y is always met.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
> > Acked-by: Andrii Nakryiko <andrii@kernel.org>
> > Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> > ---
> >
>
> Masahiro,
>
> Are you planning to take this through your tree, or you'd prefer us
> routing it through bpf-next?

Hi,

If possible, could you apply it to bpf-next
for the upcoming MW?







-- 
Best Regards
Masahiro Yamada

Re: [PATCH v2 1/3] btf: remove redundant CONFIG_BPF test in scripts/link-vmlinux.sh

[Alexei Starovoitov]

On Fri, Sep 13, 2024 at 6:52 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> On Sat, Sep 14, 2024 at 7:26 AM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Fri, Sep 13, 2024 at 10:38 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> > >
> > > CONFIG_DEBUG_INFO_BTF depends on CONFIG_BPF_SYSCALL, which in turn
> > > selects CONFIG_BPF.
> > >
> > > When CONFIG_DEBUG_INFO_BTF=y, CONFIG_BPF=y is always met.
> > >
> > > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > > Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
> > > Acked-by: Andrii Nakryiko <andrii@kernel.org>
> > > Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> > > ---
> > >
> >
> > Masahiro,
> >
> > Are you planning to take this through your tree, or you'd prefer us
> > routing it through bpf-next?
>
> Hi,
>
> If possible, could you apply it to bpf-next
> for the upcoming MW?

Sure thing. We'll do.

Re: [PATCH v2 1/3] btf: remove redundant CONFIG_BPF test in scripts/link-vmlinux.sh

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Sat, 14 Sep 2024 02:37:52 +0900 you wrote:
> CONFIG_DEBUG_INFO_BTF depends on CONFIG_BPF_SYSCALL, which in turn
> selects CONFIG_BPF.
> 
> When CONFIG_DEBUG_INFO_BTF=y, CONFIG_BPF=y is always met.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
> Acked-by: Andrii Nakryiko <andrii@kernel.org>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> 
> [...]

Here is the summary with links:
  - [v2,1/3] btf: remove redundant CONFIG_BPF test in scripts/link-vmlinux.sh
    https://git.kernel.org/bpf/bpf-next/c/c980dc9c67a9
  - [v2,2/3] btf: move pahole check in scripts/link-vmlinux.sh to lib/Kconfig.debug
    https://git.kernel.org/bpf/bpf-next/c/42450f7a9086
  - [v2,3/3] btf: require pahole 1.21+ for DEBUG_INFO_BTF with default DWARF version
    https://git.kernel.org/bpf/bpf-next/c/5277d130947b

You are awesome, thank you!
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