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

[PATCH 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>
---

 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 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 at 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>
---

 lib/Kconfig.debug       |  3 ++-
 scripts/link-vmlinux.sh | 12 ------------
 2 files changed, 2 insertions(+), 13 deletions(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 5e2f30921cb2..eff408a88dfd 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -379,12 +379,13 @@ 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
+	  Turning this on requires presence of pahole tool, which will convert
 	  DWARF type info into equivalent deduplicated BTF type info.
 
 config PAHOLE_HAS_SPLIT_BTF
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 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+. (At least, it is uncertain whether the requirement is
pahole 1.16+ or 1.21+.)

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

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

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index eff408a88dfd..011a7abc68a8 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 2/3] btf: move pahole check in scripts/link-vmlinux.sh to lib/Kconfig.debug

[Alan Maguire]

On 11/09/2024 12:03, Masahiro Yamada wrote:
> 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 at 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>

Nice cleanup! For the series

Reviewed-by: Alan Maguire <alan.maguire@oracle.com>

One small thing below..

> ---
> 
>  lib/Kconfig.debug       |  3 ++-
>  scripts/link-vmlinux.sh | 12 ------------
>  2 files changed, 2 insertions(+), 13 deletions(-)
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5e2f30921cb2..eff408a88dfd 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -379,12 +379,13 @@ 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
> +	  Turning this on requires presence of pahole tool, which will convert
>  	  DWARF type info into equivalent deduplicated BTF type info.
>  

One thing we lose from the change below is an explicit message about the
minimal pahole version required. While it is codified in the
dependendencies, given that we used to loudly warn about this,
would it make sense to note it in the help text here; just a sentence
like "BTF generation requires pahole v1.16 or later."? Thanks!

Alan

>  config PAHOLE_HAS_SPLIT_BTF
> 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}
>  

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

[Nathan Chancellor]

On Wed, Sep 11, 2024 at 08:03:56PM +0900, Masahiro Yamada 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: Nathan Chancellor <nathan@kernel.org>

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

[Andrii Nakryiko]

On Wed, Sep 11, 2024 at 4:04 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>
> ---
>
>  scripts/link-vmlinux.sh | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>

LGTM

Acked-by: Andrii Nakryiko <andrii@kernel.org>

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

[Andrii Nakryiko]

On Wed, Sep 11, 2024 at 4:04 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> 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 at 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>
> ---
>

LGTM

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>  lib/Kconfig.debug       |  3 ++-
>  scripts/link-vmlinux.sh | 12 ------------
>  2 files changed, 2 insertions(+), 13 deletions(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5e2f30921cb2..eff408a88dfd 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -379,12 +379,13 @@ 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
> +         Turning this on requires presence of pahole tool, which will convert
>           DWARF type info into equivalent deduplicated BTF type info.
>
>  config PAHOLE_HAS_SPLIT_BTF
> 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
>

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

[Andrii Nakryiko]

On Wed, Sep 11, 2024 at 4:04 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> 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+. (At least, it is uncertain whether the requirement is
> pahole 1.16+ or 1.21+.)
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>

Make sense

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>  lib/Kconfig.debug | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index eff408a88dfd..011a7abc68a8 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 2/3] btf: move pahole check in scripts/link-vmlinux.sh to lib/Kconfig.debug

[Nathan Chancellor]

On Wed, Sep 11, 2024 at 08:03:57PM +0900, Masahiro Yamada wrote:
> 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 at 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: Nathan Chancellor <nathan@kernel.org>

> ---
> 
>  lib/Kconfig.debug       |  3 ++-
>  scripts/link-vmlinux.sh | 12 ------------
>  2 files changed, 2 insertions(+), 13 deletions(-)
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 5e2f30921cb2..eff408a88dfd 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -379,12 +379,13 @@ 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
> +	  Turning this on requires presence of pahole tool, which will convert
>  	  DWARF type info into equivalent deduplicated BTF type info.
>  
>  config PAHOLE_HAS_SPLIT_BTF
> 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
> 

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

[Nathan Chancellor]

On Wed, Sep 11, 2024 at 08:03:58PM +0900, Masahiro Yamada wrote:
> 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+. (At least, it is uncertain whether the requirement is
> pahole 1.16+ or 1.21+.)
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Indeed, I think this is a safer, longterm dependency, until we bump the
minimum versions to the ones listed in the commit message, unless there
is DWARF6 by that point :)

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
> 
>  lib/Kconfig.debug | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index eff408a88dfd..011a7abc68a8 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 2/3] btf: move pahole check in scripts/link-vmlinux.sh to lib/Kconfig.debug

[Masahiro Yamada]

On Thu, Sep 12, 2024 at 2:25 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>
> On 11/09/2024 12:03, Masahiro Yamada wrote:
> > 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 at 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>
>
> Nice cleanup! For the series
>
> Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
>
> One small thing below..
>
> > ---
> >
> >  lib/Kconfig.debug       |  3 ++-
> >  scripts/link-vmlinux.sh | 12 ------------
> >  2 files changed, 2 insertions(+), 13 deletions(-)
> >
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 5e2f30921cb2..eff408a88dfd 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -379,12 +379,13 @@ 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
> > +       Turning this on requires presence of pahole tool, which will convert
> >         DWARF type info into equivalent deduplicated BTF type info.
> >
>
> One thing we lose from the change below is an explicit message about the
> minimal pahole version required. While it is codified in the
> dependendencies, given that we used to loudly warn about this,
> would it make sense to note it in the help text here; just a sentence
> like "BTF generation requires pahole v1.16 or later."? Thanks!


How about this help message?



help
  Generate deduplicated BTF type information from DWARF debug info.
  Turning this on requires pahole v1.16 or later (v1.21 or later
  for DWARF 5), which will convert DWARF type info into equivalent
  deduplicated BTF type info.








-- 
Best Regards
Masahiro Yamada