[PATCH bpf-next] kbuild,bpf: switch to using --btf_features for pahole v1.26 and later

[PATCH bpf-next] kbuild,bpf: switch to using --btf_features for pahole v1.26 and later

[Alan Maguire]

The btf_features list can be used for pahole v1.26 and later -
it is useful because if a feature is not yet implemented it will
not exit with a failure message.  This will allow us to add feature
requests to the pahole options without having to check pahole versions
in future; if the version of pahole supports the feature it will be
added.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 scripts/Makefile.btf | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
index 82377e470aed..8e6a9d4b492e 100644
--- a/scripts/Makefile.btf
+++ b/scripts/Makefile.btf
@@ -12,8 +12,11 @@ pahole-flags-$(call test-ge, $(pahole-ver), 121)	+= --btf_gen_floats
 
 pahole-flags-$(call test-ge, $(pahole-ver), 122)	+= -j
 
-pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)		+= --lang_exclude=rust
-
 pahole-flags-$(call test-ge, $(pahole-ver), 125)	+= --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
 
+# Switch to using --btf_features for v1.26 and later.
+pahole-flags-$(call test-ge, $(pahole-ver), 126)	= -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func
+
+pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)		+= --lang_exclude=rust
+
 export PAHOLE_FLAGS := $(pahole-flags-y)
-- 
2.39.3

Re: [PATCH bpf-next] kbuild,bpf: switch to using --btf_features for pahole v1.26 and later

[Eduard Zingerman]

On Wed, 2024-05-01 at 18:50 +0100, Alan Maguire wrote:
> The btf_features list can be used for pahole v1.26 and later -
> it is useful because if a feature is not yet implemented it will
> not exit with a failure message.  This will allow us to add feature
> requests to the pahole options without having to check pahole versions
> in future; if the version of pahole supports the feature it will be
> added.
> 
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---

I tried building kernel and running bpf selftests using this patch and
two pahole versions: tags 1.25 and 1.26 (from git@github.com:acmel/dwarves.git).
Selftests are passing (test_{verifier,progs})

Tested-by: Eduard Zingerman <eddyz87@gmail.com>

Re: [PATCH bpf-next] kbuild,bpf: switch to using --btf_features for pahole v1.26 and later

[Andrii Nakryiko]

On Wed, May 1, 2024 at 10:51 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>
> The btf_features list can be used for pahole v1.26 and later -
> it is useful because if a feature is not yet implemented it will
> not exit with a failure message.  This will allow us to add feature
> requests to the pahole options without having to check pahole versions
> in future; if the version of pahole supports the feature it will be
> added.
>
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
> ---
>  scripts/Makefile.btf | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
> index 82377e470aed..8e6a9d4b492e 100644
> --- a/scripts/Makefile.btf
> +++ b/scripts/Makefile.btf
> @@ -12,8 +12,11 @@ pahole-flags-$(call test-ge, $(pahole-ver), 121)     += --btf_gen_floats
>
>  pahole-flags-$(call test-ge, $(pahole-ver), 122)       += -j
>
> -pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)         += --lang_exclude=rust
> -
>  pahole-flags-$(call test-ge, $(pahole-ver), 125)       += --skip_encoding_btf_inconsistent_proto --btf_gen_optimized

given starting from 1.26 we use --btf-features, this should be `==
1.25` condition, not `>= 1.25`, right? It doesn't hurt right now, but
it's best to be explicitly that below `-j --btf_features=...` is all
that's necessary.

pw-bot: cr


>
> +# Switch to using --btf_features for v1.26 and later.
> +pahole-flags-$(call test-ge, $(pahole-ver), 126)       = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func
> +
> +pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)         += --lang_exclude=rust
> +
>  export PAHOLE_FLAGS := $(pahole-flags-y)
> --
> 2.39.3
>

Re: [PATCH bpf-next] kbuild,bpf: switch to using --btf_features for pahole v1.26 and later

[Alan Maguire]

On 07/05/2024 00:15, Andrii Nakryiko wrote:
> On Wed, May 1, 2024 at 10:51 AM Alan Maguire <alan.maguire@oracle.com> wrote:
>>
>> The btf_features list can be used for pahole v1.26 and later -
>> it is useful because if a feature is not yet implemented it will
>> not exit with a failure message.  This will allow us to add feature
>> requests to the pahole options without having to check pahole versions
>> in future; if the version of pahole supports the feature it will be
>> added.
>>
>> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>> ---
>>  scripts/Makefile.btf | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/scripts/Makefile.btf b/scripts/Makefile.btf
>> index 82377e470aed..8e6a9d4b492e 100644
>> --- a/scripts/Makefile.btf
>> +++ b/scripts/Makefile.btf
>> @@ -12,8 +12,11 @@ pahole-flags-$(call test-ge, $(pahole-ver), 121)     += --btf_gen_floats
>>
>>  pahole-flags-$(call test-ge, $(pahole-ver), 122)       += -j
>>
>> -pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)         += --lang_exclude=rust
>> -
>>  pahole-flags-$(call test-ge, $(pahole-ver), 125)       += --skip_encoding_btf_inconsistent_proto --btf_gen_optimized
> 
> given starting from 1.26 we use --btf-features, this should be `==
> 1.25` condition, not `>= 1.25`, right? It doesn't hurt right now, but
> it's best to be explicitly that below `-j --btf_features=...` is all
> that's necessary.
>

Good point; I've tried to make this a bit clearer in v2 [1].

Thanks!

Alan

[1]
https://lore.kernel.org/bpf/20240507135514.490467-1-alan.maguire@oracle.com/

> pw-bot: cr
> 
> 
>>
>> +# Switch to using --btf_features for v1.26 and later.
>> +pahole-flags-$(call test-ge, $(pahole-ver), 126)       = -j --btf_features=encode_force,var,float,enum64,decl_tag,type_tag,optimized_func,consistent_func
>> +
>> +pahole-flags-$(CONFIG_PAHOLE_HAS_LANG_EXCLUDE)         += --lang_exclude=rust
>> +
>>  export PAHOLE_FLAGS := $(pahole-flags-y)
>> --
>> 2.39.3
>>