Support creation of module BTF along with distilled base BTF;
the latter is stored in a .BTF.base ELF section and supplements
split BTF references to base BTF with information about base types,
allowing for later relocation of split BTF with a (possibly
changed) base. resolve_btfids detects the presence of a .BTF.base
section and will use it instead of the base BTF it is passed in
BTF id resolution.
Modules will be built with a distilled .BTF.base section for external
module build, i.e.
make -C. -M=path2/module
...while in-tree module build as part of a normal kernel build will
not generate distilled base BTF; this is because in-tree modules
change with the kernel and do not require BTF relocation for the
running vmlinux.
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20240620091733.1967885-6-alan.maguire@oracle.com
There is no need to set the pahole v1.25-only flags in an
"ifeq" version clause; we are already in a <= v1.25 branch
of "ifeq", so that combined with a "test-ge" v1.25 ensures the
flags will be applied for v1.25 only.
Suggested-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240514162716.2448265-1-alan.maguire@oracle.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240507135514.490467-1-alan.maguire@oracle.com
scripts/pahole-flags.sh is executed so many times.
You can confirm it, as follows:
$ cat <<EOF >> scripts/pahole-flags.sh
> echo "scripts/pahole-flags.sh was executed" >&2
> EOF
$ make -s
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
scripts/pahole-flags.sh was executed
[ lots of repeated lines... ]
This scripts is executed more than 20 times during the kernel build
because PAHOLE_FLAGS is a recursively expanded variable and exported
to sub-processes.
With GNU Make >= 4.4, it is executed more than 60 times because
exported variables are also passed to other $(shell ) invocations.
Without careful coding, it is known to cause an exponential fork
explosion. [1]
The use of $(shell ) in an exported recursive variable is likely wrong
because $(shell ) is always evaluated due to the 'export' keyword, and
the evaluation can occur multiple times by the nature of recursive
variables.
Convert the shell script to a Makefile, which is included only when
CONFIG_DEBUG_INFO_BTF=y.
[1]: https://savannah.gnu.org/bugs/index.php?64746
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Reviewed-by: Nicolas Schier <n.schier@avm.de>
Tested-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
