On Tue, Jun 18, 2024 at 9:25 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
>
> Share relocation implementation with the kernel. As part of this,
> we also need the type/string iteration functions so add them to a
> btf_iter.c file that also gets shared with the kernel. Relocation
> code in kernel and userspace is identical save for the impementation
> of the reparenting of split BTF to the relocated base BTF and
> retrieval of BTF header from "struct btf"; these small functions
> need separate user-space and kernel implementations.
>
> One other wrinkle on the kernel side is we have to map .BTF.ids in
> modules as they were generated with the type ids used at BTF encoding
> time. btf_relocate() optionally returns an array mapping from old BTF
> ids to relocated ids, so we use that to fix up these references where
> needed for kfuncs.
>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> include/linux/btf.h | 64 +++++++++++++
> kernel/bpf/Makefile | 10 +-
> kernel/bpf/btf.c | 176 ++++++++++++++++++++++++----------
> tools/lib/bpf/Build | 2 +-
> tools/lib/bpf/btf.c | 162 --------------------------------
> tools/lib/bpf/btf_iter.c | 177 +++++++++++++++++++++++++++++++++++
> tools/lib/bpf/btf_relocate.c | 23 +++++
> 7 files changed, 398 insertions(+), 216 deletions(-)
> create mode 100644 tools/lib/bpf/btf_iter.c
>
I'd do btf_iter.c addition in a separate patch, but other than that
looks good. See a nit below.
> diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
> index 7eb9ad3a3ae6..d9d148992fbf 100644
> --- a/kernel/bpf/Makefile
> +++ b/kernel/bpf/Makefile
> @@ -50,5 +50,13 @@ endif
> obj-$(CONFIG_BPF_PRELOAD) += preload/
>
> obj-$(CONFIG_BPF_SYSCALL) += relo_core.o
> -$(obj)/relo_core.o: $(srctree)/tools/lib/bpf/relo_core.c FORCE
> +
> +obj-$(CONFIG_BPF_SYSCALL) += btf_iter.o
> +
> +obj-$(CONFIG_BPF_SYSCALL) += btf_relocate.o
nit: do we need those empty lines above? let's keep all the shared
kernel/libbpf object files in one group without empty lines
> +
> +# Some source files are common to libbpf.
> +vpath %.c $(srctree)/kernel/bpf:$(srctree)/tools/lib/bpf
this is something new, what does vpath do? (sorry if this was
discussed before and I missed it)
> +
> +$(obj)/%.o: %.c FORCE
> $(call if_changed_rule,cc_o_c)
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index ce4707968217..8e12cb80ba73 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -274,6 +274,7 @@ struct btf {
> u32 start_str_off; /* first string offset (0 for base BTF) */
> char name[MODULE_NAME_LEN];
> bool kernel_btf;
> + __u32 *base_id_map; /* map from distilled base BTF -> vmlinux BTF ids */
> };
>
[...]
