bpf: Introduce global percpu data

Introduce global percpu data, inspired by the commit
6316f78306c1 ("Merge branch 'support-global-data'"). It enables the
definition of global percpu variables in BPF, similar to the
include/linux/percpu-defs.h::DEFINE_PER_CPU() macro.

For example, in BPF, it is able to define a global percpu variable like:

int data SEC(".percpu");

With this patch, tools like retsnoop [1] and bpfsnoop [2] can simplify
their BPF code for handling LBRs. The code can be updated from

static struct perf_branch_entry lbrs[1][MAX_LBR_ENTRIES] SEC(".data.lbrs");

to

static struct perf_branch_entry lbrs[MAX_LBR_ENTRIES] SEC(".percpu.lbrs");

This eliminates the need to retrieve the CPU ID using the
bpf_get_smp_processor_id() helper.

Additionally, by reusing global percpu data map, sharing information
between tail callers and callees or freplace callers and callees becomes
simpler compared to reusing percpu_array maps.

Links:
[1] https://github.com/anakryiko/retsnoop
[2] https://github.com/bpfsnoop/bpfsnoop

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260813152324.97937-4-leon.hwang@linux.dev

0 files changed, 0 insertions, 0 deletions