I'm looking for how BTF type definition '__type(key, int)' is being changed
to '__uint(key_size, sizeof(int))'. (Not exactly "changed" but wonder how
it can be considered the same)
__uint(type, BPF_MAP_TYPE_ARRAY);
__type(key, int); => __uint(key_size, sizeof(int))
__type(value, u32); => __uint(value_size, sizeof(u32))
__uint(max_entries, 2);
Whether the specific map type supports BTF or not can be inferred from
the file in kernel/bpf/*map.c and by checking each MAP type's
bpf_map_ops .map_check_btf pointer is initialized as map_check_no_btf.
But how can I figure out that specific types of map support BTF types for
key/value? And how can I determine how this BTF key/value type is
converted?
I am aware that BTF information is created in the form of a compact
type by using pahole to deduplicate repeated types, strings information
from DWARF information. However, looking at the *btf or pahole file
in dwarves repository, it seemed that it was not responsible for the
conversion of the BTF key/value.
The remaining guess is that LLVM's BPF target compiler is responsible
for this, or it's probably somewhere in the kernel, but I'm not sure
where it is.
--
Best,
Daniel T. Lee
