On Thu, Feb 25, 2021 at 1:35 AM Yonghong Song <yhs@xxxxxx> wrote:
>
> A new relocation RELO_SUBPROG_ADDR is added to capture
> subprog addresses loaded with ld_imm64 insns. Such ld_imm64
> insns are marked with BPF_PSEUDO_FUNC and will be passed to
> kernel. For bpf_for_each_map_elem() case, kernel will
> check that the to-be-used subprog address must be a static
> function and replace it with proper actual jited func address.
>
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 64 ++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 61 insertions(+), 3 deletions(-)
>
LGTM. I'll still need to relax it a bit more for static functions, but
it can come as part of static linker work.
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
[...]
> +static bool sym_is_subprog(const GElf_Sym *sym, int text_shndx)
> +{
> + int bind = GELF_ST_BIND(sym->st_info);
> + int type = GELF_ST_TYPE(sym->st_info);
> +
> + /* in .text section */
> + if (sym->st_shndx != text_shndx)
> + return false;
> +
> + /* local function */
> + if (bind == STB_LOCAL && type == STT_SECTION)
> + return true;
> +
> + /* global function */
> + return bind == STB_GLOBAL && type == STT_FUNC;
theoretically STT_FUNC could be STB_LOCAL here, though Clang doesn't
emit it that way today. It will be easy to fix later, though. Just
mentioning, because I intend to have STB_LOCAL + STT_FUNC relocations
with BPF static linker.
> +}
> +
> static int find_extern_btf_id(const struct btf *btf, const char *ext_name)
> {
> const struct btf_type *t;
[...]
