On Thu, Jun 18, 2020 at 05:56:38PM -0700, Andrii Nakryiko wrote: > On Tue, Jun 16, 2020 at 3:05 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > > > Adding support to generate .BTF_ids section that would > > hold various BTF IDs list for verifier. > > > > Adding macros help to define lists of BTF IDs placed in > > .BTF_ids section. They are initially filled with zeros > > (during compilation) and resolved later during the > > linking phase by btfid tool. > > > > Following defines list of one BTF ID that is accessible > > within kernel code as bpf_skb_output_btf_ids array. > > > > extern int bpf_skb_output_btf_ids[]; > > > > BTF_ID_LIST(bpf_skb_output_btf_ids) > > BTF_ID(struct, sk_buff) > > > > Suggested-by: Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> > > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx> > > --- > > include/asm-generic/vmlinux.lds.h | 4 ++ > > kernel/bpf/Makefile | 2 +- > > kernel/bpf/btf_ids.c | 3 ++ > > kernel/bpf/btf_ids.h | 70 +++++++++++++++++++++++++++++++ > > 4 files changed, 78 insertions(+), 1 deletion(-) > > create mode 100644 kernel/bpf/btf_ids.c > > create mode 100644 kernel/bpf/btf_ids.h > > > > [...] > > > +/* > > + * Following macros help to define lists of BTF IDs placed > > + * in .BTF_ids section. They are initially filled with zeros > > + * (during compilation) and resolved later during the > > + * linking phase by btfid tool. > > + * > > + * Any change in list layout must be reflected in btfid > > + * tool logic. > > + */ > > + > > +#define SECTION ".BTF_ids" > > nit: SECTION is super generic and non-greppable. BTF_IDS_SECTION? ok > > > + > > +#define ____BTF_ID(symbol) \ > > +asm( \ > > +".pushsection " SECTION ",\"a\"; \n" \ > > section should be also read-only? Either immediately here, of btfid > tool should mark it? Unless I missed that it's already doing it :) hm, it's there next to the .BTF section within RO_DATA macro, so I thought that was enough.. I'll double check > > > +".local " #symbol " ; \n" \ > > +".type " #symbol ", @object; \n" \ > > +".size " #symbol ", 4; \n" \ > > +#symbol ": \n" \ > > +".zero 4 \n" \ > > +".popsection; \n"); > > + > > +#define __BTF_ID(...) \ > > + ____BTF_ID(__VA_ARGS__) > > why varargs, if it's always a single argument? Or it's one of those > macro black magic things were it works only in this particular case, > but not others? yea, I kind of struggled in here, because any other would not expand the name concat together with the unique ID bit, __VA_ARGS__ did it nicely ;-) I'll revisit this thanks, jirka
