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? > + > +#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 :) > +".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? > + > +#define __ID(prefix) \ > + __PASTE(prefix, __COUNTER__) > + > + > +/* > + * The BTF_ID defines unique symbol for each ID pointing > + * to 4 zero bytes. > + */ > +#define BTF_ID(prefix, name) \ > + __BTF_ID(__ID(__BTF_ID__##prefix##__##name##__)) > + > + > +/* > + * The BTF_ID_LIST macro defines pure (unsorted) list > + * of BTF IDs, with following layout: > + * > + * BTF_ID_LIST(list1) > + * BTF_ID(type1, name1) > + * BTF_ID(type2, name2) > + * > + * list1: > + * __BTF_ID__type1__name1__1: > + * .zero 4 > + * __BTF_ID__type2__name2__2: > + * .zero 4 > + * > + */ > +#define BTF_ID_LIST(name) \ nit: btw, you call it a list here, but btfids tool talks about "sorts". Maybe stick to consistent naming. Either "list" or "set" seems to be appropriate. Set implies a sorted aspect a bit more, IMO. > +asm( \ > +".pushsection " SECTION ",\"a\"; \n" \ > +".global " #name "; \n" \ I was expecting to see reserved 4 bytes for list size? I also couldn't find where btfids tool prepends it. From what I could understand, it just assumed the first 4 bytes are the length prefix? Sorry if I'm slow... > +#name ":; \n" \ > +".popsection; \n"); > + > +#endif > -- > 2.25.4 >
