| Message ID | 20210414200146.2663044-1-andrii@kernel.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | BPF static linker: support externs | expand |
On Wed, Apr 14, 2021 at 1:02 PM Andrii Nakryiko <andrii@kernel.org> wrote: > > Add BPF static linker support for extern resolution of global variables, > functions, and BTF-defined maps. > > This patch set consists of 4 parts: > - few patches are extending bpftool to simplify working with BTF dump; > - libbpf object loading logic is extended to support __hidden functions and > overriden (unused) __weak functions; also BTF-defined map parsing logic is > refactored to be re-used by linker; > - the crux of the patch set is BPF static linker logic extension to perform > extern resolution for three categories: global variables, BPF > sub-programs, BTF-defined maps; > - a set of selftests that validate that all the combinations of > extern/weak/__hidden are working as expected. > > See respective patches for more details. > > One aspect hasn't been addressed yet and is going to be resolved in the next > patch set, but is worth mentioning. With BPF static linking of multiple .o > files, dealing with static everything becomes more problematic for BPF > skeleton and in general for any by name look up APIs. This is due to static > entities are allowed to have non-unique name. Historically this was never > a problem due to BPF programs were always confined to a single C file. That > changes now and needs to be addressed. The thinking so far is for BPF static > linker to prepend filename to each static variable and static map (which is > currently not supported by libbpf, btw), so that they can be unambiguously > resolved by (mostly) unique name. Mostly, because even filenames can be > duplicated, but that should be rare and easy to address by wiser choice of > filenames by users. Fortunately, static BPF subprograms don't suffer from this > issues, as they are not independent entities and are neither exposed in BPF > skeleton, nor is lookup-able by any of libbpf APIs (and there is little reason > to do that anyways). > > This and few other things will be the topic of the next set of patches. > I forgot to mention that selftests are relying on Clang fix [0], which is not yet in nightly builds, so kernel-patches CI is currently failing a test. So, when/if testing locally, please make sure to build Clang from latest main. [0] https://reviews.llvm.org/D100362 > Andrii Nakryiko (17): > bpftool: support dumping BTF VAR's "extern" linkage > bpftool: dump more info about DATASEC members > libbpf: suppress compiler warning when using SEC() macro with externs > libbpf: mark BPF subprogs with hidden visibility as static for BPF > verifier > libbpf: allow gaps in BPF program sections to support overriden weak > functions > libbpf: refactor BTF map definition parsing > libbpf: factor out symtab and relos sanity checks > libbpf: make few internal helpers available outside of libbpf.c > libbpf: extend sanity checking ELF symbols with externs validation > libbpf: tighten BTF type ID rewriting with error checking > libbpf: add linker extern resolution support for functions and global > variables > libbpf: support extern resolution for BTF-defined maps in .maps > section > selftests/bpf: use -O0 instead of -Og in selftests builds > selftests/bpf: omit skeleton generation for multi-linked BPF object > files > selftests/bpf: add function linking selftest > selftests/bpf: add global variables linking selftest > sleftests/bpf: add map linking selftest > > tools/bpf/bpftool/btf.c | 30 +- > tools/lib/bpf/bpf_helpers.h | 19 +- > tools/lib/bpf/btf.c | 5 - > tools/lib/bpf/libbpf.c | 370 +++-- > tools/lib/bpf/libbpf_internal.h | 45 + > tools/lib/bpf/linker.c | 1292 ++++++++++++++--- > tools/testing/selftests/bpf/Makefile | 18 +- > .../selftests/bpf/prog_tests/linked_funcs.c | 42 + > .../selftests/bpf/prog_tests/linked_maps.c | 33 + > .../selftests/bpf/prog_tests/linked_vars.c | 43 + > .../selftests/bpf/progs/linked_funcs1.c | 73 + > .../selftests/bpf/progs/linked_funcs2.c | 73 + > .../selftests/bpf/progs/linked_maps1.c | 102 ++ > .../selftests/bpf/progs/linked_maps2.c | 112 ++ > .../selftests/bpf/progs/linked_vars1.c | 60 + > .../selftests/bpf/progs/linked_vars2.c | 61 + > 16 files changed, 2028 insertions(+), 350 deletions(-) > create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_funcs.c > create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_maps.c > create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_vars.c > create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs1.c > create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs2.c > create mode 100644 tools/testing/selftests/bpf/progs/linked_maps1.c > create mode 100644 tools/testing/selftests/bpf/progs/linked_maps2.c > create mode 100644 tools/testing/selftests/bpf/progs/linked_vars1.c > create mode 100644 tools/testing/selftests/bpf/progs/linked_vars2.c > > -- > 2.30.2 >
Add BPF static linker support for extern resolution of global variables, functions, and BTF-defined maps. This patch set consists of 4 parts: - few patches are extending bpftool to simplify working with BTF dump; - libbpf object loading logic is extended to support __hidden functions and overriden (unused) __weak functions; also BTF-defined map parsing logic is refactored to be re-used by linker; - the crux of the patch set is BPF static linker logic extension to perform extern resolution for three categories: global variables, BPF sub-programs, BTF-defined maps; - a set of selftests that validate that all the combinations of extern/weak/__hidden are working as expected. See respective patches for more details. One aspect hasn't been addressed yet and is going to be resolved in the next patch set, but is worth mentioning. With BPF static linking of multiple .o files, dealing with static everything becomes more problematic for BPF skeleton and in general for any by name look up APIs. This is due to static entities are allowed to have non-unique name. Historically this was never a problem due to BPF programs were always confined to a single C file. That changes now and needs to be addressed. The thinking so far is for BPF static linker to prepend filename to each static variable and static map (which is currently not supported by libbpf, btw), so that they can be unambiguously resolved by (mostly) unique name. Mostly, because even filenames can be duplicated, but that should be rare and easy to address by wiser choice of filenames by users. Fortunately, static BPF subprograms don't suffer from this issues, as they are not independent entities and are neither exposed in BPF skeleton, nor is lookup-able by any of libbpf APIs (and there is little reason to do that anyways). This and few other things will be the topic of the next set of patches. Andrii Nakryiko (17): bpftool: support dumping BTF VAR's "extern" linkage bpftool: dump more info about DATASEC members libbpf: suppress compiler warning when using SEC() macro with externs libbpf: mark BPF subprogs with hidden visibility as static for BPF verifier libbpf: allow gaps in BPF program sections to support overriden weak functions libbpf: refactor BTF map definition parsing libbpf: factor out symtab and relos sanity checks libbpf: make few internal helpers available outside of libbpf.c libbpf: extend sanity checking ELF symbols with externs validation libbpf: tighten BTF type ID rewriting with error checking libbpf: add linker extern resolution support for functions and global variables libbpf: support extern resolution for BTF-defined maps in .maps section selftests/bpf: use -O0 instead of -Og in selftests builds selftests/bpf: omit skeleton generation for multi-linked BPF object files selftests/bpf: add function linking selftest selftests/bpf: add global variables linking selftest sleftests/bpf: add map linking selftest tools/bpf/bpftool/btf.c | 30 +- tools/lib/bpf/bpf_helpers.h | 19 +- tools/lib/bpf/btf.c | 5 - tools/lib/bpf/libbpf.c | 370 +++-- tools/lib/bpf/libbpf_internal.h | 45 + tools/lib/bpf/linker.c | 1292 ++++++++++++++--- tools/testing/selftests/bpf/Makefile | 18 +- .../selftests/bpf/prog_tests/linked_funcs.c | 42 + .../selftests/bpf/prog_tests/linked_maps.c | 33 + .../selftests/bpf/prog_tests/linked_vars.c | 43 + .../selftests/bpf/progs/linked_funcs1.c | 73 + .../selftests/bpf/progs/linked_funcs2.c | 73 + .../selftests/bpf/progs/linked_maps1.c | 102 ++ .../selftests/bpf/progs/linked_maps2.c | 112 ++ .../selftests/bpf/progs/linked_vars1.c | 60 + .../selftests/bpf/progs/linked_vars2.c | 61 + 16 files changed, 2028 insertions(+), 350 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_funcs.c create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_maps.c create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_vars.c create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs1.c create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs2.c create mode 100644 tools/testing/selftests/bpf/progs/linked_maps1.c create mode 100644 tools/testing/selftests/bpf/progs/linked_maps2.c create mode 100644 tools/testing/selftests/bpf/progs/linked_vars1.c create mode 100644 tools/testing/selftests/bpf/progs/linked_vars2.c