| Message ID | 20200820231250.1293069-1-andriin@fb.com |
|---|---|
| Headers | show |
| Series | Add libbpf full support for BPF-to-BPF calls | expand |
On Thu, Aug 20, 2020 at 04:12:34PM -0700, Andrii Nakryiko wrote: > Currently, libbpf supports a limited form of BPF-to-BPF subprogram calls. The > restriction is that entry-point BPF program should use *all* of defined > sub-programs in BPF .o file. If any of the subprograms is not used, such > entry-point BPF program will be rejected by verifier as containing unreachable > dead code. This is not a big limitation for cases with single entry-point BPF > programs, but is quite a havy restriction for multi-programs that use only > partially overlapping set of subprograms. > > This patch sets removes all such restrictions and adds complete support for > using BPF sub-program calls on BPF side. This is achieved through libbpf > tracking subprograms individually and detecting which subprograms are used by > any given entry-point BPF program, and subsequently only appending and > relocating code for just those used subprograms. > > In addition, libbpf now also supports multiple entry-point BPF programs within > the same ELF section. This allows to structure code so that there are few > variants of BPF programs of the same type and attaching to the same target > (e.g., for tracepoints and kprobes) without the need to worry about ELF > section name clashes. > > This patch set opens way for more wider adoption of BPF subprogram calls, > especially for real-world production use-cases with complicated net of > subprograms. This will allow to further scale BPF verification process through > good use of global functions, which can be verified independently. This is > also important prerequisite for static linking which allows static BPF > libraries to not worry about naming clashes for section names, as well as use > static non-inlined functions (subprograms) without worries of verifier > rejecting program due to dead code. > > Patch set is structured as follows: > - patches 1-5 contain various smaller improvements to logging and selftests; > - patched 6-11 contain all the libbpf changes necessary to support multi-prog > sections and bpf2bpf subcalls; > - patch 12 adds dedicated selftests validating all combinations of possible > sub-calls (within and across sections, static vs global functions); > - patch 13 deprecated bpf_program__title() in favor of > bpf_program__section_name(). The intent was to also deprecate > bpf_object__find_program_by_title() as it's now non-sensical with multiple > programs per section. But there were too many selftests uses of this and > I didn't want to delay this patches further and make it even bigger, so left > it for a follow up cleanup; > - patches 14-15 remove uses for title-related APIs from bpftool and > bpf_program__title() use from selftests; > - patch 16 is converting fexit_bpf2bpf to have explicit subtest (it does > contain 4 subtests, which are not handled as sub-tests). I've applied the first 5 patches. Cleanup of 'elf:' logs is nice. Thanks for doing it. The rest of the patches look fine as well, but minimalistic selftest is a bit concerning for such major update to libbpf. Please consider expanding the tests. May be cloudflare's test_cls_redirect.c can be adopted for this purpose? test_xdp_noinline.c can also be extended by doing two copies of balancer_ingress(). One to process ipv4 another ipv6. Then it will make libbpf to do plenty of intersting call adjustments and function munipulations for three programs in "xdp-test" section that use different sets of sub-programs. test_l4lb_noinline.c can be another candidate. The selftest that is part of this set is nice for targeted debugging, but would be great to see production bpf prog adopting this exciting libbpf feature.
On Fri, Aug 21, 2020 at 4:00 PM Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote: > > On Thu, Aug 20, 2020 at 04:12:34PM -0700, Andrii Nakryiko wrote: > > Currently, libbpf supports a limited form of BPF-to-BPF subprogram calls. The > > restriction is that entry-point BPF program should use *all* of defined > > sub-programs in BPF .o file. If any of the subprograms is not used, such > > entry-point BPF program will be rejected by verifier as containing unreachable > > dead code. This is not a big limitation for cases with single entry-point BPF > > programs, but is quite a havy restriction for multi-programs that use only > > partially overlapping set of subprograms. > > > > This patch sets removes all such restrictions and adds complete support for > > using BPF sub-program calls on BPF side. This is achieved through libbpf > > tracking subprograms individually and detecting which subprograms are used by > > any given entry-point BPF program, and subsequently only appending and > > relocating code for just those used subprograms. > > > > In addition, libbpf now also supports multiple entry-point BPF programs within > > the same ELF section. This allows to structure code so that there are few > > variants of BPF programs of the same type and attaching to the same target > > (e.g., for tracepoints and kprobes) without the need to worry about ELF > > section name clashes. > > > > This patch set opens way for more wider adoption of BPF subprogram calls, > > especially for real-world production use-cases with complicated net of > > subprograms. This will allow to further scale BPF verification process through > > good use of global functions, which can be verified independently. This is > > also important prerequisite for static linking which allows static BPF > > libraries to not worry about naming clashes for section names, as well as use > > static non-inlined functions (subprograms) without worries of verifier > > rejecting program due to dead code. > > > > Patch set is structured as follows: > > - patches 1-5 contain various smaller improvements to logging and selftests; > > - patched 6-11 contain all the libbpf changes necessary to support multi-prog > > sections and bpf2bpf subcalls; > > - patch 12 adds dedicated selftests validating all combinations of possible > > sub-calls (within and across sections, static vs global functions); > > - patch 13 deprecated bpf_program__title() in favor of > > bpf_program__section_name(). The intent was to also deprecate > > bpf_object__find_program_by_title() as it's now non-sensical with multiple > > programs per section. But there were too many selftests uses of this and > > I didn't want to delay this patches further and make it even bigger, so left > > it for a follow up cleanup; > > - patches 14-15 remove uses for title-related APIs from bpftool and > > bpf_program__title() use from selftests; > > - patch 16 is converting fexit_bpf2bpf to have explicit subtest (it does > > contain 4 subtests, which are not handled as sub-tests). > > I've applied the first 5 patches. Cleanup of 'elf:' logs is nice. > Thanks for doing it. > The rest of the patches look fine as well, but minimalistic selftest is > a bit concerning for such major update to libbpf. > Please consider expanding the tests. That test is not that minimalistic, actually. It tests all combinations of bpf2bpf calls (global/static * same/other section), plus with only subsets of functions used by entry-point BPF programs. Similarly, fentry_bpf2bpf tests have also pretty complicated patterns, as well as test_pkt_access.c. > May be cloudflare's test_cls_redirect.c can be adopted for this purpose? > test_xdp_noinline.c can also be extended by doing two copies of > balancer_ingress(). One to process ipv4 another ipv6. I'll take a look at those, if they are using sub-program calls (not __always_inline), they are already testing this. I'll see if I can un-inline some more functions, though. > Then it will make libbpf to do plenty of intersting call adjustments > and function munipulations for three programs in "xdp-test" section > that use different sets of sub-programs. > test_l4lb_noinline.c can be another candidate. > The selftest that is part of this set is nice for targeted debugging, but would > be great to see production bpf prog adopting this exciting libbpf feature. Sure, I'll also see if strobemeta examples can be modified minimally to allow non-inlined functions.
Currently, libbpf supports a limited form of BPF-to-BPF subprogram calls. The restriction is that entry-point BPF program should use *all* of defined sub-programs in BPF .o file. If any of the subprograms is not used, such entry-point BPF program will be rejected by verifier as containing unreachable dead code. This is not a big limitation for cases with single entry-point BPF programs, but is quite a havy restriction for multi-programs that use only partially overlapping set of subprograms. This patch sets removes all such restrictions and adds complete support for using BPF sub-program calls on BPF side. This is achieved through libbpf tracking subprograms individually and detecting which subprograms are used by any given entry-point BPF program, and subsequently only appending and relocating code for just those used subprograms. In addition, libbpf now also supports multiple entry-point BPF programs within the same ELF section. This allows to structure code so that there are few variants of BPF programs of the same type and attaching to the same target (e.g., for tracepoints and kprobes) without the need to worry about ELF section name clashes. This patch set opens way for more wider adoption of BPF subprogram calls, especially for real-world production use-cases with complicated net of subprograms. This will allow to further scale BPF verification process through good use of global functions, which can be verified independently. This is also important prerequisite for static linking which allows static BPF libraries to not worry about naming clashes for section names, as well as use static non-inlined functions (subprograms) without worries of verifier rejecting program due to dead code. Patch set is structured as follows: - patches 1-5 contain various smaller improvements to logging and selftests; - patched 6-11 contain all the libbpf changes necessary to support multi-prog sections and bpf2bpf subcalls; - patch 12 adds dedicated selftests validating all combinations of possible sub-calls (within and across sections, static vs global functions); - patch 13 deprecated bpf_program__title() in favor of bpf_program__section_name(). The intent was to also deprecate bpf_object__find_program_by_title() as it's now non-sensical with multiple programs per section. But there were too many selftests uses of this and I didn't want to delay this patches further and make it even bigger, so left it for a follow up cleanup; - patches 14-15 remove uses for title-related APIs from bpftool and bpf_program__title() use from selftests; - patch 16 is converting fexit_bpf2bpf to have explicit subtest (it does contain 4 subtests, which are not handled as sub-tests). Andrii Nakryiko (16): selftests/bpf: BPF object files should depend only on libbpf headers libbpf: factor out common ELF operations and improve logging libbpf: add __noinline macro to bpf_helpers.h libbpf: skip well-known ELF sections when iterating ELF libbpf: normalize and improve logging across few functions libbpf: ensure ELF symbols table is found before further ELF processing libbpf: parse multi-function sections into multiple BPF programs libbpf: support CO-RE relocations for multi-prog sections libbpf: make RELO_CALL work for multi-prog sections and sub-program calls libbpf: implement generalized .BTF.ext func/line info adjustment libbpf: add multi-prog section support for struct_ops selftests/bpf: add selftest for multi-prog sections and bpf-to-bpf calls tools/bpftool: replace bpf_program__title() with bpf_program__section_name() selftests/bpf: don't use deprecated libbpf APIs libbpf: deprecate notion of BPF program "title" in favor of "section name" selftests/bpf: turn fexit_bpf2bpf into test with subtests tools/bpf/bpftool/prog.c | 4 +- tools/lib/bpf/bpf_helpers.h | 3 + tools/lib/bpf/btf.h | 18 +- tools/lib/bpf/libbpf.c | 1695 ++++++++++------- tools/lib/bpf/libbpf.h | 5 +- tools/lib/bpf/libbpf.map | 5 + tools/lib/bpf/libbpf_common.h | 2 + tools/testing/selftests/bpf/Makefile | 2 +- .../selftests/bpf/flow_dissector_load.h | 8 +- .../selftests/bpf/prog_tests/fexit_bpf2bpf.c | 12 +- .../bpf/prog_tests/reference_tracking.c | 2 +- .../selftests/bpf/prog_tests/subprogs.c | 31 + .../selftests/bpf/progs/test_subprogs.c | 92 + .../selftests/bpf/test_socket_cookie.c | 2 +- 14 files changed, 1218 insertions(+), 663 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/subprogs.c create mode 100644 tools/testing/selftests/bpf/progs/test_subprogs.c