This series introduces a new helper, bpf_trace_vprintk, which functions like bpf_trace_printk but supports > 3 arguments via a pseudo-vararg u64 array. The bpf_printk libbpf convenience macro is modified to use bpf_trace_vprintk when > 3 varargs are passed, otherwise the previous behavior - using bpf_trace_printk - is retained. Helper functions and macros added during the implementation of bpf_seq_printf and bpf_snprintf do most of the heavy lifting for bpf_trace_vprintk. There's no novel format string wrangling here. Usecase here is straightforward: Giving BPF program writers a more powerful printk will ease development of BPF programs, particularly during debugging and testing, where printk tends to be used. This feature was proposed by Andrii in libbpf mirror's issue tracker [1]. [1] https://github.com/libbpf/libbpf/issues/315 v5 -> v6: Rebase to pick up newly-added helper v4 -> v5: * patch 8: added test for "%pS" format string w/ NULL fmt arg [Daniel] * patch 8: dmesg -> /sys/kernel/debug/tracing/trace_pipe in commit message [Andrii] * patch 9: squash into patch 8, remove the added test in favor of just bpf_printk'ing in patch 8's test [Andrii] * migrate comment to /* */ * header comments improved$ * uapi/linux/bpf.h: u64 -> long return type [Daniel] * uapi/linux/bpf.h: function description explains benefit of bpf_trace_vprintk over bpf_trace_printk [Daniel] * uapi/linux/bpf.h: added patch explaining that data_len should be a multiple of 8 in bpf_seq_printf, bpf_snprintf descriptions [Daniel] * tools/lib/bpf/bpf_helpers.h: move comment to new bpf_printk [Andrii] * rebase v3 -> v4: * Add patch 2, which migrates reference_tracking prog_test away from bpf_program__load. Could be placed a bit later in the series, but wanted to keep the actual vprintk-related patches contiguous * Add patch 9, which adds a program w/ 0 fmt arg bpf_printk to vprintk test * bpf_printk convenience macro isn't multiline anymore, so simplify [Andrii] * Add some comments to ___bpf_pick_printk to make it more obvious when implementation switches from printk to vprintk [Andrii] * BPF_PRINTK_FMT_TYPE -> BPF_PRINTK_FMT_MOD for 'static const' fmt string in printk wrapper macro [Andrii] * checkpatch.pl doesn't like this, says "Macros with complex values should be enclosed in parentheses". Strange that it didn't have similar complaints about v3's BPF_PRINTK_FMT_TYPE. Regardless, IMO the complaint is not highlighting a real issue in the case of this macro. * Fix alignment of __bpf_vprintk and __bpf_pick_printk [Andrii] * rebase v2 -> v3: * Clean up patch 3's commit message [Alexei] * Add patch 4, which modifies __bpf_printk to use 'static const char' to store fmt string with fallback for older kernels [Andrii] * rebase v1 -> v2: * Naming conversation seems to have gone in favor of keeping bpf_trace_vprintk, names are unchanged * Patch 3 now modifies bpf_printk convenience macro to choose between __bpf_printk and __bpf_vprintk 'implementation' macros based on arg count. __bpf_vprintk is a renaming of bpf_vprintk convenience macro from v1, __bpf_printk is the existing bpf_printk implementation. This patch could use some scrutiny as I think current implementation may regress developer experience in a specific case, turning a compile-time error into a load-time error. Unclear to me how common the case is, or whether the macro magic I chose is ideal. * char ___fmt[] to static const char ___fmt[] change was not done, wanted to leave __bpf_printk 'implementation' macro unchanged for v2 to ease discussion of above point * Removed __always_inline from __set_printk_clr_event [Andrii] * Simplified bpf_trace_printk docstring to refer to other functions instead of copy/pasting and avoid specifying 12 vararg limit [Andrii] * Migrated trace_printk selftest to use ASSERT_ instead of CHECK * Adds new patch 5, previous patch 5 is now 6 * Migrated trace_vprintk selftest to use ASSERT_ instead of CHECK, open_and_load instead of separate open, load [Andrii] * Patch 2's commit message now correctly mentions trace_pipe instead of dmesg [Andrii] Dave Marchevsky (9): bpf: merge printk and seq_printf VARARG max macros selftests/bpf: stop using bpf_program__load bpf: add bpf_trace_vprintk helper libbpf: Modify bpf_printk to choose helper based on arg count libbpf: use static const fmt string in __bpf_printk bpftool: only probe trace_vprintk feature in 'full' mode selftests/bpf: Migrate prog_tests/trace_printk CHECKs to ASSERTs selftests/bpf: add trace_vprintk test prog bpf: Clarify data_len param in bpf_snprintf and bpf_seq_printf comments include/linux/bpf.h | 3 + include/uapi/linux/bpf.h | 16 ++++- kernel/bpf/core.c | 5 ++ kernel/bpf/helpers.c | 6 +- kernel/trace/bpf_trace.c | 54 ++++++++++++++- tools/bpf/bpftool/feature.c | 1 + tools/include/uapi/linux/bpf.h | 16 ++++- tools/lib/bpf/bpf_helpers.h | 51 +++++++++++--- tools/testing/selftests/bpf/Makefile | 3 +- .../bpf/prog_tests/reference_tracking.c | 39 ++++++++--- .../selftests/bpf/prog_tests/trace_printk.c | 24 +++---- .../selftests/bpf/prog_tests/trace_vprintk.c | 68 +++++++++++++++++++ .../selftests/bpf/progs/trace_vprintk.c | 33 +++++++++ tools/testing/selftests/bpf/test_bpftool.py | 22 +++--- 14 files changed, 286 insertions(+), 55 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/trace_vprintk.c create mode 100644 tools/testing/selftests/bpf/progs/trace_vprintk.c -- 2.30.2
