Re: [PATCH bpf-next v4 5/9] selftests/bpf: Add basic libarena scaffolding

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Tue Apr 7, 2026 at 12:21 PM EDT, Alexei Starovoitov wrote:
> On Mon, Apr 6, 2026 at 9:57 PM Emil Tsalapatis <emil@etsalapatis.com> wrote:
>>
>> Add initial code for an arena-based BPF library. The current commit
>> introduces a test runner and Makefile for the library. Library code
>> can be added just by including the source file in the library's src/
>> subdirectory. Future commits will introduce the library code itself.
>>
>> The current commit also includes a standalone test runner. This is
>> to keep libarena self-contained and testable even when copied out
>> of the kernel tree. Subsequent commits add integration with test_progs.
>>
>> Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
>> ---
>>  tools/testing/selftests/bpf/.gitignore        |   1 +
>>  tools/testing/selftests/bpf/Makefile          |  15 ++
>>  tools/testing/selftests/bpf/libarena/Makefile |  50 ++++++
>>  .../selftests/bpf/libarena/include/common.h   |  49 ++++++
>>  .../bpf/libarena/include/selftest_helpers.h   |  81 ++++++++++
>>  .../selftests/bpf/libarena/include/userapi.h  |  26 +++
>>  .../bpf/libarena/selftests/selftest.c         | 153 ++++++++++++++++++
>>  .../bpf/libarena/selftests/selftest.h         |  12 ++
>>  .../selftests/bpf/libarena/src/common.bpf.c   |  65 ++++++++
>>  9 files changed, 452 insertions(+)
>>  create mode 100644 tools/testing/selftests/bpf/libarena/Makefile
>>  create mode 100644 tools/testing/selftests/bpf/libarena/include/common.h
>>  create mode 100644 tools/testing/selftests/bpf/libarena/include/selftest_helpers.h
>>  create mode 100644 tools/testing/selftests/bpf/libarena/include/userapi.h
>>  create mode 100644 tools/testing/selftests/bpf/libarena/selftests/selftest.c
>>  create mode 100644 tools/testing/selftests/bpf/libarena/selftests/selftest.h
>>  create mode 100644 tools/testing/selftests/bpf/libarena/src/common.bpf.c
>>
>> diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
>> index bfdc5518ecc8..7f1960d6b59e 100644
>> --- a/tools/testing/selftests/bpf/.gitignore
>> +++ b/tools/testing/selftests/bpf/.gitignore
>> @@ -49,3 +49,4 @@ verification_cert.h
>>  *.BTF.base
>>  usdt_1
>>  usdt_2
>> +libarena/test_libarena
>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
>> index f75c4f52c028..0d332c991023 100644
>> --- a/tools/testing/selftests/bpf/Makefile
>> +++ b/tools/testing/selftests/bpf/Makefile
>> @@ -153,6 +153,7 @@ override define CLEAN
>>         $(Q)$(RM) -r $(TEST_KMODS)
>>         $(Q)$(RM) -r $(EXTRA_CLEAN)
>>         $(Q)$(MAKE) -C test_kmods clean
>> +       $(Q)$(MAKE) -C libarena clean
>>         $(Q)$(MAKE) docs-clean
>>  endef
>>
>> @@ -739,6 +740,17 @@ $(VERIFY_SIG_HDR): $(VERIFICATION_CERT)
>>          echo "};"; \
>>          echo "unsigned int test_progs_verification_cert_len = $$(wc -c < $<);") > $@
>>
>> +LIBARENA_MAKE_ARGS = \
>> +               BPFTOOL="$(BPFTOOL)" \
>> +               INCLUDE_DIR="$(HOST_INCLUDE_DIR)" \
>> +               LIBBPF_INCLUDE="$(HOST_INCLUDE_DIR)" \
>> +               BPFOBJ="$(BPFOBJ)" \
>> +               LDLIBS="$(LDLIBS) -lzstd" \
>> +               CLANG="$(CLANG)" \
>> +               BPF_CFLAGS="$(BPF_CFLAGS) $(CLANG_CFLAGS)" \
>> +               BPF_TARGET_ENDIAN="$(BPF_TARGET_ENDIAN)" \
>> +               Q="$(Q)"
>> +
>>  # Define test_progs test runner.
>>  TRUNNER_TESTS_DIR := prog_tests
>>  TRUNNER_BPF_PROGS_DIR := progs
>> @@ -931,3 +943,6 @@ override define INSTALL_RULE
>>                 rsync -a $(OUTPUT)/$$DIR/*.bpf.o $(INSTALL_PATH)/$$DIR;\
>>         done
>>  endef
>> +
>> +test_libarena: $(INCLUDE_DIR)/vmlinux.h $(BPFOBJ)
>> +       +$(MAKE) -C libarena $@ $(LIBARENA_MAKE_ARGS)
>> diff --git a/tools/testing/selftests/bpf/libarena/Makefile b/tools/testing/selftests/bpf/libarena/Makefile
>> new file mode 100644
>> index 000000000000..151ab6d0509c
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/libarena/Makefile
>> @@ -0,0 +1,50 @@
>> +# SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
>> +# Copyright (c) 2026 Meta Platforms, Inc. and affiliates.
>> +
>> +.PHONY: clean
>> +
>> +LIBARENA=$(abspath .)
>> +
>> +
>> +LIBARENA_SOURCES = $(wildcard $(LIBARENA)/src/*.bpf.c) $(wildcard $(LIBARENA)/selftests/*.bpf.c)
>> +LIBARENA_OBJECTS = $(notdir $(LIBARENA_SOURCES:.bpf.c=.bpf.o))
>> +
>> +INCLUDES = -I$(LIBARENA)/include -I$(LIBARENA)/..
>> +ifneq ($(INCLUDE_DIR),)
>> +INCLUDES += -I$(INCLUDE_DIR)
>> +endif
>> +ifneq ($(LIBBPF_INCLUDE),)
>> +INCLUDES += -I$(LIBBPF_INCLUDE)
>> +endif
>> +
>> +# ENABLE_ATOMICS_TESTS required because we use arena spinlocks
>> +override BPF_CFLAGS += -DENABLE_ATOMICS_TESTS
>> +override BPF_CFLAGS += -O2 -Wno-incompatible-pointer-types-discards-qualifiers
>> +override BPF_CFLAGS += $(INCLUDES)
>> +
>> +CFLAGS = -O2 -no-pie
>> +CFLAGS += $(INCLUDES)
>> +
>> +vpath %.bpf.c $(LIBARENA)/src $(LIBARENA)/selftests
>> +vpath %.c $(LIBARENA)/src $(LIBARENA)/selftests
>> +
>> +all: test_libarena
>> +
>> +test_libarena: selftest.c $(BPFOBJ) libarena.skel.h
>> +       $(call msg,BINARY,libarena,$@)
>> +       $(Q)$(CLANG) $(CFLAGS) $< $(BPFOBJ) $(LDLIBS) -o $@
>> +
>> +libarena.skel.h: main.bpf.o
>> +       $(call msg,GEN-SKEL,libarena,$@)
>> +       $(Q)$(BPFTOOL) gen skeleton $< name "libarena" > $@
>> +
>> +main.bpf.o: $(LIBARENA_OBJECTS)
>> +       $(call msg,GEN-OBJ,libarena,$@)
>> +       $(Q)$(BPFTOOL) gen object $@ $^
>> +
>> +%.bpf.o: %.bpf.c
>> +       $(call msg,CLNG-BPF,libarena,$@)
>> +       $(Q)$(CLANG) $(BPF_CFLAGS) $(BPF_TARGET_ENDIAN) -c $< -o $@
>> +
>> +clean:
>> +       $(Q)rm -f *.skel.h *.bpf.o test_libarena
>> diff --git a/tools/testing/selftests/bpf/libarena/include/common.h b/tools/testing/selftests/bpf/libarena/include/common.h
>> new file mode 100644
>> index 000000000000..544a398a0d1e
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/libarena/include/common.h
>> @@ -0,0 +1,49 @@
>> +// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
>> +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
>> +#pragma once
>> +
>> +#ifdef __BPF__
>
> Are you trying to re-use this common.h in user space code?
>
>> +
>> +#include <vmlinux.h>
>> +
>> +#include "bpf_experimental.h"
>> +#include "bpf_arena_common.h"
>> +#include "bpf_arena_spin_lock.h"
>> +
>> +#include <asm-generic/errno.h>
>> +
>> +#ifndef __BPF_FEATURE_ADDR_SPACE_CAST
>> +#error "Arena allocators require bpf_addr_space_cast feature"
>> +#endif
>> +
>> +#define arena_stdout(fmt, ...) bpf_stream_printk(1, (fmt), ##__VA_ARGS__)
>> +#define arena_stderr(fmt, ...) bpf_stream_printk(2, (fmt), ##__VA_ARGS__)
>> +
>> +#ifndef __maybe_unused
>> +#define __maybe_unused __attribute__((__unused__))
>> +#endif
>> +
>> +#define private(name) SEC(".data." #name) __hidden __attribute__((aligned(8)))
>> +
>> +#define ARENA_PAGES (1UL << (32 - __builtin_ffs(__PAGE_SIZE) + 1))
>> +
>> +struct {
>> +       __uint(type, BPF_MAP_TYPE_ARENA);
>> +       __uint(map_flags, BPF_F_MMAPABLE);
>> +       __uint(max_entries, ARENA_PAGES); /* number of pages */
>> +#if defined(__TARGET_ARCH_arm64) || defined(__aarch64__)
>> +        __ulong(map_extra, (1ull << 32)); /* start of mmap() region */
>> +#else
>> +        __ulong(map_extra, (1ull << 44)); /* start of mmap() region */
>> +#endif
>> +} arena __weak SEC(".maps");
>> +
>> +extern const volatile u32 zero;
>> +
>> +int arena_fls(__u64 word);
>> +
>> +#endif /* __BPF__ */
>> +
>> +struct arena_get_base_args {
>> +       void __arena *arena_base;
>> +};
>
> If so, then how above suppose to compile in user space?
> __arena is not defined yet.
>
>> diff --git a/tools/testing/selftests/bpf/libarena/include/selftest_helpers.h b/tools/testing/selftests/bpf/libarena/include/selftest_helpers.h
>> new file mode 100644
>> index 000000000000..ee445d8f5b26
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/libarena/include/selftest_helpers.h
>> @@ -0,0 +1,81 @@
>> +// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
>> +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
>> +#pragma once
>> +
>> +#include <errno.h>
>> +#include <stdlib.h>
>> +#include <unistd.h>
>> +#include <sys/mman.h>
>> +
>> +#include <bpf/libbpf.h>
>> +#include <bpf/bpf.h>
>> +
>> +static inline int libarena_run_prog(int prog_fd)
>> +{
>> +       LIBBPF_OPTS(bpf_test_run_opts, opts);
>> +       int ret;
>> +
>> +       ret = bpf_prog_test_run_opts(prog_fd, &opts);
>> +       if (ret)
>> +               return ret;
>> +
>> +       return opts.retval;
>> +}
>> +
>> +static inline int libarena_get_arena_base(int arena_get_base_fd,
>> +                                         void **arena_base)
>> +{
>> +       LIBBPF_OPTS(bpf_test_run_opts, opts);
>> +       struct arena_get_base_args args = { .arena_base = NULL };
>> +       int ret;
>> +
>> +       opts.ctx_in = &args;
>> +       opts.ctx_size_in = sizeof(args);
>> +
>> +       ret = bpf_prog_test_run_opts(arena_get_base_fd, &opts);
>> +       if (ret)
>> +               return ret;
>> +       if (opts.retval)
>> +               return opts.retval;
>> +
>> +       *arena_base = args.arena_base;
>> +       return 0;
>> +}
>> +
>> +static inline int libarena_get_globals_pages(int arena_get_base_fd,
>> +                                            size_t arena_all_pages,
>> +                                            u64 *globals_pages)
>> +{
>> +       size_t pgsize = sysconf(_SC_PAGESIZE);
>> +       void *arena_base;
>> +       ssize_t i;
>> +       u8 *vec;
>> +       int ret;
>> +
>> +       ret = libarena_get_arena_base(arena_get_base_fd, &arena_base);
>> +       if (ret)
>> +               return ret;
>> +
>> +       if (!arena_base)
>> +               return -EINVAL;
>> +
>> +       vec = calloc(arena_all_pages, sizeof(*vec));
>> +       if (!vec)
>> +               return -ENOMEM;
>> +
>> +       if (mincore(arena_base, arena_all_pages * pgsize, vec) < 0) {
>> +               ret = -errno;
>> +               free(vec);
>> +               return ret;
>> +       }
>> +
>> +       *globals_pages = 0;
>> +       for (i = arena_all_pages - 1; i >= 0; i--) {
>> +               if (!(vec[i] & 0x1))
>> +                       break;
>> +               *globals_pages += 1;
>> +       }
>> +
>> +       free(vec);
>> +       return 0;
>> +}
>> diff --git a/tools/testing/selftests/bpf/libarena/include/userapi.h b/tools/testing/selftests/bpf/libarena/include/userapi.h
>> new file mode 100644
>> index 000000000000..b4ac6bc9bd79
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/libarena/include/userapi.h
>> @@ -0,0 +1,26 @@
>> +// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
>> +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
>> +#pragma once
>> +
>> +#include <stdint.h>
>> +
>> +/*
>> + * Header for the userspace C programs that load
>> + * and initialize the BPF code.
>> + */
>> +
>> +#define __arena
>> +
>> +typedef uint8_t u8;
>> +typedef uint16_t u16;
>> +typedef uint32_t u32;
>> +typedef uint64_t u64;
>> +typedef int8_t s8;
>> +typedef int16_t s16;
>> +typedef int32_t s32;
>> +typedef int64_t s64;
>> +
>> +/* Dummy "definition" for userspace. */
>> +#define arena_spinlock_t u64
>> +
>> +#include "common.h"
>
> ohh. So user space _must_ include userapi.h first ?
> Why is this not part of common.h ?
> Why bother with extra userapi.h header?
>
>> diff --git a/tools/testing/selftests/bpf/libarena/selftests/selftest.c b/tools/testing/selftests/bpf/libarena/selftests/selftest.c
>> new file mode 100644
>> index 000000000000..b69adc7baaab
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/libarena/selftests/selftest.c
>> @@ -0,0 +1,153 @@
>> +// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
>> +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
>> +
>> +#define _GNU_SOURCE
>> +#include <assert.h>
>> +#include <errno.h>
>> +#include <stdio.h>
>> +#include <string.h>
>> +#include <unistd.h>
>> +
>> +#include <bpf/libbpf.h>
>> +#include <bpf/bpf.h>
>> +
>> +#include <sys/mman.h>
>> +#include <sys/resource.h>
>> +#include <sys/sysinfo.h>
>> +
>> +#include <userapi.h>
>> +#include <selftest_helpers.h>
>> +
>> +#include "../libarena.skel.h"
>> +typedef struct libarena selftest;
>> +#define selftest__open libarena__open
>> +#define selftest__open_and_load libarena__open_and_load
>> +#define selftest__load libarena__load
>> +#define selftest__attach libarena__attach
>> +#define selftest__destroy libarena__destroy
>
> I don't like this obfuscation.
> What's the point of these #define-s?
>
>> +
>> +static bool verbose = false;
>> +static int testno = 1;
>> +
>> +static int
>> +run_prog_verbose(int prog_fd)
>> +{
>> +       char buf[1024];
>> +       int ret, err;
>> +
>> +       ret = libarena_run_prog(prog_fd);
>> +
>> +       if (ret)
>> +               fprintf(stderr, "error %d in %s\n", ret, __func__);
>> +
>> +       if (verbose) {
>> +               printf("BPF stdout:\n");
>> +               while ((err = bpf_prog_stream_read(prog_fd, 1, buf, 1024, NULL)) > 0)
>> +                       printf("%.*s", err, buf);
>> +
>> +               if (err)
>> +                       return err;
>> +
>> +               printf("BPF stderr:\n");
>> +               while ((err = bpf_prog_stream_read(prog_fd, 2, buf, 1024, NULL)) > 0)
>> +                       printf("%.*s", err, buf);
>> +
>> +               if (err)
>> +                       return err;
>> +       }
>> +
>> +       return ret;
>> +}
>> +
>> +static int libbpf_print_fn(enum libbpf_print_level level,
>> +               const char *format, va_list args)
>> +{
>> +       if (level == LIBBPF_DEBUG)
>> +               return 0;
>> +       return vfprintf(stderr, format, args);
>> +}
>> +
>> +int run_test(selftest *skel, const struct bpf_program *prog)
>> +{
>> +       int prog_fd;
>> +       int ret;
>> +
>> +       ret = libarena_run_prog(bpf_program__fd(skel->progs.arena_alloc_reserve));
>> +       if (ret)
>> +               return ret;
>> +
>> +       prog_fd = bpf_program__fd(prog);
>> +       if (prog_fd < 0)
>> +               return prog_fd;
>> +
>> +       return run_prog_verbose(prog_fd);
>> +}
>> +
>> +#define TEST(__test)                                   \
>> +int run_##__test(void)                                 \
>> +{                                                      \
>> +       selftest *skel;                                 \
>> +       int ret;                                        \
>> +                                                       \
>> +       skel = selftest__open_and_load();               \
>> +       if (!skel) {                                    \
>> +               ret = -EINVAL;                          \
>> +               goto error_no_destroy;                  \
>> +       }                                               \
>> +                                                       \
>> +       ret = selftest__attach(skel);                   \
>> +       if (ret)                                        \
>> +               goto error;                             \
>> +                                                       \
>> +       ret = run_test(skel, skel->progs.__test);       \
>> +       if (ret)                                        \
>> +               goto error;                             \
>> +                                                       \
>> +       selftest__destroy(skel);                        \
>> +                                                       \
>> +       printf("ok %d - %s\n", testno++, #__test);      \
>> +       return 0;                                       \
>> +                                                       \
>> +error:                                                 \
>> +       selftest__destroy(skel);                        \
>> +error_no_destroy:                                      \
>> +       printf("not ok %d - %s\n", testno++, #__test);  \
>> +       return ret;                                     \
>> +}
>> +
>> +static void
>> +banner(const char *progpath)
>> +{
>> +       char *name = basename(progpath);
>> +
>> +       printf("%s\n", name);
>> +
>> +       printf("=== %s ===\n", "libarena selftests");
>> +}
>> +
>> +int main(int argc, char *argv[])
>> +{
>> +       int ret;
>> +
>> +       struct rlimit rlim = {
>> +               .rlim_cur = RLIM_INFINITY,
>> +               .rlim_max = RLIM_INFINITY,
>> +       };
>> +
>> +       banner(argv[0]);
>> +
>> +       for (int i = 1; i < argc; i++) {
>> +               if (strcmp(argv[i], "-v") == 0 || strcmp(argv[i], "--verbose") == 0)
>> +                       verbose = true;
>> +       }
>> +
>> +       ret = setrlimit(RLIMIT_MEMLOCK, &rlim);
>
> where did you copy this from?
> It wasn't necessary for very long time.
>
>> +       if (ret) {
>> +               perror("setrlimit");
>> +               return ret;
>> +       }
>> +
>> +       libbpf_set_print(libbpf_print_fn);
>> +
>> +       return 0;
>> +}
>> diff --git a/tools/testing/selftests/bpf/libarena/selftests/selftest.h b/tools/testing/selftests/bpf/libarena/selftests/selftest.h
>> new file mode 100644
>> index 000000000000..b1cbff4d343b
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/libarena/selftests/selftest.h
>> @@ -0,0 +1,12 @@
>> +// SPDX-License-Identifier: LGPL-2.1 OR BSD-2-Clause
>> +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
>> +#pragma once
>> +
>> +#define ALLOC_SELFTEST(func, ...)              \
>> +       do {                            \
>> +               int ret = func(__VA_ARGS__);    \
>> +               if (ret) {              \
>> +                       arena_stderr("SELFTEST %s FAIL: %d", #func, ret);       \
>> +                       return ret;     \
>> +               }                       \
>> +       } while (0)
>
> I'm not excited about yet another special macro that hides control flow.
> Pls stick to ASSERT*() family.

Reusing test_progs.h would require us to other include the header in
libarena or complicate exporting it. Since as it is right now it's not
immediately exportable, I can everything to ASSERT and we can either
factor them out of test_progs.h later if necessary.

>
> pw-bot: cr