Re: [PATCH bpf-next v7 7/7] selftests/bpf: Test "bpftool gen min_core_btf"

This commit reuses the core_reloc test to check if the BTF files
generated with "bpftool gen min_core_btf" are correct. This introduces
test_core_btfgen() that runs all the core_reloc tests, but this time
the source BTF files are generated by using "bpftool gen min_core_btf".

The goal of this test is to check that the generated files are usable,
and not to check if the algorithm is creating an optimized BTF file.

Signed-off-by: Mauricio Vásquez <redacted>
Signed-off-by: Rafael David Tinoco <redacted>
Signed-off-by: Lorenzo Fontana <redacted>
Signed-off-by: Leonardo Di Donato <redacted>
---
 .../selftests/bpf/prog_tests/core_reloc.c     | 50 ++++++++++++++++++-
 1 file changed, 48 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/core_reloc.c b/tools/testing/selftests/bpf/prog_tests/core_reloc.c
index 68e4c8dafa00..fa2908879c77 100644
--- a/tools/testing/selftests/bpf/prog_tests/core_reloc.c
+++ b/tools/testing/selftests/bpf/prog_tests/core_reloc.c

@@ -2,6 +2,7 @@
 #include <test_progs.h>
 #include "progs/core_reloc_types.h"
 #include "bpf_testmod/bpf_testmod.h"
+#include <linux/limits.h>
 #include <sys/mman.h>
 #include <sys/syscall.h>
 #include <bpf/btf.h>

@@ -836,13 +837,27 @@ static size_t roundup_page(size_t sz)
        return (sz + page_size - 1) / page_size * page_size;
 }

-void test_core_reloc(void)
+static int run_btfgen(const char *src_btf, const char *dst_btf, const char *objpath)
+{
+       char command[4096];
+       int n;
+
+       n = snprintf(command, sizeof(command),
+                    "./tools/build/bpftool/bpftool gen min_core_btf %s %s %s",
+                    src_btf, dst_btf, objpath);
+       if (n < 0 || n >= sizeof(command))
+               return -1;
+
+       return system(command);
+}
+
+static void run_core_reloc_tests(bool use_btfgen)
 {
        const size_t mmap_sz = roundup_page(sizeof(struct data));
        DECLARE_LIBBPF_OPTS(bpf_object_open_opts, open_opts);
        struct core_reloc_test_case *test_case;
        const char *tp_name, *probe_name;
-       int err, i, equal;
+       int err, i, equal, fd;
        struct bpf_link *link = NULL;
        struct bpf_map *data_map;
        struct bpf_program *prog;

@@ -854,6 +869,7 @@ void test_core_reloc(void)
        my_pid_tgid = getpid() | ((uint64_t)syscall(SYS_gettid) << 32);

        for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
+               char btf_file[] = "/tmp/core_reloc.btf.XXXXXX";
                test_case = &test_cases[i];
                if (!test__start_subtest(test_case->case_name))
                        continue;

@@ -863,6 +879,25 @@ void test_core_reloc(void)
                        continue;
                }

+               /* generate a "minimal" BTF file and use it as source */
+               if (use_btfgen) {
+                       if (!test_case->btf_src_file || test_case->fails) {
+                               test__skip();
+                               continue;
+                       }
+
+                       fd = mkstemp(btf_file);
+                       if (CHECK(fd < 0, "btf_tmp", "failed to create file: %d\n", fd))
+                               goto cleanup;

+                       close(fd); /* we only need the path */
+                       err = run_btfgen(test_case->btf_src_file, btf_file,
+                                        test_case->bpf_obj_file);
+                       if (!ASSERT_OK(err, "run_btfgen"))
+                               goto cleanup;
+
+                       test_case->btf_src_file = btf_file;
+               }
+
                if (test_case->setup) {
                        err = test_case->setup(test_case);
                        if (CHECK(err, "test_setup", "test #%d setup failed: %d\n", i, err))

@@ -954,8 +989,19 @@ void test_core_reloc(void)
                        CHECK_FAIL(munmap(mmap_data, mmap_sz));
                        mmap_data = NULL;
                }
+               remove(btf_file);