selftests/bpf: Query BPF_MAX_TRAMP_LINKS using BTF

Do not hard-code the value, since for s390x it will be smaller than
for x86.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Link: https://lore.kernel.org/r/20230128000650.1516334-4-iii@linux.ibm.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 38 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
index c5f852163246..6d5e3022c75f 100644
--- a/tools/testing/selftests/bpf/test_progs.c
+++ b/tools/testing/selftests/bpf/test_progs.c
@@ -17,6 +17,7 @@
 #include <sys/select.h>
 #include <sys/socket.h>
 #include <sys/un.h>
+#include <bpf/btf.h>
 
 static bool verbose(void)
 {
@@ -967,6 +968,43 @@ int write_sysctl(const char *sysctl, const char *value)
 	return 0;
 }
 
+int get_bpf_max_tramp_links_from(struct btf *btf)
+{
+	const struct btf_enum *e;
+	const struct btf_type *t;
+	__u32 i, type_cnt;
+	const char *name;
+	__u16 j, vlen;
+
+	for (i = 1, type_cnt = btf__type_cnt(btf); i < type_cnt; i++) {
+		t = btf__type_by_id(btf, i);
+		if (!t || !btf_is_enum(t) || t->name_off)
+			continue;
+		e = btf_enum(t);
+		for (j = 0, vlen = btf_vlen(t); j < vlen; j++, e++) {
+			name = btf__str_by_offset(btf, e->name_off);
+			if (name && !strcmp(name, "BPF_MAX_TRAMP_LINKS"))
+				return e->val;
+		}
+	}
+
+	return -1;
+}
+
+int get_bpf_max_tramp_links(void)
+{
+	struct btf *vmlinux_btf;
+	int ret;
+
+	vmlinux_btf = btf__load_vmlinux_btf();
+	if (!ASSERT_OK_PTR(vmlinux_btf, "vmlinux btf"))
+		return -1;
+	ret = get_bpf_max_tramp_links_from(vmlinux_btf);
+	btf__free(vmlinux_btf);
+
+	return ret;
+}
+
 #define MAX_BACKTRACE_SZ 128
 void crash_handler(int signum)
 {