Add a basic test for the ability to mmap /sys/kernel/btf/vmlinux. Since
libbpf doesn't have an API to parse BTF from memory we do some basic
sanity checks ourselves.
Signed-off-by: Lorenz Bauer <l...@isovalent.com>
---
tools/testing/selftests/bpf/prog_tests/btf_sysfs.c | 79 ++++++++++++++++++++++
1 file changed, 79 insertions(+)
diff --git a/tools/testing/selftests/bpf/prog_tests/btf_sysfs.c
b/tools/testing/selftests/bpf/prog_tests/btf_sysfs.c
new file mode 100644
index
0000000000000000000000000000000000000000..8dffed136b4757779028ec0971b56ff541f2218c
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/btf_sysfs.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
+/* Copyright (c) 2025 Isovalent */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#define BTF_MAGIC 0xeB9F
+
+static const char *btf_path = "/sys/kernel/btf/vmlinux";
+
+void test_btf_sysfs(void)
+{
+ struct stat st;
+ __u64 btf_size;
+ void *raw_data = NULL;
+ int fd = -1;
+ size_t trailing;
+ long page_size;
+
+ page_size = sysconf(_SC_PAGESIZE);
+ if (!ASSERT_GE(page_size, 0, "get_page_size"))
+ goto cleanup;
+
+ if (!ASSERT_OK(stat(btf_path, &st), "stat_btf"))
+ goto cleanup;
+
+ btf_size = st.st_size;
+ trailing = page_size - (btf_size % page_size) % page_size;
+
+ fd = open(btf_path, O_RDONLY);
+ if (!ASSERT_GE(fd, 0, "open_btf"))
+ goto cleanup;
+
+ raw_data = mmap(NULL, btf_size, PROT_READ | PROT_WRITE, MAP_PRIVATE,
fd, 0);
+ if (!ASSERT_EQ(raw_data, MAP_FAILED, "mmap_btf_writable"))
+ goto cleanup;
+
+ raw_data = mmap(NULL, btf_size, PROT_READ, MAP_SHARED, fd, 0);
+ if (!ASSERT_EQ(raw_data, MAP_FAILED, "mmap_btf_shared"))
+ goto cleanup;
+
+ raw_data = mmap(NULL, btf_size + trailing + 1, PROT_READ, MAP_PRIVATE,
fd, 0);
+ if (!ASSERT_EQ(raw_data, MAP_FAILED, "mmap_btf_invalid_size"))
+ goto cleanup;
+
+ raw_data = mmap(NULL, btf_size, PROT_READ, MAP_PRIVATE, fd, 0);
+ if (!ASSERT_NEQ(raw_data, MAP_FAILED, "mmap_btf"))
+ goto cleanup;
+
+ if (!ASSERT_EQ(mprotect(raw_data, btf_size, PROT_READ | PROT_WRITE), -1,
+ "mprotect_writable"))
+ goto cleanup;
+
+ if (!ASSERT_EQ(mprotect(raw_data, btf_size, PROT_READ | PROT_EXEC), -1,
+ "mprotect_executable"))
+ goto cleanup;
+
+ /* Check BTF magic value */
+ if (!ASSERT_EQ(*(__u16 *)raw_data, BTF_MAGIC, "btf_magic"))
+ goto cleanup;
+
+ /* Check padding is zeroed */
+ for (int i = 0; i < trailing; i++) {
+ if (((__u8 *)raw_data)[btf_size + i] != 0) {
+ PRINT_FAIL("tail of BTF is not zero at page offset
%d\n", i);
+ goto cleanup;
+ }
+ }
+
+cleanup:
+ if (raw_data && raw_data != MAP_FAILED)
+ munmap(raw_data, btf_size);
+ if (fd >= 0)
+ close(fd);
+}
--
2.49.0
