tools/testing/selftests/bpf/progs/fexit_bpf2bpf.c

Source file repositories/reference/linux-study-clean/tools/testing/selftests/bpf/progs/fexit_bpf2bpf.c

File Facts

System
Linux kernel
Corpus path
tools/testing/selftests/bpf/progs/fexit_bpf2bpf.c
Extension
.c
Size
4515 bytes
Lines
189
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

struct sk_buff {
	unsigned int len;
};

__u64 test_result = 0;
SEC("fexit/test_pkt_access")
int BPF_PROG(test_main, struct sk_buff *skb, int ret)
{
	int len;

	__builtin_preserve_access_index(({
		len = skb->len;
	}));
	if (len != 74 || ret != 0)
		return 0;
	test_result = 1;
	return 0;
}

__u64 test_result_subprog1 = 0;
SEC("fexit/test_pkt_access_subprog1")
int BPF_PROG(test_subprog1, struct sk_buff *skb, int ret)
{
	int len;

	__builtin_preserve_access_index(({
		len = skb->len;
	}));
	if (len != 74 || ret != 148)
		return 0;
	test_result_subprog1 = 1;
	return 0;
}

/* Though test_pkt_access_subprog2() is defined in C as:
 * static __attribute__ ((noinline))
 * int test_pkt_access_subprog2(int val, volatile struct __sk_buff *skb)
 * {
 *     return skb->len * val;
 * }
 * llvm optimizations remove 'int val' argument and generate BPF assembly:
 *   r0 = *(u32 *)(r1 + 0)
 *   w0 <<= 1
 *   exit
 * Before llvm23, in such case the verifier falls back to conservative and
 * tracing program can access arguments and return value as u64
 * instead of accurate types. With llvm23, the true signature
 *   int test_pkt_access_subprog2(volatile struct __sk_buff *skb)
 * is available in btf.
 */
#if __clang_major__ >= 23
struct args_subprog2 {
	__u64 args[1];
	__u64 ret;
};
#else
struct args_subprog2 {
	__u64 args[5];
	__u64 ret;
};
#endif
__u64 test_result_subprog2 = 0;
SEC("fexit/test_pkt_access_subprog2")
int test_subprog2(struct args_subprog2 *ctx)
{
	struct sk_buff *skb = (void *)ctx->args[0];
	__u64 ret;
	int len;

	bpf_probe_read_kernel(&len, sizeof(len),
			      __builtin_preserve_access_index(&skb->len));

	ret = ctx->ret;
	/* bpf_prog_test_load() loads "test_pkt_access.bpf.o" with
	 * BPF_F_TEST_RND_HI32 which randomizes upper 32 bits after BPF_ALU32
	 * insns. Hence after 'w0 <<= 1' upper bits of $rax are random. That is
	 * expected and correct. Trim them.
	 */
	ret = (__u32) ret;
	if (len != 74 || ret != 148)
		return 0;
	test_result_subprog2 = 1;
	return 0;
}

__u64 test_result_subprog3 = 0;
SEC("fexit/test_pkt_access_subprog3")
int BPF_PROG(test_subprog3, int val, struct sk_buff *skb, int ret)
{
	int len;

Annotation

Implementation Notes