netdev - [PATCH bpf-next v4 2/2] selftests/bpf: test linking with duplicate extern functions

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Message-Id: <20241002-libbpf-dup-extern-funcs-v4-2-560eb460ff90@hack3r.moe>
Date: Wed, 02 Oct 2024 14:25:07 +0800
From: Eric Long via B4 Relay <devnull+i.hack3r.moe@...nel.org>
To: bpf@...r.kernel.org
Cc: Andrii Nakryiko <andrii@...nel.org>, 
 Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org, 
 Eric Long <i@...k3r.moe>
Subject: [PATCH bpf-next v4 2/2] selftests/bpf: test linking with duplicate
 extern functions

From: Eric Long <i@...k3r.moe>

Previously when multiple BPF object files referencing the same extern
function (usually kfunc) are statically linked using `bpftool gen
object`, libbpf tries to get the nonexistent size of BTF_KIND_FUNC_PROTO
and fails. This test ensures it is fixed.

Signed-off-by: Eric Long <i@...k3r.moe>
---
 tools/testing/selftests/bpf/progs/linked_funcs1.c | 8 ++++++++
 tools/testing/selftests/bpf/progs/linked_funcs2.c | 8 ++++++++
 2 files changed, 16 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/linked_funcs1.c b/tools/testing/selftests/bpf/progs/linked_funcs1.c
index cc79dddac182c20da69a1a57fa39bc81004184f1..049a1f78de3f835e7658dde6f2d03161b6a5a07f 100644
--- a/tools/testing/selftests/bpf/progs/linked_funcs1.c
+++ b/tools/testing/selftests/bpf/progs/linked_funcs1.c
@@ -63,6 +63,8 @@ extern int set_output_val2(int x);
 /* here we'll force set_output_ctx2() to be __hidden in the final obj file */
 __hidden extern void set_output_ctx2(__u64 *ctx);
 
+void *bpf_cast_to_kern_ctx(void *obj) __ksym;
+
 SEC("?raw_tp/sys_enter")
 int BPF_PROG(handler1, struct pt_regs *regs, long id)
 {
@@ -86,4 +88,10 @@ int BPF_PROG(handler1, struct pt_regs *regs, long id)
 	return 0;
 }
 
+/* Generate BTF FUNC record and test linking with duplicate extern functions */
+void kfunc_gen1(void)
+{
+	bpf_cast_to_kern_ctx(0);
+}
+
 char LICENSE[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/linked_funcs2.c b/tools/testing/selftests/bpf/progs/linked_funcs2.c
index 942cc5526ddf02004bf82d1f72c74cfba6eaf486..96850759fd8d0074249bbf1f743aab08e20de0fc 100644
--- a/tools/testing/selftests/bpf/progs/linked_funcs2.c
+++ b/tools/testing/selftests/bpf/progs/linked_funcs2.c
@@ -63,6 +63,8 @@ extern int set_output_val1(int x);
 /* here we'll force set_output_ctx1() to be __hidden in the final obj file */
 __hidden extern void set_output_ctx1(__u64 *ctx);
 
+void *bpf_cast_to_kern_ctx(void *obj) __ksym;
+
 SEC("?raw_tp/sys_enter")
 int BPF_PROG(handler2, struct pt_regs *regs, long id)
 {
@@ -86,4 +88,10 @@ int BPF_PROG(handler2, struct pt_regs *regs, long id)
 	return 0;
 }
 
+/* Generate BTF FUNC record and test linking with duplicate extern functions */
+void kfunc_gen2(void)
+{
+	bpf_cast_to_kern_ctx(0);
+}
+
 char LICENSE[] SEC("license") = "GPL";

-- 
2.46.2