testdata: loader - read from anonymous (global) constant

https://lore.kernel.org/bpf/CAK3+h2wcDceeGyFVDU3n7kPm=zgp7r1q4WK0=abxBsj9pyFN-g@mail.gmail.com

Signed-off-by: Timo Beckers <[email protected]>

Author: ti-mo

elf_reader_test.go

@@ -131,6 +131,12 @@ func TestLoadCollectionSpec(t *testing.T) {
 				SectionName: "static",
 				License:     "MIT",
 			},
+			"anon_const": {
+				Name:        "anon_const",
+				Type:        SocketFilter,
+				SectionName: "socket/4",
+				License:     "MIT",
+			},
 		},
 	}
 

testdata/loader-clang-14-eb.elf

@@ -166,3 +166,26 @@ __section("socket/3") int data_sections() {
 	return 0;
 }
 #endif
+
+/*
+ * Up until LLVM 14, this program results in an .rodata.cst32 section
+ * that is accessed by 'return values[i]'. For this section, no BTF is
+ * emitted. 'values' cannot be rewritten, since there is no BTF info
+ * describing the data section.
+ */
+__section("socket/4") int anon_const() {
+	volatile int ctx = 0;
+
+// 32 bytes wide results in a .rodata.cst32 section.
+#define values \
+	(uint64_t[]) { 0x0, 0x1, 0x2, 0x3 }
+
+	int i;
+	for (i = 0; i < 3; i++) {
+		if (ctx == values[i]) {
+			return values[i];
+		}
+	}
+
+	return 0;
+}