selftests/bpf: Make CO-RE reloc test impartial to test_progs flavor

test_core_reloc_kernel test captures its own process name and validates
it as part of the test. Given extra "flavors" of test_progs, this break
for anything by default test_progs binary. Fix the test to cut out
flavor part of the process name.

Fixes: ee2eb063 ("selftests/bpf: Add BPF_CORE_READ and BPF_CORE_READ_STR_INTO macro tests")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191016060051.2024182-3-andriin@fb.com

tools/testing/selftests/bpf/prog_tests/core_reloc.c

@@ -211,8 +211,8 @@ static struct core_reloc_test_case test_cases[] = {
 		.input_len = 0,
 		.output = STRUCT_TO_CHAR_PTR(core_reloc_kernel_output) {
 			.valid = { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, },
-			.comm = "test_progs\0\0\0\0\0",
-			.comm_len = 11,
+			.comm = "test_progs",
+			.comm_len = sizeof("test_progs"),
 		},
 		.output_len = sizeof(struct core_reloc_kernel_output),
 	},

tools/testing/selftests/bpf/progs/core_reloc_types.h

@@ -6,7 +6,7 @@
 
 struct core_reloc_kernel_output {
 	int valid[10];
-	char comm[16];
+	char comm[sizeof("test_progs")];
 	int comm_len;
 };
 

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

@@ -15,7 +15,8 @@ static volatile struct data {
 
 struct core_reloc_kernel_output {
 	int valid[10];
-	char comm[16];
+	/* we have test_progs[-flavor], so cut flavor part */
+	char comm[sizeof("test_progs")];
 	int comm_len;
 };