Merge branch 'libbpf-field-existence'

Andrii Nakryiko says:

====================
This patch set generalizes libbpf's CO-RE relocation support. In addition to
existing field's byte offset relocation, libbpf now supports field existence
relocations, which are emitted by Clang when using
__builtin_preserve_field_info(<field>, BPF_FIELD_EXISTS). A convenience
bpf_core_field_exists() macro is added to bpf_core_read.h BPF-side header,
along the bpf_field_info_kind enum containing currently supported types of
field information libbpf supports. This list will grow as libbpf gains support
for other relo kinds.

This patch set upgrades the format of .BTF.ext's relocation record to match
latest Clang's format (12 -> 16 bytes). This is not a breaking change, as the
previous format hasn't been released yet as part of official Clang version
release.

v1->v2:
- unify bpf_field_info_kind enum and naming changes (Alexei);
- added bpf_core_field_exists() to bpf_core_read.h.
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

11 files changed, 233 insertions, 2 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/core_reloc.c b/tools/testing/selftests/bpf/prog_tests/core_reloc.c
index 21a0dff66241..7e2f5b4bf7f3 100644
--- a/tools/testing/selftests/bpf/prog_tests/core_reloc.c
+++ b/tools/testing/selftests/bpf/prog_tests/core_reloc.c
@@ -174,6 +174,21 @@
 	.fails = true,							\
 }
 
+#define EXISTENCE_DATA(struct_name) STRUCT_TO_CHAR_PTR(struct_name) {	\
+	.a = 42,							\
+}
+
+#define EXISTENCE_CASE_COMMON(name)					\
+	.case_name = #name,						\
+	.bpf_obj_file = "test_core_reloc_existence.o",			\
+	.btf_src_file = "btf__core_reloc_" #name ".o",			\
+	.relaxed_core_relocs = true					\
+
+#define EXISTENCE_ERR_CASE(name) {					\
+	EXISTENCE_CASE_COMMON(name),					\
+	.fails = true,							\
+}
+
 struct core_reloc_test_case {
 	const char *case_name;
 	const char *bpf_obj_file;
@@ -183,6 +198,7 @@ struct core_reloc_test_case {
 	const char *output;
 	int output_len;
 	bool fails;
+	bool relaxed_core_relocs;
 };
 
 static struct core_reloc_test_case test_cases[] = {
@@ -283,6 +299,59 @@ static struct core_reloc_test_case test_cases[] = {
 		},
 		.output_len = sizeof(struct core_reloc_misc_output),
 	},
+
+	/* validate field existence checks */
+	{
+		EXISTENCE_CASE_COMMON(existence),
+		.input = STRUCT_TO_CHAR_PTR(core_reloc_existence) {
+			.a = 1,
+			.b = 2,
+			.c = 3,
+			.arr = { 4 },
+			.s = { .x = 5 },
+		},
+		.input_len = sizeof(struct core_reloc_existence),
+		.output = STRUCT_TO_CHAR_PTR(core_reloc_existence_output) {
+			.a_exists = 1,
+			.b_exists = 1,
+			.c_exists = 1,
+			.arr_exists = 1,
+			.s_exists = 1,
+			.a_value = 1,
+			.b_value = 2,
+			.c_value = 3,
+			.arr_value = 4,
+			.s_value = 5,
+		},
+		.output_len = sizeof(struct core_reloc_existence_output),
+	},
+	{
+		EXISTENCE_CASE_COMMON(existence___minimal),
+		.input = STRUCT_TO_CHAR_PTR(core_reloc_existence___minimal) {
+			.a = 42,
+		},
+		.input_len = sizeof(struct core_reloc_existence),
+		.output = STRUCT_TO_CHAR_PTR(core_reloc_existence_output) {
+			.a_exists = 1,
+			.b_exists = 0,
+			.c_exists = 0,
+			.arr_exists = 0,
+			.s_exists = 0,
+			.a_value = 42,
+			.b_value = 0xff000002u,
+			.c_value = 0xff000003u,
+			.arr_value = 0xff000004u,
+			.s_value = 0xff000005u,
+		},
+		.output_len = sizeof(struct core_reloc_existence_output),
+	},
+
+	EXISTENCE_ERR_CASE(existence__err_int_sz),
+	EXISTENCE_ERR_CASE(existence__err_int_type),
+	EXISTENCE_ERR_CASE(existence__err_int_kind),
+	EXISTENCE_ERR_CASE(existence__err_arr_kind),
+	EXISTENCE_ERR_CASE(existence__err_arr_value_type),
+	EXISTENCE_ERR_CASE(existence__err_struct_type),
 };
 
 struct data {
@@ -305,11 +374,14 @@ void test_core_reloc(void)
 
 	for (i = 0; i < ARRAY_SIZE(test_cases); i++) {
 		test_case = &test_cases[i];
-
 		if (!test__start_subtest(test_case->case_name))
 			continue;
 
-		obj = bpf_object__open(test_case->bpf_obj_file);
+		LIBBPF_OPTS(bpf_object_open_opts, opts,
+			.relaxed_core_relocs = test_case->relaxed_core_relocs,
+		);
+
+		obj = bpf_object__open_file(test_case->bpf_obj_file, &opts);
 		if (CHECK(IS_ERR_OR_NULL(obj), "obj_open",
 			  "failed to open '%s': %ld\n",
 			  test_case->bpf_obj_file, PTR_ERR(obj)))
diff --git a/tools/testing/selftests/bpf/progs/btf__core_reloc_existence.c b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence.c
new file mode 100644
index 000000000000..0b62315ad46c
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence.c
@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence x) {}
diff --git a/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_arr_kind.c b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_arr_kind.c
new file mode 100644
index 000000000000..dd0ffa518f36
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_arr_kind.c
@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_arr_kind x) {}
diff --git a/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_arr_value_type.c b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_arr_value_type.c
new file mode 100644
index 000000000000..bc83372088ad
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_arr_value_type.c
@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_arr_value_type x) {}
diff --git a/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_int_kind.c b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_int_kind.c
new file mode 100644
index 000000000000..917bec41be08
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_int_kind.c
@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_int_kind x) {}
diff --git a/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_int_sz.c b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_int_sz.c
new file mode 100644
index 000000000000..6ec7e6ec1c91
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_int_sz.c
@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_int_sz x) {}
diff --git a/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_int_type.c b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_int_type.c
new file mode 100644
index 000000000000..7bbcacf2b0d1
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_int_type.c
@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_int_type x) {}
diff --git a/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_struct_type.c b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_struct_type.c
new file mode 100644
index 000000000000..f384dd38ec70
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___err_wrong_struct_type.c
@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___err_wrong_struct_type x) {}
diff --git a/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___minimal.c b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___minimal.c
new file mode 100644
index 000000000000..aec2dec20e90
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf__core_reloc_existence___minimal.c
@@ -0,0 +1,3 @@
+#include "core_reloc_types.h"
+
+void f(struct core_reloc_existence___minimal x) {}
diff --git a/tools/testing/selftests/bpf/progs/core_reloc_types.h b/tools/testing/selftests/bpf/progs/core_reloc_types.h
index 9a6bdeb4894c..ad763ec0ba8f 100644
--- a/tools/testing/selftests/bpf/progs/core_reloc_types.h
+++ b/tools/testing/selftests/bpf/progs/core_reloc_types.h
@@ -674,3 +674,59 @@ struct core_reloc_misc_extensible {
 	int c;
 	int d;
 };
+
+/*
+ * EXISTENCE
+ */
+struct core_reloc_existence_output {
+	int a_exists;
+	int a_value;
+	int b_exists;
+	int b_value;
+	int c_exists;
+	int c_value;
+	int arr_exists;
+	int arr_value;
+	int s_exists;
+	int s_value;
+};
+
+struct core_reloc_existence {
+	int a;
+	struct {
+		int b;
+	};
+	int c;
+	int arr[1];
+	struct {
+		int x;
+	} s;
+};
+
+struct core_reloc_existence___minimal {
+	int a;
+};
+
+struct core_reloc_existence___err_wrong_int_sz {
+	short a;
+};
+
+struct core_reloc_existence___err_wrong_int_type {
+	int b[1];
+};
+
+struct core_reloc_existence___err_wrong_int_kind {
+	struct{ int x; } c;
+};
+
+struct core_reloc_existence___err_wrong_arr_kind {
+	int arr;
+};
+
+struct core_reloc_existence___err_wrong_arr_value_type {
+	short arr[1];
+};
+
+struct core_reloc_existence___err_wrong_struct_type {
+	int s;
+};
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_existence.c b/tools/testing/selftests/bpf/progs/test_core_reloc_existence.c
new file mode 100644
index 000000000000..c3cac95a19f1
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_existence.c
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2019 Facebook
+
+#include <linux/bpf.h>
+#include <stdint.h>
+#include "bpf_helpers.h"
+#include "bpf_core_read.h"
+
+char _license[] SEC("license") = "GPL";
+
+static volatile struct data {
+	char in[256];
+	char out[256];
+} data;
+
+struct core_reloc_existence_output {
+	int a_exists;
+	int a_value;
+	int b_exists;
+	int b_value;
+	int c_exists;
+	int c_value;
+	int arr_exists;
+	int arr_value;
+	int s_exists;
+	int s_value;
+};
+
+struct core_reloc_existence {
+	struct {
+		int x;
+	} s;
+	int arr[1];
+	int a;
+	struct {
+		int b;
+	};
+	int c;
+};
+
+SEC("raw_tracepoint/sys_enter")
+int test_core_existence(void *ctx)
+{
+	struct core_reloc_existence *in = (void *)&data.in;
+	struct core_reloc_existence_output *out = (void *)&data.out;
+
+	out->a_exists = bpf_core_field_exists(in->a);
+	if (bpf_core_field_exists(in->a))
+		out->a_value = BPF_CORE_READ(in, a);
+	else
+		out->a_value = 0xff000001u;
+
+	out->b_exists = bpf_core_field_exists(in->b);
+	if (bpf_core_field_exists(in->b))
+		out->b_value = BPF_CORE_READ(in, b);
+	else
+		out->b_value = 0xff000002u;
+
+	out->c_exists = bpf_core_field_exists(in->c);
+	if (bpf_core_field_exists(in->c))
+		out->c_value = BPF_CORE_READ(in, c);
+	else
+		out->c_value = 0xff000003u;
+
+	out->arr_exists = bpf_core_field_exists(in->arr);
+	if (bpf_core_field_exists(in->arr))
+		out->arr_value = BPF_CORE_READ(in, arr[0]);
+	else
+		out->arr_value = 0xff000004u;
+
+	out->s_exists = bpf_core_field_exists(in->s);
+	if (bpf_core_field_exists(in->s))
+		out->s_value = BPF_CORE_READ(in, s.x);
+	else
+		out->s_value = 0xff000005u;
+
+	return 0;
+}
+