libbpf: Support initialized global variables

Initialized global variables are no different in ELF from static variables,
and don't require any extra support from libbpf. But they are matching
semantics of global data (backed by BPF maps) more closely, preventing
LLVM/Clang from aggressively inlining constant values and not requiring
volatile incantations to prevent those. This patch enables global variables.
It still disables uninitialized variables, which will be put into special COM
(common) ELF section, because BPF doesn't allow uninitialized data to be
accessed.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191121070743.1309473-5-andriin@fb.com

14 files changed, 28 insertions, 33 deletions

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 64bc75fc6723..a4e250a369c6 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1835,8 +1835,8 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
 		return -LIBBPF_ERRNO__RELOC;
 	}
 	if (!shdr_idx || shdr_idx >= SHN_LORESERVE) {
-		pr_warn("relocation: not yet supported relo for non-static global \'%s\' variable in special section (0x%x) found in insns[%d].code 0x%x\n",
-			name, shdr_idx, insn_idx, insn->code);
+		pr_warn("invalid relo for \'%s\' in special section 0x%x; forgot to initialize global var?..\n",
+			name, shdr_idx);
 		return -LIBBPF_ERRNO__RELOC;
 	}
 
@@ -1876,11 +1876,6 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
 		pr_warn("bad data relo against section %u\n", shdr_idx);
 		return -LIBBPF_ERRNO__RELOC;
 	}
-	if (GELF_ST_BIND(sym->st_info) == STB_GLOBAL) {
-		pr_warn("relocation: not yet supported relo for non-static global \'%s\' variable found in insns[%d].code 0x%x\n",
-			name, insn_idx, insn->code);
-		return -LIBBPF_ERRNO__RELOC;
-	}
 	if (!obj->caps.global_data) {
 		pr_warn("relocation: kernel does not support global \'%s\' variable access in insns[%d]\n",
 			name, insn_idx);
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_arrays.c b/tools/testing/selftests/bpf/progs/test_core_reloc_arrays.c
index 96b1f5f3b07a..89951b684282 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_arrays.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_arrays.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_arrays_output {
 	int a2;
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_bitfields_direct.c b/tools/testing/selftests/bpf/progs/test_core_reloc_bitfields_direct.c
index 738b34b72655..edc0f7c9e56d 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_bitfields_direct.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_bitfields_direct.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_bitfields {
 	/* unsigned bitfields */
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_bitfields_probed.c b/tools/testing/selftests/bpf/progs/test_core_reloc_bitfields_probed.c
index e466e3ab7de4..6c20e433558b 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_bitfields_probed.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_bitfields_probed.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_bitfields {
 	/* unsigned bitfields */
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_existence.c b/tools/testing/selftests/bpf/progs/test_core_reloc_existence.c
index c3cac95a19f1..1b7f0ae49cfb 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_existence.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_existence.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_existence_output {
 	int a_exists;
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_flavors.c b/tools/testing/selftests/bpf/progs/test_core_reloc_flavors.c
index 71fd7cebc9d7..b5dbeef540fd 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_flavors.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_flavors.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_flavors {
 	int a;
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_ints.c b/tools/testing/selftests/bpf/progs/test_core_reloc_ints.c
index ad5c3f59c9c6..c78ab6d28a14 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_ints.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_ints.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_ints {
 	uint8_t		u8_field;
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_kernel.c b/tools/testing/selftests/bpf/progs/test_core_reloc_kernel.c
index a4b5e0562ed5..5d499ebdc4bd 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_kernel.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_kernel.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_kernel_output {
 	int valid[10];
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_misc.c b/tools/testing/selftests/bpf/progs/test_core_reloc_misc.c
index 1a36b0856653..292a5c4ee76a 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_misc.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_misc.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_misc_output {
 	int a, b, c;
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_mods.c b/tools/testing/selftests/bpf/progs/test_core_reloc_mods.c
index 3199fafede2c..0b28bfacc8fd 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_mods.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_mods.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_mods_output {
 	int a, b, c, d, e, f, g, h;
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_nesting.c b/tools/testing/selftests/bpf/progs/test_core_reloc_nesting.c
index 98238cb64fbd..39279bf0c9db 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_nesting.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_nesting.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_nesting_substruct {
 	int a;
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_primitives.c b/tools/testing/selftests/bpf/progs/test_core_reloc_primitives.c
index 4f3ecb9127bb..ea57973cdd19 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_primitives.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_primitives.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 enum core_reloc_primitives_enum {
 	A = 0,
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_ptr_as_arr.c b/tools/testing/selftests/bpf/progs/test_core_reloc_ptr_as_arr.c
index 27f602f00419..d1eb59d4ea64 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_ptr_as_arr.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_ptr_as_arr.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_ptr_as_arr {
 	int a;
diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_size.c b/tools/testing/selftests/bpf/progs/test_core_reloc_size.c
index 9a92998d9107..9e091124d3bd 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_size.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_size.c
@@ -8,10 +8,10 @@
 
 char _license[] SEC("license") = "GPL";
 
-static volatile struct data {
+struct {
 	char in[256];
 	char out[256];
-} data;
+} data = {};
 
 struct core_reloc_size_output {
 	int int_sz;