Commit 393cdfbe authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Alexei Starovoitov
Browse files

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: default avatarAndrii Nakryiko <andriin@fb.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191121070743.1309473-5-andriin@fb.com
parent 8983b731

tools/lib/bpf/libbpf.c

+2 −7
Original line number Original line Diff line number Diff line
@@ -1835,8 +1835,8 @@ static int bpf_program__record_reloc(struct bpf_program *prog, 
		return -LIBBPF_ERRNO__RELOC;

		return -LIBBPF_ERRNO__RELOC;

	}

	}

	if (!shdr_idx || shdr_idx >= SHN_LORESERVE) {

	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",

		pr_warn("invalid relo for \'%s\' in special section 0x%x; forgot to initialize global var?..\n",

			name, shdr_idx, insn_idx, insn->code);

			name, shdr_idx);

		return -LIBBPF_ERRNO__RELOC;

		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);

		pr_warn("bad data relo against section %u\n", shdr_idx);

		return -LIBBPF_ERRNO__RELOC;

		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) {

	if (!obj->caps.global_data) {

		pr_warn("relocation: kernel does not support global \'%s\' variable access in insns[%d]\n",

		pr_warn("relocation: kernel does not support global \'%s\' variable access in insns[%d]\n",

			name, insn_idx);

			name, insn_idx);

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

+2 −2
Original line number Original line Diff line number Diff line
@@ -8,10 +8,10 @@ 




char _license[] SEC("license") = "GPL";

char _license[] SEC("license") = "GPL";





static volatile struct data {

struct {

	char in[256];

	char in[256];

	char out[256];

	char out[256];

} data;

} data = {};





struct core_reloc_arrays_output {

struct core_reloc_arrays_output {

	int a2;

	int a2;

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

+2 −2
Original line number Original line Diff line number Diff line
@@ -8,10 +8,10 @@ 




char _license[] SEC("license") = "GPL";

char _license[] SEC("license") = "GPL";





static volatile struct data {

struct {

	char in[256];

	char in[256];

	char out[256];

	char out[256];

} data;

} data = {};





struct core_reloc_bitfields {

struct core_reloc_bitfields {

	/* unsigned bitfields */

	/* unsigned bitfields */

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

+2 −2
Original line number Original line Diff line number Diff line
@@ -8,10 +8,10 @@ 




char _license[] SEC("license") = "GPL";

char _license[] SEC("license") = "GPL";





static volatile struct data {

struct {

	char in[256];

	char in[256];

	char out[256];

	char out[256];

} data;

} data = {};





struct core_reloc_bitfields {

struct core_reloc_bitfields {

	/* unsigned bitfields */

	/* unsigned bitfields */

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

+2 −2
Original line number Original line Diff line number Diff line
@@ -8,10 +8,10 @@ 




char _license[] SEC("license") = "GPL";

char _license[] SEC("license") = "GPL";





static volatile struct data {

struct {

	char in[256];

	char in[256];

	char out[256];

	char out[256];

} data;

} data = {};





struct core_reloc_existence_output {

struct core_reloc_existence_output {

	int a_exists;

	int a_exists;

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