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libbpf: Support initialized global variables

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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
This commit is contained in:
Andrii Nakryiko 2019-11-20 23:07:43 -08:00 committed by Andrii Nakryiko
parent 3f05b513d4
commit 83535cb2bf
1 changed files with 2 additions and 7 deletions
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9
src/libbpf.c
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@ -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);