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libbpf: Fix global variable relocation

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Similarly to a0d7da26ce ("libbpf: Fix call relocation offset calculation
bug"), relocations against global variables need to take into account
referenced symbol's st_value, which holds offset into a corresponding data
section (and, subsequently, offset into internal backing map). For static
variables this offset is always zero and data offset is completely described
by respective instruction's imm field.

Convert a bunch of selftests to global variables. Previously they were relying
on `static volatile` trick to ensure Clang doesn't inline static variables,
which with global variables is not necessary anymore.

Fixes: 393cdfbee8 ("libbpf: Support initialized global variables")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20191127200651.1381348-1-andriin@fb.com
This commit is contained in:
Andrii Nakryiko
2019-11-27 12:06:50 -08:00
committed by Alexei Starovoitov
parent b568405856
commit 53f8dd434b
5 changed files with 36 additions and 41 deletions
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43
tools/lib/bpf/libbpf.c
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@@ -171,10 +171,8 @@ struct bpf_program {
RELO_DATA,
} type;
int insn_idx;
union {
int map_idx;
int text_off;
};
int map_idx;
int sym_off;
} *reloc_desc;
int nr_reloc;
int log_level;
@@ -1824,7 +1822,7 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
}
reloc_desc->type = RELO_CALL;
reloc_desc->insn_idx = insn_idx;
reloc_desc->text_off = sym->st_value / 8;
reloc_desc->sym_off = sym->st_value;
obj->has_pseudo_calls = true;
return 0;
}
@@ -1868,6 +1866,7 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
reloc_desc->type = RELO_LD64;
reloc_desc->insn_idx = insn_idx;
reloc_desc->map_idx = map_idx;
reloc_desc->sym_off = 0; /* sym->st_value determines map_idx */
return 0;
}
@@ -1899,6 +1898,7 @@ static int bpf_program__record_reloc(struct bpf_program *prog,
reloc_desc->type = RELO_DATA;
reloc_desc->insn_idx = insn_idx;
reloc_desc->map_idx = map_idx;
reloc_desc->sym_off = sym->st_value;
return 0;
}
@@ -3563,8 +3563,8 @@ bpf_program__reloc_text(struct bpf_program *prog, struct bpf_object *obj,
return -LIBBPF_ERRNO__RELOC;
if (prog->idx == obj->efile.text_shndx) {
pr_warn("relo in .text insn %d into off %d\n",
relo->insn_idx, relo->text_off);
pr_warn("relo in .text insn %d into off %d (insn #%d)\n",
relo->insn_idx, relo->sym_off, relo->sym_off / 8);
return -LIBBPF_ERRNO__RELOC;
}
@@ -3599,7 +3599,7 @@ bpf_program__reloc_text(struct bpf_program *prog, struct bpf_object *obj,
prog->section_name);
}
insn = &prog->insns[relo->insn_idx];
insn->imm += relo->text_off + prog->main_prog_cnt - relo->insn_idx;
insn->imm += relo->sym_off / 8 + prog->main_prog_cnt - relo->insn_idx;
return 0;
}
@@ -3622,31 +3622,26 @@ bpf_program__relocate(struct bpf_program *prog, struct bpf_object *obj)
return 0;
for (i = 0; i < prog->nr_reloc; i++) {
if (prog->reloc_desc[i].type == RELO_LD64 ||
prog->reloc_desc[i].type == RELO_DATA) {
bool relo_data = prog->reloc_desc[i].type == RELO_DATA;
struct bpf_insn *insns = prog->insns;
int insn_idx, map_idx;
struct reloc_desc *relo = &prog->reloc_desc[i];
insn_idx = prog->reloc_desc[i].insn_idx;
map_idx = prog->reloc_desc[i].map_idx;
if (relo->type == RELO_LD64 || relo->type == RELO_DATA) {
struct bpf_insn *insn = &prog->insns[relo->insn_idx];
if (insn_idx + 1 >= (int)prog->insns_cnt) {
if (relo->insn_idx + 1 >= (int)prog->insns_cnt) {
pr_warn("relocation out of range: '%s'\n",
prog->section_name);
return -LIBBPF_ERRNO__RELOC;
}
if (!relo_data) {
insns[insn_idx].src_reg = BPF_PSEUDO_MAP_FD;
if (relo->type != RELO_DATA) {
insn[0].src_reg = BPF_PSEUDO_MAP_FD;
} else {
insns[insn_idx].src_reg = BPF_PSEUDO_MAP_VALUE;
insns[insn_idx + 1].imm = insns[insn_idx].imm;
insn[0].src_reg = BPF_PSEUDO_MAP_VALUE;
insn[1].imm = insn[0].imm + relo->sym_off;
}
insns[insn_idx].imm = obj->maps[map_idx].fd;
} else if (prog->reloc_desc[i].type == RELO_CALL) {
err = bpf_program__reloc_text(prog, obj,
&prog->reloc_desc[i]);
insn[0].imm = obj->maps[relo->map_idx].fd;
} else if (relo->type == RELO_CALL) {
err = bpf_program__reloc_text(prog, obj, relo);
if (err)
return err;
}