From: Joe Stringer <joe@wand.net.nz>
To: bpf@vger.kernel.org
Cc: netdev@vger.kernel.org, daniel@iogearbox.net, ast@kernel.org
Subject: [PATCH bpf-next 3/4] libbpf: Support relocations for bss.
Date: Mon, 11 Feb 2019 16:47:28 -0800 [thread overview]
Message-ID: <20190212004729.535-4-joe@wand.net.nz> (raw)
In-Reply-To: <20190212004729.535-1-joe@wand.net.nz>
The BSS section in an ELF generated by LLVM represents constants for
uninitialized variables or variables that are configured with a zero
value. Support initializing zeroed static data by parsing the
relocations with references to the .bss section and zeroing them.
Signed-off-by: Joe Stringer <joe@wand.net.nz>
---
tools/lib/bpf/libbpf.c | 14 +++++++++++++-
1 file changed, 13 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index da35d5559b22..ff66d7e970c9 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -141,6 +141,7 @@ struct bpf_program {
RELO_LD64,
RELO_CALL,
RELO_DATA,
+ RELO_ZERO,
} type;
int insn_idx;
union {
@@ -222,6 +223,7 @@ struct bpf_object {
int maps_shndx;
int text_shndx;
int data_shndx;
+ int bss_shndx;
} efile;
/*
* All loaded bpf_object is linked in a list, which is
@@ -901,6 +903,8 @@ static int bpf_object__elf_collect(struct bpf_object *obj, int flags)
obj->efile.reloc[n].shdr = sh;
obj->efile.reloc[n].data = data;
}
+ } else if (sh.sh_type == SHT_NOBITS && strcmp(name, ".bss") == 0) {
+ obj->efile.bss_shndx = idx;
} else {
pr_debug("skip section(%d) %s\n", idx, name);
}
@@ -971,6 +975,7 @@ bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
int text_shndx = obj->efile.text_shndx;
int maps_shndx = obj->efile.maps_shndx;
int data_shndx = obj->efile.data_shndx;
+ int bss_shndx = obj->efile.bss_shndx;
struct bpf_map *maps = obj->maps;
size_t nr_maps = obj->nr_maps;
int i, nrels;
@@ -1010,7 +1015,7 @@ bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
(long long) sym.st_value, sym.st_name);
if (sym.st_shndx != maps_shndx && sym.st_shndx != text_shndx &&
- sym.st_shndx != data_shndx) {
+ sym.st_shndx != data_shndx && sym.st_shndx != bss_shndx) {
pr_warning("Program '%s' contains unrecognized relo data pointing to section %u\n",
prog->section_name, sym.st_shndx);
return -LIBBPF_ERRNO__RELOC;
@@ -1070,6 +1075,9 @@ bpf_program__collect_reloc(struct bpf_program *prog, GElf_Shdr *shdr,
prog->reloc_desc[i].type = RELO_DATA;
prog->reloc_desc[i].insn_idx = insn_idx;
prog->reloc_desc[i].data = *static_data;
+ } else if (sym.st_shndx == bss_shndx) {
+ prog->reloc_desc[i].type = RELO_ZERO;
+ prog->reloc_desc[i].insn_idx = insn_idx;
}
}
return 0;
@@ -1429,6 +1437,10 @@ bpf_program__relocate(struct bpf_program *prog, struct bpf_object *obj)
insn_idx = prog->reloc_desc[i].insn_idx;
insns[insn_idx].imm = prog->reloc_desc[i].data;
+ } else if (prog->reloc_desc[i].type == RELO_ZERO) {
+ int insn_idx = prog->reloc_desc[i].insn_idx;
+
+ prog->insns[insn_idx].imm = 0;
}
}
--
2.19.1
next prev parent reply other threads:[~2019-02-12 0:47 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-12 0:47 [PATCH bpf-next 0/4] libbpf: Add support for 32-bit static data Joe Stringer
2019-02-12 0:47 ` [PATCH bpf-next 1/4] libbpf: Refactor relocations Joe Stringer
2019-02-12 0:47 ` [PATCH bpf-next 2/4] libbpf: Support 32-bit static data loads Joe Stringer
2019-02-15 5:38 ` Y Song
2019-02-15 7:16 ` Joe Stringer
2019-02-15 20:18 ` Y Song
2019-02-27 22:42 ` Y Song
2019-02-15 16:17 ` Alexei Starovoitov
2019-02-12 0:47 ` Joe Stringer [this message]
2019-02-12 0:47 ` [PATCH bpf-next 4/4] selftests/bpf: Test static data relocation Joe Stringer
2019-02-12 5:01 ` Alexei Starovoitov
2019-02-12 20:43 ` Joe Stringer
2019-02-14 0:35 ` Alexei Starovoitov
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