With llvm 7.0 or earlier, the map symbol type is STT_NOTYPE.
-bash-4.4$ cat t.c
__attribute__((section("maps"))) int g;
-bash-4.4$ clang -target bpf -O2 -c t.c
-bash-4.4$ readelf -s t.o
Symbol table '.symtab' contains 2 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 3 g
-bash-4.4$
The following llvm commit enables BPF target to generate
proper symbol type and size.
commit bf6ec206615b9718869d48b4e5400d0c6e3638dd
Author: Yonghong Song <[email protected]>
Date: Wed Sep 19 16:04:13 2018 +0000
[bpf] Symbol sizes and types in object file
Clang-compiled object files currently don't include the symbol sizes and
types. Some tools however need that information. For example, ctfconvert
uses that information to generate FreeBSD's CTF representation from ELF
files.
With this patch, symbol sizes and types are included in object files.
Signed-off-by: Paul Chaignon <[email protected]>
Reported-by: Yutaro Hayakawa <[email protected]>
Hence, for llvm 8.0.0 (currently trunk), symbol type will be not NOTYPE, but
OBJECT.
-bash-4.4$ clang -target bpf -O2 -c t.c
-bash-4.4$ readelf -s t.o
Symbol table '.symtab' contains 3 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 0000000000000000 0 FILE LOCAL DEFAULT ABS t.c
2: 0000000000000000 4 OBJECT GLOBAL DEFAULT 3 g
-bash-4.4$
This patch makes sure bpf library accepts both NOTYPE and OBJECT types
of global map symbols.
Signed-off-by: Yonghong Song <[email protected]>
---
lib/bpf.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/lib/bpf.c b/lib/bpf.c
index d093d0bd..45f279fa 100644
--- a/lib/bpf.c
+++ b/lib/bpf.c
@@ -1758,11 +1758,13 @@ static const char *bpf_map_fetch_name(struct
bpf_elf_ctx *ctx, int which)
int i;
for (i = 0; i < ctx->sym_num; i++) {
+ int type = GELF_ST_TYPE(sym.st_info);
+
if (gelf_getsym(ctx->sym_tab, i, &sym) != &sym)
continue;
if (GELF_ST_BIND(sym.st_info) != STB_GLOBAL ||
- GELF_ST_TYPE(sym.st_info) != STT_NOTYPE ||
+ (type != STT_NOTYPE && type != STT_OBJECT) ||
sym.st_shndx != ctx->sec_maps ||
sym.st_value / ctx->map_len != which)
continue;
@@ -1849,11 +1851,13 @@ static int bpf_map_num_sym(struct bpf_elf_ctx *ctx)
GElf_Sym sym;
for (i = 0; i < ctx->sym_num; i++) {
+ int type = GELF_ST_TYPE(sym.st_info);
+
if (gelf_getsym(ctx->sym_tab, i, &sym) != &sym)
continue;
if (GELF_ST_BIND(sym.st_info) != STB_GLOBAL ||
- GELF_ST_TYPE(sym.st_info) != STT_NOTYPE ||
+ (type != STT_NOTYPE && type != STT_OBJECT) ||
sym.st_shndx != ctx->sec_maps)
continue;
num++;
@@ -1927,10 +1931,12 @@ static int bpf_map_verify_all_offs(struct bpf_elf_ctx
*ctx, int end)
* the table again.
*/
for (i = 0; i < ctx->sym_num; i++) {
+ int type = GELF_ST_TYPE(sym.st_info);
+
if (gelf_getsym(ctx->sym_tab, i, &sym) != &sym)
continue;
if (GELF_ST_BIND(sym.st_info) != STB_GLOBAL ||
- GELF_ST_TYPE(sym.st_info) != STT_NOTYPE ||
+ (type != STT_NOTYPE && type != STT_OBJECT) ||
sym.st_shndx != ctx->sec_maps)
continue;
if (sym.st_value == off)
--
2.17.1
