BTF_KIND_FUNC is generated by llvm (latest trunk, 8.0 or later).
Without BTF_KIND_FUNC support, we will see the following errors,
-bash-4.4$ cat t.c
struct t {
int a;
char b1:1;
char b2:3;
int c;
} g;
int main() { return 0; }
-bash-4.4$ clang -O2 -target bpf -g -c t.c -Xclang -target-feature -Xclang +dwarfris
-bash-4.4$ pahole -F btf t.o
BTF: idx: 3, off: 28, Unknown
struct t {
int a; /* 0 4 */
/* Bitfield combined with previous fields */
<ERROR(__class__fprintf:1342): 5 not found!>
/* Bitfield combined with previous fields */
<ERROR(__class__fprintf:1342): 5 not found!>
int c; /* 8 4 */
/* size: 12, cachelines: 1, members: 4 */
/* last cacheline: 12 bytes */
/* BRAIN FART ALERT! 12 != 8 + 0(holes), diff = 4 */
};
-bash-4.4$
The reason is that llvm generates BTF_KIND_FUNC which btf_loader does not
recognize.
This patch added support for BTF_KIND_FUNC. Since BTF_KIND_FUNC represents
a defined subprogram and not a real type. A null type is used to
represent BTF_KIND_FUNC to avoid skipping type index.
With this fix,
-bash-4.4$ pahole -F btf t.o
struct t {
int a; /* 0 4 */
char b1:1; /* 4: 0 1 */
char b2:3; /* 4: 1 1 */
int c; /* 8 4 */
/* size: 12, cachelines: 1, members: 4 */
/* last cacheline: 12 bytes */
/* BRAIN FART ALERT! 12 != 9 + 0(holes), diff = 3 */
};
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
btf_loader.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/btf_loader.c b/btf_loader.c
index eeb0c8b..ad4cd23 100644
--- a/btf_loader.c
+++ b/btf_loader.c
@@ -421,6 +421,16 @@ static int btf__load_types(struct btf *btf)
vlen = 0;
} else if (type == BTF_KIND_FUNC_PROTO) {
vlen = create_new_subroutine_type(btf, ptr, vlen, type_ptr, type_index);
+ } else if (type == BTF_KIND_FUNC) {
+ /* BTF_KIND_FUNC corresponding to a defined subprogram.
+ * This is not really a type and it won't be referred by any other types
+ * either. Since types cannot be skipped, let us replace it with
+ * a nullify_type_entry.
+ *
+ * No warning here since BTF_KIND_FUNC is a legal entry in BTF.
+ */
+ cu__table_nullify_type_entry(btf->priv, type_index);
+ vlen = 0;
} else {
fprintf(stderr,
"BTF: idx: %d, off: %zd, Unknown\n",
--
2.17.1
