On 7/13/22 11:00 PM, Andrii Nakryiko wrote:
On Wed, Jul 13, 2022 at 3:37 PM Indu Bhagat <indu.bhagat@xxxxxxxxxx> wrote:
The vlen bits in the BTF type of kind BTF_KIND_FUNC are used to convey the
linkage information for functions.
Signed-off-by: Indu Bhagat <indu.bhagat@xxxxxxxxxx>
---
Documentation/bpf/btf.rst | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index f49aeef62d0c..b3a9d5ac882c 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -369,7 +369,7 @@ No additional type data follow ``btf_type``.
* ``name_off``: offset to a valid C identifier
* ``info.kind_flag``: 0
* ``info.kind``: BTF_KIND_FUNC
- * ``info.vlen``: 0
+ * ``info.vlen``: linkage information (static=0, global=1)
there is also extern=2, but I think we should just refer to enum
btf_func_linkage, defined in UAPI (include/uapi/linux/btf.h) ?
Currently kernel rejects extern=2. In kernel btf.c, we have
if (btf_type_vlen(t) > BTF_FUNC_GLOBAL) {
btf_verifier_log_type(env, t, "Invalid func linkage");
return -EINVAL;
}
and extern=2 will cause btf loading failure.
The BTF_FUNC_EXTERN is generated when you call an extern *global*
function. I suspect that during static linking, all these
extern globals should become true global/static functions and
not extern func's any more so kernel is okay.
So looks like it is worthwhile to mention that BTF_KIND_FUNC
supports all three modes as specified in enum btf_func_linkage.
But only static/global is supported in the kernel.
* ``type``: a BTF_KIND_FUNC_PROTO type
No additional type data follow ``btf_type``.
--
2.31.1
