This adds the BTF specification and UAPI bits for supporting BTF Var
and DataSec kinds. This is following LLVM upstream commit ac4082b77e07
("[BPF] Add BTF Var and DataSec Support") which has been merged recently.
Var itself is for describing a global variable and DataSec to describe
ELF sections e.g. data/bss/rodata sections that hold one or multiple
global variables.
Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
Acked-by: Martin KaFai Lau <kafai@xxxxxx>
---
Documentation/bpf/btf.rst | 57 +++++++++++++++++++++++++++++++++++++++
include/uapi/linux/btf.h | 32 +++++++++++++++++++---
2 files changed, 85 insertions(+), 4 deletions(-)
diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index 9a60a5d60e38..60d87d7363ec 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -82,6 +82,8 @@ sequentially and type id is assigned to each recognized type starting from id
#define BTF_KIND_RESTRICT 11 /* Restrict */
#define BTF_KIND_FUNC 12 /* Function */
#define BTF_KIND_FUNC_PROTO 13 /* Function Proto */
+ #define BTF_KIND_VAR 14 /* Variable */
+ #define BTF_KIND_DATASEC 15 /* Section */
Note that the type section encodes debug info, not just pure types.
``BTF_KIND_FUNC`` is not a type, and it represents a defined subprogram.
@@ -393,6 +395,61 @@ refers to parameter type.
If the function has variable arguments, the last parameter is encoded with
``name_off = 0`` and ``type = 0``.
+2.2.14 BTF_KIND_VAR
+~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+ * ``name_off``: offset to a valid C identifier
+ * ``info.kind_flag``: 0
+ * ``info.kind``: BTF_KIND_VAR
+ * ``info.vlen``: 0
+ * ``type``: the type of the variable
+
+``btf_type`` is followed by a single ``struct btf_variable`` with the
+following data::
+
+ struct btf_var {
+ __u32 linkage;
+ };
+
+``struct btf_var`` encoding:
+ * ``linkage``: currently only static variable 0, or globally allocated
+ variable in ELF sections 1
+
+Not all type of global variables are supported by LLVM at this point.
+The following is currently available:
+
+ * static variables with or without section attributes
+ * global variables with section attributes
+
+The latter is for future extraction of map key/value type id's from a
+map definition.
+
+2.2.15 BTF_KIND_DATASEC
+~~~~~~~~~~~~~~~~~~~~~~~
+
+``struct btf_type`` encoding requirement:
+ * ``name_off``: offset to a valid name associated with a variable or
+ one of .data/.bss/.rodata
+ * ``info.kind_flag``: 0
+ * ``info.kind``: BTF_KIND_DATASEC
+ * ``info.vlen``: # of variables
+ * ``size``: total section size in bytes (0 at compilation time, patched
+ to actual size by BPF loaders such as libbpf)
+
+``btf_type`` is followed by ``info.vlen`` number of ``struct btf_var_secinfo``.::
+
+ struct btf_var_secinfo {
+ __u32 type;
+ __u32 offset;
+ __u32 size;
+ };
+
+``struct btf_var_secinfo`` encoding:
+ * ``type``: the type of the BTF_KIND_VAR variable
+ * ``offset``: the in-section offset of the variable
+ * ``size``: the size of the variable in bytes
+
3. BTF Kernel API
*****************
diff --git a/include/uapi/linux/btf.h b/include/uapi/linux/btf.h
index 7b7475ef2f17..9310652ca4f9 100644
--- a/include/uapi/linux/btf.h
+++ b/include/uapi/linux/btf.h
@@ -39,11 +39,11 @@ struct btf_type {
* struct, union and fwd
*/
__u32 info;
- /* "size" is used by INT, ENUM, STRUCT and UNION.
+ /* "size" is used by INT, ENUM, STRUCT, UNION and DATASEC.
* "size" tells the size of the type it is describing.
*
* "type" is used by PTR, TYPEDEF, VOLATILE, CONST, RESTRICT,
- * FUNC and FUNC_PROTO.
+ * FUNC, FUNC_PROTO and VAR.
* "type" is a type_id referring to another type.
*/
union {
@@ -70,8 +70,10 @@ struct btf_type {
#define BTF_KIND_RESTRICT 11 /* Restrict */
#define BTF_KIND_FUNC 12 /* Function */
#define BTF_KIND_FUNC_PROTO 13 /* Function Proto */
-#define BTF_KIND_MAX 13
-#define NR_BTF_KINDS 14
+#define BTF_KIND_VAR 14 /* Variable */
+#define BTF_KIND_DATASEC 15 /* Section */
+#define BTF_KIND_MAX BTF_KIND_DATASEC
+#define NR_BTF_KINDS (BTF_KIND_MAX + 1)
/* For some specific BTF_KIND, "struct btf_type" is immediately
* followed by extra data.
@@ -138,4 +140,26 @@ struct btf_param {
__u32 type;
};
+enum {
+ BTF_VAR_STATIC = 0,
+ BTF_VAR_GLOBAL_ALLOCATED,
+};
+
+/* BTF_KIND_VAR is followed by a single "struct btf_var" to describe
+ * additional information related to the variable such as its linkage.
+ */
+struct btf_var {
+ __u32 linkage;
+};
+
+/* BTF_KIND_DATASEC is followed by multiple "struct btf_var_secinfo"
+ * to describe all BTF_KIND_VAR types it contains along with it's
+ * in-section offset as well as size.
+ */
+struct btf_var_secinfo {
+ __u32 type;
+ __u32 offset;
+ __u32 size;
+};
+
#endif /* _UAPI__LINUX_BTF_H__ */
--
2.17.1
