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-rw-r--r--Documentation/bpf/btf.rst57
1 files changed, 57 insertions, 0 deletions
diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index 7313d354f20e..29396e6943b0 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
*****************