On 8/19/24 3:30 PM, Will Hawkins wrote:
Make the values of the symbolic constants that define the valid linkages
for functions and variables explicit.
Signed-off-by: Will Hawkins <hawkinsw@xxxxxx>
---
Documentation/bpf/btf.rst | 44 +++++++++++++++++++++++++++++++++++----
1 file changed, 40 insertions(+), 4 deletions(-)
diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index 257a7e1cdf5d..cce03f1e552a 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -368,7 +368,7 @@ No additional type data follow ``btf_type``.
* ``info.kind_flag``: 0
* ``info.kind``: BTF_KIND_FUNC
* ``info.vlen``: linkage information (BTF_FUNC_STATIC, BTF_FUNC_GLOBAL
- or BTF_FUNC_EXTERN)
+ or BTF_FUNC_EXTERN - see :ref:`BTF_Function_Linkage_Constants`)
* ``type``: a BTF_KIND_FUNC_PROTO type
No additional type data follow ``btf_type``.
@@ -424,9 +424,9 @@ following data::
__u32 linkage;
};
-``struct btf_var`` encoding:
- * ``linkage``: currently only static variable 0, or globally allocated
- variable in ELF sections 1
+``btf_var.linkage`` may take the values: BTF_VAR_STATIC (for a static variable),
+or BTF_VAR_GLOBAL_ALLOCATED (for a globally allocated variable stored in ELF sections 1) -
Let us remove the above '1', just say '(... stored in explicit ELF sections)'.
Actually, for btf_var linkage, we actually have 3 values. See
enum {
BTF_VAR_STATIC = 0,
BTF_VAR_GLOBAL_ALLOCATED = 1,
BTF_VAR_GLOBAL_EXTERN = 2,
};
See https://github.com/torvalds/linux/blob/master/include/uapi/linux/btf.h#L150-L154
Similar to BTF_VAR_GLOBAL_ALLOCATED, BTF_VAR_GLOBAL_EXTERN is encoded in datasec only
if the variable is stored in explicit ELF sections.
Since you are touching this doc, could you add BTF_VAR_GLOBAL_EXTERN as well?
+see :ref:`BTF_Var_Linkage_Constants`.
Not all type of global variables are supported by LLVM at this point.
The following is currently available:
@@ -549,6 +549,42 @@ The ``btf_enum64`` encoding:
If the original enum value is signed and the size is less than 8,
that value will be sign extended into 8 bytes.
+2.3 Constant Values
+-------------------
+
+.. _BTF_Function_Linkage_Constants:
+
+2.3.1 Function Linkage Constant Values
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.. list-table::
+ :widths: 1 1
+ :header-rows: 1
+
+ * - Name
+ - Value
+ * - ``BTF_FUNC_STATIC``
+ - ``0``
+ * - ``BTF_FUNC_GLOBAL``
+ - ``1``
+ * - ``BTF_FUNC_EXTERN``
+ - ``2``
+
+.. _BTF_Var_Linkage_Constants:
+
+2.3.2 Variable Linkage Constant Values
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.. list-table::
+ :widths: 1 1
+ :header-rows: 1
+
+ * - Name
+ - Value
+ * - ``BTF_VAR_STATIC``
+ - ``0``
+ * - ``BTF_VAR_GLOBAL_ALLOCATED``
+ - ``1``
+
+
Form the above, could you use similar format as in Documentation/bpf/standardization/instruction-set.rst? For example,
.. table:: Instruction class
===== ===== =============================== ===================================
class value description reference
===== ===== =============================== ===================================
LD 0x0 non-standard load operations `Load and store instructions`_
LDX 0x1 load into register operations `Load and store instructions`_
ST 0x2 store from immediate operations `Load and store instructions`_
STX 0x3 store from register operations `Load and store instructions`_
ALU 0x4 32-bit arithmetic operations `Arithmetic and jump instructions`_
JMP 0x5 64-bit jump operations `Arithmetic and jump instructions`_
JMP32 0x6 32-bit jump operations `Arithmetic and jump instructions`_
ALU64 0x7 64-bit arithmetic operations `Arithmetic and jump instructions`_
===== ===== =============================== ===================================
I would like we have consistant table presentation between instruction set and btf.
3. BTF Kernel API
=================
