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docs/bpf: Add constant values for linkages

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Make the values of the symbolic constants that define the valid linkages
for functions and variables explicit.

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/bpf/20240911055033.2084881-1-hawkinsw@obs.cr
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Will Hawkins 2024-09-11 01:50:32 -04:00 committed by Andrii Nakryiko
parent 376bd59e2a
commit c229c17a76
1 changed files with 35 additions and 4 deletions
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39
Documentation/bpf/btf.rst
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@ -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 +424,8 @@ 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, BTF_VAR_GLOBAL_ALLOCATED or BTF_VAR_GLOBAL_EXTERN -
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 +548,38 @@ 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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. table:: Function Linkage Values and Meanings
=================== ===== ===========
kind value description
=================== ===== ===========
``BTF_FUNC_STATIC`` 0x0 definition of subprogram not visible outside containing compilation unit
``BTF_FUNC_GLOBAL`` 0x1 definition of subprogram visible outside containing compilation unit
``BTF_FUNC_EXTERN`` 0x2 declaration of a subprogram whose definition is outside the containing compilation unit
=================== ===== ===========
.. _BTF_Var_Linkage_Constants:
2.3.2 Variable Linkage Constant Values
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. table:: Variable Linkage Values and Meanings
============================ ===== ===========
kind value description
============================ ===== ===========
``BTF_VAR_STATIC`` 0x0 definition of global variable not visible outside containing compilation unit
``BTF_VAR_GLOBAL_ALLOCATED`` 0x1 definition of global variable visible outside containing compilation unit
``BTF_VAR_GLOBAL_EXTERN`` 0x2 declaration of global variable whose definition is outside the containing compilation unit
============================ ===== ===========
3. BTF Kernel API
=================