On 2/6/25 11:54 AM, David Faust wrote:
gcc/
* doc/extend.texi (Common Variable Attributes): Document
btf_decl_tag attribute.
(Common Type Attributes): Document btf_type_tag attribute.
---
gcc/doc/extend.texi | 68 +++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 68 insertions(+)
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 2764597a479..4536cfd7c68 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -8037,6 +8037,41 @@ align them on any target.
The @code{aligned} attribute can also be used for functions
(@pxref{Common Function Attributes}.)
+@cindex @code{btf_decl_tag} variable attribute
+@item btf_decl_tag (@var{argument})
+The @code{btf_decl_tag} attribute may be used to associate variable
+declarations, struct or union member declarations, function
+declarations, and function parameter declarations with arbitrary strings.
Currently we add this in the @node Common Variable Attributes. The
btf_decl_tag attribute is unique in that the effect is the same, be it
associated with a variable decl or function. But I wonder if some
placeholder text also be included in the documentation for Common
Function Attributes for clarity ?
+These strings are not interpreted by the compiler in any way, and have
+no effect on code generation. Instead, these user-provided strings
+are recorded in DWARF (via @code{DW_AT_GNU_annotation} and
+@code{DW_TAG_GNU_annotation} extensions) and BTF information (via
+@code{BTF_KIND_DECL_TAG} records), and associated to the attributed
+declaration. If neither DWARF nor BTF information is generated, the
+attribute has no effect.
+
+The argument is treated as an ordinary string in the source language
+with no additional special rules.
+
+The attribute may be supplied multiple times for a single declaration,
+in which case each distinct argument string will be recorded in a
+separate DIE or BTF record, each associated to the declaration. For
+a single declaration with multiple @code{btf_decl_tag} attributes,
+the order of the @code{DW_TAG_GNU_annotation} DIEs produced is not
+guaranteed to maintain the order of attributes in the source code.
+
+For example:
+
+@smallexample
+int *foo __attribute__ ((btf_decl_tag ("__percpu")));
+@end smallexample
+
+@noindent
+when compiled with @code{-gbtf} results in an additional
+@code{BTF_KIND_DECL_TAG} BTF record to be emitted in the BTF info,
+associating the string ``__percpu'' with the normal @code{BTF_KIND_VAR}
+record for the variable ``foo''.
+
Remove "normal" or do you intend to say something specific ?
@cindex @code{counted_by} variable attribute
@item counted_by (@var{count})
The @code{counted_by} attribute may be attached to the C99 flexible array
@@ -9226,6 +9261,39 @@ is given by the product of arguments 1 and 2, and that
@code{malloc_type}, like the standard C function @code{malloc},
returns an object whose size is given by argument 1 to the function.
+@cindex @code{btf_type_tag} type attribute
+@item btf_type_tag (@var{argument})
+The @code{btf_type_tag} attribute may be used to associate (to ``tag'')
+particular types with arbitrary string annotations. These annotations
+are recorded in debugging info by supported debug formats, currently
+DWARF (via @code{DW_AT_GNU_annotation} and @code{DW_TAG_GNU_annotation}
+extensions) and BTF (via @code{BTF_KIND_TYPE_TAG} records). These
+annotation strings are not interpreted by the compiler in any way, and
+have no effect on code generation. If neither DWARF nor BTF
+information is generated, the attribute has no effect.
+
+The argument is treated as an ordinary string in the source language
+with no additional special rules.
+
+The attribute may be supplied multiple times for a single declaration,
+in which case each distinct argument string will be recorded in a
+separate DIE or BTF record, each associated to the type. For a single
+type with multiple @code{btf_type_tag} attributes, the order of the
+@code{DW_TAG_GNU_annotation} DIEs produced is not guaranteed to
+maintain the order of attributes in the source code.
+> +For example the following code:
+
+@smallexample
+int * __attribute__ ((btf_type_tag ("__user"))) foo;
+@end smallexample
+
+@noindent
+when compiled with @code{-gbtf} results in an additional
+@code{BTF_KIND_TYPE_TAG} BTF record to be emitted in the BTF info,
+associating the string ``__user'' with the normal @code{BTF_KIND_PTR}
+record for the pointer-to-integer type used in the declaration.
+
@cindex @code{copy} type attribute
@item copy
@itemx copy (@var{expression})
