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A new attribute btf_tag is added. The syntax looks like
__attribute__((btf_tag(<string>)))
Users may tag a particular structure/member/function/variable
declaration with an arbitrary string and the intention is
that this string is passed to dwarf so it is available for
post-compilation analysis. The string will be also passed
to .BTF section if the target is BPF. For detailed use cases,
please see
https://lists.llvm.org/pipermail/llvm-dev/2021-June/151009.html
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D106614
Files:
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/lib/Sema/SemaDeclAttr.cpp
clang/test/Misc/pragma-attribute-supported-attributes-list.test
clang/test/Sema/attr-btf_tag.c
Index: clang/test/Sema/attr-btf_tag.c
===================================================================
--- /dev/null
+++ clang/test/Sema/attr-btf_tag.c
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 -x c -triple x86_64-pc-linux-gnu -dwarf-version=4 -fsyntax-only -verify %s
+
+#define __tag __attribute__((btf_tag("tag")))
+#define __invalid __attribute__((btf_tag(1)))
+
+struct t1 {
+ int a __tag;
+} __tag;
+
+int g1 __tag;
+int i1 __invalid; // expected-error {{'btf_tag' attribute requires a string}}
+
+int __tag foo(struct t1 __tag *arg) {
+ return arg->a;
+}
Index: clang/test/Misc/pragma-attribute-supported-attributes-list.test
===================================================================
--- clang/test/Misc/pragma-attribute-supported-attributes-list.test
+++ clang/test/Misc/pragma-attribute-supported-attributes-list.test
@@ -22,6 +22,7 @@
// CHECK-NEXT: Assumption (SubjectMatchRule_function, SubjectMatchRule_objc_method)
// CHECK-NEXT: Availability ((SubjectMatchRule_record, SubjectMatchRule_enum, SubjectMatchRule_enum_constant, SubjectMatchRule_field, SubjectMatchRule_function, SubjectMatchRule_namespace, SubjectMatchRule_objc_category, SubjectMatchRule_objc_implementation, SubjectMatchRule_objc_interface, SubjectMatchRule_objc_method, SubjectMatchRule_objc_property, SubjectMatchRule_objc_protocol, SubjectMatchRule_record, SubjectMatchRule_type_alias, SubjectMatchRule_variable))
// CHECK-NEXT: BPFPreserveAccessIndex (SubjectMatchRule_record)
+// CHECK-NEXT: BTFTag (SubjectMatchRule_variable, SubjectMatchRule_function, SubjectMatchRule_record, SubjectMatchRule_field)
// CHECK-NEXT: BuiltinAlias (SubjectMatchRule_function)
// CHECK-NEXT: CFAuditedTransfer (SubjectMatchRule_function)
// CHECK-NEXT: CFConsumed (SubjectMatchRule_variable_is_parameter)
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -6753,6 +6753,14 @@
Rec->addAttr(::new (S.Context) BPFPreserveAccessIndexAttr(S.Context, AL));
}
+static void handleBTFTagAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+ StringRef Str;
+ if (!S.checkStringLiteralArgumentAttr(AL, 0, Str))
+ return;
+
+ D->addAttr(::new (S.Context) BTFTagAttr(S.Context, AL, Str));
+}
+
static void handleWebAssemblyExportNameAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
if (!isFunctionOrMethod(D)) {
S.Diag(D->getLocation(), diag::warn_attribute_wrong_decl_type)
@@ -7790,6 +7798,9 @@
case ParsedAttr::AT_BPFPreserveAccessIndex:
handleBPFPreserveAccessIndexAttr(S, D, AL);
break;
+ case ParsedAttr::AT_BTFTag:
+ handleBTFTagAttr(S, D, AL);
+ break;
case ParsedAttr::AT_WebAssemblyExportName:
handleWebAssemblyExportNameAttr(S, D, AL);
break;
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -2011,6 +2011,16 @@
struct or union, similar to clang ``__builtin_preserve_access_index()``.
}];
}
+def BTFTagDocs : Documentation {
+ let Category = DocCatFunction;
+ let Content = [{
+Clang supports the ``__attribute__((btf_tag("ARGUMENT")))`` attribute for all
+targets. This attribute may be attached to a struct/union, struct/union field,
+function or variables declaration. If -g is specified, the ARGUMENT info will
+be preserved in IR and be emitted to dwarf. For BPF target, the ARGUMENT info
+will be emitted to .BTF ELF section too.
+ }];
+}
def MipsInterruptDocs : Documentation {
let Category = DocCatFunction;
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -1829,6 +1829,14 @@
let LangOpts = [COnly];
}
+def BTFTag : InheritableAttr {
+ let Spellings = [Clang<"btf_tag">];
+ let Args = [StringArgument<"BTFTag">];
+ let Subjects = SubjectList<[Var, Function, Record, Field], ErrorDiag>;
+ let Documentation = [BTFTagDocs];
+ let LangOpts = [COnly];
+}
+
def WebAssemblyExportName : InheritableAttr,
TargetSpecificAttr<TargetWebAssembly> {
let Spellings = [Clang<"export_name">];
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