yonghong-song created this revision.
yonghong-song added reviewers: ast, anakryiko.
Herald added subscribers: cfe-commits, arphaman.
Herald added a project: clang.
This patch introduced a new bpf specific attribute which can
be added to struct or union definition. For example,
struct s { ... } __attribute__((preserve_access_index));
The goal is to simplify user codes for cases
where preserve access index happens for certain struct/union,
so user does not need to use clang __builtin_preserve_access_index
for every members.
The attribute has no effect if -g is not specified.
When the attribute is specified and -g is specified, any member
access to that structure or union will be preserved through
__builtin_preserve_{struct,union}_access_index() IR intrinsics.
For bpf target, relocation will be generated.
Any access beyond member access is not preserved.
The following is an example to illustrate the usage:
-bash-4.4$ cat t.c
union s {
int a;
struct {
int used1;
int b;
} __attribute__((preserve_access_index));
struct {
int used2;
int c;
};
int d[3];
} __attribute__((preserve_access_index));
int test1(union s *arg) { return arg->a; }
int test2(union s *arg) { return arg->b; }
int test3(union s *arg) { return arg->c; }
int test4(union s *arg) { return arg->d[1]; }
int test5(union s *arg) { return __builtin_preserve_access_index(arg->d[1]); }
-bash-4.4$ clang -target bpf -O2 -S -g t.c
test1() generates a relocation for &s->a.
test2() generates a relocation for &s->b.
test3() generates a relocation for the anonymous
struct which includes member "c", but no
relocation is generated for anonymous structure
member "c" access.
test4() generates a relocation for &s->d, but
no relocation is generated for array acceess
with index 1.
test5() generates a relocation for &s->d[1].
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D69759
Files:
clang/include/clang/Basic/Attr.td
clang/include/clang/Basic/AttrDocs.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/CodeGen/CGExpr.cpp
clang/lib/Sema/SemaDeclAttr.cpp
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -5700,6 +5700,19 @@
handleSimpleAttribute<AVRSignalAttr>(S, D, AL);
}
+static void handleBPFPreserveAccessIndex(Sema &S, Decl *D, const ParsedAttr &AL) {
+ if (!isa<RecordDecl>(D)) {
+ S.Diag(D->getLocation(), diag::err_preserve_access_index_wrong_type)
+ << "preserve_addess_index" << "struct or union type";
+ return;
+ }
+
+ if (!checkAttributeNumArgs(S, AL, 0))
+ return;
+
+ D->addAttr(::new (S.Context) BPFPreserveAccessIndexAttr(S.Context, AL));
+}
+
static void handleWebAssemblyImportModuleAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
if (!isFunctionOrMethod(D)) {
S.Diag(D->getLocation(), diag::warn_attribute_wrong_decl_type)
@@ -6576,6 +6589,9 @@
case ParsedAttr::AT_AVRSignal:
handleAVRSignalAttr(S, D, AL);
break;
+ case ParsedAttr::AT_BPFPreserveAccessIndex:
+ handleBPFPreserveAccessIndex(S, D, AL);
+ break;
case ParsedAttr::AT_WebAssemblyImportModule:
handleWebAssemblyImportModuleAttr(S, D, AL);
break;
Index: clang/lib/CodeGen/CGExpr.cpp
===================================================================
--- clang/lib/CodeGen/CGExpr.cpp
+++ clang/lib/CodeGen/CGExpr.cpp
@@ -3992,12 +3992,13 @@
const CGBitFieldInfo &Info = RL.getBitFieldInfo(field);
Address Addr = base.getAddress();
unsigned Idx = RL.getLLVMFieldNo(field);
- if (!IsInPreservedAIRegion) {
+ const RecordDecl *rec = field->getParent();
+ if (!IsInPreservedAIRegion &&
+ (!getDebugInfo() || !rec->hasAttr<BPFPreserveAccessIndexAttr>())) {
if (Idx != 0)
// For structs, we GEP to the field that the record layout suggests.
Addr = Builder.CreateStructGEP(Addr, Idx, field->getName());
} else {
- const RecordDecl *rec = field->getParent();
llvm::DIType *DbgInfo = getDebugInfo()->getOrCreateRecordType(
getContext().getRecordType(rec), rec->getLocation());
Addr = Builder.CreatePreserveStructAccessIndex(Addr, Idx,
@@ -4080,7 +4081,8 @@
addr = Address(Builder.CreateLaunderInvariantGroup(addr.getPointer()),
addr.getAlignment());
- if (IsInPreservedAIRegion) {
+ if (IsInPreservedAIRegion ||
+ (getDebugInfo() && rec->hasAttr<BPFPreserveAccessIndexAttr>())) {
// Remember the original union field index
llvm::DIType *DbgInfo = getDebugInfo()->getOrCreateRecordType(
getContext().getRecordType(rec), rec->getLocation());
@@ -4094,7 +4096,8 @@
addr = Builder.CreateElementBitCast(
addr, CGM.getTypes().ConvertTypeForMem(FieldType), field->getName());
} else {
- if (!IsInPreservedAIRegion)
+ if (!IsInPreservedAIRegion &&
+ (!getDebugInfo() || !rec->hasAttr<BPFPreserveAccessIndexAttr>()))
// For structs, we GEP to the field that the record layout suggests.
addr = emitAddrOfFieldStorage(*this, addr, field);
else
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -10065,6 +10065,7 @@
"__builtin_preserve_field_info argument %0 not a field access">;
def err_preserve_field_info_not_const: Error<
"__builtin_preserve_field_info argument %0 not a constant">;
+def err_preserve_access_index_wrong_type: Error<"%0 attribute only applies to %1">;
def err_bit_cast_non_trivially_copyable : Error<
"__builtin_bit_cast %select{source|destination}0 type must be trivially copyable">;
Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -1634,6 +1634,17 @@
}];
}
+def BPFPreserveAccessIndexDocs : Documentation {
+ let Category = DocCatFunction;
+ let Content = [{
+Clang supports the ``__attribute__((preserve_access_index))``
+attribute for the BPF target. This attribute may be attached to a
+struct or union declaration, where if -g is specified, it enables
+preserving struct or union member access debuginfo indicies of this
+struct or union, similar to clang ``__builtin_preserve_acceess_index()``.
+ }];
+}
+
def MipsInterruptDocs : Documentation {
let Category = DocCatFunction;
let Heading = "interrupt (MIPS)";
Index: clang/include/clang/Basic/Attr.td
===================================================================
--- clang/include/clang/Basic/Attr.td
+++ clang/include/clang/Basic/Attr.td
@@ -332,6 +332,7 @@
}
def TargetARM : TargetArch<["arm", "thumb", "armeb", "thumbeb"]>;
def TargetAVR : TargetArch<["avr"]>;
+def TargetBPF : TargetArch<["bpfel", "bpfeb"]>;
def TargetMips32 : TargetArch<["mips", "mipsel"]>;
def TargetAnyMips : TargetArch<["mips", "mipsel", "mips64", "mips64el"]>;
def TargetMSP430 : TargetArch<["msp430"]>;
@@ -1578,6 +1579,12 @@
let Subjects = SubjectList<[Function], ErrorDiag, "kernel functions">;
}
+def BPFPreserveAccessIndex : InheritableAttr,
+ TargetSpecificAttr<TargetBPF> {
+ let Spellings = [Clang<"preserve_access_index">];
+ let Documentation = [BPFPreserveAccessIndexDocs];
+}
+
def WebAssemblyImportModule : InheritableAttr,
TargetSpecificAttr<TargetWebAssembly> {
let Spellings = [Clang<"import_module">];
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