[BPF] use base lvalue type for preserve_{struct,union}_access_index metadata
authorYonghong Song <yhs@fb.com>
Sun, 2 Feb 2020 22:54:16 +0000 (14:54 -0800)
committerYonghong Song <yhs@fb.com>
Tue, 4 Feb 2020 17:28:30 +0000 (09:28 -0800)
Linux commit
  https://github.com/torvalds/linux/commit/1cf5b23988ea0086a252a5c8b005b075f1e9b030#diff-289313b9fec99c6f0acfea19d9cfd949
uses "#pragma clang attribute push (__attribute__((preserve_access_index)),
      apply_to = record)"
to apply CO-RE relocations to all records including the following pattern:
  #pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)
  typedef struct {
    int a;
  } __t;
  #pragma clang attribute pop
  int test(__t *arg) { return arg->a; }

The current approach to use struct type in the relocation record will
result in an anonymous struct, which make later type matching difficult
    in bpf loader. In fact, current BPF backend will fail the above program
with assertion:
  clang: ../lib/Target/BPF/BPFAbstractMemberAccess.cpp:796: ...
     Assertion `TypeName.size()' failed.

The patch use the base lvalue type for the "base" value to annotate
preservee_{struct,union}_access_index intrinsics. In the above example,
the type will be "__t" which preserved the type name.

Differential Revision: https://reviews.llvm.org/D73900

clang/lib/CodeGen/CGExpr.cpp
clang/test/CodeGen/builtin-preserve-access-index-typedef.c [new file with mode: 0644]

index 4b8a31c..17fc16a 100644 (file)
@@ -4024,17 +4024,17 @@ static Address emitAddrOfFieldStorage(CodeGenFunction &CGF, Address base,
   return CGF.Builder.CreateStructGEP(base, idx, field->getName());
 }
 
-static Address emitPreserveStructAccess(CodeGenFunction &CGF, Address base,
-                                        const FieldDecl *field) {
+static Address emitPreserveStructAccess(CodeGenFunction &CGF, LValue base,
+                                        Address addr, const FieldDecl *field) {
   const RecordDecl *rec = field->getParent();
-  llvm::DIType *DbgInfo = CGF.getDebugInfo()->getOrCreateRecordType(
-      CGF.getContext().getRecordType(rec), rec->getLocation());
+  llvm::DIType *DbgInfo = CGF.getDebugInfo()->getOrCreateStandaloneType(
+      base.getType(), rec->getLocation());
 
   unsigned idx =
       CGF.CGM.getTypes().getCGRecordLayout(rec).getLLVMFieldNo(field);
 
   return CGF.Builder.CreatePreserveStructAccessIndex(
-      base, idx, CGF.getDebugInfoFIndex(rec, field->getFieldIndex()), DbgInfo);
+      addr, idx, CGF.getDebugInfoFIndex(rec, field->getFieldIndex()), DbgInfo);
 }
 
 static bool hasAnyVptr(const QualType Type, const ASTContext &Context) {
@@ -4158,8 +4158,8 @@ LValue CodeGenFunction::EmitLValueForField(LValue base,
     if (IsInPreservedAIRegion ||
         (getDebugInfo() && rec->hasAttr<BPFPreserveAccessIndexAttr>())) {
       // Remember the original union field index
-      llvm::DIType *DbgInfo = getDebugInfo()->getOrCreateRecordType(
-          getContext().getRecordType(rec), rec->getLocation());
+      llvm::DIType *DbgInfo = getDebugInfo()->getOrCreateStandaloneType(base.getType(),
+          rec->getLocation());
       addr = Address(
           Builder.CreatePreserveUnionAccessIndex(
               addr.getPointer(), getDebugInfoFIndex(rec, field->getFieldIndex()), DbgInfo),
@@ -4176,7 +4176,7 @@ LValue CodeGenFunction::EmitLValueForField(LValue base,
       addr = emitAddrOfFieldStorage(*this, addr, field);
     else
       // Remember the original struct field index
-      addr = emitPreserveStructAccess(*this, addr, field);
+      addr = emitPreserveStructAccess(*this, base, addr, field);
   }
 
   // If this is a reference field, load the reference right now.
diff --git a/clang/test/CodeGen/builtin-preserve-access-index-typedef.c b/clang/test/CodeGen/builtin-preserve-access-index-typedef.c
new file mode 100644 (file)
index 0000000..c7752cd
--- /dev/null
@@ -0,0 +1,24 @@
+// REQUIRES: bpf-registered-target
+// RUN: %clang -target bpf -emit-llvm -S -g %s -o - | FileCheck %s
+
+#pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)
+typedef struct {
+   int a;
+} __t;
+typedef union {
+   int b;
+} __u;
+#pragma clang attribute pop
+
+int test1(__t *arg) { return arg->a; }
+int test2(const __u *arg) { return arg->b; }
+
+
+// CHECK: define dso_local i32 @test1
+// CHECK: call i32* @llvm.preserve.struct.access.index.p0i32.p0s_struct.__ts(%struct.__t* %{{[0-9a-z]+}}, i32 0, i32 0), !dbg !{{[0-9]+}}, !llvm.preserve.access.index ![[TYPEDEF_STRUCT:[0-9]+]]
+// CHECK: define dso_local i32 @test2
+// CHECK: call %union.__u* @llvm.preserve.union.access.index.p0s_union.__us.p0s_union.__us(%union.__u* %{{[0-9a-z]+}}, i32 0), !dbg !{{[0-9]+}}, !llvm.preserve.access.index ![[CONST_TYPEDEF:[0-9]+]]
+//
+// CHECK: ![[TYPEDEF_STRUCT]] = !DIDerivedType(tag: DW_TAG_typedef, name: "__t"
+// CHECK: ![[CONST_TYPEDEF]] = !DIDerivedType(tag: DW_TAG_const_type, baseType: ![[TYPEDEF_UNION:[0-9]+]]
+// CHECK: ![[TYPEDEF_UNION]] = !DIDerivedType(tag: DW_TAG_typedef, name: "__u"