[PATCH] D73900: [BPF] use base lvalue type for preserve_{struct,union}_access_index metadata

[Yonghong Song via Phabricator via cfe-commits]

yonghong-song created this revision.
yonghong-song added reviewers: ast, anakryiko.
Herald added subscribers: cfe-commits, arphaman.
Herald added a project: clang.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73900

Files:
  clang/lib/CodeGen/CGExpr.cpp
  clang/test/CodeGen/builtin-preserve-access-index-typedef.c


Index: clang/test/CodeGen/builtin-preserve-access-index-typedef.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/builtin-preserve-access-index-typedef.c
@@ -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"
Index: clang/lib/CodeGen/CGExpr.cpp
===================================================================
--- clang/lib/CodeGen/CGExpr.cpp
+++ clang/lib/CodeGen/CGExpr.cpp
@@ -4024,17 +4024,17 @@
   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 @@
     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 @@
       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.


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