[PATCH] D67980: [WIP][CLANG][BPF] implement clang __builtin_bitfield_info() intrinsic

[Yonghong Song via Phabricator via cfe-commits]

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

The patch is still work in progress.

The signature:

  u64 __builtin_bitfield_info(bitfield_member_access)

return value:

  ret >> 16 : bitfield offset from the start of the struct
  (ret >> 15) & 0x1 : bitfield signness
  ret & (1 << 15 - 1) : bitfield size

The information is extracted from:

  https://clang.llvm.org/doxygen/structclang_1_1CodeGen_1_1CGBitFieldInfo.html

An example:
-bash-4.4$ cat bit.c

struct s {

  int a;
  long long p1; 
  int p2; 
  int b1:2;
  int b2:10;
  int b3:2;
  int b4:10;
  int b5:3;
  int d;

};
struct s *a; 
int main () {

  unsigned long long x = __builtin_bitfield_info(a->b3);
  printf("offset = %lld, sign = %lld, size = %lld\n",
         x >> 16, (x >> 15) & 1, x & ((1 << 15) - 1));
  return 0;

}
-bash-4.4$ clang -O2 -g bit.c
-bash-4.4$ ./a.out
offset = 172, sign = 1, size = 2 
-bash-4.4$

This builtin returns necessary information to user space
to extract values from the bitfields.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D67980

Files:
  clang/include/clang/Basic/Builtins.def
  clang/lib/CodeGen/CGBuiltin.cpp
  clang/lib/Sema/SemaChecking.cpp


Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -1429,6 +1429,19 @@
     if (SemaBuiltinPreserveAI(*this, TheCall))
       return ExprError();
     break;
+  case Builtin::BI__builtin_bitfield_info: {
+    if (checkArgCount(*this, TheCall, 1))
+      return ExprError();
+
+    Expr *Arg = TheCall->getArg(0);
+    if (Arg->getType()->getAsPlaceholderType())
+      return ExprError();
+    if (Arg->IgnoreParens()->getObjectKind() != OK_BitField)
+      return ExprError();
+
+    TheCall->setType(Context.UnsignedLongLongTy);
+    break;
+  }
   case Builtin::BI__builtin_call_with_static_chain:
     if (SemaBuiltinCallWithStaticChain(*this, TheCall))
       return ExprError();
Index: clang/lib/CodeGen/CGBuiltin.cpp
===================================================================
--- clang/lib/CodeGen/CGBuiltin.cpp
+++ clang/lib/CodeGen/CGBuiltin.cpp
@@ -1882,6 +1882,13 @@
     IsInPreservedAIRegion = false;
     return RValue::get(Res);
   }
+  case Builtin::BI__builtin_bitfield_info: {
+    const CGBitFieldInfo &Info = EmitLValue(E->getArg(0)).getBitFieldInfo();
+    uint64_t Val = ((Info.StorageOffset.getQuantity() * 8 + Info.Offset) << 16) |
+                   (Info.IsSigned << 15) |
+                   Info.Size;
+    return RValue::get(ConstantInt::get(Int64Ty, Val));
+  }
 
   case Builtin::BI__builtin_cimag:
   case Builtin::BI__builtin_cimagf:
Index: clang/include/clang/Basic/Builtins.def
===================================================================
--- clang/include/clang/Basic/Builtins.def
+++ clang/include/clang/Basic/Builtins.def
@@ -1469,6 +1469,7 @@
 BUILTIN(__builtin_char_memchr, "c*cC*iz", "n")
 BUILTIN(__builtin_dump_struct, "ivC*v*", "tn")
 BUILTIN(__builtin_preserve_access_index, "v.", "t")
+BUILTIN(__builtin_bitfield_info, "LLUi.", "t")
 
 // Safestack builtins
 BUILTIN(__builtin___get_unsafe_stack_start, "v*", "Fn")


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