Re: bpf_core_type_id_kernel is not consistent with bpf_core_type_id_local

[Yonghong Song <yonghong.song@linux.dev>]

On 11/1/23 3:42 PM, Andrii Nakryiko wrote:
> On Wed, Nov 1, 2023 at 7:18 AM Lorenz Bauer <lorenz.bauer@isovalent.com> wrote:
>> On Tue, Oct 31, 2023 at 6:24 PM Andrii Nakryiko
>> <andrii.nakryiko@gmail.com> wrote:
>>>> Did you get round to fixing this, or did you decide to leave it as is?
>>> Trying to recall, was there anything to do on the libbpf side, or was
>>> it purely a compiler-side change?
>> I'm not 100% sure TBH. I'd like clang to behave consistently for
>> local_id and target_id. I don't know whether that would break libbpf.
>>
> *checks code* libbpf just passes through whatever ID compiler
> generated, so there doesn't seem to be any change to libbpf. Seems
> like compiler-only change. cc'ing Eduard  as well, if he's curious
> enough to check

Okay, let us try to have a consistent behavior in local/remote type_id
by changing local_id semantics to be the same as target_id.

The corresponding llvm change is similar to

[yhs@devbig309.ftw3 ~/work/llvm-project (ed)]$ git diff
diff --git a/llvm/lib/Target/BPF/BPFPreserveDIType.cpp b/llvm/lib/Target/BPF/BPFPreserveDIType.cpp
index 78e1bf90f1bd..1fbe1207dc6e 100644
--- a/llvm/lib/Target/BPF/BPFPreserveDIType.cpp
+++ b/llvm/lib/Target/BPF/BPFPreserveDIType.cpp
@@ -86,15 +86,17 @@ static bool BPFPreserveDITypeImpl(Function &F) {
        Reloc = BTF::BTF_TYPE_ID_LOCAL;
      } else {
        Reloc = BTF::BTF_TYPE_ID_REMOTE;
-      DIType *Ty = cast<DIType>(MD);
-      while (auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
-        unsigned Tag = DTy->getTag();
-        if (Tag != dwarf::DW_TAG_const_type &&
-            Tag != dwarf::DW_TAG_volatile_type)
-          break;
-        Ty = DTy->getBaseType();
-      }
+    }
+    DIType *Ty = cast<DIType>(MD);
+    while (auto *DTy = dyn_cast<DIDerivedType>(Ty)) {
+      unsigned Tag = DTy->getTag();
+      if (Tag != dwarf::DW_TAG_const_type &&
+          Tag != dwarf::DW_TAG_volatile_type)
+        break;
+      Ty = DTy->getBaseType();
+    }
  
+    if (Reloc == BTF::BTF_TYPE_ID_REMOTE) {
        if (Ty->getName().empty()) {
          if (isa<DISubroutineType>(Ty))
            report_fatal_error(
@@ -102,8 +104,8 @@ static bool BPFPreserveDITypeImpl(Function &F) {
          else
            report_fatal_error("Empty type name for BTF_TYPE_ID_REMOTE reloc");
        }
-      MD = Ty;
      }
+    MD = Ty;
  
      BasicBlock *BB = Call->getParent();
      IntegerType *VarType = Type::getInt64Ty(BB->getContext());

Either Eduard or Myself will submit a llvm patch to fix this in llvm18.

>
>
>> Lorenz