[llvm] [BPF] Do not emit names for PTR, CONST, VOLATILE and RESTRICT BTF types (PR #163174)

[Michal R via llvm-commits]

https://github.com/vadorovsky updated https://github.com/llvm/llvm-project/pull/163174

>From bdcfba56f8fe52eca854c7c5333bab1a137e9015 Mon Sep 17 00:00:00 2001
From: Michal R <vad.sol at proton.me>
Date: Sun, 12 Oct 2025 18:58:58 +0200
Subject: [PATCH] [BPF] Do not emit names for PTR, CONST, VOLATILE and RESTRICT
 BTF types

We currently raise a warning in `print_btf.py` when any of these types
have a name. Linux kernel doesn't allow names in these types either.

However, there is nothing stopping frontends from giving names to these
types. To make sure that they are always anonymous, explicitly skip the
name emission.
---
 llvm/lib/Target/BPF/BTFDebug.cpp       | 13 ++++-
 llvm/test/CodeGen/BPF/BTF/ptr-named.ll | 75 ++++++++++++++++++++++++++
 2 files changed, 87 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/CodeGen/BPF/BTF/ptr-named.ll

diff --git a/llvm/lib/Target/BPF/BTFDebug.cpp b/llvm/lib/Target/BPF/BTFDebug.cpp
index ba4b48990c647..2a59502dcdd14 100644
--- a/llvm/lib/Target/BPF/BTFDebug.cpp
+++ b/llvm/lib/Target/BPF/BTFDebug.cpp
@@ -93,7 +93,18 @@ void BTFTypeDerived::completeType(BTFDebug &BDebug) {
     return;
   IsCompleted = true;
 
-  BTFType.NameOff = BDebug.addString(Name);
+  switch (Kind) {
+  case BTF::BTF_KIND_PTR:
+  case BTF::BTF_KIND_CONST:
+  case BTF::BTF_KIND_VOLATILE:
+  case BTF::BTF_KIND_RESTRICT:
+    // Do not emit names for these types.
+    BTFType.NameOff = 0;
+    break;
+  default:
+    BTFType.NameOff = BDebug.addString(Name);
+    break;
+  }
 
   if (NeedsFixup || !DTy)
     return;
diff --git a/llvm/test/CodeGen/BPF/BTF/ptr-named.ll b/llvm/test/CodeGen/BPF/BTF/ptr-named.ll
new file mode 100644
index 0000000000000..675c34e976abb
--- /dev/null
+++ b/llvm/test/CodeGen/BPF/BTF/ptr-named.ll
@@ -0,0 +1,75 @@
+; RUN: llc -mtriple=bpfel -filetype=obj -o %t1 %s
+; RUN: llvm-objcopy --dump-section='.BTF'=%t2 %t1
+; RUN: %python %p/print_btf.py %t2 | FileCheck -check-prefixes=CHECK-BTF %s
+; RUN: llc -mtriple=bpfeb -filetype=obj -o %t1 %s
+; RUN: llvm-objcopy --dump-section='.BTF'=%t2 %t1
+; RUN: %python %p/print_btf.py %t2 | FileCheck -check-prefixes=CHECK-BTF %s
+;
+; Source:
+;   #![no_std]
+;   #![no_main]
+;
+;   pub struct MyType {
+;       ptr: *const u32,
+;   }
+;
+;   impl MyType {
+;       pub const fn new() -> Self {
+;           let ptr = core::ptr::null();
+;           Self { ptr }
+;       }
+;   }
+;
+;   unsafe impl Sync for MyType {}
+;
+;   #[unsafe(no_mangle)]
+;   pub static X: MyType = MyType::new();
+;
+;   #[cfg(not(test))]
+;   #[panic_handler]
+;   fn panic(_info: &core::panic::PanicInfo) -> ! {
+;       loop {}
+;   }
+; Compilation flag:
+;   cargo +nightly rustc -Zbuild-std=core --target=bpfel-unknown-none -- --emit=llvm-bc
+;   llvm-extract --glob=X $(find target/ -name "*.bc" | head -n 1) -o ptr-named.bc
+;   llvm-dis ptr-named.bc -o ptr-named.ll
+
+; ModuleID = 'ptr-named.bc'
+source_filename = "1m2uqe50qkwxmo53ydydvou91"
+target datalayout = "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128"
+target triple = "bpfel"
+
+ at X = constant [8 x i8] zeroinitializer, align 8, !dbg !0
+
+!llvm.module.flags = !{!11, !12, !13, !14}
+!llvm.ident = !{!15}
+!llvm.dbg.cu = !{!16}
+
+; CHECK-BTF:      [1] STRUCT 'MyType' size=8 vlen=1
+; CHECK-BTF-NEXT:         'ptr' type_id=2 bits_offset=0
+; CHECK-BTF-NEXT: [2] PTR '(anon)' type_id=3
+; CHECK-BTF-NEXT: [3] INT 'u32' size=4 bits_offset=0 nr_bits=32 encoding=(none)
+; CHECK-BTF-NEXT: [4] VAR 'X' type_id=1, linkage=global
+; CHECK-BTF-NEXT: [5] DATASEC '.rodata' size=0 vlen=1
+; CHECK-BTF-NEXT:         type_id=4 offset=0 size=8
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "X", scope: !2, file: !3, line: 19, type: !4, isLocal: false, isDefinition: true, align: 64)
+!2 = !DINamespace(name: "ptr_named", scope: null)
+!3 = !DIFile(filename: "ptr-named/src/main.rs", directory: "/tmp/ptr-named", checksumkind: CSK_MD5, checksum: "e37168304600b30cbb5ba168f0384932")
+!4 = !DICompositeType(tag: DW_TAG_structure_type, name: "MyType", scope: !2, file: !5, size: 64, align: 64, flags: DIFlagPublic, elements: !6, templateParams: !10, identifier: "7609fa40332dd486922f074276a171c3")
+!5 = !DIFile(filename: "<unknown>", directory: "")
+!6 = !{!7}
+!7 = !DIDerivedType(tag: DW_TAG_member, name: "ptr", scope: !4, file: !5, baseType: !8, size: 64, align: 64, flags: DIFlagPrivate)
+!8 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "*const u32", baseType: !9, size: 64, align: 64, dwarfAddressSpace: 0)
+!9 = !DIBasicType(name: "u32", size: 32, encoding: DW_ATE_unsigned)
+!10 = !{}
+!11 = !{i32 8, !"PIC Level", i32 2}
+!12 = !{i32 7, !"PIE Level", i32 2}
+!13 = !{i32 7, !"Dwarf Version", i32 4}
+!14 = !{i32 2, !"Debug Info Version", i32 3}
+!15 = !{!"rustc version 1.92.0-nightly (c8905eaa6 2025-09-28)"}
+!16 = distinct !DICompileUnit(language: DW_LANG_Rust, file: !17, producer: "clang LLVM (rustc version 1.92.0-nightly (c8905eaa6 2025-09-28))", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, globals: !18, splitDebugInlining: false, nameTableKind: None)
+!17 = !DIFile(filename: "ptr-named/src/main.rs/@/1m2uqe50qkwxmo53ydydvou91", directory: "/tmp/ptr-named")
+!18 = !{!0}