[llvm] [BPF] Do not emit names for PTR, CONST, VOLATILE and RESTRICT BTF types (PR #163174)
Michal R via llvm-commits
llvm-commits at lists.llvm.org
Mon Oct 20 13:01:04 PDT 2025
https://github.com/vadorovsky updated https://github.com/llvm/llvm-project/pull/163174
>From 5454bb800480c4bea72223f693715e466d711a5a 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.[0]
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.
[0] https://elixir.bootlin.com/linux/v6.17.1/source/kernel/bpf/btf.c#L2586
---
llvm/lib/Target/BPF/BTFDebug.cpp | 19 +++++-
llvm/test/CodeGen/BPF/BTF/ptr-named-2.ll | 59 +++++++++++++++++++
llvm/test/CodeGen/BPF/BTF/ptr-named.ll | 75 ++++++++++++++++++++++++
3 files changed, 152 insertions(+), 1 deletion(-)
create mode 100644 llvm/test/CodeGen/BPF/BTF/ptr-named-2.ll
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 9b5fc9d05e336..a652b7e9c537f 100644
--- a/llvm/lib/Target/BPF/BTFDebug.cpp
+++ b/llvm/lib/Target/BPF/BTFDebug.cpp
@@ -95,7 +95,24 @@ 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:
+ // Debug info might contain names for these types, but given that we want
+ // to keep BTF minimal and naming reference types doesn't bring any value
+ // (what matters is the completeness of the base type), we don't emit them.
+ //
+ // Furthermore, the Linux kernel refuses to load BPF programs that contain
+ // BTF with these types named:
+ // https://elixir.bootlin.com/linux/v6.17.1/source/kernel/bpf/btf.c#L2586
+ 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-2.ll b/llvm/test/CodeGen/BPF/BTF/ptr-named-2.ll
new file mode 100644
index 0000000000000..df0cbeb3dd625
--- /dev/null
+++ b/llvm/test/CodeGen/BPF/BTF/ptr-named-2.ll
@@ -0,0 +1,59 @@
+; 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
+;
+; This IR is hand-written.
+
+; ModuleID = 'ptr-named-2.ll'
+source_filename = "ptr-named-2.ll"
+target datalayout = "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128"
+target triple = "bpfel-unknown-none"
+
+%struct.TypeExamples = type { i32*, i32, i32, i32* }
+
+ at type_examples = internal global %struct.TypeExamples zeroinitializer, align 8, !dbg !0
+
+!llvm.dbg.cu = !{!1}
+!llvm.module.flags = !{!2, !3, !4}
+!llvm.ident = !{!21}
+
+; CHECK-BTF: [1] STRUCT 'TypeExamples' size=32 vlen=4
+; CHECK-BTF-NEXT: 'ptr' type_id=2 bits_offset=0
+; CHECK-BTF-NEXT: 'volatile' type_id=4 bits_offset=64
+; CHECK-BTF-NEXT: 'const' type_id=5 bits_offset=128
+; CHECK-BTF-NEXT: 'restrict_ptr' type_id=6 bits_offset=192
+; CHECK-BTF-NEXT: [2] PTR '(anon)' type_id=3
+; CHECK-BTF-NEXT: [3] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED
+; CHECK-BTF-NEXT: [4] VOLATILE '(anon)' type_id=3
+; CHECK-BTF-NEXT: [5] CONST '(anon)' type_id=3
+; CHECK-BTF-NEXT: [6] RESTRICT '(anon)' type_id=7
+; CHECK-BTF-NEXT: [7] PTR '(anon)' type_id=3
+; CHECK-BTF-NEXT: [8] VAR 'type_examples' type_id=1, linkage=static
+; CHECK-BTF-NEXT: [9] DATASEC '.bss' size=0 vlen=1
+; CHECK-BTF-NEXT: type_id=8 offset=0 size=24
+
+!0 = !DIGlobalVariableExpression(var: !5, expr: !DIExpression())
+!1 = distinct !DICompileUnit(language: DW_LANG_C99, file: !6, isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !7, globals: !8, splitDebugInlining: false, nameTableKind: None)
+!2 = !{i32 2, !"Dwarf Version", i32 4}
+!3 = !{i32 2, !"Debug Info Version", i32 3}
+!4 = !{i32 1, !"wchar_size", i32 4}
+!5 = distinct !DIGlobalVariable(name: "type_examples", scope: !1, file: !6, line: 12, type: !9, isLocal: true, isDefinition: true)
+!6 = !DIFile(filename: "ptr-named-2.ll", directory: "/tmp")
+!7 = !{}
+!8 = !{!0}
+!9 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "TypeExamples", file: !6, line: 5, size: 256, elements: !10)
+!10 = !{!11, !12, !13, !14}
+!11 = !DIDerivedType(tag: DW_TAG_member, name: "ptr", scope: !9, file: !6, line: 6, baseType: !15, size: 64)
+!12 = !DIDerivedType(tag: DW_TAG_member, name: "volatile", scope: !9, file: !6, line: 7, baseType: !17, size: 64, offset: 64)
+!13 = !DIDerivedType(tag: DW_TAG_member, name: "const", scope: !9, file: !6, line: 8, baseType: !18, size: 64, offset: 128)
+!14 = !DIDerivedType(tag: DW_TAG_member, name: "restrict_ptr", scope: !9, file: !6, line: 9, baseType: !19, size: 64, offset: 192)
+!15 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "*int", baseType: !16, size: 64)
+!16 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!17 = !DIDerivedType(tag: DW_TAG_volatile_type, name: "volatile int", baseType: !16)
+!18 = !DIDerivedType(tag: DW_TAG_const_type, name: "const int", baseType: !16)
+!19 = !DIDerivedType(tag: DW_TAG_restrict_type, name: "*int restrict", baseType: !20)
+!20 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !16, size: 64)
+!21 = !{!"my hand-written IR"}
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}
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