From 21da7b88fe4b4aa94730208c9704aca0ae7f02f3 Mon Sep 17 00:00:00 2001 From: Michal R 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* } + +@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" + +@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: "", 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}