From a5a6cfe2f030e81e689ed9af4e95ddf95c4d8675 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Thu, 4 Mar 2021 12:58:22 -0800 Subject: [PATCH] BPF: permit type modifiers for __builtin_btf_type_id() relocation Lorenz Bauer from Cloudflare tried to use "const struct " as the type for __builtin_btf_type_id(*(const struct )0, 1) relocation and hit a llvm BPF fatal error. https://lore.kernel.org/bpf/a3782f71-3f6b-1e75-17a9-1827822c2030@fb.com/ ... fatal error: error in backend: Empty type name for BTF_TYPE_ID_REMOTE reloc Currently, we require the debuginfo type itself must have a name. In this case, the debuginfo type is "const" which points to "struct ". The "const" type does not have a name, hence the above fatal error will be triggered. Let us permit "const" and "volatile" type modifiers. We skip modifiers in some other cases as well like structure member type tracing. This can aviod the above fatal error. Differential Revision: https://reviews.llvm.org/D97986 (cherry picked from commit 9c0274cdeae904089806be6faee72b9126d2cf5b) --- llvm/lib/Target/BPF/BPFPreserveDIType.cpp | 9 +++ .../CodeGen/BPF/BTF/builtin-btf-type-id-2.ll | 73 +++++++++++++++++++ 2 files changed, 82 insertions(+) create mode 100644 llvm/test/CodeGen/BPF/BTF/builtin-btf-type-id-2.ll diff --git a/llvm/lib/Target/BPF/BPFPreserveDIType.cpp b/llvm/lib/Target/BPF/BPFPreserveDIType.cpp index 18a4f60c171ae5..0348e2200acbc1 100644 --- a/llvm/lib/Target/BPF/BPFPreserveDIType.cpp +++ b/llvm/lib/Target/BPF/BPFPreserveDIType.cpp @@ -85,8 +85,17 @@ static bool BPFPreserveDITypeImpl(Function &F) { } else { Reloc = BPFCoreSharedInfo::BTF_TYPE_ID_REMOTE; DIType *Ty = cast(MD); + while (auto *DTy = dyn_cast(Ty)) { + unsigned Tag = DTy->getTag(); + if (Tag != dwarf::DW_TAG_const_type && + Tag != dwarf::DW_TAG_volatile_type) + break; + Ty = DTy->getBaseType(); + } + if (Ty->getName().empty()) report_fatal_error("Empty type name for BTF_TYPE_ID_REMOTE reloc"); + MD = Ty; } BasicBlock *BB = Call->getParent(); diff --git a/llvm/test/CodeGen/BPF/BTF/builtin-btf-type-id-2.ll b/llvm/test/CodeGen/BPF/BTF/builtin-btf-type-id-2.ll new file mode 100644 index 00000000000000..63c56c4dfec57a --- /dev/null +++ b/llvm/test/CodeGen/BPF/BTF/builtin-btf-type-id-2.ll @@ -0,0 +1,73 @@ +; RUN: opt -O2 -mtriple=bpf-pc-linux -S -o %t1 %s +; RUN: llc -filetype=asm -o - %t1 | FileCheck -check-prefixes=CHECK %s +; RUN: llc -mattr=+alu32 -filetype=asm -o - %t1 | FileCheck -check-prefixes=CHECK %s +; Source code: +; struct s { +; int a; +; }; +; int test(void) { +; return __builtin_btf_type_id(*(const struct s *)0, 1); +; } +; Compilation flag: +; clang -target bpf -O2 -g -S -emit-llvm -Xclang -disable-llvm-passes test.c + +; Function Attrs: nounwind +define dso_local i32 @test() #0 !dbg !7 { +entry: + %0 = call i64 @llvm.bpf.btf.type.id(i32 0, i64 1), !dbg !11, !llvm.preserve.access.index !12 + %conv = trunc i64 %0 to i32, !dbg !11 + ret i32 %conv, !dbg !16 +} + +; CHECK: .long 1 # BTF_KIND_INT(id = 2) +; CHECK-NEXT: .long 16777216 # 0x1000000 +; CHECK-NEXT: .long 4 +; CHECK-NEXT: .long 16777248 # 0x1000020 + +; CHECK: .long 16 # BTF_KIND_STRUCT(id = 4) +; CHECK-NEXT: .long 67108865 # 0x4000001 +; CHECK-NEXT: .long 4 +; CHECK-NEXT: .long 18 +; CHECK-NEXT: .long 2 + +; CHECK: .ascii "int" # string offset=1 +; CHECK: .ascii ".text" # string offset=10 +; CHECK: .byte 115 # string offset=16 +; CHECK: .byte 97 # string offset=18 +; CHECK: .byte 48 # string offset=20 + +; CHECK: .long 16 # FieldReloc +; CHECK-NEXT: .long 10 # Field reloc section string offset=10 +; CHECK-NEXT: .long 1 +; CHECK-NEXT: .long .Ltmp{{[0-9]+}} +; CHECK-NEXT: .long 4 +; CHECK-NEXT: .long 20 +; CHECK-NEXT: .long 7 + +; Function Attrs: nounwind readnone +declare i64 @llvm.bpf.btf.type.id(i32, i64) #1 + +attributes #0 = { nounwind "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" } +attributes #1 = { nounwind readnone } + +!llvm.dbg.cu = !{!0} +!llvm.module.flags = !{!3, !4, !5} +!llvm.ident = !{!6} + +!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 13.0.0 (https://github.com/llvm/llvm-project.git 9783e2098800b954c55ae598a1ce5c4b93444fc0)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None) +!1 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/bpf/test") +!2 = !{} +!3 = !{i32 7, !"Dwarf Version", i32 4} +!4 = !{i32 2, !"Debug Info Version", i32 3} +!5 = !{i32 1, !"wchar_size", i32 4} +!6 = !{!"clang version 13.0.0 (https://github.com/llvm/llvm-project.git 9783e2098800b954c55ae598a1ce5c4b93444fc0)"} +!7 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 4, type: !8, scopeLine: 4, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2) +!8 = !DISubroutineType(types: !9) +!9 = !{!10} +!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed) +!11 = !DILocation(line: 5, column: 10, scope: !7) +!12 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !13) +!13 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "s", file: !1, line: 1, size: 32, elements: !14) +!14 = !{!15} +!15 = !DIDerivedType(tag: DW_TAG_member, name: "a", scope: !13, file: !1, line: 2, baseType: !10, size: 32) +!16 = !DILocation(line: 5, column: 3, scope: !7)