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BPF: permit type modifiers for __builtin_btf_type_id() relocation

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Lorenz Bauer from Cloudflare tried to use "const struct <name>"
as the type for __builtin_btf_type_id(*(const struct <name>)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 <name>".
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
This commit is contained in:
Yonghong Song 2021-03-04 12:58:22 -08:00
parent 2677513543
commit 6efa716e20
2 changed files with 82 additions and 0 deletions
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9
lib/Target/BPF/BPFPreserveDIType.cpp
View File

@ -85,8 +85,17 @@ static bool BPFPreserveDITypeImpl(Function &F) {
} else {
Reloc = BPFCoreSharedInfo::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();
}
if (Ty->getName().empty())
report_fatal_error("Empty type name for BTF_TYPE_ID_REMOTE reloc");
MD = Ty;
}
BasicBlock *BB = Call->getParent();

73
test/CodeGen/BPF/BTF/builtin-btf-type-id-2.ll Normal file
View File

@ -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)