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[BPF] disable ReduceLoadWidth during SelectionDag phase
The compiler may transform the following code ctx = ctx + reloc_offset ... (*(u32 *)ctx) & 0x8000 ... to ctx = ctx + reloc_offset ... (*(u8 *)(ctx + 1)) & 0x80 ... where reloc_offset will be replaced with a constant during AsmPrinter phase. The above transformed code will be rejected the kernel verifier as it does not allow *(type *)((ctx + non_zero_offset1) + non_zero_offset2) style access pattern. It is hard at SelectionDag phase to identify whether a load is related to context or not. Sometime, interprocedure analysis may be needed. So let us simply prevent such optimization from happening. Differential Revision: https://reviews.llvm.org/D73997 (cherry picked from commit d96c1bb)
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‎llvm/lib/Target/BPF/BPFISelLowering.h

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@@ -110,6 +110,19 @@ class BPFTargetLowering : public TargetLowering {
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return true;
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}
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// Prevent reducing load width during SelectionDag phase.
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// Otherwise, we may transform the following
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// ctx = ctx + reloc_offset
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// ... (*(u32 *)ctx) & 0x8000...
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// to
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// ctx = ctx + reloc_offset
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// ... (*(u8 *)(ctx + 1)) & 0x80 ...
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// which will be rejected by the verifier.
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bool shouldReduceLoadWidth(SDNode *Load, ISD::LoadExtType ExtTy,
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EVT NewVT) const override {
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return false;
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}
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unsigned EmitSubregExt(MachineInstr &MI, MachineBasicBlock *BB, unsigned Reg,
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bool isSigned) const;
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‎llvm/test/CodeGen/BPF/CORE/no-narrow-load.ll

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@@ -0,0 +1,156 @@
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; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
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; RUN: llc -march=bpfeb -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
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; Source code:
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; struct data_t {
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; int d1;
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; int d2;
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; };
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; struct info_t {
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; int pid;
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; int flags;
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; } __attribute__((preserve_access_index));
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;
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; extern void output(void *);
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; void test(struct info_t * args) {
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; int is_mask2 = args->flags & 0x10000;
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; struct data_t data = {};
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;
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; data.d1 = is_mask2 ? 2 : args->pid;
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; data.d2 = (is_mask2 || (args->flags & 0x8000)) ? 1 : 2;
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; output(&data);
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; }
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; Compilation flag:
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; clang -target bpf -O2 -g -S -emit-llvm test.c
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%struct.info_t = type { i32, i32 }
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%struct.data_t = type { i32, i32 }
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; Function Attrs: nounwind
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define dso_local void @test(%struct.info_t* readonly %args) local_unnamed_addr #0 !dbg !12 {
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entry:
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%data = alloca i64, align 8
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%tmpcast = bitcast i64* %data to %struct.data_t*
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call void @llvm.dbg.value(metadata %struct.info_t* %args, metadata !22, metadata !DIExpression()), !dbg !29
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%0 = tail call i32* @llvm.preserve.struct.access.index.p0i32.p0s_struct.info_ts(%struct.info_t* %args, i32 1, i32 1), !dbg !30, !llvm.preserve.access.index !16
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%1 = load i32, i32* %0, align 4, !dbg !30, !tbaa !31
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%and = and i32 %1, 65536, !dbg !36
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call void @llvm.dbg.value(metadata i32 %and, metadata !23, metadata !DIExpression()), !dbg !29
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%2 = bitcast i64* %data to i8*, !dbg !37
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call void @llvm.lifetime.start.p0i8(i64 8, i8* nonnull %2) #5, !dbg !37
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call void @llvm.dbg.declare(metadata %struct.data_t* %tmpcast, metadata !24, metadata !DIExpression()), !dbg !38
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store i64 0, i64* %data, align 8, !dbg !38
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%tobool = icmp eq i32 %and, 0, !dbg !39
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br i1 %tobool, label %cond.false, label %lor.end.critedge, !dbg !39
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cond.false: ; preds = %entry
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%3 = tail call i32* @llvm.preserve.struct.access.index.p0i32.p0s_struct.info_ts(%struct.info_t* %args, i32 0, i32 0), !dbg !40, !llvm.preserve.access.index !16
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%4 = load i32, i32* %3, align 4, !dbg !40, !tbaa !41
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%d1 = bitcast i64* %data to i32*, !dbg !42
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store i32 %4, i32* %d1, align 8, !dbg !43, !tbaa !44
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%5 = load i32, i32* %0, align 4, !dbg !46, !tbaa !31
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%and2 = and i32 %5, 32768, !dbg !47
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%tobool3 = icmp eq i32 %and2, 0, !dbg !48
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%phitmp = select i1 %tobool3, i32 2, i32 1, !dbg !48
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br label %lor.end, !dbg !48
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lor.end.critedge: ; preds = %entry
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%d1.c = bitcast i64* %data to i32*, !dbg !42
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store i32 2, i32* %d1.c, align 8, !dbg !43, !tbaa !44
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br label %lor.end, !dbg !48
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lor.end: ; preds = %lor.end.critedge, %cond.false
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%6 = phi i32 [ %phitmp, %cond.false ], [ 1, %lor.end.critedge ]
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%d2 = getelementptr inbounds %struct.data_t, %struct.data_t* %tmpcast, i64 0, i32 1, !dbg !49
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store i32 %6, i32* %d2, align 4, !dbg !50, !tbaa !51
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call void @output(i8* nonnull %2) #5, !dbg !52
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call void @llvm.lifetime.end.p0i8(i64 8, i8* nonnull %2) #5, !dbg !53
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ret void, !dbg !53
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}
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; CHECK: r[[LOAD1:[0-9]+]] = *(u32 *)(r{{[0-9]+}} + 4)
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; CHECK: r[[LOAD1]] &= 65536
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; CHECK: r[[LOAD2:[0-9]+]] = *(u32 *)(r{{[0-9]+}} + 4)
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; CHECK: r[[LOAD2]] &= 32768
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; Function Attrs: nounwind readnone speculatable willreturn
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declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
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; Function Attrs: argmemonly nounwind willreturn
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declare void @llvm.lifetime.start.p0i8(i64 immarg, i8* nocapture) #2
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; Function Attrs: nounwind readnone
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declare i32* @llvm.preserve.struct.access.index.p0i32.p0s_struct.info_ts(%struct.info_t*, i32 immarg, i32 immarg) #3
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declare !dbg !4 dso_local void @output(i8*) local_unnamed_addr #4
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; Function Attrs: argmemonly nounwind willreturn
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declare void @llvm.lifetime.end.p0i8(i64 immarg, i8* nocapture) #2
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; Function Attrs: nounwind readnone speculatable willreturn
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declare void @llvm.dbg.value(metadata, metadata, metadata) #1
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attributes #0 = { nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
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attributes #1 = { nounwind readnone speculatable willreturn }
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attributes #2 = { argmemonly nounwind willreturn }
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attributes #3 = { nounwind readnone }
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attributes #4 = { "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
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attributes #5 = { nounwind }
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!8, !9, !10}
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!llvm.ident = !{!11}
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!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0 (https://github.com/llvm/llvm-project.git 5884aae58f56786475bbc0f13ad8bd35f7f1ce69)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !3, splitDebugInlining: false, nameTableKind: None)
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!1 = !DIFile(filename: "test.c", directory: "/tmp/home/yhs/work/tests/core")
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!2 = !{}
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!3 = !{!4}
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!4 = !DISubprogram(name: "output", scope: !1, file: !1, line: 10, type: !5, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
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!5 = !DISubroutineType(types: !6)
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!6 = !{null, !7}
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!7 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
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!8 = !{i32 7, !"Dwarf Version", i32 4}
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!9 = !{i32 2, !"Debug Info Version", i32 3}
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!10 = !{i32 1, !"wchar_size", i32 4}
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!11 = !{!"clang version 11.0.0 (https://github.com/llvm/llvm-project.git 5884aae58f56786475bbc0f13ad8bd35f7f1ce69)"}
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!12 = distinct !DISubprogram(name: "test", scope: !1, file: !1, line: 11, type: !13, scopeLine: 11, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !21)
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!13 = !DISubroutineType(types: !14)
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!14 = !{null, !15}
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!15 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !16, size: 64)
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!16 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "info_t", file: !1, line: 5, size: 64, elements: !17)
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!17 = !{!18, !20}
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!18 = !DIDerivedType(tag: DW_TAG_member, name: "pid", scope: !16, file: !1, line: 6, baseType: !19, size: 32)
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!19 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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!20 = !DIDerivedType(tag: DW_TAG_member, name: "flags", scope: !16, file: !1, line: 7, baseType: !19, size: 32, offset: 32)
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!21 = !{!22, !23, !24}
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!22 = !DILocalVariable(name: "args", arg: 1, scope: !12, file: !1, line: 11, type: !15)
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!23 = !DILocalVariable(name: "is_mask2", scope: !12, file: !1, line: 12, type: !19)
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!24 = !DILocalVariable(name: "data", scope: !12, file: !1, line: 13, type: !25)
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!25 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "data_t", file: !1, line: 1, size: 64, elements: !26)
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!26 = !{!27, !28}
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!27 = !DIDerivedType(tag: DW_TAG_member, name: "d1", scope: !25, file: !1, line: 2, baseType: !19, size: 32)
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!28 = !DIDerivedType(tag: DW_TAG_member, name: "d2", scope: !25, file: !1, line: 3, baseType: !19, size: 32, offset: 32)
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!29 = !DILocation(line: 0, scope: !12)
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!30 = !DILocation(line: 12, column: 24, scope: !12)
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!31 = !{!32, !33, i64 4}
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!32 = !{!"info_t", !33, i64 0, !33, i64 4}
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!33 = !{!"int", !34, i64 0}
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!34 = !{!"omnipotent char", !35, i64 0}
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!35 = !{!"Simple C/C++ TBAA"}
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!36 = !DILocation(line: 12, column: 30, scope: !12)
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!37 = !DILocation(line: 13, column: 3, scope: !12)
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!38 = !DILocation(line: 13, column: 17, scope: !12)
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!39 = !DILocation(line: 15, column: 13, scope: !12)
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!40 = !DILocation(line: 15, column: 34, scope: !12)
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!41 = !{!32, !33, i64 0}
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!42 = !DILocation(line: 15, column: 8, scope: !12)
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!43 = !DILocation(line: 15, column: 11, scope: !12)
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!44 = !{!45, !33, i64 0}
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!45 = !{!"data_t", !33, i64 0, !33, i64 4}
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!46 = !DILocation(line: 16, column: 33, scope: !12)
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!47 = !DILocation(line: 16, column: 39, scope: !12)
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!48 = !DILocation(line: 16, column: 23, scope: !12)
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!49 = !DILocation(line: 16, column: 8, scope: !12)
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!50 = !DILocation(line: 16, column: 11, scope: !12)
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!51 = !{!45, !33, i64 4}
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!52 = !DILocation(line: 17, column: 3, scope: !12)
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!53 = !DILocation(line: 18, column: 1, scope: !12)

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