Yonghong Song 61809186ed [BPF] add new intrinsics preserve_{array,union,struct}_access_index ... For background of BPF CO-RE project, please refer to http://vger.kernel.org/bpfconf2019.html In summary, BPF CO-RE intends to compile bpf programs adjustable on struct/union layout change so the same program can run on multiple kernels with adjustment before loading based on native kernel structures. In order to do this, we need keep track of GEP(getelementptr) instruction base and result debuginfo types, so we can adjust on the host based on kernel BTF info. Capturing such information as an IR optimization is hard as various optimization may have tweaked GEP and also union is replaced by structure it is impossible to track fieldindex for union member accesses. Three intrinsic functions, preserve_{array,union,struct}_access_index, are introducted. addr = preserve_array_access_index(base, index, dimension) addr = preserve_union_access_index(base, di_index) addr = preserve_struct_access_index(base, gep_index, di_index) here, base: the base pointer for the array/union/struct access. index: the last access index for array, the same for IR/DebugInfo layout. dimension: the array dimension. gep_index: the access index based on IR layout. di_index: the access index based on user/debuginfo types. For example, for the following example, $ cat test.c struct sk_buff { int i; int b1:1; int b2:2; union { struct { int o1; int o2; } o; struct { char flags; char dev_id; } dev; int netid; } u[10]; }; static int (*bpf_probe_read)(void *dst, int size, const void *unsafe_ptr) = (void *) 4; #define _(x) (__builtin_preserve_access_index(x)) int bpf_prog(struct sk_buff *ctx) { char dev_id; bpf_probe_read(&dev_id, sizeof(char), _(&ctx->u[5].dev.dev_id)); return dev_id; } $ clang -target bpf -O2 -g -emit-llvm -S -mllvm -print-before-all \ test.c >& log The generated IR looks like below: ... define dso_local i32 @bpf_prog(%struct.sk_buff*) #0 !dbg !15 { %2 = alloca %struct.sk_buff*, align 8 %3 = alloca i8, align 1 store %struct.sk_buff* %0, %struct.sk_buff** %2, align 8, !tbaa !45 call void @llvm.dbg.declare(metadata %struct.sk_buff** %2, metadata !43, metadata !DIExpression()), !dbg !49 call void @llvm.lifetime.start.p0i8(i64 1, i8* %3) #4, !dbg !50 call void @llvm.dbg.declare(metadata i8* %3, metadata !44, metadata !DIExpression()), !dbg !51 %4 = load i32 (i8*, i32, i8*)*, i32 (i8*, i32, i8*)** @bpf_probe_read, align 8, !dbg !52, !tbaa !45 %5 = load %struct.sk_buff*, %struct.sk_buff** %2, align 8, !dbg !53, !tbaa !45 %6 = call [10 x %union.anon]* @llvm.preserve.struct.access.index.p0a10s_union.anons.p0s_struct.sk_buffs( %struct.sk_buff* %5, i32 2, i32 3), !dbg !53, !llvm.preserve.access.index !19 %7 = call %union.anon* @llvm.preserve.array.access.index.p0s_union.anons.p0a10s_union.anons( [10 x %union.anon]* %6, i32 1, i32 5), !dbg !53 %8 = call %union.anon* @llvm.preserve.union.access.index.p0s_union.anons.p0s_union.anons( %union.anon* %7, i32 1), !dbg !53, !llvm.preserve.access.index !26 %9 = bitcast %union.anon* %8 to %struct.anon.0*, !dbg !53 %10 = call i8* @llvm.preserve.struct.access.index.p0i8.p0s_struct.anon.0s( %struct.anon.0* %9, i32 1, i32 1), !dbg !53, !llvm.preserve.access.index !34 %11 = call i32 %4(i8* %3, i32 1, i8* %10), !dbg !52 %12 = load i8, i8* %3, align 1, !dbg !54, !tbaa !55 %13 = sext i8 %12 to i32, !dbg !54 call void @llvm.lifetime.end.p0i8(i64 1, i8* %3) #4, !dbg !56 ret i32 %13, !dbg !57 } !19 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "sk_buff", file: !3, line: 1, size: 704, elements: !20) !26 = distinct !DICompositeType(tag: DW_TAG_union_type, scope: !19, file: !3, line: 5, size: 64, elements: !27) !34 = distinct !DICompositeType(tag: DW_TAG_structure_type, scope: !26, file: !3, line: 10, size: 16, elements: !35) Note that @llvm.preserve.{struct,union}.access.index calls have metadata llvm.preserve.access.index attached to instructions to provide struct/union debuginfo type information. For &ctx->u[5].dev.dev_id, . The "%6 = ..." represents struct member "u" with index 2 for IR layout and index 3 for DI layout. . The "%7 = ..." represents array subscript "5". . The "%8 = ..." represents union member "dev" with index 1 for DI layout. . The "%10 = ..." represents struct member "dev_id" with index 1 for both IR and DI layout. Basically, traversing the use-def chain recursively for the 3rd argument of bpf_probe_read() and examining all preserve_*_access_index calls, the debuginfo struct/union/array access index can be achieved. The intrinsics also contain enough information to regenerate codes for IR layout. For array and structure intrinsics, the proper GEP can be constructed. For union intrinsics, replacing all uses of "addr" with "base" should be enough. The test case ThinLTO/X86/lazyload_metadata.ll is adjusted to reflect the new addition of the metadata. Signed-off-by: Yonghong Song <yhs@fb.com> Differential Revision: https://reviews.llvm.org/D61810 llvm-svn: 365423		2019-07-09 01:51:36 +00:00
..
AbstractCallSite.cpp
AsmWriter.cpp	[ThinLTO] Attempt to recommit r365188 after alignment fix	2019-07-05 15:25:05 +00:00
AttributeImpl.h
Attributes.cpp	Add, and infer, a nofree function attribute	2019-07-08 15:57:56 +00:00
AttributesCompatFunc.td
AutoUpgrade.cpp	Change semantics of fadd/fmul vector reductions.	2019-06-11 08:22:10 +00:00
BasicBlock.cpp
CMakeLists.txt
Comdat.cpp
ConstantFold.cpp
ConstantFold.h
ConstantRange.cpp
Constants.cpp
ConstantsContext.h
Core.cpp
DataLayout.cpp	Cleanup: llvm::bsearch -> llvm::partition_point after r364719	2019-06-30 11:19:56 +00:00
DebugInfo.cpp
DebugInfoMetadata.cpp	[DebugInfo] Avoid adding too much indirection to pointer-valued variables	2019-07-01 09:38:23 +00:00
DebugLoc.cpp
DiagnosticHandler.cpp
DiagnosticInfo.cpp
DiagnosticPrinter.cpp
DIBuilder.cpp
Dominators.cpp
Function.cpp	Cleanup: llvm::bsearch -> llvm::partition_point after r364719	2019-06-30 11:19:56 +00:00
Globals.cpp
GVMaterializer.cpp
InlineAsm.cpp
Instruction.cpp
Instructions.cpp
IntrinsicInst.cpp	Teach the IRBuilder about fadd and friends.	2019-07-08 16:18:18 +00:00
IRBuilder.cpp	Improve reduction intrinsics by overloading result value.	2019-06-13 09:37:38 +00:00
IRPrintingPasses.cpp
LegacyPassManager.cpp
LLVMBuild.txt
LLVMContext.cpp	[BPF] add new intrinsics preserve_{array,union,struct}_access_index	2019-07-09 01:51:36 +00:00
LLVMContextImpl.cpp
LLVMContextImpl.h	Scalable Vector IR Type with further LTO fixes	2019-07-05 12:48:16 +00:00
Mangler.cpp	Standardize on MSVC behavior for triples with no environment	2019-07-08 21:05:20 +00:00
MDBuilder.cpp
Metadata.cpp
MetadataImpl.h
Module.cpp
ModuleSummaryIndex.cpp	[ThinLTO] Attempt to recommit r365188 after alignment fix	2019-07-05 15:25:05 +00:00
Operator.cpp
OptBisect.cpp
Pass.cpp
PassInstrumentation.cpp
PassManager.cpp
PassRegistry.cpp
PassTimingInfo.cpp
ProfileSummary.cpp
RemarkStreamer.cpp	[Remarks] Extend -fsave-optimization-record to specify the format	2019-06-17 16:06:00 +00:00
SafepointIRVerifier.cpp
Statepoint.cpp
SymbolTableListTraitsImpl.h
Type.cpp	Scalable Vector IR Type with further LTO fixes	2019-07-05 12:48:16 +00:00
TypeFinder.cpp
Use.cpp
User.cpp
Value.cpp	Introduce Value::stripPointerCastsSameRepresentation	2019-06-04 20:21:46 +00:00
ValueSymbolTable.cpp
Verifier.cpp	Teach the IRBuilder about fadd and friends.	2019-07-08 16:18:18 +00:00