yonghong-song created this revision.
yonghong-song added reviewers: aprantl, dblaikie, RKSimon, ast.
yonghong-song added a project: debug-info.
Herald added subscribers: llvm-commits, cfe-commits, ormris, hiraditya.
Herald added projects: clang, LLVM.
extern variable usage in BPF is different from traditional
pure user space application. Recent discussion in linux bpf
mailing list has two use cases where debug info types are
required to use extern variables:
- extern types are required to have a suitable interface in libbpf (bpf loader)
to provide kernel config parameters to bpf programs.
https://lore.kernel.org/bpf/CAEf4BzYCNo5GeVGMhp3fhysQ=_axAf=23ptwazs-yayafmx...@mail.gmail.com/T/#t
- extern types are required so kernel bpf verifier can verify program which
uses external functions more precisely. This will make later link with actual
external function no need to reverify.
https://lore.kernel.org/bpf/87eez4odqp@toke.dk/T/#m8d5c3e87ffe7f2764e02d722cb0d8cbc136880ed
This patch added clang support to emit debuginfo for extern variables,
and bpf support to consume such info into BTF, which can then be used
by bpf loader.
A few more things need to do:
- currently, I added clang EmitGlobalDeclVariable() to emit debuginfo for
extern variables. It might be possible to reuse existing EmitGlobalVariable().
Need double check.
- BPF is C only, so I only tested C. I am not sure whether adding other
language support is necessary at this point.
- add clang test cases and a few more bpf backend tests.
But some early feedback will be great!
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D70625
Files:
clang/include/clang/AST/ASTConsumer.h
clang/include/clang/Basic/TargetInfo.h
clang/include/clang/Sema/Sema.h
clang/lib/Basic/Targets/BPF.h
clang/lib/CodeGen/CGDebugInfo.cpp
clang/lib/CodeGen/CGDebugInfo.h
clang/lib/CodeGen/CodeGenAction.cpp
clang/lib/CodeGen/CodeGenModule.cpp
clang/lib/CodeGen/CodeGenModule.h
clang/lib/CodeGen/ModuleBuilder.cpp
clang/lib/Sema/Sema.cpp
clang/lib/Sema/SemaDecl.cpp
llvm/include/llvm/IR/DIBuilder.h
llvm/lib/IR/DIBuilder.cpp
llvm/lib/IR/DebugInfo.cpp
llvm/lib/Target/BPF/BTF.h
llvm/lib/Target/BPF/BTFDebug.cpp
llvm/lib/Target/BPF/BTFDebug.h
llvm/test/CodeGen/BPF/BTF/extern-var-func.ll
llvm/test/CodeGen/BPF/BTF/extern-var-section.ll
llvm/test/CodeGen/BPF/BTF/extern-var-struct.ll
llvm/unittests/Transforms/Utils/CloningTest.cpp
Index: llvm/unittests/Transforms/Utils/CloningTest.cpp
===
--- llvm/unittests/Transforms/Utils/CloningTest.cpp
+++ llvm/unittests/Transforms/Utils/CloningTest.cpp
@@ -764,7 +764,7 @@
DBuilder.createGlobalVariableExpression(
Subprogram, "unattached", "unattached", File, 1,
-DBuilder.createNullPtrType(), false, Expr);
+DBuilder.createNullPtrType(), false, true, Expr);
auto *Entry = BasicBlock::Create(C, "", F);
IBuilder.SetInsertPoint(Entry);
Index: llvm/test/CodeGen/BPF/BTF/extern-var-struct.ll
===
--- /dev/null
+++ llvm/test/CodeGen/BPF/BTF/extern-var-struct.ll
@@ -0,0 +1,101 @@
+; RUN: llc -march=bpfel -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+; RUN: llc -march=bpfeb -filetype=asm -o - %s | FileCheck -check-prefixes=CHECK %s
+;
+; Source code:
+; typedef struct t1 { int f1; } __t1;
+; int test() { return global.f1; }
+; Compilation flag:
+; clang -target bpf -O2 -g -S -emit-llvm test.c
+
+%struct.t1 = type { i32 }
+
+@global = external dso_local local_unnamed_addr global %struct.t1, align 4, !dbg !0
+
+; Function Attrs: norecurse nounwind readonly
+define dso_local i32 @test() local_unnamed_addr #0 !dbg !15 {
+entry:
+ %0 = load i32, i32* getelementptr inbounds (%struct.t1, %struct.t1* @global, i64 0, i32 0), align 4, !dbg !18, !tbaa !19
+ ret i32 %0, !dbg !24
+}
+
+; CHECK: .section.BTF,"",@progbits
+; CHECK-NEXT:.short 60319 # 0xeb9f
+; CHECK-NEXT:.byte 1
+; CHECK-NEXT:.byte 0
+; CHECK-NEXT:.long 24
+; CHECK-NEXT:.long 0
+; CHECK-NEXT:.long 92
+; CHECK-NEXT:.long 92
+; CHECK-NEXT:.long 73
+; CHECK-NEXT:.long 0 # BTF_KIND_FUNC_PROTO(id = 1)
+; CHECK-NEXT:.long 218103808 # 0xd00
+; CHECK-NEXT:.long 2
+; CHECK-NEXT:.long 1 # BTF_KIND_INT(id = 2)
+; CHECK-NEXT:.long 16777216# 0x100
+; CHECK-NEXT:.long 4
+; CHECK-NEXT:.long 16777248# 0x120
+; CHECK-NEXT:.long 5 # BTF_KIND_FUNC(id = 3)
+; CHECK-NEXT:.long 201326592 # 0xc00
+; CHECK-NEXT:.long 1
+; CHECK-NEXT:.long 55 # BTF_KIND_TYPEDEF(id = 4)
+; CHECK-NEXT:
