[clang] [llvm] [BPF] Fix linking issues in static map initializers (PR #91310)
Nick Zavaritsky via llvm-commits
llvm-commits at lists.llvm.org
Fri May 17 12:30:56 PDT 2024
https://github.com/mejedi updated https://github.com/llvm/llvm-project/pull/91310
>From 88f895cc1a761681edd1dff15170ab42d563da49 Mon Sep 17 00:00:00 2001
From: Nick Zavaritsky <nick.zavaritsky at emnify.com>
Date: Sun, 5 May 2024 10:20:52 +0000
Subject: [PATCH] [BPF] Fix linking issues in static map initializers
When BPF object files are linked with bpftool, every symbol must be
accompanied by BTF info. Ensure that extern functions referenced by
global variable initializers are included in BTF.
The primary motivation is "static" initialization of PROG maps:
extern int elsewhere(struct xdp_md *);
struct {
__uint(type, BPF_MAP_TYPE_PROG_ARRAY);
__uint(max_entries, 1);
__type(key, int);
__type(value, int);
__array(values, int (struct xdp_md *));
} prog_map SEC(".maps") = { .values = { elsewhere } };
BPF backend needs debug info to produce BTF. Debug info is not
normally generated for external variables and functions. Previously, it
was solved differently for variables (collecting variable declarations
in ExternalDeclarations vector) and functions (logic invoked during
codegen in CGExpr.cpp).
This patch generalises ExternalDefclarations to include both function
and variable declarations. This change ensures that function references
are not missed no matter the context. Previously external functions
referenced in constant expressions lacked debug info.
---
clang/include/clang/AST/ASTConsumer.h | 3 +-
.../clang/Frontend/MultiplexConsumer.h | 2 +-
clang/include/clang/Sema/Sema.h | 2 +-
clang/lib/CodeGen/BackendConsumer.h | 2 +-
clang/lib/CodeGen/CGExpr.cpp | 17 +-----
clang/lib/CodeGen/CodeGenAction.cpp | 2 +-
clang/lib/CodeGen/CodeGenModule.cpp | 19 ++++++-
clang/lib/CodeGen/CodeGenModule.h | 3 +-
clang/lib/CodeGen/ModuleBuilder.cpp | 2 +-
clang/lib/Frontend/MultiplexConsumer.cpp | 2 +-
clang/lib/Interpreter/IncrementalParser.cpp | 2 +-
clang/lib/Sema/SemaDecl.cpp | 8 +++
clang/test/bpf-debug-info-extern-func.c | 9 ++++
llvm/lib/Target/BPF/BTFDebug.cpp | 23 ++++++++
llvm/lib/Target/BPF/BTFDebug.h | 4 ++
llvm/test/CodeGen/BPF/BTF/extern-var-func2.ll | 54 +++++++++++++++++++
16 files changed, 128 insertions(+), 26 deletions(-)
create mode 100644 clang/test/bpf-debug-info-extern-func.c
create mode 100644 llvm/test/CodeGen/BPF/BTF/extern-var-func2.ll
diff --git a/clang/include/clang/AST/ASTConsumer.h b/clang/include/clang/AST/ASTConsumer.h
index ebcd8059284d8..447f2592d2359 100644
--- a/clang/include/clang/AST/ASTConsumer.h
+++ b/clang/include/clang/AST/ASTConsumer.h
@@ -23,6 +23,7 @@ namespace clang {
class ASTDeserializationListener; // layering violation because void* is ugly
class SemaConsumer; // layering violation required for safe SemaConsumer
class TagDecl;
+ class DeclaratorDecl;
class VarDecl;
class FunctionDecl;
class ImportDecl;
@@ -105,7 +106,7 @@ class ASTConsumer {
/// CompleteExternalDeclaration - Callback invoked at the end of a translation
/// unit to notify the consumer that the given external declaration should be
/// completed.
- virtual void CompleteExternalDeclaration(VarDecl *D) {}
+ virtual void CompleteExternalDeclaration(DeclaratorDecl *D) {}
/// Callback invoked when an MSInheritanceAttr has been attached to a
/// CXXRecordDecl.
diff --git a/clang/include/clang/Frontend/MultiplexConsumer.h b/clang/include/clang/Frontend/MultiplexConsumer.h
index 4ed0d86d3cdfb..e49e3392d1f31 100644
--- a/clang/include/clang/Frontend/MultiplexConsumer.h
+++ b/clang/include/clang/Frontend/MultiplexConsumer.h
@@ -67,7 +67,7 @@ class MultiplexConsumer : public SemaConsumer {
void HandleTopLevelDeclInObjCContainer(DeclGroupRef D) override;
void HandleImplicitImportDecl(ImportDecl *D) override;
void CompleteTentativeDefinition(VarDecl *D) override;
- void CompleteExternalDeclaration(VarDecl *D) override;
+ void CompleteExternalDeclaration(DeclaratorDecl *D) override;
void AssignInheritanceModel(CXXRecordDecl *RD) override;
void HandleVTable(CXXRecordDecl *RD) override;
ASTMutationListener *GetASTMutationListener() override;
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 873592a2d430a..adc716681bfe6 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -2611,7 +2611,7 @@ class Sema final : public SemaBase {
TentativeDefinitionsType TentativeDefinitions;
/// All the external declarations encoutered and used in the TU.
- SmallVector<VarDecl *, 4> ExternalDeclarations;
+ SmallVector<DeclaratorDecl *, 4> ExternalDeclarations;
/// Generally null except when we temporarily switch decl contexts,
/// like in \see SemaObjC::ActOnObjCTemporaryExitContainerContext.
diff --git a/clang/lib/CodeGen/BackendConsumer.h b/clang/lib/CodeGen/BackendConsumer.h
index 0fe9929dca2b3..92ff19ab30844 100644
--- a/clang/lib/CodeGen/BackendConsumer.h
+++ b/clang/lib/CodeGen/BackendConsumer.h
@@ -107,7 +107,7 @@ class BackendConsumer : public ASTConsumer {
void HandleTagDeclDefinition(TagDecl *D) override;
void HandleTagDeclRequiredDefinition(const TagDecl *D) override;
void CompleteTentativeDefinition(VarDecl *D) override;
- void CompleteExternalDeclaration(VarDecl *D) override;
+ void CompleteExternalDeclaration(DeclaratorDecl *D) override;
void AssignInheritanceModel(CXXRecordDecl *RD) override;
void HandleVTable(CXXRecordDecl *RD) override;
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index d96c7bb1e5682..7aeb6868191b5 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -3129,21 +3129,8 @@ LValue CodeGenFunction::EmitDeclRefLValue(const DeclRefExpr *E) {
return LV;
}
- if (const auto *FD = dyn_cast<FunctionDecl>(ND)) {
- LValue LV = EmitFunctionDeclLValue(*this, E, FD);
-
- // Emit debuginfo for the function declaration if the target wants to.
- if (getContext().getTargetInfo().allowDebugInfoForExternalRef()) {
- if (CGDebugInfo *DI = CGM.getModuleDebugInfo()) {
- auto *Fn =
- cast<llvm::Function>(LV.getPointer(*this)->stripPointerCasts());
- if (!Fn->getSubprogram())
- DI->EmitFunctionDecl(FD, FD->getLocation(), T, Fn);
- }
- }
-
- return LV;
- }
+ if (const auto *FD = dyn_cast<FunctionDecl>(ND))
+ return EmitFunctionDeclLValue(*this, E, FD);
// FIXME: While we're emitting a binding from an enclosing scope, all other
// DeclRefExprs we see should be implicitly treated as if they also refer to
diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
index 6d3efdb5ffe34..c6e3cb6b3dee2 100644
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -378,7 +378,7 @@ void BackendConsumer::CompleteTentativeDefinition(VarDecl *D) {
Gen->CompleteTentativeDefinition(D);
}
-void BackendConsumer::CompleteExternalDeclaration(VarDecl *D) {
+void BackendConsumer::CompleteExternalDeclaration(DeclaratorDecl *D) {
Gen->CompleteExternalDeclaration(D);
}
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index 489c08a4d4819..22895f4cd108a 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -5155,8 +5155,11 @@ void CodeGenModule::EmitTentativeDefinition(const VarDecl *D) {
EmitGlobalVarDefinition(D);
}
-void CodeGenModule::EmitExternalDeclaration(const VarDecl *D) {
- EmitExternalVarDeclaration(D);
+void CodeGenModule::EmitExternalDeclaration(const DeclaratorDecl *D) {
+ if (auto const *V = dyn_cast<const VarDecl>(D))
+ EmitExternalVarDeclaration(V);
+ if (auto const *FD = dyn_cast<const FunctionDecl>(D))
+ EmitExternalFunctionDeclaration(FD);
}
CharUnits CodeGenModule::GetTargetTypeStoreSize(llvm::Type *Ty) const {
@@ -5580,6 +5583,18 @@ void CodeGenModule::EmitExternalVarDeclaration(const VarDecl *D) {
}
}
+void CodeGenModule::EmitExternalFunctionDeclaration(const FunctionDecl *FD) {
+ if (CGDebugInfo *DI = getModuleDebugInfo())
+ if (getCodeGenOpts().hasReducedDebugInfo()) {
+ auto *Ty = getTypes().ConvertType(FD->getType());
+ StringRef MangledName = getMangledName(FD);
+ auto *Fn = dyn_cast<llvm::Function>(
+ GetOrCreateLLVMFunction(MangledName, Ty, FD, /* ForVTable */ false));
+ if (!Fn->getSubprogram())
+ DI->EmitFunctionDecl(FD, FD->getLocation(), FD->getType(), Fn);
+ }
+}
+
static bool isVarDeclStrongDefinition(const ASTContext &Context,
CodeGenModule &CGM, const VarDecl *D,
bool NoCommon) {
diff --git a/clang/lib/CodeGen/CodeGenModule.h b/clang/lib/CodeGen/CodeGenModule.h
index 0f68418130ead..e470c7f0ae0b8 100644
--- a/clang/lib/CodeGen/CodeGenModule.h
+++ b/clang/lib/CodeGen/CodeGenModule.h
@@ -1285,7 +1285,7 @@ class CodeGenModule : public CodeGenTypeCache {
void EmitTentativeDefinition(const VarDecl *D);
- void EmitExternalDeclaration(const VarDecl *D);
+ void EmitExternalDeclaration(const DeclaratorDecl *D);
void EmitVTable(CXXRecordDecl *Class);
@@ -1635,6 +1635,7 @@ class CodeGenModule : public CodeGenTypeCache {
void EmitGlobalVarDefinition(const VarDecl *D, bool IsTentative = false);
void EmitExternalVarDeclaration(const VarDecl *D);
+ void EmitExternalFunctionDeclaration(const FunctionDecl *D);
void EmitAliasDefinition(GlobalDecl GD);
void emitIFuncDefinition(GlobalDecl GD);
void emitCPUDispatchDefinition(GlobalDecl GD);
diff --git a/clang/lib/CodeGen/ModuleBuilder.cpp b/clang/lib/CodeGen/ModuleBuilder.cpp
index df85295cfb2e2..d4e0ab0339a8b 100644
--- a/clang/lib/CodeGen/ModuleBuilder.cpp
+++ b/clang/lib/CodeGen/ModuleBuilder.cpp
@@ -310,7 +310,7 @@ namespace {
Builder->EmitTentativeDefinition(D);
}
- void CompleteExternalDeclaration(VarDecl *D) override {
+ void CompleteExternalDeclaration(DeclaratorDecl *D) override {
Builder->EmitExternalDeclaration(D);
}
diff --git a/clang/lib/Frontend/MultiplexConsumer.cpp b/clang/lib/Frontend/MultiplexConsumer.cpp
index 8fdc7f55a5003..651c55aeed540 100644
--- a/clang/lib/Frontend/MultiplexConsumer.cpp
+++ b/clang/lib/Frontend/MultiplexConsumer.cpp
@@ -357,7 +357,7 @@ void MultiplexConsumer::CompleteTentativeDefinition(VarDecl *D) {
Consumer->CompleteTentativeDefinition(D);
}
-void MultiplexConsumer::CompleteExternalDeclaration(VarDecl *D) {
+void MultiplexConsumer::CompleteExternalDeclaration(DeclaratorDecl *D) {
for (auto &Consumer : Consumers)
Consumer->CompleteExternalDeclaration(D);
}
diff --git a/clang/lib/Interpreter/IncrementalParser.cpp b/clang/lib/Interpreter/IncrementalParser.cpp
index ef90fe9e6f545..84ba0e29cf095 100644
--- a/clang/lib/Interpreter/IncrementalParser.cpp
+++ b/clang/lib/Interpreter/IncrementalParser.cpp
@@ -79,7 +79,7 @@ class IncrementalASTConsumer final : public ASTConsumer {
void CompleteTentativeDefinition(VarDecl *D) override final {
Consumer->CompleteTentativeDefinition(D);
}
- void CompleteExternalDeclaration(VarDecl *D) override final {
+ void CompleteExternalDeclaration(DeclaratorDecl *D) override final {
Consumer->CompleteExternalDeclaration(D);
}
void AssignInheritanceModel(CXXRecordDecl *RD) override final {
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 0dbdf923df95a..15ebf460d9257 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -10972,6 +10972,14 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
break;
}
+ // Similar to no_builtin logic above, at this point of the code
+ // FunctionDecl::isThisDeclarationADefinition() always returns `false`
+ // because Sema::ActOnStartOfFunctionDef has not been called yet.
+ if (Context.getTargetInfo().allowDebugInfoForExternalRef() &&
+ !NewFD->isInvalidDecl() &&
+ D.getFunctionDefinitionKind() == FunctionDefinitionKind::Declaration)
+ ExternalDeclarations.push_back(NewFD);
+
return NewFD;
}
diff --git a/clang/test/bpf-debug-info-extern-func.c b/clang/test/bpf-debug-info-extern-func.c
new file mode 100644
index 0000000000000..da324630a314d
--- /dev/null
+++ b/clang/test/bpf-debug-info-extern-func.c
@@ -0,0 +1,9 @@
+// RUN: %clang -g -O2 -target bpf -S -emit-llvm %s -o - | FileCheck %s
+//
+// When linking BPF object files via bpftool, BTF info is required for
+// every symbol. BTF is generated from debug info. Ensure that debug info
+// is emitted for extern functions referenced via variable initializers.
+//
+// CHECK: !DISubprogram(name: "fn"
+extern void fn(void);
+void (*pfn) (void) = &fn;
diff --git a/llvm/lib/Target/BPF/BTFDebug.cpp b/llvm/lib/Target/BPF/BTFDebug.cpp
index b6d3b460005c9..7d64f2e04bc26 100644
--- a/llvm/lib/Target/BPF/BTFDebug.cpp
+++ b/llvm/lib/Target/BPF/BTFDebug.cpp
@@ -1494,6 +1494,29 @@ void BTFDebug::processGlobals(bool ProcessingMapDef) {
DataSecEntries[std::string(SecName)]->addDataSecEntry(VarId,
Asm->getSymbol(&Global), Size);
+
+ if (Global.hasInitializer())
+ processGlobalInitializer(Global.getInitializer());
+ }
+}
+
+/// Process global variable initializer in pursuit for function
+/// pointers. Add discovered (extern) functions to BTF. Some (extern)
+/// functions might have been missed otherwise. Every symbol needs BTF
+/// info when linking with bpftool. Primary use case: "static"
+/// initialization of BPF maps.
+///
+/// struct {
+/// __uint(type, BPF_MAP_TYPE_PROG_ARRAY);
+/// ...
+/// } prog_map SEC(".maps") = { .values = { extern_func } };
+///
+void BTFDebug::processGlobalInitializer(const Constant *C) {
+ if (auto *Fn = dyn_cast<Function>(C))
+ processFuncPrototypes(Fn);
+ if (auto *CA = dyn_cast<ConstantAggregate>(C)) {
+ for (unsigned I = 0, N = CA->getNumOperands(); I < N; ++I)
+ processGlobalInitializer(CA->getOperand(I));
}
}
diff --git a/llvm/lib/Target/BPF/BTFDebug.h b/llvm/lib/Target/BPF/BTFDebug.h
index 11a0c59ba6c90..02181d3013be9 100644
--- a/llvm/lib/Target/BPF/BTFDebug.h
+++ b/llvm/lib/Target/BPF/BTFDebug.h
@@ -352,6 +352,10 @@ class BTFDebug : public DebugHandlerBase {
/// Generate types and variables for globals.
void processGlobals(bool ProcessingMapDef);
+ /// Process global variable initializer in pursuit for function
+ /// pointers.
+ void processGlobalInitializer(const Constant *C);
+
/// Generate types for function prototypes.
void processFuncPrototypes(const Function *);
diff --git a/llvm/test/CodeGen/BPF/BTF/extern-var-func2.ll b/llvm/test/CodeGen/BPF/BTF/extern-var-func2.ll
new file mode 100644
index 0000000000000..700486d9f3515
--- /dev/null
+++ b/llvm/test/CodeGen/BPF/BTF/extern-var-func2.ll
@@ -0,0 +1,54 @@
+; 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:
+; extern int elsewhere(void);
+; struct {
+; void *values[];
+; } prog_map = { .values = { elsewhere } };
+; Compilation flag:
+; clang -target bpf -O2 -g -S -emit-llvm test.c
+; ModuleID = 'b.c'
+
+ at prog_map = dso_local local_unnamed_addr global { [1 x ptr] } { [1 x ptr] [ptr @elsewhere] }, align 8, !dbg !0
+
+declare !dbg !17 dso_local i32 @elsewhere() #0
+
+; CHECK: .long 0 # BTF_KIND_FUNC_PROTO(id = 6)
+; CHECK-NEXT: .long 218103808 # 0xd000000
+; CHECK-NEXT: .long 7
+; CHECK-NEXT: .long 37 # BTF_KIND_INT(id = 7)
+; CHECK-NEXT: .long 16777216 # 0x1000000
+; CHECK-NEXT: .long 4
+; CHECK-NEXT: .long 16777248 # 0x1000020
+; CHECK-NEXT: .long 41 # BTF_KIND_FUNC(id = 8)
+; CHECK-NEXT: .long 201326594 # 0xc000002
+; CHECK-NEXT: .long 6
+
+attributes #0 = { "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" }
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!12, !13, !14, !15}
+!llvm.ident = !{!16}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "prog_map", scope: !2, file: !3, line: 4, type: !5, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C11, file: !3, producer: "clang version 19.0.0git (git at github.com:llvm/llvm-project.git 0390a6803608e3a5314315b73740c2d3f5a5723f)", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "b.c", directory: "/home/nickz/llvm-project.git", checksumkind: CSK_MD5, checksum: "41cc17375f1261a0e072590833492553")
+!4 = !{!0}
+!5 = distinct !DICompositeType(tag: DW_TAG_structure_type, file: !3, line: 2, elements: !6)
+!6 = !{!7}
+!7 = !DIDerivedType(tag: DW_TAG_member, name: "values", scope: !5, file: !3, line: 3, baseType: !8)
+!8 = !DICompositeType(tag: DW_TAG_array_type, baseType: !9, elements: !10)
+!9 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
+!10 = !{!11}
+!11 = !DISubrange(count: -1)
+!12 = !{i32 7, !"Dwarf Version", i32 5}
+!13 = !{i32 2, !"Debug Info Version", i32 3}
+!14 = !{i32 1, !"wchar_size", i32 4}
+!15 = !{i32 7, !"frame-pointer", i32 2}
+!16 = !{!"clang version 19.0.0git (git at github.com:llvm/llvm-project.git 0390a6803608e3a5314315b73740c2d3f5a5723f)"}
+!17 = !DISubprogram(name: "elsewhere", scope: !3, file: !3, line: 1, type: !18, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized)
+!18 = !DISubroutineType(types: !19)
+!19 = !{!20}
+!20 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
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