[AVR] emit 'MCSA_Global' references to '__do_global_ctors' and '__do_global_dtors'

Emit references to '__do_global_ctors' and '__do_global_dtors' to allow
constructor/destructor routines to run.

Reviewed by: MaskRay

Differential Revision: https://reviews.llvm.org/D107133

Author: mhjacobson

llvm/lib/Target/AVR/AVRAsmPrinter.cpp

@@ -24,6 +24,7 @@
 #include "llvm/CodeGen/TargetRegisterInfo.h"
 #include "llvm/CodeGen/TargetSubtargetInfo.h"
 #include "llvm/IR/Mangler.h"
+#include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCInst.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbol.h"
@@ -38,9 +39,8 @@ namespace llvm {
 /// An AVR assembly code printer.
 class AVRAsmPrinter : public AsmPrinter {
 public:
-  AVRAsmPrinter(TargetMachine &TM,
-                std::unique_ptr<MCStreamer> Streamer)
-      : AsmPrinter(TM, std::move(Streamer)), MRI(*TM.getMCRegisterInfo()) { }
+  AVRAsmPrinter(TargetMachine &TM, std::unique_ptr<MCStreamer> Streamer)
+      : AsmPrinter(TM, std::move(Streamer)), MRI(*TM.getMCRegisterInfo()) {}
 
   StringRef getPassName() const override { return "AVR Assembly Printer"; }
 
@@ -56,8 +56,13 @@ class AVRAsmPrinter : public AsmPrinter {
 
   const MCExpr *lowerConstant(const Constant *CV) override;
 
+  void emitXXStructor(const DataLayout &DL, const Constant *CV) override;
+
+  bool doFinalization(Module &M) override;
+
 private:
   const MCRegisterInfo &MRI;
+  bool EmittedStructorSymbolAttrs = false;
 };
 
 void AVRAsmPrinter::printOperand(const MachineInstr *MI, unsigned OpNo,
@@ -193,9 +198,47 @@ const MCExpr *AVRAsmPrinter::lowerConstant(const Constant *CV) {
   return AsmPrinter::lowerConstant(CV);
 }
 
+void AVRAsmPrinter::emitXXStructor(const DataLayout &DL, const Constant *CV) {
+  if (!EmittedStructorSymbolAttrs) {
+    OutStreamer->emitRawComment(
+        " Emitting these undefined symbol references causes us to link the"
+        " libgcc code that runs our constructors/destructors");
+    OutStreamer->emitRawComment(" This matches GCC's behavior");
+
+    MCSymbol *CtorsSym = OutContext.getOrCreateSymbol("__do_global_ctors");
+    OutStreamer->emitSymbolAttribute(CtorsSym, MCSA_Global);
+
+    MCSymbol *DtorsSym = OutContext.getOrCreateSymbol("__do_global_dtors");
+    OutStreamer->emitSymbolAttribute(DtorsSym, MCSA_Global);
+
+    EmittedStructorSymbolAttrs = true;
+  }
+
+  AsmPrinter::emitXXStructor(DL, CV);
+}
+
+bool AVRAsmPrinter::doFinalization(Module &M) {
+  MCSymbol *DoCopyData = OutContext.getOrCreateSymbol("__do_copy_data");
+  MCSymbol *DoClearBss = OutContext.getOrCreateSymbol("__do_clear_bss");
+
+  // FIXME: We can disable __do_copy_data if there are no static RAM variables.
+
+  OutStreamer->emitRawComment(
+      " Declaring this symbol tells the CRT that it should");
+  OutStreamer->emitRawComment(
+      "copy all variables from program memory to RAM on startup");
+  OutStreamer->emitSymbolAttribute(DoCopyData, MCSA_Global);
+
+  OutStreamer->emitRawComment(
+      " Declaring this symbol tells the CRT that it should");
+  OutStreamer->emitRawComment("clear the zeroed data section on startup");
+  OutStreamer->emitSymbolAttribute(DoClearBss, MCSA_Global);
+
+  return AsmPrinter::doFinalization(M);
+}
+
 } // end of namespace llvm
 
 extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeAVRAsmPrinter() {
   llvm::RegisterAsmPrinter<llvm::AVRAsmPrinter> X(llvm::getTheAVRTarget());
 }
-

llvm/lib/Target/AVR/MCTargetDesc/AVRTargetStreamer.cpp

@@ -21,23 +21,4 @@ AVRTargetStreamer::AVRTargetStreamer(MCStreamer &S) : MCTargetStreamer(S) {}
 AVRTargetAsmStreamer::AVRTargetAsmStreamer(MCStreamer &S)
     : AVRTargetStreamer(S) {}
 
-void AVRTargetStreamer::finish() {
-  MCStreamer &OS = getStreamer();
-  MCContext &Context = OS.getContext();
-
-  MCSymbol *DoCopyData = Context.getOrCreateSymbol("__do_copy_data");
-  MCSymbol *DoClearBss = Context.getOrCreateSymbol("__do_clear_bss");
-
-  // FIXME: We can disable __do_copy_data if there are no static RAM variables.
-
-  OS.emitRawComment(" Declaring this symbol tells the CRT that it should");
-  OS.emitRawComment("copy all variables from program memory to RAM on startup");
-  OS.emitSymbolAttribute(DoCopyData, MCSA_Global);
-
-  OS.emitRawComment(" Declaring this symbol tells the CRT that it should");
-  OS.emitRawComment("clear the zeroed data section on startup");
-  OS.emitSymbolAttribute(DoClearBss, MCSA_Global);
-}
-
 } // end namespace llvm
-

llvm/lib/Target/AVR/MCTargetDesc/AVRTargetStreamer.h

@@ -18,8 +18,6 @@ class MCStreamer;
 class AVRTargetStreamer : public MCTargetStreamer {
 public:
   explicit AVRTargetStreamer(MCStreamer &S);
-
-  void finish() override;
 };
 
 /// A target streamer for textual AVR assembly code.

llvm/test/CodeGen/AVR/ctors.ll

@@ -0,0 +1,15 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -march=avr | FileCheck %s
+
+define void @do_nothing() addrspace(1) #0 {
+; CHECK-LABEL: do_nothing:
+; CHECK:       ; %bb.0:
+; CHECK-NEXT:    ret
+  ret void
+}
+
+; CHECK: .globl __do_global_ctors
+@llvm.global_ctors = appending global [1 x { i32, void () addrspace(1)*, i8* }] [{ i32, void () addrspace(1)*, i8* } { i32 65535, void () addrspace(1)* @do_nothing, i8* null }]
+
+; CHECK: .globl __do_global_dtors
+@llvm.global_dtors = appending global [1 x { i32, void () addrspace(1)*, i8* }] [{ i32, void () addrspace(1)*, i8* } { i32 65535, void () addrspace(1)* @do_nothing, i8* null }]