Merging r312905:

------------------------------------------------------------------------
r312905 | dylanmckay | 2017-09-11 22:32:51 +1200 (Mon, 11 Sep 2017) | 10 lines

[AVR] Enable the '__do_copy_data' function

Also enables '__do_clear_bss'.

These functions are automaticalled called by the CRT if they are
declared.

We need these to be called otherwise RAM will start completely
uninitialised, even though we need to copy RAM variables from progmem to
RAM.
------------------------------------------------------------------------

llvm-svn: 314356

Author: dylanmckay

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

@@ -13,12 +13,32 @@
 
 #include "AVRTargetStreamer.h"
 
+#include "llvm/MC/MCContext.h"
+
 namespace llvm {
 
 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

@@ -19,6 +19,8 @@ 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/clear-bss.ll

@@ -0,0 +1,5 @@
+; RUN: llc < %s -march=avr | FileCheck %s
+
+; CHECK: .globl __do_clear_bss
+@zeroed = internal constant [3 x i8] zeroinitializer
+

llvm/test/CodeGen/AVR/copy-data-to-ram.ll

@@ -0,0 +1,5 @@
+; RUN: llc < %s -march=avr | FileCheck %s
+
+; CHECK: .globl __do_copy_data
+@str = internal global [3 x i8] c"foo"
+