ELF Code Emitter now uses CurBufferPtr, BufferBegin and BufferEnd, as do JIT and

MachO Writer. This will change with the arrival of ObjectCodeEmitter and
BinaryObject


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72906 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/ELFCodeEmitter.cpp

@@ -7,17 +7,17 @@
 //
 //===----------------------------------------------------------------------===//
 
+#define DEBUG_TYPE "elfce"
+
 #include "ELFCodeEmitter.h"
 #include "llvm/Constants.h"
 #include "llvm/DerivedTypes.h"
 #include "llvm/Function.h"
 #include "llvm/CodeGen/MachineConstantPool.h"
 #include "llvm/CodeGen/MachineJumpTableInfo.h"
-#include "llvm/Target/TargetAsmInfo.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/Target/TargetMachine.h"
-#include "llvm/Support/Mangler.h"
-#include "llvm/Support/OutputBuffer.h"
+#include "llvm/Support/Debug.h"
 
 //===----------------------------------------------------------------------===//
 //                       ELFCodeEmitter Implementation
@@ -27,39 +27,54 @@ namespace llvm {
 
 /// startFunction - This callback is invoked when a new machine function is
 /// about to be emitted.
-void ELFCodeEmitter::startFunction(MachineFunction &F) {
-  // Align the output buffer to the appropriate alignment.
-  unsigned Align = 16;   // FIXME: GENERICIZE!!
+void ELFCodeEmitter::startFunction(MachineFunction &MF) {
+  const TargetData *TD = TM.getTargetData();
+  const Function *F = MF.getFunction();
+
+  // Align the output buffer to the appropriate alignment, power of 2.
+  unsigned FnAlign = F->getAlignment();
+  unsigned TDAlign = TD->getPrefTypeAlignment(F->getType());
+  unsigned Align = std::max(FnAlign, TDAlign);
+  assert(!(Align & (Align-1)) && "Alignment is not a power of two!");
+
   // Get the ELF Section that this function belongs in.
-  ES = &EW.getSection(".text", ELFWriter::ELFSection::SHT_PROGBITS,
-                      ELFWriter::ELFSection::SHF_EXECINSTR |
-                      ELFWriter::ELFSection::SHF_ALLOC);
-  OutBuffer = &ES->SectionData;
-  cerr << "FIXME: This code needs to be updated for changes in the "
-       << "CodeEmitter interfaces.  In particular, this should set "
-       << "BufferBegin/BufferEnd/CurBufferPtr, not deal with OutBuffer!";
-  abort();
+  ES = &EW.getTextSection();
+
+  // FIXME: better memory management, this will be replaced by BinaryObjects
+  ES->SectionData.reserve(4096);
+  BufferBegin = &ES->SectionData[0];
+  BufferEnd = BufferBegin + ES->SectionData.capacity();
 
   // Upgrade the section alignment if required.
   if (ES->Align < Align) ES->Align = Align;
 
-  // Add padding zeros to the end of the buffer to make sure that the
-  // function will start on the correct byte alignment within the section.
-  OutputBuffer OB(*OutBuffer,
-                  TM.getTargetData()->getPointerSizeInBits() == 64,
-                  TM.getTargetData()->isLittleEndian());
-  OB.align(Align);
-  FnStart = OutBuffer->size();
+  // Round the size up to the correct alignment for starting the new function.
+  ES->Size = (ES->Size + (Align-1)) & (-Align);
+
+  // Snaity check on allocated space for text section
+  assert( ES->Size < 4096 && "no more space in TextSection" );
+
+  // FIXME: Using ES->Size directly here instead of calculating it from the
+  // output buffer size (impossible because the code emitter deals only in raw
+  // bytes) forces us to manually synchronize size and write padding zero bytes
+  // to the output buffer for all non-text sections.  For text sections, we do
+  // not synchonize the output buffer, and we just blow up if anyone tries to
+  // write non-code to it.  An assert should probably be added to
+  // AddSymbolToSection to prevent calling it on the text section.
+  CurBufferPtr = BufferBegin + ES->Size;
+
+  // Record function start address relative to BufferBegin
+  FnStartPtr = CurBufferPtr;
 }
 
 /// finishFunction - This callback is invoked after the function is completely
 /// finished.
-bool ELFCodeEmitter::finishFunction(MachineFunction &F) {
-  // We now know the size of the function, add a symbol to represent it.
-  ELFWriter::ELFSym FnSym(F.getFunction());
+bool ELFCodeEmitter::finishFunction(MachineFunction &MF) {
+  // Add a symbol to represent the function.
+  ELFWriter::ELFSym FnSym(MF.getFunction());
 
   // Figure out the binding (linkage) of the symbol.
-  switch (F.getFunction()->getLinkage()) {
+  switch (MF.getFunction()->getLinkage()) {
   default:
     // appending linkage is illegal for functions.
     assert(0 && "Unknown linkage type!");
@@ -79,15 +94,20 @@ bool ELFCodeEmitter::finishFunction(MachineFunction &F) {
     break;
   }
 
-  ES->Size = OutBuffer->size();
-
+  // Set the symbol type as a function
   FnSym.SetType(ELFWriter::ELFSym::STT_FUNC);
+
   FnSym.SectionIdx = ES->SectionIdx;
-  FnSym.Value = FnStart;   // Value = Offset from start of Section.
-  FnSym.Size = OutBuffer->size()-FnStart;
+  FnSym.Size = CurBufferPtr-FnStartPtr;
+
+  // Offset from start of Section
+  FnSym.Value = FnStartPtr-BufferBegin;
 
   // Finally, add it to the symtab.
   EW.SymbolTable.push_back(FnSym);
+
+  // Update Section Size
+  ES->Size = CurBufferPtr - BufferBegin;
   return false;
 }
 

lib/CodeGen/ELFCodeEmitter.h

@@ -22,10 +22,9 @@ namespace llvm {
     ELFWriter &EW;
     TargetMachine &TM;
     ELFWriter::ELFSection *ES;  // Section to write to.
-    std::vector<unsigned char> *OutBuffer;
-    size_t FnStart;
+    uint8_t *FnStartPtr;
   public:
-    explicit ELFCodeEmitter(ELFWriter &ew) : EW(ew), TM(EW.TM), OutBuffer(0) {}
+    explicit ELFCodeEmitter(ELFWriter &ew) : EW(ew), TM(EW.TM) {}
 
     void startFunction(MachineFunction &F);
     bool finishFunction(MachineFunction &F);

lib/CodeGen/ELFWriter.h

@@ -168,6 +168,12 @@ namespace llvm {
       return *SN;
     }
 
+    ELFSection &getTextSection() {
+      return getSection(".text", ELFWriter::ELFSection::SHT_PROGBITS,
+                        ELFWriter::ELFSection::SHF_EXECINSTR |
+                        ELFWriter::ELFSection::SHF_ALLOC);
+    }
+
     ELFSection &getDataSection() {
       return getSection(".data", ELFSection::SHT_PROGBITS,
                         ELFSection::SHF_WRITE | ELFSection::SHF_ALLOC);