From 7ddde32ead1b704be807937fa0947e3c57ee51ac Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sat, 20 Nov 2004 23:54:33 +0000
Subject: [PATCH] Implement the X86 JIT interfaces

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@18067 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/X86/X86JITInfo.cpp | 140 ++++++++++++++++++++++++++++++++++
 1 file changed, 140 insertions(+)
 create mode 100644 lib/Target/X86/X86JITInfo.cpp

diff --git a/lib/Target/X86/X86JITInfo.cpp b/lib/Target/X86/X86JITInfo.cpp
new file mode 100644
index 00000000000..a976d232f5b
--- /dev/null
+++ b/lib/Target/X86/X86JITInfo.cpp
@@ -0,0 +1,140 @@
+//===-- X86JITInfo.cpp - Implement the JIT interfaces for the X86 target --===//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+//
+// This file implements the JIT interfaces for the X86 target.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "jit"
+#include "X86JITInfo.h"
+#include "X86Relocations.h"
+#include "llvm/CodeGen/MachineCodeEmitter.h"
+#include "llvm/Config/alloca.h"
+using namespace llvm;
+
+void *X86JITInfo::emitFunctionStub(void *Fn, MachineCodeEmitter &MCE) {
+  MCE.startFunctionStub(6);
+  MCE.emitByte(0xE8);   // Call with 32 bit pc-rel destination...
+
+  MCE.emitWord((intptr_t)Fn-MCE.getCurrentPCValue()-4);
+
+  MCE.emitByte(0xCD);   // Interrupt - Just a marker identifying the stub!
+  return MCE.finishFunctionStub(0);
+}
+
+void X86JITInfo::replaceMachineCodeForFunction(void *Old, void *New) {
+  unsigned char *OldByte = (unsigned char *)Old;
+  *OldByte++ = 0xE9;                // Emit JMP opcode.
+  unsigned *OldWord = (unsigned *)OldByte;
+  unsigned NewAddr = (intptr_t)New;
+  unsigned OldAddr = (intptr_t)OldWord;
+  *OldWord = NewAddr - OldAddr - 4; // Emit PC-relative addr of New code.
+}
+
+
+#ifdef _MSC_VER
+#pragma optimize("y", off)
+#endif
+
+/// JITCompilerFunction - This contains the address of the JIT function used to
+/// compile a function lazily.
+static TargetJITInfo::JITCompilerFn JITCompilerFunction;
+
+/// CompilationCallback - This is the target-specific function invoked by the
+/// function stub when we did not know the real target of a call.  This function
+/// must locate the start of the stub or call site and pass it into the JIT
+/// compiler function.
+static void CompilationCallback() {
+#ifdef _MSC_VER
+  unsigned *StackPtr, RetAddr;
+  __asm mov StackPtr, ebp;
+  __asm mov eax, DWORD PTR [ebp + 4];
+  __asm mov RetAddr, eax;
+#else
+  unsigned *StackPtr = (unsigned*)__builtin_frame_address(0);
+  unsigned RetAddr = (unsigned)(intptr_t)__builtin_return_address(0);
+
+  // NOTE: __builtin_frame_address doesn't work if frame pointer elimination has
+  // been performed.  Having a variable sized alloca disables frame pointer
+  // elimination currently, even if it's dead.  This is a gross hack.
+  alloca(10+(RetAddr >> 31));
+  
+#endif
+  assert(StackPtr[1] == RetAddr &&
+         "Could not find return address on the stack!");
+
+  // It's a stub if there is an interrupt marker after the call.
+  bool isStub = ((unsigned char*)(intptr_t)RetAddr)[0] == 0xCD;
+
+  // The call instruction should have pushed the return value onto the stack...
+  RetAddr -= 4;  // Backtrack to the reference itself...
+
+#if 0
+  DEBUG(std::cerr << "In callback! Addr=" << (void*)RetAddr
+                  << " ESP=" << (void*)StackPtr
+                  << ": Resolving call to function: "
+                  << TheVM->getFunctionReferencedName((void*)RetAddr) << "\n");
+#endif
+
+  // Sanity check to make sure this really is a call instruction.
+  assert(((unsigned char*)(intptr_t)RetAddr)[-1] == 0xE8 &&"Not a call instr!");
+  
+  unsigned NewVal = (intptr_t)JITCompilerFunction((void*)(intptr_t)RetAddr);
+
+  // Rewrite the call target... so that we don't end up here every time we
+  // execute the call.
+  *(unsigned*)(intptr_t)RetAddr = NewVal-RetAddr-4;
+
+  if (isStub) {
+    // If this is a stub, rewrite the call into an unconditional branch
+    // instruction so that two return addresses are not pushed onto the stack
+    // when the requested function finally gets called.  This also makes the
+    // 0xCD byte (interrupt) dead, so the marker doesn't effect anything.
+    ((unsigned char*)(intptr_t)RetAddr)[-1] = 0xE9;
+  }
+
+  // Change the return address to reexecute the call instruction...
+  StackPtr[1] -= 5;
+}
+
+#ifdef _MSC_VER
+#pragma optimize( "", on )
+#endif
+
+TargetJITInfo::LazyResolverFn
+X86JITInfo::getLazyResolverFunction(JITCompilerFn F) {
+  JITCompilerFunction = F;
+  return CompilationCallback;
+}
+
+
+/// relocate - Before the JIT can run a block of code that has been emitted,
+/// it must rewrite the code to contain the actual addresses of any
+/// referenced global symbols.
+void X86JITInfo::relocate(void *Function, MachineRelocation *MR,
+                          unsigned NumRelocs) {
+  for (unsigned i = 0; i != NumRelocs; ++i, ++MR) {
+    void *RelocPos = (char*)Function + MR->getMachineCodeOffset();
+    intptr_t ResultPtr = (intptr_t)MR->getResultPointer();
+    switch ((X86::RelocationType)MR->getRelocationType()) {
+    case X86::reloc_pcrel_word:
+      // PC relative relocation, add the relocated value to the value already in
+      // memory, after we adjust it for where the PC is.
+      ResultPtr = ResultPtr-(intptr_t)RelocPos-4;
+      *((intptr_t*)RelocPos) += ResultPtr;
+      break;
+    case X86::reloc_absolute_word:
+      // Absolute relocation, just add the relocated value to the value already
+      // in memory.
+      *((intptr_t*)RelocPos) += ResultPtr;
+      break;
+    }
+  }
+}
+