Implement LLVM JIT side of GDB JIT debugging interface

lib/ExecutionEngine/JIT/JITDebugRegisterer.cpp

 //===-- JITDebugRegisterer.cpp - Register debug symbols for JIT -----------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines a JITDebugRegisterer object that is used by the JIT to
 // register debug info with debuggers like GDB.
 //
 //===----------------------------------------------------------------------===//
 
 #include "JITDebugRegisterer.h"
 #include "../../CodeGen/ELF.h"
 #include "../../CodeGen/ELFWriter.h"
 #include "llvm/LLVMContext.h"
 #include "llvm/Function.h"
 #include "llvm/Module.h"
 #include "llvm/Target/TargetMachine.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/OwningPtr.h"
+#include "llvm/Support/MutexGuard.h"
 #include "llvm/Support/raw_ostream.h"
-#include "llvm/System/Path.h"
-#include <map>
+#include "llvm/System/Mutex.h"
 #include <string>
 #include <vector>
 
 namespace llvm {
 
-JITDebugRegisterer::JITDebugRegisterer(TargetMachine &tm) : TM(tm), FnMap() {
-  TmpDir = sys::Path::GetTemporaryDirectory();

[Jeffrey Yasskin, 2009/07/08 00:40:45]

If you initialize TmpDir in the initializer list, you can make it const.

[Reid Kleckner, 2009/07/08 01:35:05]

On 2009/07/08 00:40:45, Jeffrey Yasskin wrote:
> If you initialize TmpDir in the initializer list, you can make it const.

Done.

-}
+// This must be kept in sync with gdb/gdb/jit.h .
+extern "C" {
+
+  // Debuggers puts a breakpoint in this function.
+  void __attribute__((noinline)) __jit_debug_register_code() { }
+
+  // We put information about the JITed function in this global, which the
+  // debugger reads.  Make sure to specify the version statically, because the
+  // debugger checks the version before we can set it during runtime.
+  struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };
+
+}
+
+namespace {
+
+  /// JITDebugLock - Used to serialize all code registration events, since they
+  /// modify global variables.
+  sys::Mutex JITDebugLock;
+
+}
+
+JITDebugRegisterer::JITDebugRegisterer(TargetMachine &tm) : TM(tm), FnMap() { }
 
 JITDebugRegisterer::~JITDebugRegisterer() {
-  // Clean up all the temporary files.
-  for (std::map<const Function*, sys::Path>::iterator I = FnMap.begin(),

[Jeffrey Yasskin, 2009/07/08 00:40:45]

Almost never use std::map. DenseMap is better.

[Reid Kleckner, 2009/07/08 01:35:05]

On 2009/07/08 00:40:45, Jeffrey Yasskin wrote:
> Almost never use std::map. DenseMap is better.

Done.

-       E = FnMap.end(); I != E; ++I) {
+  // Free all ELF memory.
+  for (RegisteredFunctionsMap::iterator I = FnMap.begin(), E = FnMap.end();
+       I != E; ++I) {
     // Call the private method that doesn't update the map so our iterator
     // doesn't break.
-    _UnregisterFunction(I->first);

[Jeffrey Yasskin, 2009/07/08 00:40:45]

In LLVM, don't start names with '_'+Capital. It strictly causes undefined
behavior (as does "__"+anything). Just make it a private function instead.

[Reid Kleckner, 2009/07/08 01:35:05]

On 2009/07/08 00:40:45, Jeffrey Yasskin wrote:
> In LLVM, don't start names with '_'+Capital. It strictly causes undefined
> behavior (as does "__"+anything). Just make it a private function instead.

Done.

+    UnregisterFunctionInternal(I);
   }
   FnMap.clear();
-  TmpDir.eraseFromDisk();
-}
-
-sys::Path JITDebugRegisterer::MakeFilename(const Function *F,
-                                           uint8_t *FnStart) {
-  std::string Filename;
-  raw_string_ostream O(Filename);
-  // Address first so it's easier to find the right filename when trying to add
-  // the symbol file interactively.
-  O << "llvm_function_" << FnStart << "_" << F->getNameStr() << ".o";
-  O.flush();
-  sys::Path TmpPath(TmpDir);  // Copy path.
-  TmpPath.appendComponent(Filename);
-  return TmpPath;
-}
-
-void JITDebugRegisterer::RegisterFunction(const Function *F, DebugInfo &I) {
-  // Pick the filename for the function.
-  sys::Path Filename = MakeFilename(F, I.FnStart);
-
-  // Add a mapping from F to Filename, so we can delete this function later.
-  FnMap[F] = Filename;
-
-  // Stack allocate an empty module for the ELFWriter API.  We don't use the
-  // real module because then the ELFWriter would write out unnecessary
-  // GlobalValues during finalization.
-  Module M("", getGlobalContext());
-
-  // Open the ELF file.
-  // TODO: Keep the ELF in memory.
-  std::string Error;
-  raw_fd_ostream O(Filename.c_str(), /*Binary=*/ true, Error);
-  if (Error != "") {
-    fprintf(stderr, "Error opening file '%s': %s",
-            Filename.c_str(), Error.c_str());
-    abort();
-  }
+}
+
+std::string JITDebugRegisterer::MakeELF(const Function *F, DebugInfo &I) {
+  // Stack allocate an empty module with an empty LLVMContext for the ELFWriter
+  // API.  We don't use the real module because then the ELFWriter would write
+  // out unnecessary GlobalValues during finalization.
+  LLVMContext Context;
+  Module M("", Context);
+
+  // Make a buffer for the ELF in memory.
+  std::string Buffer;
+  raw_string_ostream O(Buffer);
   ELFWriter EW(O, TM);
   EW.doInitialization(M);
 
   // Copy the binary into the .text section.  This isn't necessary, but it's
   // useful to be able to disassemble the ELF by hand.
-  ELFSection &Text = EW.getTextSection();
+  ELFSection &Text = EW.getTextSection((Function *)F);
   Text.Addr = (uint64_t)I.FnStart;
+  // TODO: We could eliminate this copy if we somehow used a pointer/size pair
+  // instead of a vector.
   Text.getData().assign(I.FnStart, I.FnEnd);
 
   // Copy the exception handling call frame information into the .eh_frame
   // section.  This allows GDB to get a good stack trace, particularly on
   // linux x86_64.  Mark this as a PROGBITS section that needs to be loaded
   // into memory at runtime.
   ELFSection &EH = EW.getSection(".eh_frame", ELFSection::SHT_PROGBITS,
                                  ELFSection::SHF_ALLOC);
   // Pointers in the DWARF EH info are all relative to the EH frame start,
   // which is stored here.
   EH.Addr = (uint64_t)I.EhStart;
+  // TODO: We could eliminate this copy if we somehow used a pointer/size pair
+  // instead of a vector.
   EH.getData().assign(I.EhStart, I.EhEnd);
 
-  // Add this single function to the symbol table, so GDB prints the name
-  // instead of '???'.
-  ELFSym FnSym(F);
-  FnSym.setBind(ELFSym::STB_GLOBAL);  // Make it globally visible.
-  FnSym.setType(ELFSym::STT_FUNC);
-  FnSym.SectionIdx = Text.SectionIdx;
-  FnSym.Size = I.FnEnd - I.FnStart;
-  FnSym.Value = 0;  // Offset from start of section.
+  // Add this single function to the symbol table, so the debugger prints the
+  // name instead of '???'.  We give the symbol default global visibility.
+  ELFSym *FnSym = ELFSym::getGV(F,
+                                ELFSym::STB_GLOBAL,
+                                ELFSym::STT_FUNC,
+                                ELFSym::STV_DEFAULT);
+  FnSym->SectionIdx = Text.SectionIdx;
+  FnSym->Size = I.FnEnd - I.FnStart;
+  FnSym->Value = 0;  // Offset from start of section.
   EW.SymbolList.push_back(FnSym);
 
   EW.doFinalization(M);
-
-  // TODO: Automatically register the ELF with GDB.
-}
-
-void JITDebugRegisterer::_UnregisterFunction(const Function *F) {
-  // It would be nice if we could actually unregister the debug info, but for
-  // now there is no way to undo an add-symbol-file.  However, more the most

[Jeffrey Yasskin, 2009/07/08 00:40:45]

"However, more the most"?

[Reid Kleckner, 2009/07/08 01:35:05]

On 2009/07/08 00:40:45, Jeffrey Yasskin wrote:
> "However, more the most"?

Dropped "more".

-  // recently loaded symbols take precedence, so if we reuse memory for new
-  // machine functions everything should just work.
-
-  // Delete the ELF file.  We don't catch any errors since deleting this temp
-  // file isn't critical.
-  sys::Path &P = FnMap[F];

[Jeffrey Yasskin, 2009/07/08 00:40:45]

Try to avoid using operator[] on maps, since it inserts into the map if the
element isn't there. Use the find() method instead, which returns an iterator.

It looks like _UnregisterFunction should actually take an iterator so that it
doesn't have to look up the function redundantly. I think its callers should be
responsible for ensuring that the iterator isn't FnMap.end().

[Reid Kleckner, 2009/07/08 01:35:05]

On 2009/07/08 00:40:45, Jeffrey Yasskin wrote:
> Try to avoid using operator[] on maps, since it inserts into the map if the
> element isn't there. Use the find() method instead, which returns an iterator.
> 
> It looks like _UnregisterFunction should actually take an iterator so that it
> doesn't have to look up the function redundantly. I think its callers should
be
> responsible for ensuring that the iterator isn't FnMap.end().

Sure.  I made the public method just swallow the error, since it swallows the
other filesystem errors.

-  P.eraseFromDisk();
+  O.flush();
+
+  // When trying to debug this code, it's awfully helpful to write the object
+  // file to disk.
+  std::string Filename;
+  raw_string_ostream O2(Filename);
+  O2 << "/tmp/llvm_function_" << I.FnStart << "_" << F->getNameStr() << ".o";
+  O2.flush();
+  std::string Errors;
+  raw_fd_ostream O3(Filename.c_str(), Errors);
+  O3 << Buffer;
+  O3.close();
+
+  return Buffer;
+}
+
+void JITDebugRegisterer::RegisterFunction(const Function *F, DebugInfo &I) {
+  // TODO: Support non-ELF platforms.
+  if (!TM.getELFWriterInfo())
+    return;
+
+  std::string Buffer = MakeELF(F, I);
+
+  jit_code_entry *JITCodeEntry = new jit_code_entry();
+  JITCodeEntry->symfile_addr = Buffer.c_str();
+  JITCodeEntry->symfile_size = Buffer.size();
+
+  // Add a mapping from F to the entry and buffer, so we can delete this
+  // info later.
+  FnMap[F] = std::make_pair<std::string, jit_code_entry*>(Buffer, JITCodeEntry);
+
+  // Acquire the lock and do the registration.
+  {
+    MutexGuard locked(JITDebugLock);
+    __jit_debug_descriptor.action_flag = JIT_REGISTER_FN;
+
+    // Insert this entry at the head of the list.
+    JITCodeEntry->prev_entry = NULL;
+    jit_code_entry *NextEntry = __jit_debug_descriptor.first_entry;
+    JITCodeEntry->next_entry = NextEntry;
+    if (NextEntry != NULL) {
+      NextEntry->prev_entry = JITCodeEntry;
+    }
+    __jit_debug_descriptor.first_entry = JITCodeEntry;
+    __jit_debug_descriptor.relevant_entry = JITCodeEntry;
+    __jit_debug_register_code();
+  }
+}
+
+void JITDebugRegisterer::UnregisterFunctionInternal(
+    RegisteredFunctionsMap::iterator I) {
+  jit_code_entry *JITCodeEntry = I->second.second;
+
+  // Acquire the lock and do the unregistration.
+  {
+    MutexGuard locked(JITDebugLock);
+    __jit_debug_descriptor.action_flag = JIT_UNREGISTER_FN;
+
+    // Remove the jit_code_entry from the linked list.
+    jit_code_entry *PrevEntry = JITCodeEntry->prev_entry;
+    jit_code_entry *NextEntry = JITCodeEntry->next_entry;
+    if (NextEntry) {
+      NextEntry->prev_entry = PrevEntry;
+    }
+    if (PrevEntry) {
+      PrevEntry->next_entry = NextEntry;
+    } else {
+      assert(__jit_debug_descriptor.first_entry == JITCodeEntry);
+      __jit_debug_descriptor.first_entry = NextEntry;
+    }
+
+    // Tell GDB which entry we removed, and unregister the code.
+    __jit_debug_descriptor.relevant_entry = JITCodeEntry;
+    __jit_debug_register_code();
+  }
+
+  // Free the ELF file in memory.
+  std::string &Buffer = I->second.first;
+  Buffer.clear();
 }
 
 void JITDebugRegisterer::UnregisterFunction(const Function *F) {
-  _UnregisterFunction(F);
-  FnMap.erase(F);
+  // TODO: Support non-ELF platforms.
+  if (!TM.getELFWriterInfo())
+    return;
+
+  RegisteredFunctionsMap::iterator I = FnMap.find(F);
+  if (I == FnMap.end()) return;
+  UnregisterFunctionInternal(I);
+  FnMap.erase(I);
 }
 
 } // end namespace llvm