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//===-- JITDebugRegisterer.cpp - Register debug symbols for JIT -----------===//
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// The LLVM Compiler Infrastructure
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//===----------------------------------------------------------------------===//
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// This file defines a JITDebugRegisterer object that is used by the JIT to
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// register debug info with debuggers like GDB.
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//===----------------------------------------------------------------------===//
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#include "JITDebugRegisterer.h"
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#include "../../CodeGen/ELF.h"
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#include "../../CodeGen/ELFWriter.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Function.h"
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#include "llvm/Module.h"
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#include "llvm/Target/TargetMachine.h"
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#include "llvm/Target/TargetOptions.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/OwningPtr.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/MutexGuard.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/System/Mutex.h"
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// This must be kept in sync with gdb/gdb/jit.h .
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// Debuggers puts a breakpoint in this function.
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DISABLE_INLINE void __jit_debug_register_code() { }
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// We put information about the JITed function in this global, which the
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// debugger reads. Make sure to specify the version statically, because the
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// debugger checks the version before we can set it during runtime.
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struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };
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/// JITDebugLock - Used to serialize all code registration events, since they
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/// modify global variables.
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sys::Mutex JITDebugLock;
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JITDebugRegisterer::JITDebugRegisterer(TargetMachine &tm) : TM(tm), FnMap() { }
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JITDebugRegisterer::~JITDebugRegisterer() {
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// Free all ELF memory.
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for (RegisteredFunctionsMap::iterator I = FnMap.begin(), E = FnMap.end();
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// Call the private method that doesn't update the map so our iterator
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UnregisterFunctionInternal(I);
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std::string JITDebugRegisterer::MakeELF(const Function *F, DebugInfo &I) {
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// Stack allocate an empty module with an empty LLVMContext for the ELFWriter
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// API. We don't use the real module because then the ELFWriter would write
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// out unnecessary GlobalValues during finalization.
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Module M("", Context);
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// Make a buffer for the ELF in memory.
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raw_string_ostream O(Buffer);
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EW.doInitialization(M);
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// Copy the binary into the .text section. This isn't necessary, but it's
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// useful to be able to disassemble the ELF by hand.
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ELFSection &Text = EW.getTextSection((Function *)F);
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Text.Addr = (uint64_t)I.FnStart;
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// TODO: We could eliminate this copy if we somehow used a pointer/size pair
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// instead of a vector.
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Text.getData().assign(I.FnStart, I.FnEnd);
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// Copy the exception handling call frame information into the .eh_frame
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// section. This allows GDB to get a good stack trace, particularly on
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// linux x86_64. Mark this as a PROGBITS section that needs to be loaded
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// into memory at runtime.
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ELFSection &EH = EW.getSection(".eh_frame", ELFSection::SHT_PROGBITS,
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ELFSection::SHF_ALLOC);
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// Pointers in the DWARF EH info are all relative to the EH frame start,
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// which is stored here.
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EH.Addr = (uint64_t)I.EhStart;
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// TODO: We could eliminate this copy if we somehow used a pointer/size pair
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// instead of a vector.
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EH.getData().assign(I.EhStart, I.EhEnd);
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// Add this single function to the symbol table, so the debugger prints the
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// name instead of '???'. We give the symbol default global visibility.
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ELFSym *FnSym = ELFSym::getGV(F,
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ELFSym::STV_DEFAULT);
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FnSym->SectionIdx = Text.SectionIdx;
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FnSym->Size = I.FnEnd - I.FnStart;
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FnSym->Value = 0; // Offset from start of section.
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EW.SymbolList.push_back(FnSym);
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EW.doFinalization(M);
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// When trying to debug why GDB isn't getting the debug info right, it's
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// awfully helpful to write the object file to disk so that it can be
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// inspected with readelf and objdump.
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if (JITEmitDebugInfoToDisk) {
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std::string Filename;
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raw_string_ostream O2(Filename);
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O2 << "/tmp/llvm_function_" << I.FnStart << "_" << F->getNameStr() << ".o";
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raw_fd_ostream O3(Filename.c_str(), Errors);
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void JITDebugRegisterer::RegisterFunction(const Function *F, DebugInfo &I) {
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// TODO: Support non-ELF platforms.
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if (!TM.getELFWriterInfo())
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std::string Buffer = MakeELF(F, I);
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jit_code_entry *JITCodeEntry = new jit_code_entry();
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JITCodeEntry->symfile_addr = Buffer.c_str();
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JITCodeEntry->symfile_size = Buffer.size();
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// Add a mapping from F to the entry and buffer, so we can delete this
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FnMap[F] = std::make_pair<std::string, jit_code_entry*>(Buffer, JITCodeEntry);
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// Acquire the lock and do the registration.
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MutexGuard locked(JITDebugLock);
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__jit_debug_descriptor.action_flag = JIT_REGISTER_FN;
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// Insert this entry at the head of the list.
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JITCodeEntry->prev_entry = NULL;
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jit_code_entry *NextEntry = __jit_debug_descriptor.first_entry;
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JITCodeEntry->next_entry = NextEntry;
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if (NextEntry != NULL) {
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NextEntry->prev_entry = JITCodeEntry;
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__jit_debug_descriptor.first_entry = JITCodeEntry;
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__jit_debug_descriptor.relevant_entry = JITCodeEntry;
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__jit_debug_register_code();
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void JITDebugRegisterer::UnregisterFunctionInternal(
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RegisteredFunctionsMap::iterator I) {
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jit_code_entry *JITCodeEntry = I->second.second;
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// Acquire the lock and do the unregistration.
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MutexGuard locked(JITDebugLock);
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__jit_debug_descriptor.action_flag = JIT_UNREGISTER_FN;
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// Remove the jit_code_entry from the linked list.
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jit_code_entry *PrevEntry = JITCodeEntry->prev_entry;
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jit_code_entry *NextEntry = JITCodeEntry->next_entry;
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NextEntry->prev_entry = PrevEntry;
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PrevEntry->next_entry = NextEntry;
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assert(__jit_debug_descriptor.first_entry == JITCodeEntry);
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__jit_debug_descriptor.first_entry = NextEntry;
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// Tell GDB which entry we removed, and unregister the code.
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__jit_debug_descriptor.relevant_entry = JITCodeEntry;
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__jit_debug_register_code();
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// Free the ELF file in memory.
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std::string &Buffer = I->second.first;
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void JITDebugRegisterer::UnregisterFunction(const Function *F) {
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// TODO: Support non-ELF platforms.
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if (!TM.getELFWriterInfo())
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RegisteredFunctionsMap::iterator I = FnMap.find(F);
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if (I == FnMap.end()) return;
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UnregisterFunctionInternal(I);
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} // end namespace llvm