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//===-- 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/Target/TargetOptions.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/OwningPtr.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/MutexGuard.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Support/Mutex.h"
#include <string>
namespace llvm {
// This must be kept in sync with gdb/gdb/jit.h .
extern "C" {
// Debuggers puts a breakpoint in this function.
LLVM_ATTRIBUTE_NOINLINE void __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() {
// 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.
UnregisterFunctionInternal(I);
}
FnMap.clear();
}
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(const_cast<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", ELF::SHT_PROGBITS,
ELF::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 the debugger prints the
// name instead of '???'. We give the symbol default global visibility.
ELFSym *FnSym = ELFSym::getGV(F,
ELF::STB_GLOBAL,
ELF::STT_FUNC,
ELF::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);
O.flush();
// When trying to debug why GDB isn't getting the debug info right, it's
// awfully helpful to write the object file to disk so that it can be
// inspected with readelf and objdump.
if (JITEmitDebugInfoToDisk) {
std::string Filename;
raw_string_ostream O2(Filename);
O2 << "/tmp/llvm_function_" << I.FnStart << "_" << F->getName() << ".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(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();
}
delete JITCodeEntry;
JITCodeEntry = NULL;
// Free the ELF file in memory.
std::string &Buffer = I->second.first;
Buffer.clear();
}
void JITDebugRegisterer::UnregisterFunction(const Function *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
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