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https://github.com/c64scene-ar/llvm-6502.git
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feature, either build the JIT in debug mode to enable it by default or pass -jit-emit-debug to lli. Right now, the only debug information that this communicates to GDB is call frame information, since it's already being generated to support exceptions in the JIT. Eventually, when DWARF generation isn't tied so tightly to AsmPrinter, it will be easy to push that information to GDB through this interface. Here's a step-by-step breakdown of how the feature works: - The JIT generates the machine code and DWARF call frame info (.eh_frame/.debug_frame) for a function into memory. - The JIT copies that info into an in-memory ELF file with a symbol for the function. - The JIT creates a code entry pointing to the ELF buffer and adds it to a linked list hanging off of a global descriptor at a special symbol that GDB knows about. - The JIT calls a function marked noinline that GDB knows about and has put an internal breakpoint in. - GDB catches the breakpoint and reads the global descriptor to look for new code. - When sees there is new code, it reads the ELF from the inferior's memory and adds it to itself as an object file. - The JIT continues, and the next time we stop the program, we are able to produce a proper backtrace. Consider running the following program through the JIT: #include <stdio.h> void baz(short z) { long w = z + 1; printf("%d, %x\n", w, *((int*)NULL)); // SEGFAULT here } void bar(short y) { int z = y + 1; baz(z); } void foo(char x) { short y = x + 1; bar(y); } int main(int argc, char** argv) { char x = 1; foo(x); } Here is a backtrace before this patch: Program received signal SIGSEGV, Segmentation fault. [Switching to Thread 0x2aaaabdfbd10 (LWP 25476)] 0x00002aaaabe7d1a8 in ?? () (gdb) bt #0 0x00002aaaabe7d1a8 in ?? () #1 0x0000000000000003 in ?? () #2 0x0000000000000004 in ?? () #3 0x00032aaaabe7cfd0 in ?? () #4 0x00002aaaabe7d12c in ?? () #5 0x00022aaa00000003 in ?? () #6 0x00002aaaabe7d0aa in ?? () #7 0x01000002abe7cff0 in ?? () #8 0x00002aaaabe7d02c in ?? () #9 0x0100000000000001 in ?? () #10 0x00000000014388e0 in ?? () #11 0x00007fff00000001 in ?? () #12 0x0000000000b870a2 in llvm::JIT::runFunction (this=0x1405b70, F=0x14024e0, ArgValues=@0x7fffffffe050) at /home/rnk/llvm-gdb/lib/ExecutionEngine/JIT/JIT.cpp:395 #13 0x0000000000baa4c5 in llvm::ExecutionEngine::runFunctionAsMain (this=0x1405b70, Fn=0x14024e0, argv=@0x13f06f8, envp=0x7fffffffe3b0) at /home/rnk/llvm-gdb/lib/ExecutionEngine/ExecutionEngine.cpp:377 #14 0x00000000007ebd52 in main (argc=2, argv=0x7fffffffe398, envp=0x7fffffffe3b0) at /home/rnk/llvm-gdb/tools/lli/lli.cpp:208 And a backtrace after this patch: Program received signal SIGSEGV, Segmentation fault. 0x00002aaaabe7d1a8 in baz () (gdb) bt #0 0x00002aaaabe7d1a8 in baz () #1 0x00002aaaabe7d12c in bar () #2 0x00002aaaabe7d0aa in foo () #3 0x00002aaaabe7d02c in main () #4 0x0000000000b870a2 in llvm::JIT::runFunction (this=0x1405b70, F=0x14024e0, ArgValues=...) at /home/rnk/llvm-gdb/lib/ExecutionEngine/JIT/JIT.cpp:395 #5 0x0000000000baa4c5 in llvm::ExecutionEngine::runFunctionAsMain (this=0x1405b70, Fn=0x14024e0, argv=..., envp=0x7fffffffe3c0) at /home/rnk/llvm-gdb/lib/ExecutionEngine/ExecutionEngine.cpp:377 #6 0x00000000007ebd52 in main (argc=2, argv=0x7fffffffe3a8, envp=0x7fffffffe3c0) at /home/rnk/llvm-gdb/tools/lli/lli.cpp:208 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82418 91177308-0d34-0410-b5e6-96231b3b80d8
251 lines
9.4 KiB
C++
251 lines
9.4 KiB
C++
//===-- ELFWriter.h - Target-independent ELF writer support -----*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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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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//===----------------------------------------------------------------------===//
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//
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// This file defines the ELFWriter class.
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//
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//===----------------------------------------------------------------------===//
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#ifndef ELFWRITER_H
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#define ELFWRITER_H
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#include "llvm/ADT/SetVector.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include <map>
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namespace llvm {
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class BinaryObject;
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class Constant;
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class ConstantInt;
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class ConstantStruct;
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class ELFCodeEmitter;
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class ELFRelocation;
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class ELFSection;
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struct ELFSym;
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class GlobalVariable;
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class JITDebugRegisterer;
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class Mangler;
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class MachineCodeEmitter;
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class MachineConstantPoolEntry;
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class ObjectCodeEmitter;
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class MCAsmInfo;
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class TargetELFWriterInfo;
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class TargetLoweringObjectFile;
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class raw_ostream;
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class SectionKind;
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class MCContext;
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typedef std::vector<ELFSym*>::iterator ELFSymIter;
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typedef std::vector<ELFSection*>::iterator ELFSectionIter;
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typedef SetVector<const GlobalValue*>::const_iterator PendingGblsIter;
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typedef SetVector<const char *>::const_iterator PendingExtsIter;
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typedef std::pair<const Constant *, int64_t> CstExprResTy;
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/// ELFWriter - This class implements the common target-independent code for
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/// writing ELF files. Targets should derive a class from this to
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/// parameterize the output format.
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///
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class ELFWriter : public MachineFunctionPass {
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friend class ELFCodeEmitter;
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friend class JITDebugRegisterer;
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public:
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static char ID;
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/// Return the ELFCodeEmitter as an instance of ObjectCodeEmitter
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ObjectCodeEmitter *getObjectCodeEmitter() {
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return reinterpret_cast<ObjectCodeEmitter*>(ElfCE);
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}
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ELFWriter(raw_ostream &O, TargetMachine &TM);
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~ELFWriter();
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protected:
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/// Output stream to send the resultant object file to.
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raw_ostream &O;
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/// Target machine description.
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TargetMachine &TM;
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/// Context object for machine code objects.
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MCContext &OutContext;
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/// Target Elf Writer description.
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const TargetELFWriterInfo *TEW;
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/// Mang - The object used to perform name mangling for this module.
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Mangler *Mang;
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/// MCE - The MachineCodeEmitter object that we are exposing to emit machine
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/// code for functions to the .o file.
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ELFCodeEmitter *ElfCE;
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/// TLOF - Target Lowering Object File, provide section names for globals
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/// and other object file specific stuff
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const TargetLoweringObjectFile &TLOF;
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/// MAI - Target Asm Info, provide information about section names for
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/// globals and other target specific stuff.
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const MCAsmInfo *MAI;
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//===------------------------------------------------------------------===//
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// Properties inferred automatically from the target machine.
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//===------------------------------------------------------------------===//
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/// is64Bit/isLittleEndian - This information is inferred from the target
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/// machine directly, indicating whether to emit a 32- or 64-bit ELF file.
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bool is64Bit, isLittleEndian;
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/// doInitialization - Emit the file header and all of the global variables
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/// for the module to the ELF file.
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bool doInitialization(Module &M);
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bool runOnMachineFunction(MachineFunction &MF);
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/// doFinalization - Now that the module has been completely processed, emit
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/// the ELF file to 'O'.
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bool doFinalization(Module &M);
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private:
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/// Blob containing the Elf header
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BinaryObject ElfHdr;
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/// SectionList - This is the list of sections that we have emitted to the
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/// file. Once the file has been completely built, the section header table
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/// is constructed from this info.
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std::vector<ELFSection*> SectionList;
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unsigned NumSections; // Always = SectionList.size()
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/// SectionLookup - This is a mapping from section name to section number in
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/// the SectionList. Used to quickly gather the Section Index from MAI names
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std::map<std::string, ELFSection*> SectionLookup;
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/// PendingGlobals - Globals not processed as symbols yet.
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SetVector<const GlobalValue*> PendingGlobals;
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/// GblSymLookup - This is a mapping from global value to a symbol index
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/// in the symbol table or private symbols list. This is useful since reloc
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/// symbol references must be quickly mapped to their indices on the lists.
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std::map<const GlobalValue*, uint32_t> GblSymLookup;
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/// PendingExternals - Externals not processed as symbols yet.
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SetVector<const char *> PendingExternals;
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/// ExtSymLookup - This is a mapping from externals to a symbol index
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/// in the symbol table list. This is useful since reloc symbol references
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/// must be quickly mapped to their symbol table indices.
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std::map<const char *, uint32_t> ExtSymLookup;
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/// SymbolList - This is the list of symbols emitted to the symbol table.
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/// When the SymbolList is finally built, local symbols must be placed in
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/// the beginning while non-locals at the end.
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std::vector<ELFSym*> SymbolList;
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/// PrivateSyms - Record private symbols, every symbol here must never be
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/// present in the SymbolList.
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std::vector<ELFSym*> PrivateSyms;
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/// getSection - Return the section with the specified name, creating a new
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/// section if one does not already exist.
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ELFSection &getSection(const std::string &Name, unsigned Type,
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unsigned Flags = 0, unsigned Align = 0) {
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ELFSection *&SN = SectionLookup[Name];
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if (SN) return *SN;
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SectionList.push_back(new ELFSection(Name, isLittleEndian, is64Bit));
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SN = SectionList.back();
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SN->SectionIdx = NumSections++;
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SN->Type = Type;
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SN->Flags = Flags;
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SN->Link = ELFSection::SHN_UNDEF;
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SN->Align = Align;
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return *SN;
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}
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ELFSection &getNonExecStackSection() {
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return getSection(".note.GNU-stack", ELFSection::SHT_PROGBITS, 0, 1);
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}
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ELFSection &getSymbolTableSection() {
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return getSection(".symtab", ELFSection::SHT_SYMTAB, 0);
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}
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ELFSection &getStringTableSection() {
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return getSection(".strtab", ELFSection::SHT_STRTAB, 0, 1);
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}
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ELFSection &getSectionHeaderStringTableSection() {
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return getSection(".shstrtab", ELFSection::SHT_STRTAB, 0, 1);
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}
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ELFSection &getNullSection() {
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return getSection("", ELFSection::SHT_NULL, 0);
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}
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ELFSection &getDataSection();
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ELFSection &getBSSSection();
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ELFSection &getCtorSection();
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ELFSection &getDtorSection();
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ELFSection &getJumpTableSection();
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ELFSection &getConstantPoolSection(MachineConstantPoolEntry &CPE);
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ELFSection &getTextSection(Function *F);
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ELFSection &getRelocSection(ELFSection &S);
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// Helpers for obtaining ELF specific info.
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unsigned getGlobalELFBinding(const GlobalValue *GV);
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unsigned getGlobalELFType(const GlobalValue *GV);
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unsigned getGlobalELFVisibility(const GlobalValue *GV);
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// AddPendingGlobalSymbol - Add a global to be processed and to
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// the global symbol lookup, use a zero index because the table
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// index will be determined later.
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void AddPendingGlobalSymbol(const GlobalValue *GV,
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bool AddToLookup = false);
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// AddPendingExternalSymbol - Add the external to be processed
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// and to the external symbol lookup, use a zero index because
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// the symbol table index will be determined later.
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void AddPendingExternalSymbol(const char *External);
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// AddToSymbolList - Update the symbol lookup and If the symbol is
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// private add it to PrivateSyms list, otherwise to SymbolList.
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void AddToSymbolList(ELFSym *GblSym);
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// As we complete the ELF file, we need to update fields in the ELF header
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// (e.g. the location of the section table). These members keep track of
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// the offset in ELFHeader of these various pieces to update and other
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// locations in the file.
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unsigned ELFHdr_e_shoff_Offset; // e_shoff in ELF header.
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unsigned ELFHdr_e_shstrndx_Offset; // e_shstrndx in ELF header.
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unsigned ELFHdr_e_shnum_Offset; // e_shnum in ELF header.
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private:
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void EmitGlobal(const GlobalValue *GV);
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void EmitGlobalConstant(const Constant *C, ELFSection &GblS);
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void EmitGlobalConstantStruct(const ConstantStruct *CVS,
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ELFSection &GblS);
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void EmitGlobalConstantLargeInt(const ConstantInt *CI, ELFSection &S);
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void EmitGlobalDataRelocation(const GlobalValue *GV, unsigned Size,
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ELFSection &GblS, int64_t Offset = 0);
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bool EmitSpecialLLVMGlobal(const GlobalVariable *GV);
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void EmitXXStructorList(Constant *List, ELFSection &Xtor);
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void EmitRelocations();
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void EmitRelocation(BinaryObject &RelSec, ELFRelocation &Rel, bool HasRelA);
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void EmitSectionHeader(BinaryObject &SHdrTab, const ELFSection &SHdr);
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void EmitSectionTableStringTable();
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void EmitSymbol(BinaryObject &SymbolTable, ELFSym &Sym);
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void EmitSymbolTable();
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void EmitStringTable(const std::string &ModuleName);
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void OutputSectionsAndSectionTable();
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void RelocateField(BinaryObject &BO, uint32_t Offset, int64_t Value,
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unsigned Size);
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unsigned SortSymbols();
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CstExprResTy ResolveConstantExpr(const Constant *CV);
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};
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}
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#endif
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