feat(linker): Phase C dynamic linking — GOT/PLT, CRT objects, PIE emission
Implement Phase C of the internal ELF linker: produce position-independent ET_DYN executables linked against libc through dynamic GOT/PLT dispatch. New capabilities: - SetDynamic(True) switches the linker to PIE mode - AddCrtObject() loads system CRT startup objects (Scrt1.o, crti.o, crtn.o, crtbeginS.o, crtendS.o) - CollectExternals scans undefined non-weak symbols and creates PLT entries - CollectGotSlots creates non-PLT GOT slots for GOTPCREL references to locally-defined symbols (e.g. main, __dso_handle) - BuildDynamic generates .interp, .dynstr, .dynsym, SysV .hash, .got (3 reserved + N PLT + M non-PLT slots), .plt (header + stubs), .rela.plt (JUMP_SLOT entries) - LayoutDynamic assigns PIE virtual addresses (base 0): RO metadata → .text/.plt → RELRO (.init_array, .fini_array, .dynamic, .got) → .data/.bss, with page-aligned PT_LOAD boundaries - EmitDynExecutable writes the full PIE byte image with ELF header, 10 program headers (PHDR, INTERP, 4×LOAD, DYNAMIC, TLS, GNU_STACK, GNU_RELRO), and section data at virtual offsets Relocation handling extended: - R_X86_64_64 → R_X86_64_RELATIVE in .rela.dyn - R_X86_64_32/32S for absolute symbol references - R_X86_64_GOTPCREL/GOTPCRELX/REX_GOTPCRELX → GOT slot lookup - R_X86_64_TPOFF32 → TLS offset calculation Tests: TDynLinkerTests (2 structural), TDynLinkerE2ETests (1 E2E that links a main() calling write via PLT, runs the binary, asserts exit code 42 + correct stdout). All 3528 tests pass.
This commit is contained in:
Graeme Geldenhuys
parent
8f38fd1416
commit
078dc81e46
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@ -76,6 +76,25 @@ type
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procedure TestRun_SyscallHelloWorld;
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end;
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TDynLinkerTests = class(TTestCase)
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private
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function ProjectRoot: string;
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published
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procedure TestDyn_CollectsExternals;
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procedure TestDyn_PieHeaderEmitted;
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end;
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TDynLinkerE2ETests = class(TTestCase)
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private
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FScratch: string;
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function ProjectRoot: string;
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function RunBin(const AExe: string; out AStdout: string): Integer;
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protected
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procedure SetUp; override;
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published
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procedure TestRun_DynHelloWorld;
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end;
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implementation
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function TElfReaderTests.ProjectRoot: string;
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@ -876,10 +895,244 @@ begin
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'Hello, linker!' + Chr(10), Output);
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end;
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{ ---- TDynLinkerTests ---- }
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function TDynLinkerTests.ProjectRoot: string;
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var
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Dir, Parent: string;
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Steps: Integer;
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begin
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Result := GetEnvironmentVariable('BLAISE_PROJECT_ROOT');
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if Result <> '' then
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begin
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Result := IncludeTrailingPathDelimiter(Result);
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Exit;
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end;
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Dir := GetCurrentDir();
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for Steps := 0 to 5 do
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begin
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if DirectoryExists(IncludeTrailingPathDelimiter(Dir) + 'vendor/qbe') and
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DirectoryExists(IncludeTrailingPathDelimiter(Dir) + 'runtime') then
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begin
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Result := IncludeTrailingPathDelimiter(Dir);
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Exit;
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end;
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Parent := ExtractFileDir(Dir);
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if (Parent = '') or (Parent = Dir) then Break;
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Dir := Parent;
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end;
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Result := IncludeTrailingPathDelimiter(GetCurrentDir());
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end;
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procedure TDynLinkerTests.TestDyn_CollectsExternals;
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const
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MainAsm =
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'.text' + LineEnding +
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'.globl main' + LineEnding +
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'main:' + LineEnding +
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' callq write' + LineEnding +
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' xorl %eax, %eax' + LineEnding +
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' ret' + LineEnding;
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var
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Lk: TLinker;
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Obj: TElfObjectFile;
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Bytes: string;
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begin
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Lk := TLinker.Create();
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try
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Lk.SetDynamic(True);
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Obj := ParseElfObject(AssembleToBytes(MainAsm), 'main.o');
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Lk.AddOwnedObject(Obj);
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Bytes := Lk.LinkToBytes('main');
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AssertTrue('output should be non-empty', Length(Bytes) > 64);
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{ e_type at offset 16 must be ET_DYN (3). }
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AssertEquals('e_type ET_DYN', 3,
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(Ord(Bytes[16]) and $FF) or ((Ord(Bytes[17]) and $FF) shl 8));
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finally
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Lk.Free();
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end;
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end;
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procedure TDynLinkerTests.TestDyn_PieHeaderEmitted;
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const
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MainAsm =
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'.text' + LineEnding +
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'.globl main' + LineEnding +
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'main:' + LineEnding +
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' xorl %eax, %eax' + LineEnding +
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' ret' + LineEnding;
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var
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Lk: TLinker;
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Obj: TElfObjectFile;
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Bytes: string;
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PhOff, PhCount, PhEntSz: Integer;
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J, PType: Integer;
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FoundInterp, FoundDynamic: Boolean;
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begin
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Lk := TLinker.Create();
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try
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Lk.SetDynamic(True);
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Obj := ParseElfObject(AssembleToBytes(MainAsm), 'main.o');
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Lk.AddOwnedObject(Obj);
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Bytes := Lk.LinkToBytes('main');
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{ Parse e_phoff (offset 32, 8 bytes LE), e_phentsize (54, 2 bytes),
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e_phnum (56, 2 bytes). }
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PhOff := Ord(Bytes[32]) or (Ord(Bytes[33]) shl 8) or
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(Ord(Bytes[34]) shl 16) or (Ord(Bytes[35]) shl 24);
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PhEntSz := Ord(Bytes[54]) or (Ord(Bytes[55]) shl 8);
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PhCount := Ord(Bytes[56]) or (Ord(Bytes[57]) shl 8);
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AssertTrue('should have at least 4 phdrs', PhCount >= 4);
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AssertEquals('phdr entry size', 56, PhEntSz);
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FoundInterp := False;
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FoundDynamic := False;
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for J := 0 to PhCount - 1 do
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begin
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PType := Ord(Bytes[PhOff + J * PhEntSz]) or
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(Ord(Bytes[PhOff + J * PhEntSz + 1]) shl 8) or
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(Ord(Bytes[PhOff + J * PhEntSz + 2]) shl 16) or
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(Ord(Bytes[PhOff + J * PhEntSz + 3]) shl 24);
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if PType = 3 then FoundInterp := True; { PT_INTERP }
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if PType = 2 then FoundDynamic := True; { PT_DYNAMIC }
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end;
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AssertTrue('PT_INTERP present', FoundInterp);
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AssertTrue('PT_DYNAMIC present', FoundDynamic);
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finally
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Lk.Free();
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end;
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end;
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{ ---- TDynLinkerE2ETests ---- }
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function TDynLinkerE2ETests.ProjectRoot: string;
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var
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Dir, Parent: string;
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Steps: Integer;
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begin
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Result := GetEnvironmentVariable('BLAISE_PROJECT_ROOT');
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if Result <> '' then
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begin
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Result := IncludeTrailingPathDelimiter(Result);
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Exit;
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end;
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Dir := GetCurrentDir();
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for Steps := 0 to 5 do
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begin
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if DirectoryExists(IncludeTrailingPathDelimiter(Dir) + 'vendor/qbe') and
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DirectoryExists(IncludeTrailingPathDelimiter(Dir) + 'runtime') then
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begin
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Result := IncludeTrailingPathDelimiter(Dir);
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Exit;
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end;
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Parent := ExtractFileDir(Dir);
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if (Parent = '') or (Parent = Dir) then Break;
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Dir := Parent;
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end;
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Result := IncludeTrailingPathDelimiter(GetCurrentDir());
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end;
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procedure TDynLinkerE2ETests.SetUp;
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begin
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inherited SetUp();
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FScratch := ProjectRoot() + 'compiler/target/linker-e2e';
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ForceDirectories(FScratch);
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end;
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function TDynLinkerE2ETests.RunBin(const AExe: string;
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out AStdout: string): Integer;
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var
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Proc: TProcess;
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Chunk: string;
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begin
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Proc := TProcess.Create(nil);
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try
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Proc.Executable := AExe;
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Proc.Execute();
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AStdout := '';
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repeat
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Chunk := Proc.ReadOutput();
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AStdout := AStdout + Chunk;
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until (Chunk = '') and not Proc.Running;
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Proc.WaitOnExit();
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Result := Proc.ExitCode;
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finally
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Proc.Free();
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end;
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end;
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procedure TDynLinkerE2ETests.TestRun_DynHelloWorld;
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const
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{ A minimal main() that calls write(1, msg, 15) via PLT and returns 42.
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Scrt1.o provides _start which calls __libc_start_main(main,...). }
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MainAsm =
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'.text' + LineEnding +
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'.globl main' + LineEnding +
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'main:' + LineEnding +
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' subq $8, %rsp' + LineEnding +
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' movl $1, %edi' + LineEnding +
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' leaq msg(%rip), %rsi' + LineEnding +
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' movl $16, %edx' + LineEnding +
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' callq write' + LineEnding +
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' movl $42, %eax' + LineEnding +
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' addq $8, %rsp' + LineEnding +
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' ret' + LineEnding +
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'.section .rodata' + LineEnding +
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'msg:' + LineEnding +
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' .ascii "Hello, dynlink!\n"' + LineEnding;
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var
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Lk: TLinker;
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Obj: TElfObjectFile;
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BinPath, Output: string;
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Rc: Integer;
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Crt1, Crti, Crtn, CrtBegin, CrtEnd: string;
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begin
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BinPath := FScratch + '/hello_dyn';
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{ Locate CRT objects. }
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Crt1 := '/usr/lib/x86_64-linux-gnu/Scrt1.o';
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Crti := '/usr/lib/x86_64-linux-gnu/crti.o';
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Crtn := '/usr/lib/x86_64-linux-gnu/crtn.o';
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CrtBegin := '/usr/lib/gcc/x86_64-linux-gnu/13/crtbeginS.o';
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CrtEnd := '/usr/lib/gcc/x86_64-linux-gnu/13/crtendS.o';
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if not FileExists(Crt1) then
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begin
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{ Try GCC 14. }
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CrtBegin := '/usr/lib/gcc/x86_64-linux-gnu/14/crtbeginS.o';
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CrtEnd := '/usr/lib/gcc/x86_64-linux-gnu/14/crtendS.o';
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end;
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if not FileExists(Crt1) or not FileExists(CrtBegin) then
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Exit;
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Lk := TLinker.Create();
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try
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Lk.SetDynamic(True);
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Lk.AddCrtObject(Crt1);
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Lk.AddCrtObject(Crti);
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Lk.AddCrtObject(CrtBegin);
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Obj := ParseElfObject(AssembleToBytes(MainAsm), 'main.o');
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Lk.AddOwnedObject(Obj);
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Lk.AddCrtObject(CrtEnd);
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Lk.AddCrtObject(Crtn);
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Lk.Link('_start', BinPath);
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finally
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Lk.Free();
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end;
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AssertTrue('linked binary missing', FileExists(BinPath));
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Rc := RunBin(BinPath, Output);
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AssertEquals('exit code', 42, Rc);
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AssertEquals('stdout', 'Hello, dynlink!' + Chr(10), Output);
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end;
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initialization
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RegisterTest(TElfReaderTests);
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RegisterTest(TSectionMergerTests);
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RegisterTest(TLinkerTests);
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RegisterTest(TLinkerE2ETests);
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RegisterTest(TDynLinkerTests);
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RegisterTest(TDynLinkerE2ETests);
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end.
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