Add gdb-object-file-libc.go
This commit is contained in:
parent
eaa1125b7c
commit
3759a0bd14
GPG Key ID:
B715679E3A361BE6
685
gdb-object-file-libc.go
Normal file
685
gdb-object-file-libc.go
Normal file
@ -0,0 +1,685 @@
|
||||
// Non-optimizing Brainfuck compiler generating object files for *nix on x86-64
|
||||
// with debugging information mapping instructions onto an IR dump.
|
||||
// gofmt has been tried, with disappointing results.
|
||||
// codegen{} is also pretty ugly in the way it works but damn convenient.
|
||||
package main
|
||||
|
||||
import (
|
||||
"encoding/binary"
|
||||
"errors"
|
||||
"fmt"
|
||||
"io/ioutil"
|
||||
"log"
|
||||
"os"
|
||||
"strconv"
|
||||
|
||||
// Let's not repeat all those constants here onstants
|
||||
"debug/dwarf"
|
||||
"debug/elf"
|
||||
)
|
||||
|
||||
const ( RIGHT = iota; LEFT; INC; DEC; IN; OUT; BEGIN; END )
|
||||
|
||||
var info = []struct {
|
||||
grouped bool
|
||||
name string
|
||||
}{
|
||||
{true, "RIGHT"},
|
||||
{true, "LEFT"},
|
||||
{true, "INC"},
|
||||
{true, "DEC"},
|
||||
{false, "IN"},
|
||||
{false, "OUT"},
|
||||
{false, "BEGIN"},
|
||||
{false, "END"},
|
||||
}
|
||||
|
||||
type instruction struct {
|
||||
command int
|
||||
arg int
|
||||
}
|
||||
|
||||
// Dump internal representation to a file for debugging purposes
|
||||
func dump(filename string, irb []instruction) error {
|
||||
out, err := os.Create(filename)
|
||||
if err != nil {
|
||||
return err
|
||||
}
|
||||
|
||||
indent := 0
|
||||
for _, x := range irb {
|
||||
if x.command == END {
|
||||
indent--
|
||||
}
|
||||
for i := 0; i < indent; i++ {
|
||||
out.WriteString(" ")
|
||||
}
|
||||
out.WriteString(info[x.command].name)
|
||||
if info[x.command].grouped {
|
||||
fmt.Fprintf(out, " %d", x.arg)
|
||||
}
|
||||
out.WriteString("\n")
|
||||
if x.command == BEGIN {
|
||||
indent++
|
||||
}
|
||||
}
|
||||
if err = out.Close(); err != nil {
|
||||
return err
|
||||
}
|
||||
return nil
|
||||
}
|
||||
|
||||
// Decode a Brainfuck program into internal representation,
|
||||
// coalescing identical commands together as the most basic optimization
|
||||
func decode(program []byte) (irb []instruction) {
|
||||
for _, c := range program {
|
||||
var command int
|
||||
switch c {
|
||||
case '>': command = RIGHT
|
||||
case '<': command = LEFT
|
||||
case '+': command = INC
|
||||
case '-': command = DEC
|
||||
case '.': command = OUT
|
||||
case ',': command = IN
|
||||
case '[': command = BEGIN
|
||||
case ']': command = END
|
||||
default: continue
|
||||
}
|
||||
|
||||
if len(irb) == 0 || !info[command].grouped ||
|
||||
irb[len(irb)-1].command != command {
|
||||
irb = append(irb, instruction{command, 1})
|
||||
} else {
|
||||
irb[len(irb)-1].arg++
|
||||
}
|
||||
}
|
||||
return
|
||||
}
|
||||
|
||||
// Match loop commands so that we know where to jump
|
||||
func pairLoops(irb []instruction) error {
|
||||
nesting := 0
|
||||
stack := make([]int, len(irb))
|
||||
for i, x := range irb {
|
||||
switch x.command {
|
||||
case BEGIN:
|
||||
stack[nesting] = i
|
||||
nesting++
|
||||
case END:
|
||||
if nesting <= 0 {
|
||||
return errors.New("unbalanced loops")
|
||||
}
|
||||
nesting--
|
||||
irb[stack[nesting]].arg = i + 1
|
||||
irb[i].arg = stack[nesting] + 1
|
||||
}
|
||||
}
|
||||
if nesting != 0 {
|
||||
return errors.New("unbalanced loops")
|
||||
}
|
||||
return nil
|
||||
}
|
||||
|
||||
// --- Code generation ---------------------------------------------------------
|
||||
|
||||
type codegen struct {
|
||||
buf []byte
|
||||
}
|
||||
|
||||
// Convert an arbitrary integral value up to 8 bytes long to little endian
|
||||
func le(unknown interface{}) []byte {
|
||||
// Trying hard to avoid reflect.Value.Int/Uint
|
||||
formatted := fmt.Sprintf("%d", unknown)
|
||||
|
||||
b := make([]byte, 8)
|
||||
if unsigned, err := strconv.ParseUint(formatted, 10, 64); err == nil {
|
||||
binary.LittleEndian.PutUint64(b, unsigned)
|
||||
} else if signed, err := strconv.ParseInt(formatted, 10, 64); err == nil {
|
||||
binary.LittleEndian.PutUint64(b, uint64(signed))
|
||||
} else {
|
||||
panic("cannot convert to number")
|
||||
}
|
||||
return b
|
||||
}
|
||||
|
||||
func (a *codegen) append(v []byte) { a.buf = append(a.buf, v...) }
|
||||
func (a *codegen) code(v string) *codegen { a.append([]byte(v)); return a }
|
||||
func (a *codegen) db(v interface{}) *codegen { a.append(le(v)[:1]); return a }
|
||||
func (a *codegen) dw(v interface{}) *codegen { a.append(le(v)[:2]); return a }
|
||||
func (a *codegen) dd(v interface{}) *codegen { a.append(le(v)[:4]); return a }
|
||||
func (a *codegen) dq(v interface{}) *codegen { a.append(le(v)[:8]); return a }
|
||||
|
||||
type fixup struct { offset, addend int; typ uint32; }
|
||||
|
||||
// The linker may _add_ to offsets even with explicit addends (.rela)
|
||||
func codegenAmd64(irb []instruction) (code []byte, offsets []int,
|
||||
fixups map[string][]fixup) {
|
||||
offsets = make([]int, len(irb)+1)
|
||||
a := codegen{}
|
||||
|
||||
fixups = map[string][]fixup{}
|
||||
abs := func(name string) {
|
||||
fixups[name] = append(fixups[name],
|
||||
fixup{len(a.buf), 0, uint32(elf.R_X86_64_32)})
|
||||
a.dd(0)
|
||||
}
|
||||
call := func(name string) {
|
||||
a.code("\xE8")
|
||||
fixups[name] = append(fixups[name],
|
||||
fixup{len(a.buf), -4, uint32(elf.R_X86_64_PC32)})
|
||||
a.dd(0)
|
||||
}
|
||||
|
||||
a.code("\xB8"); abs("tape") // mov rax, "tape"
|
||||
a.code("\x30\xDB") // xor bl, bl
|
||||
|
||||
for i, x := range irb {
|
||||
offsets[i] = len(a.buf)
|
||||
if x.command == LEFT || x.command == RIGHT {
|
||||
a.code("\x88\x18") // mov [rax], bl
|
||||
}
|
||||
switch x.command {
|
||||
case RIGHT: a.code("\x48\x05").dd(x.arg) // add rax, "arg"
|
||||
case LEFT: a.code("\x48\x2D").dd(x.arg) // sub rax, "arg"
|
||||
case INC: a.code("\x80\xC3").db(x.arg) // add bl, "arg"
|
||||
case DEC: a.code("\x80\xEB").db(x.arg) // sub bl, "arg"
|
||||
case OUT: a.code("\xE8").dd(0) // call "write"
|
||||
case IN: a.code("\xE8").dd(0) // call "read"
|
||||
case BEGIN:
|
||||
// test bl, bl; jz "offsets[arg]"
|
||||
a.code("\x84\xDB" + "\x0F\x84").dd(0)
|
||||
case END:
|
||||
// test bl, bl; jnz "offsets[arg]"
|
||||
a.code("\x84\xDB" + "\x0F\x85").dd(0)
|
||||
}
|
||||
if x.command == LEFT || x.command == RIGHT {
|
||||
a.code("\x8A\x18") // mov bl, [rax]
|
||||
}
|
||||
}
|
||||
// When there is a loop at the end we need to be able to jump past it
|
||||
offsets[len(irb)] = len(a.buf)
|
||||
|
||||
// Write an epilog which handles all the OS interfacing
|
||||
//
|
||||
// System V x86-64 ABI:
|
||||
// rax <-> both syscall number and return value
|
||||
// args -> rdi, rsi, rdx, r10, r8, r9
|
||||
// trashed <- rcx, r11
|
||||
|
||||
a.code("\x48\x31\xFF") // xor rdi, rdi
|
||||
call("exit") // call [exit]
|
||||
|
||||
read := len(a.buf)
|
||||
a.code("\x50") // push rax -- save tape position
|
||||
call("getchar") // call [getchar]
|
||||
a.code("\x88\xC3") // mov bl, al
|
||||
|
||||
a.code("\x83\xF8\x00") // cmp eax, 0
|
||||
a.code("\x7D").db(2) // jge over the next instruction
|
||||
a.code("\xB3\x00") // mov bl, 0 -- translate EOF to 0
|
||||
a.code("\x58") // pop rax -- restore tape position
|
||||
a.code("\xC3") // ret
|
||||
|
||||
write := len(a.buf)
|
||||
a.code("\x50") // push rax -- save tape position
|
||||
a.code("\x66\x53") // push bx
|
||||
a.code("\x48\x0F\xB6\xFB") // movzx rdi, bl
|
||||
call("putchar") // call [putchar]
|
||||
a.code("\x66\x5B") // pop bx
|
||||
|
||||
a.code("\x83\xF8\x00") // cmp eax, 0
|
||||
a.code("\x7C").db(2) // jl over the return
|
||||
a.code("\x58") // pop rax -- restore tape position
|
||||
a.code("\xC3") // ret
|
||||
|
||||
a.code("\x48\x8b\x34\x25") // mov rsi, ["stderr"]
|
||||
abs("stderr")
|
||||
a.code("\x8D\x3D").dd(15) // lea edi, [rel write_message]
|
||||
call("fputs") // call [fputs]
|
||||
a.code("\xBF").dd(1) // mov edi, "EXIT_FAILURE"
|
||||
call("exit") // call [exit]
|
||||
a.code("fatal: write failed\n\x00")
|
||||
|
||||
// Now that we know where each instruction is, fill in relative jumps
|
||||
for i, x := range irb {
|
||||
// This must accurately reflect the code generators
|
||||
target, fixup := 0, offsets[i]
|
||||
if x.command == BEGIN || x.command == END {
|
||||
fixup += 4
|
||||
target = offsets[x.arg]
|
||||
} else if x.command == IN {
|
||||
fixup += 1
|
||||
target = read
|
||||
} else if x.command == OUT {
|
||||
fixup += 1
|
||||
target = write
|
||||
} else {
|
||||
continue
|
||||
}
|
||||
copy(a.buf[fixup:], le(target - fixup - 4)[:4])
|
||||
}
|
||||
return a.buf, offsets, fixups
|
||||
}
|
||||
|
||||
// --- Main --------------------------------------------------------------------
|
||||
|
||||
func main() {
|
||||
var err error
|
||||
if len(os.Args) > 3 {
|
||||
log.Fatalf("usage: %s [INPUT-FILE] [OUTPUT-FILE]", os.Args[0])
|
||||
}
|
||||
|
||||
input := os.Stdin
|
||||
if len(os.Args) > 1 {
|
||||
if input, err = os.Open(os.Args[1]); err != nil {
|
||||
log.Fatalf("%s", err)
|
||||
}
|
||||
}
|
||||
|
||||
outputPath := "a.out"
|
||||
if len(os.Args) > 2 {
|
||||
outputPath = os.Args[2]
|
||||
}
|
||||
|
||||
program, err := ioutil.ReadAll(input)
|
||||
input.Close()
|
||||
if err != nil {
|
||||
log.Fatalf("can't read program: %s", err)
|
||||
}
|
||||
|
||||
irb := decode(program)
|
||||
// ... various optimizations could be performed here if we give up brevity
|
||||
pairLoops(irb)
|
||||
dump("ir-dump.txt", irb)
|
||||
code, offsets, fixups := codegenAmd64(irb)
|
||||
|
||||
// - - ELF generation - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
// Now that we know how long the machine code is, we can write the header.
|
||||
// Note that for PIE we would need to depend on the dynamic linker, so no.
|
||||
//
|
||||
// Recommended reading:
|
||||
// http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html
|
||||
// man 5 elf
|
||||
//
|
||||
// In case of unexpected gdb problems, also see:
|
||||
// DWARF4.pdf
|
||||
// https://sourceware.org/elfutils/DwarfLint
|
||||
// http://wiki.osdev.org/DWARF
|
||||
|
||||
const (
|
||||
ElfHeaderSize = 64 // Size of the ELF header
|
||||
ElfProgramEntrySize = 56 // Size of a program header
|
||||
ElfSectionEntrySize = 64 // Size of a section header
|
||||
ElfDataSize = 1 << 20 // Tape length
|
||||
)
|
||||
|
||||
codeOffset := ElfHeaderSize
|
||||
pieces := [][]byte{code}
|
||||
position := codeOffset + len(code)
|
||||
|
||||
// - - Sections - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
sh := codegen{}
|
||||
shCount := 0
|
||||
|
||||
// This section is created on the go as we need to name other sections
|
||||
stringTable := codegen{}
|
||||
|
||||
// A null section is needed by several GNU tools
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code("\x00")
|
||||
sh.dd(elf.SHT_NULL).dq(0).dq(0) // Type, no flags, no memory address
|
||||
sh.dq(0).dq(0) // Byte offset, byte size
|
||||
sh.dd(0).dd(0) // No link, no info
|
||||
sh.dq(0).dq(0) // No alignment, no entry size
|
||||
shCount++
|
||||
|
||||
// - - Text - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".text\x00")
|
||||
sh.dd(elf.SHT_PROGBITS)
|
||||
sh.dq(elf.SHF_ALLOC | elf.SHF_EXECINSTR)
|
||||
sh.dq(0) // Memory address
|
||||
sh.dq(codeOffset) // Byte offset
|
||||
sh.dq(len(code)) // Byte size
|
||||
sh.dd(0).dd(0) // No link, no info
|
||||
sh.dq(0).dq(0) // No alignment, no entry size
|
||||
shTextIndex := shCount
|
||||
shCount++
|
||||
|
||||
// - - BSS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".bss\x00")
|
||||
sh.dd(elf.SHT_NOBITS)
|
||||
sh.dq(elf.SHF_ALLOC | elf.SHF_WRITE)
|
||||
sh.dq(0) // Memory address
|
||||
sh.dq(0) // Byte offset
|
||||
sh.dq(ElfDataSize) // Byte size
|
||||
sh.dd(0).dd(0) // No link, no info
|
||||
sh.dq(0).dq(0) // No alignment, no entry size
|
||||
shBSSIndex := shCount
|
||||
shCount++
|
||||
|
||||
// - - Symbol table - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
symtab := codegen{}
|
||||
symstrtab := codegen{}
|
||||
|
||||
// A null symbol is needed by several GNU tools
|
||||
|
||||
symtab.dd(len(symstrtab.buf)) // Index for symbol name
|
||||
symstrtab.code("\x00")
|
||||
symtab.db(elf.ST_INFO(elf.STB_LOCAL, elf.STT_NOTYPE))
|
||||
symtab.db(elf.STV_DEFAULT) // Default visibility rules
|
||||
symtab.dw(0).dq(0).dq(0) // No section, no offset, no length
|
||||
|
||||
symbols := map[string]uint32{}
|
||||
nextSymbol := uint32(1)
|
||||
nameSymbol := func(name string) {
|
||||
symtab.dd(len(symstrtab.buf))
|
||||
symstrtab.code(name).code("\x00")
|
||||
symbols[name] = nextSymbol
|
||||
nextSymbol++
|
||||
}
|
||||
|
||||
nameSymbol("tape")
|
||||
symtab.db(elf.ST_INFO(elf.STB_LOCAL, elf.STT_OBJECT))
|
||||
symtab.db(elf.STV_DEFAULT) // Default visibility rules
|
||||
symtab.dw(shBSSIndex) // Relative to section .bss
|
||||
symtab.dq(0) // Right at the start of BSS
|
||||
symtab.dq(ElfDataSize) // Span the entire section
|
||||
|
||||
// It can't be _start since that is already defined somewhere in libc
|
||||
// and we'd like CC to figure out where the dynamic linker is at least
|
||||
nameSymbol("main")
|
||||
symtab.db(elf.ST_INFO(elf.STB_GLOBAL, elf.STT_FUNC))
|
||||
symtab.db(elf.STV_DEFAULT) // Default visibility rules
|
||||
symtab.dw(shTextIndex) // Relative to section .text
|
||||
symtab.dq(0) // Right at the start of code
|
||||
symtab.dq(len(code)) // Span the entire section
|
||||
|
||||
// Create records for undefined symbols to be resolved by the linker
|
||||
for k, _ := range fixups {
|
||||
if _, ok := symbols[k]; ok {
|
||||
continue
|
||||
}
|
||||
nameSymbol(k)
|
||||
symtab.db(elf.ST_INFO(elf.STB_GLOBAL, elf.STT_NOTYPE))
|
||||
symtab.db(elf.STV_DEFAULT) // Default visibility rules
|
||||
symtab.dw(0).dq(0).dq(0) // No section, no offset, no length
|
||||
}
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".symstrtab\x00")
|
||||
sh.dd(elf.SHT_STRTAB).dq(0).dq(0) // Type, no flags, no memory address
|
||||
sh.dq(position) // Byte offset
|
||||
sh.dq(len(symstrtab.buf)) // Byte size
|
||||
sh.dd(0).dd(0) // No link, no info
|
||||
sh.dq(0).dq(0) // No alignment, no entry size
|
||||
shSymstrtabIndex := shCount
|
||||
shCount++
|
||||
|
||||
pieces = append(pieces, symstrtab.buf)
|
||||
position += len(symstrtab.buf)
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".symtab\x00")
|
||||
sh.dd(elf.SHT_SYMTAB).dq(0).dq(0) // Type, no flags, no memory address
|
||||
sh.dq(position) // Byte offset
|
||||
sh.dq(len(symtab.buf)) // Byte size
|
||||
sh.dd(shSymstrtabIndex).dd(2) // Link, info: index of first non-local
|
||||
sh.dq(0).dq(24) // No alignment, entry size
|
||||
shSymtabIndex := shCount
|
||||
shCount++
|
||||
|
||||
pieces = append(pieces, symtab.buf)
|
||||
position += len(symtab.buf)
|
||||
|
||||
// - - Text relocation records - - - - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
// ld.gold doesn't support SHT_REL, with SHT_RELA it overrides the target.
|
||||
// ld.bfd addends to the target even with SHT_RELA.
|
||||
// Thus, with SHT_RELA the target needs to be all zeros to be portable.
|
||||
|
||||
textRel := codegen{}
|
||||
for k, v := range fixups {
|
||||
for _, r := range v {
|
||||
textRel.dq(r.offset).dq(elf.R_INFO(symbols[k], r.typ)).dq(r.addend)
|
||||
}
|
||||
}
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".rela.text\x00")
|
||||
sh.dd(elf.SHT_RELA) // Type
|
||||
sh.dq(elf.SHF_INFO_LINK).dq(0) // Flags, no memory address
|
||||
sh.dq(position) // Byte offset
|
||||
sh.dq(len(textRel.buf)) // Byte size
|
||||
sh.dd(shSymtabIndex).dd(shTextIndex)// Link, info
|
||||
sh.dq(0).dq(24) // No alignment, entry size
|
||||
shCount++
|
||||
|
||||
pieces = append(pieces, textRel.buf)
|
||||
position += len(textRel.buf)
|
||||
|
||||
// - - Debug line - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
const (
|
||||
opcodeBase = 13 // Offset by DWARF4 standard opcodes
|
||||
lineBase = 0 // We don't need negative line indexes
|
||||
lineRange = 2 // Either we advance a line or not (we always do)
|
||||
)
|
||||
|
||||
// FIXME: we use db() a lot instead of a proper un/signed LEB128 encoder;
|
||||
// that means that values > 127/63 or < 0 would break it;
|
||||
// see Appendix C to DWARF4.pdf for an algorithm
|
||||
|
||||
lineProgram := codegen{}
|
||||
// Extended opcode DW_LNE_set_address to reset the PC to the start of code
|
||||
lineProgram.db(0).db(1 + 8).db(2)
|
||||
lineAddressOff := len(lineProgram.buf)
|
||||
lineProgram.dq(0)
|
||||
if len(irb) > 0 {
|
||||
lineProgram.db(opcodeBase + offsets[0] * lineRange)
|
||||
}
|
||||
// The epilog, which is at the very end of the offset array, is included
|
||||
for i := 1; i <= len(irb); i++ {
|
||||
size := offsets[i] - offsets[i - 1]
|
||||
lineProgram.db(opcodeBase + (1 - lineBase) + size * lineRange)
|
||||
}
|
||||
// Extended opcode DW_LNE_end_sequence is mandatory at the end
|
||||
lineProgram.db(0).db(1).db(1)
|
||||
|
||||
lineHeader := codegen{}
|
||||
lineHeader.db(1) // Minimum instruction length
|
||||
lineHeader.db(1) // Maximum operations per instruction
|
||||
lineHeader.db(1) // default_is_stmt
|
||||
lineHeader.db(lineBase)
|
||||
lineHeader.db(lineRange)
|
||||
|
||||
lineHeader.db(opcodeBase)
|
||||
// Number of operands for all standard opcodes (1..opcodeBase-1)
|
||||
opcodeLengths := []byte{0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1}
|
||||
lineHeader.buf = append(lineHeader.buf, opcodeLengths...)
|
||||
|
||||
// include_directories []string \x00
|
||||
lineHeader.db(0)
|
||||
// file_names []struct{base string; dir u8; modified u8; length u8} \x00
|
||||
lineHeader.code("ir-dump.txt\x00").db(0).db(0).db(0).db(0)
|
||||
|
||||
lineEntry := codegen{}
|
||||
lineEntry.dw(4) // .debug_line version number
|
||||
lineEntry.dd(len(lineHeader.buf))
|
||||
lineEntry.buf = append(lineEntry.buf, lineHeader.buf...)
|
||||
lineAddressOff += len(lineEntry.buf)
|
||||
lineEntry.buf = append(lineEntry.buf, lineProgram.buf...)
|
||||
|
||||
debugLine := codegen{}
|
||||
debugLine.dd(len(lineEntry.buf))
|
||||
lineAddressOff += len(debugLine.buf)
|
||||
debugLine.buf = append(debugLine.buf, lineEntry.buf...)
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".debug_line\x00")
|
||||
sh.dd(elf.SHT_PROGBITS).dq(0).dq(0) // Type, no flags, no memory address
|
||||
sh.dq(position) // Byte offset
|
||||
sh.dq(len(debugLine.buf)) // Byte size
|
||||
sh.dd(0).dd(0) // No link, no info
|
||||
sh.dq(0).dq(0) // No alignment, no entry size
|
||||
shLineIndex := shCount
|
||||
shCount++
|
||||
|
||||
pieces = append(pieces, debugLine.buf)
|
||||
position += len(debugLine.buf)
|
||||
|
||||
// - - Debug line relocation records - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
lineRel := codegen{}
|
||||
lineRel.dq(lineAddressOff).
|
||||
dq(elf.R_INFO(symbols["main"], uint32(elf.R_X86_64_64)))
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".rel.debug_line\x00")
|
||||
sh.dd(elf.SHT_REL) // Type
|
||||
sh.dq(elf.SHF_INFO_LINK).dq(0) // Flags, no memory address
|
||||
sh.dq(position) // Byte offset
|
||||
sh.dq(len(lineRel.buf)) // Byte size
|
||||
sh.dd(shSymtabIndex).dd(shLineIndex)// Link, info
|
||||
sh.dq(0).dq(16) // No alignment, entry size
|
||||
shCount++
|
||||
|
||||
pieces = append(pieces, lineRel.buf)
|
||||
position += len(lineRel.buf)
|
||||
|
||||
// - - Debug abbreviations - - - - - - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
const (
|
||||
formAddr = 0x01 // Pointer size
|
||||
formSecOffset = 0x17 // DWARF size
|
||||
)
|
||||
|
||||
debugAbbrev := codegen{}
|
||||
debugAbbrev.db(1) // Our abbreviation code
|
||||
debugAbbrev.db(dwarf.TagCompileUnit)
|
||||
debugAbbrev.db(0) // DW_CHILDREN_no
|
||||
debugAbbrev.db(dwarf.AttrLowpc).db(formAddr)
|
||||
debugAbbrev.db(dwarf.AttrHighpc).db(formAddr)
|
||||
debugAbbrev.db(dwarf.AttrStmtList).db(formSecOffset)
|
||||
debugAbbrev.db(0).db(0) // End of attributes
|
||||
debugAbbrev.db(0) // End of abbreviations
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".debug_abbrev\x00")
|
||||
sh.dd(elf.SHT_PROGBITS).dq(0).dq(0) // Type, no flags, no memory address
|
||||
sh.dq(position) // Byte offset
|
||||
sh.dq(len(debugAbbrev.buf)) // Byte size
|
||||
sh.dd(0).dd(0) // No link, no info
|
||||
sh.dq(0).dq(0) // No alignment, no entry size
|
||||
shCount++
|
||||
|
||||
pieces = append(pieces, debugAbbrev.buf)
|
||||
position += len(debugAbbrev.buf)
|
||||
|
||||
// - - Debug info - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
cuEntry := codegen{}
|
||||
cuEntry.dw(4) // .debug_info version number
|
||||
cuEntry.dd(0) // Offset into .debug_abbrev
|
||||
cuEntry.db(8) // Pointer size
|
||||
|
||||
// Single compile unit as per .debug_abbrev
|
||||
cuEntry.db(1)
|
||||
infoStartOff := len(cuEntry.buf)
|
||||
cuEntry.dq(0)
|
||||
infoEndOff := len(cuEntry.buf)
|
||||
cuEntry.dq(len(code))
|
||||
cuEntry.dd(0)
|
||||
|
||||
debugInfo := codegen{}
|
||||
debugInfo.dd(len(cuEntry.buf))
|
||||
infoStartOff += len(debugInfo.buf)
|
||||
infoEndOff += len(debugInfo.buf)
|
||||
debugInfo.buf = append(debugInfo.buf, cuEntry.buf...)
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".debug_info\x00")
|
||||
sh.dd(elf.SHT_PROGBITS).dq(0).dq(0) // Type, no flags, no memory address
|
||||
sh.dq(position) // Byte offset
|
||||
sh.dq(len(debugInfo.buf)) // Byte size
|
||||
sh.dd(0).dd(0) // No link, no info
|
||||
sh.dq(0).dq(0) // No alignment, no entry size
|
||||
shInfoIndex := shCount
|
||||
shCount++
|
||||
|
||||
pieces = append(pieces, debugInfo.buf)
|
||||
position += len(debugInfo.buf)
|
||||
|
||||
// - - Debug info relocation records - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
infoRel := codegen{}
|
||||
infoRel.dq(infoStartOff).
|
||||
dq(elf.R_INFO(symbols["main"], uint32(elf.R_X86_64_64)))
|
||||
infoRel.dq(infoEndOff).
|
||||
dq(elf.R_INFO(symbols["main"], uint32(elf.R_X86_64_64)))
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".rel.debug_info\x00")
|
||||
sh.dd(elf.SHT_REL) // Type
|
||||
sh.dq(elf.SHF_INFO_LINK).dq(0) // Flags, no memory address
|
||||
sh.dq(position) // Byte offset
|
||||
sh.dq(len(infoRel.buf)) // Byte size
|
||||
sh.dd(shSymtabIndex).dd(shInfoIndex)// Link, info
|
||||
sh.dq(0).dq(16) // No alignment, entry size
|
||||
shCount++
|
||||
|
||||
pieces = append(pieces, infoRel.buf)
|
||||
position += len(infoRel.buf)
|
||||
|
||||
// - - Section names and section table - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
sh.dd(len(stringTable.buf)) // Index for the name of the section
|
||||
stringTable.code(".shstrtab\x00")
|
||||
sh.dd(elf.SHT_STRTAB).dq(0).dq(0) // Type, no flags, no memory address
|
||||
sh.dq(position) // Byte offset
|
||||
sh.dq(len(stringTable.buf)) // Byte size
|
||||
sh.dd(0).dd(0) // No link, no info
|
||||
sh.dq(0).dq(0) // No alignment, no entry size
|
||||
shCount++
|
||||
|
||||
pieces = append(pieces, stringTable.buf)
|
||||
position += len(stringTable.buf)
|
||||
|
||||
pieces = append(pieces, sh.buf)
|
||||
// Don't increment the position, we want to know where section headers start
|
||||
|
||||
// - - Final assembly of parts - - - - - - - - - - - - - - - - - - - - - - - - -
|
||||
|
||||
bin := codegen{}
|
||||
|
||||
// ELF header
|
||||
bin.code("\x7FELF\x02\x01\x01") // ELF, 64-bit, little endian, v1
|
||||
// Unix System V ABI, v0, padding
|
||||
bin.code("\x00\x00" + "\x00\x00\x00\x00\x00\x00\x00")
|
||||
// The BFD linker will happily try to link ET_EXEC though
|
||||
bin.dw(elf.ET_REL).dw(elf.EM_X86_64).dd(elf.EV_CURRENT)
|
||||
bin.dq(0) // Entry point address
|
||||
bin.dq(0) // Program header offset
|
||||
bin.dq(position) // Section header offset
|
||||
bin.dd(0) // No processor-specific flags
|
||||
bin.dw(ElfHeaderSize) // ELF header size
|
||||
bin.dw(ElfProgramEntrySize) // Program header table entry size
|
||||
bin.dw(0) // Program header table entry count
|
||||
bin.dw(ElfSectionEntrySize) // Section header table entry size
|
||||
bin.dw(shCount) // Section header table entry count
|
||||
bin.dw(shCount - 1) // Section index for strings
|
||||
|
||||
for _, x := range pieces {
|
||||
bin.buf = append(bin.buf, x...)
|
||||
}
|
||||
if err = ioutil.WriteFile(outputPath, bin.buf, 0777); err != nil {
|
||||
log.Fatalf("%s", err)
|
||||
}
|
||||
}
|
||||
Loading…
Reference in New Issue
Block a user