elf: declare alignment, move global symbols to end of symtab
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parent
d95fa7e564
commit
082a1d4f9f
92
compile.go
92
compile.go
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@ -125,29 +125,29 @@ func (c *compiler) CreateSymbol(name string, class string, offset int64, length
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esym := Elf64_Sym{}
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if class == `.section` {
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esym.st_name = uint32(c.StringTable(name)) // Write name into public string table
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esym.st_info = sttType | (STB_LOCAL << 4)
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esym.st_other = STV_DEFAULT
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esym.st_shndx = uint16(srcSectionIdx)
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esym.St_name = uint32(c.StringTable(name)) // Write name into public string table
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esym.St_info = sttType | (STB_LOCAL << 4)
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esym.St_other = STV_DEFAULT
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esym.St_shndx = uint16(srcSectionIdx)
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} else if global {
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esym.st_name = uint32(c.StringTable(name)) // Write name into public string table
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esym.st_info = sttType | (STB_GLOBAL << 4)
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esym.st_other = STV_DEFAULT
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esym.st_shndx = uint16(srcSectionIdx)
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esym.St_name = uint32(c.StringTable(name)) // Write name into public string table
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esym.St_info = sttType | (STB_GLOBAL << 4)
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esym.St_other = STV_DEFAULT
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esym.St_shndx = uint16(srcSectionIdx)
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} else {
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// Private variable for this translation unit
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// Needs an entry, but no need to expose the name
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esym.st_name = 0 // uint32(c.StringTable(name)) // Write name into public string table // 0 // Default: unnamed (0th entry in our string table is \x00)
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esym.st_info = sttType | (STB_LOCAL << 4)
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esym.st_other = STV_HIDDEN // For this translation unit only
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esym.st_shndx = uint16(srcSectionIdx)
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esym.St_name = 0 // uint32(c.StringTable(name)) // Write name into public string table // 0 // Default: unnamed (0th entry in our string table is \x00)
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esym.St_info = sttType | (STB_LOCAL << 4)
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esym.St_other = STV_HIDDEN // For this translation unit only
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esym.St_shndx = uint16(srcSectionIdx)
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}
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fmt.Printf("-->New symbol %q in section %q (sectionidx %v)\n", name, ste.sectionName, srcSectionIdx)
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esym.st_size = uint64(length)
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esym.St_size = uint64(length)
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err := binary.Write(symtabSec.buff, binary.LittleEndian, &esym)
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if err != nil {
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@ -155,7 +155,7 @@ func (c *compiler) CreateSymbol(name string, class string, offset int64, length
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}
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// Stash in symtabEntry
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ste.name_shstrtabOffset = int(esym.st_name)
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ste.name_shstrtabOffset = int(esym.St_name)
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c.symtab[name] = ste
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return nil
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@ -240,9 +240,9 @@ func (c *compiler) Reloc(symbolName string, mode ElfRelocationType) error {
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// Add the relocation to the .rela section
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rr := Elf64_Rela{}
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rr.r_offset = uint64(c.currentSection.buff.Len())
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rr.r_info = uint64(parentSectionSyminfo.symtabSectionIndex)<<32 | uint64(mode) // high bits: Index of search symbol in the symtab (the source section). low bits: mode type
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rr.r_addend = syminfo.offset // Add to the result when relocating (offset within source section)
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rr.R_offset = uint64(c.currentSection.buff.Len())
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rr.R_info = uint64(parentSectionSyminfo.symtabSectionIndex)<<32 | uint64(mode) // high bits: Index of search symbol in the symtab (the source section). low bits: mode type
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rr.R_addend = syminfo.offset // Add to the result when relocating (offset within source section)
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err := binary.Write(relaSec.buff, binary.LittleEndian, &rr)
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if err != nil {
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@ -455,8 +455,49 @@ func (c *compiler) Compile(t Token) error {
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func (c *compiler) Finalize(dest io.Writer) error {
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// Find some well-known section indexes
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symtabSectionIndex, _ := c.FindSectionIndex(`.symtab`)
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shstrtabSectionIndex, _ := c.FindSectionIndex(`.shstrtab`)
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symtabSectionIndex, ok := c.FindSectionIndex(`.symtab`)
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if !ok {
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return fmt.Errorf("No symbol table present")
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}
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shstrtabSectionIndex, ok := c.FindSectionIndex(`.shstrtab`)
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if !ok {
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return fmt.Errorf("No string table present")
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}
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// (Safely) move all global symtab to the end
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// Because there may be existing references to global symtab entries (e.g. relocs)
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// just duplicate them in place
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tmp := c.sections[symtabSectionIndex].buff.Bytes()
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extraSymtabContent := bytes.Buffer{}
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for i := 0; i < len(tmp); i += 24 {
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sym := Elf64_Sym{}
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err := binary.Read(bytes.NewReader(tmp[i:i+24]), binary.LittleEndian, &sym)
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if err != nil {
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return err
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}
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if sym.St_info&(STB_GLOBAL<<4) == 0 {
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continue // not a global symbol
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}
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// Was a global symbol
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// Re-add the global symbol at the end
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extraSymtabContent.Write(tmp[i : i+24])
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// Patch the existing symbol
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sym.St_name = 0
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sym.St_info &= ^uint8(STB_GLOBAL << 4)
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replacement := bytes.Buffer{}
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err = binary.Write(&replacement, binary.LittleEndian, &sym)
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if err != nil {
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return err
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}
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copy(tmp[i:i+24], replacement.Bytes())
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}
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numLocalSymbols := len(tmp) / 24
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c.sections[symtabSectionIndex].buff.Write(extraSymtabContent.Bytes())
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// Write ELF header
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ehdr := Elf64_Ehdr{}
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@ -496,31 +537,35 @@ func (c *compiler) Finalize(dest io.Writer) error {
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shdr := Elf64_Shdr{}
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shdr.sh_name = uint32(sec.name_shstrtabOffset)
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shdr.sh_addralign = 1 // Not doing any proper alignment
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switch sec.name {
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case ".text":
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shdr.sh_type = SHT_PROGBITS
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shdr.sh_flags = SHF_ALLOC | SHF_EXECINSTR
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shdr.sh_addralign = 16 // Request for final linking
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case ".data":
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shdr.sh_type = SHT_PROGBITS
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shdr.sh_flags = SHF_WRITE | SHF_ALLOC
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shdr.sh_addralign = 4 // Request for final linking
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case ".symtab":
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shdr.sh_type = SHT_SYMTAB
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shdr.sh_flags = 0
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shdr.sh_info = uint32(len(c.symtab) + 1)
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shdr.sh_entsize = 24 // Size in bytes of each entry
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shdr.sh_link = 1 // The index of the section containing the actual strings. We reuse shstrtab(!?!)
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shdr.sh_info = uint32(numLocalSymbols) // sh_info points to the first global symbol. Global symbols must go after local symbols
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shdr.sh_entsize = 24 // Size in bytes of each entry
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shdr.sh_link = 1 // The index of the section containing the actual strings. We reuse shstrtab(!?!)
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shdr.sh_addralign = 8 // Request for final linking
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case ".shstrtab":
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shdr.sh_type = SHT_STRTAB
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shdr.sh_flags = 0
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shdr.sh_addralign = 1 // Not doing any proper alignment
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case ".rodata":
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shdr.sh_type = SHT_PROGBITS
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shdr.sh_flags = SHF_ALLOC
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shdr.sh_addralign = 4 // Request for final linking
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default:
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if strings.HasPrefix(sec.name, ".rela.") {
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@ -535,6 +580,7 @@ func (c *compiler) Finalize(dest io.Writer) error {
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return fmt.Errorf("Missing parent section for relocation section %q", sec.name)
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}
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shdr.sh_info = uint32(srcSectionIdx)
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shdr.sh_addralign = 8 // Request for final linking
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} else {
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return fmt.Errorf("don't know the right flags to use for section %q", sec.name)
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}
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18
elf.go
18
elf.go
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@ -105,19 +105,19 @@ const (
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// Elf64_Sym is a symbol
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type Elf64_Sym struct {
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st_name uint32
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st_info uint8
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st_other uint8
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st_shndx uint16
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st_value uint64
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st_size uint64
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St_name uint32
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St_info uint8
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St_other uint8
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St_shndx uint16
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St_value uint64
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St_size uint64
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}
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// Elf64_Rela is a relocation with addend
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type Elf64_Rela struct {
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r_offset uint64
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r_info uint64
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r_addend int64
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R_offset uint64
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R_info uint64
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R_addend int64
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}
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// Relocation types
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