Vendor things

third-party/vendor/object/src/write/elf/object.rs

@@ -0,0 +1,907 @@
+use alloc::vec::Vec;
+
+use crate::write::elf::writer::*;
+use crate::write::string::StringId;
+use crate::write::*;
+use crate::AddressSize;
+use crate::{elf, pod};
+
+#[derive(Clone, Copy)]
+struct ComdatOffsets {
+    offset: usize,
+    str_id: StringId,
+}
+
+#[derive(Clone, Copy)]
+struct SectionOffsets {
+    index: SectionIndex,
+    offset: usize,
+    str_id: StringId,
+    reloc_offset: usize,
+    reloc_str_id: Option<StringId>,
+}
+
+#[derive(Default, Clone, Copy)]
+struct SymbolOffsets {
+    index: SymbolIndex,
+    str_id: Option<StringId>,
+}
+
+// Public methods.
+impl<'a> Object<'a> {
+    /// Add a property with a u32 value to the ELF ".note.gnu.property" section.
+    ///
+    /// Requires `feature = "elf"`.
+    pub fn add_elf_gnu_property_u32(&mut self, property: u32, value: u32) {
+        if self.format != BinaryFormat::Elf {
+            return;
+        }
+
+        let align = if self.elf_is_64() { 8 } else { 4 };
+        let mut data = Vec::with_capacity(32);
+        let n_name = b"GNU\0";
+        data.extend_from_slice(pod::bytes_of(&elf::NoteHeader32 {
+            n_namesz: U32::new(self.endian, n_name.len() as u32),
+            n_descsz: U32::new(self.endian, util::align(3 * 4, align) as u32),
+            n_type: U32::new(self.endian, elf::NT_GNU_PROPERTY_TYPE_0),
+        }));
+        data.extend_from_slice(n_name);
+        // This happens to already be aligned correctly.
+        debug_assert_eq!(util::align(data.len(), align), data.len());
+        data.extend_from_slice(pod::bytes_of(&U32::new(self.endian, property)));
+        // Value size
+        data.extend_from_slice(pod::bytes_of(&U32::new(self.endian, 4)));
+        data.extend_from_slice(pod::bytes_of(&U32::new(self.endian, value)));
+        util::write_align(&mut data, align);
+
+        let section = self.section_id(StandardSection::GnuProperty);
+        self.append_section_data(section, &data, align as u64);
+    }
+}
+
+// Private methods.
+impl<'a> Object<'a> {
+    pub(crate) fn elf_section_info(
+        &self,
+        section: StandardSection,
+    ) -> (&'static [u8], &'static [u8], SectionKind, SectionFlags) {
+        match section {
+            StandardSection::Text => (&[], &b".text"[..], SectionKind::Text, SectionFlags::None),
+            StandardSection::Data => (&[], &b".data"[..], SectionKind::Data, SectionFlags::None),
+            StandardSection::ReadOnlyData | StandardSection::ReadOnlyString => (
+                &[],
+                &b".rodata"[..],
+                SectionKind::ReadOnlyData,
+                SectionFlags::None,
+            ),
+            StandardSection::ReadOnlyDataWithRel => (
+                &[],
+                b".data.rel.ro",
+                SectionKind::ReadOnlyDataWithRel,
+                SectionFlags::None,
+            ),
+            StandardSection::UninitializedData => (
+                &[],
+                &b".bss"[..],
+                SectionKind::UninitializedData,
+                SectionFlags::None,
+            ),
+            StandardSection::Tls => (&[], &b".tdata"[..], SectionKind::Tls, SectionFlags::None),
+            StandardSection::UninitializedTls => (
+                &[],
+                &b".tbss"[..],
+                SectionKind::UninitializedTls,
+                SectionFlags::None,
+            ),
+            StandardSection::TlsVariables => {
+                // Unsupported section.
+                (&[], &[], SectionKind::TlsVariables, SectionFlags::None)
+            }
+            StandardSection::Common => {
+                // Unsupported section.
+                (&[], &[], SectionKind::Common, SectionFlags::None)
+            }
+            StandardSection::GnuProperty => (
+                &[],
+                &b".note.gnu.property"[..],
+                SectionKind::Note,
+                SectionFlags::Elf {
+                    sh_flags: u64::from(elf::SHF_ALLOC),
+                },
+            ),
+        }
+    }
+
+    pub(crate) fn elf_subsection_name(&self, section: &[u8], value: &[u8]) -> Vec<u8> {
+        let mut name = section.to_vec();
+        name.push(b'.');
+        name.extend_from_slice(value);
+        name
+    }
+
+    fn elf_has_relocation_addend(&self) -> Result<bool> {
+        Ok(match self.architecture {
+            Architecture::Aarch64 => true,
+            Architecture::Aarch64_Ilp32 => true,
+            Architecture::Arm => false,
+            Architecture::Avr => true,
+            Architecture::Bpf => false,
+            Architecture::Csky => true,
+            Architecture::I386 => false,
+            Architecture::X86_64 => true,
+            Architecture::X86_64_X32 => true,
+            Architecture::Hexagon => true,
+            Architecture::LoongArch64 => true,
+            Architecture::Mips => false,
+            Architecture::Mips64 => true,
+            Architecture::Msp430 => true,
+            Architecture::PowerPc => true,
+            Architecture::PowerPc64 => true,
+            Architecture::Riscv64 => true,
+            Architecture::Riscv32 => true,
+            Architecture::S390x => true,
+            Architecture::Sbf => false,
+            Architecture::Sharc => true,
+            Architecture::Sparc64 => true,
+            Architecture::Xtensa => true,
+            _ => {
+                return Err(Error(format!(
+                    "unimplemented architecture {:?}",
+                    self.architecture
+                )));
+            }
+        })
+    }
+
+    pub(crate) fn elf_fixup_relocation(&mut self, relocation: &mut Relocation) -> Result<i64> {
+        // Determine whether the addend is stored in the relocation or the data.
+        if self.elf_has_relocation_addend()? {
+            Ok(0)
+        } else {
+            let constant = relocation.addend;
+            relocation.addend = 0;
+            Ok(constant)
+        }
+    }
+
+    pub(crate) fn elf_is_64(&self) -> bool {
+        match self.architecture.address_size().unwrap() {
+            AddressSize::U8 | AddressSize::U16 | AddressSize::U32 => false,
+            AddressSize::U64 => true,
+        }
+    }
+
+    pub(crate) fn elf_write(&self, buffer: &mut dyn WritableBuffer) -> Result<()> {
+        // Create reloc section header names so we can reference them.
+        let is_rela = self.elf_has_relocation_addend()?;
+        let reloc_names: Vec<_> = self
+            .sections
+            .iter()
+            .map(|section| {
+                let mut reloc_name = Vec::with_capacity(
+                    if is_rela { ".rela".len() } else { ".rel".len() } + section.name.len(),
+                );
+                if !section.relocations.is_empty() {
+                    reloc_name.extend_from_slice(if is_rela {
+                        &b".rela"[..]
+                    } else {
+                        &b".rel"[..]
+                    });
+                    reloc_name.extend_from_slice(&section.name);
+                }
+                reloc_name
+            })
+            .collect();
+
+        // Start calculating offsets of everything.
+        let mut writer = Writer::new(self.endian, self.elf_is_64(), buffer);
+        writer.reserve_file_header();
+
+        // Calculate size of section data.
+        let mut comdat_offsets = Vec::with_capacity(self.comdats.len());
+        for comdat in &self.comdats {
+            if comdat.kind != ComdatKind::Any {
+                return Err(Error(format!(
+                    "unsupported COMDAT symbol `{}` kind {:?}",
+                    self.symbols[comdat.symbol.0].name().unwrap_or(""),
+                    comdat.kind
+                )));
+            }
+
+            writer.reserve_section_index();
+            let offset = writer.reserve_comdat(comdat.sections.len());
+            let str_id = writer.add_section_name(b".group");
+            comdat_offsets.push(ComdatOffsets { offset, str_id });
+        }
+        let mut section_offsets = Vec::with_capacity(self.sections.len());
+        for (section, reloc_name) in self.sections.iter().zip(reloc_names.iter()) {
+            let index = writer.reserve_section_index();
+            let offset = writer.reserve(section.data.len(), section.align as usize);
+            let str_id = writer.add_section_name(&section.name);
+            let mut reloc_str_id = None;
+            if !section.relocations.is_empty() {
+                writer.reserve_section_index();
+                reloc_str_id = Some(writer.add_section_name(reloc_name));
+            }
+            section_offsets.push(SectionOffsets {
+                index,
+                offset,
+                str_id,
+                // Relocation data is reserved later.
+                reloc_offset: 0,
+                reloc_str_id,
+            });
+        }
+
+        // Calculate index of symbols and add symbol strings to strtab.
+        let mut symbol_offsets = vec![SymbolOffsets::default(); self.symbols.len()];
+        writer.reserve_null_symbol_index();
+        // Local symbols must come before global.
+        for (index, symbol) in self.symbols.iter().enumerate() {
+            if symbol.is_local() {
+                let section_index = symbol.section.id().map(|s| section_offsets[s.0].index);
+                symbol_offsets[index].index = writer.reserve_symbol_index(section_index);
+            }
+        }
+        let symtab_num_local = writer.symbol_count();
+        for (index, symbol) in self.symbols.iter().enumerate() {
+            if !symbol.is_local() {
+                let section_index = symbol.section.id().map(|s| section_offsets[s.0].index);
+                symbol_offsets[index].index = writer.reserve_symbol_index(section_index);
+            }
+        }
+        for (index, symbol) in self.symbols.iter().enumerate() {
+            if symbol.kind != SymbolKind::Section && !symbol.name.is_empty() {
+                symbol_offsets[index].str_id = Some(writer.add_string(&symbol.name));
+            }
+        }
+
+        // Calculate size of symbols.
+        writer.reserve_symtab_section_index();
+        writer.reserve_symtab();
+        if writer.symtab_shndx_needed() {
+            writer.reserve_symtab_shndx_section_index();
+        }
+        writer.reserve_symtab_shndx();
+        writer.reserve_strtab_section_index();
+        writer.reserve_strtab();
+
+        // Calculate size of relocations.
+        for (index, section) in self.sections.iter().enumerate() {
+            let count = section.relocations.len();
+            if count != 0 {
+                section_offsets[index].reloc_offset = writer.reserve_relocations(count, is_rela);
+            }
+        }
+
+        // Calculate size of section headers.
+        writer.reserve_shstrtab_section_index();
+        writer.reserve_shstrtab();
+        writer.reserve_section_headers();
+
+        // Start writing.
+        let e_type = elf::ET_REL;
+        let e_machine = match (self.architecture, self.sub_architecture) {
+            (Architecture::Aarch64, None) => elf::EM_AARCH64,
+            (Architecture::Aarch64_Ilp32, None) => elf::EM_AARCH64,
+            (Architecture::Arm, None) => elf::EM_ARM,
+            (Architecture::Avr, None) => elf::EM_AVR,
+            (Architecture::Bpf, None) => elf::EM_BPF,
+            (Architecture::Csky, None) => elf::EM_CSKY,
+            (Architecture::I386, None) => elf::EM_386,
+            (Architecture::X86_64, None) => elf::EM_X86_64,
+            (Architecture::X86_64_X32, None) => elf::EM_X86_64,
+            (Architecture::Hexagon, None) => elf::EM_HEXAGON,
+            (Architecture::LoongArch64, None) => elf::EM_LOONGARCH,
+            (Architecture::Mips, None) => elf::EM_MIPS,
+            (Architecture::Mips64, None) => elf::EM_MIPS,
+            (Architecture::Msp430, None) => elf::EM_MSP430,
+            (Architecture::PowerPc, None) => elf::EM_PPC,
+            (Architecture::PowerPc64, None) => elf::EM_PPC64,
+            (Architecture::Riscv32, None) => elf::EM_RISCV,
+            (Architecture::Riscv64, None) => elf::EM_RISCV,
+            (Architecture::S390x, None) => elf::EM_S390,
+            (Architecture::Sbf, None) => elf::EM_SBF,
+            (Architecture::Sharc, None) => elf::EM_SHARC,
+            (Architecture::Sparc64, None) => elf::EM_SPARCV9,
+            (Architecture::Xtensa, None) => elf::EM_XTENSA,
+            _ => {
+                return Err(Error(format!(
+                    "unimplemented architecture {:?} with sub-architecture {:?}",
+                    self.architecture, self.sub_architecture
+                )));
+            }
+        };
+        let (os_abi, abi_version, e_flags) = if let FileFlags::Elf {
+            os_abi,
+            abi_version,
+            e_flags,
+        } = self.flags
+        {
+            (os_abi, abi_version, e_flags)
+        } else {
+            (elf::ELFOSABI_NONE, 0, 0)
+        };
+        writer.write_file_header(&FileHeader {
+            os_abi,
+            abi_version,
+            e_type,
+            e_machine,
+            e_entry: 0,
+            e_flags,
+        })?;
+
+        // Write section data.
+        for comdat in &self.comdats {
+            writer.write_comdat_header();
+            for section in &comdat.sections {
+                writer.write_comdat_entry(section_offsets[section.0].index);
+            }
+        }
+        for (index, section) in self.sections.iter().enumerate() {
+            writer.write_align(section.align as usize);
+            debug_assert_eq!(section_offsets[index].offset, writer.len());
+            writer.write(&section.data);
+        }
+
+        // Write symbols.
+        writer.write_null_symbol();
+        let mut write_symbol = |index: usize, symbol: &Symbol| -> Result<()> {
+            let st_info = if let SymbolFlags::Elf { st_info, .. } = symbol.flags {
+                st_info
+            } else {
+                let st_type = match symbol.kind {
+                    SymbolKind::Null => elf::STT_NOTYPE,
+                    SymbolKind::Text => {
+                        if symbol.is_undefined() {
+                            elf::STT_NOTYPE
+                        } else {
+                            elf::STT_FUNC
+                        }
+                    }
+                    SymbolKind::Data => {
+                        if symbol.is_undefined() {
+                            elf::STT_NOTYPE
+                        } else if symbol.is_common() {
+                            elf::STT_COMMON
+                        } else {
+                            elf::STT_OBJECT
+                        }
+                    }
+                    SymbolKind::Section => elf::STT_SECTION,
+                    SymbolKind::File => elf::STT_FILE,
+                    SymbolKind::Tls => elf::STT_TLS,
+                    SymbolKind::Label => elf::STT_NOTYPE,
+                    SymbolKind::Unknown => {
+                        if symbol.is_undefined() {
+                            elf::STT_NOTYPE
+                        } else {
+                            return Err(Error(format!(
+                                "unimplemented symbol `{}` kind {:?}",
+                                symbol.name().unwrap_or(""),
+                                symbol.kind
+                            )));
+                        }
+                    }
+                };
+                let st_bind = if symbol.weak {
+                    elf::STB_WEAK
+                } else if symbol.is_undefined() {
+                    elf::STB_GLOBAL
+                } else if symbol.is_local() {
+                    elf::STB_LOCAL
+                } else {
+                    elf::STB_GLOBAL
+                };
+                (st_bind << 4) + st_type
+            };
+            let st_other = if let SymbolFlags::Elf { st_other, .. } = symbol.flags {
+                st_other
+            } else if symbol.scope == SymbolScope::Linkage {
+                elf::STV_HIDDEN
+            } else {
+                elf::STV_DEFAULT
+            };
+            let (st_shndx, section) = match symbol.section {
+                SymbolSection::None => {
+                    debug_assert_eq!(symbol.kind, SymbolKind::File);
+                    (elf::SHN_ABS, None)
+                }
+                SymbolSection::Undefined => (elf::SHN_UNDEF, None),
+                SymbolSection::Absolute => (elf::SHN_ABS, None),
+                SymbolSection::Common => (elf::SHN_COMMON, None),
+                SymbolSection::Section(id) => (0, Some(section_offsets[id.0].index)),
+            };
+            writer.write_symbol(&Sym {
+                name: symbol_offsets[index].str_id,
+                section,
+                st_info,
+                st_other,
+                st_shndx,
+                st_value: symbol.value,
+                st_size: symbol.size,
+            });
+            Ok(())
+        };
+        for (index, symbol) in self.symbols.iter().enumerate() {
+            if symbol.is_local() {
+                write_symbol(index, symbol)?;
+            }
+        }
+        for (index, symbol) in self.symbols.iter().enumerate() {
+            if !symbol.is_local() {
+                write_symbol(index, symbol)?;
+            }
+        }
+        writer.write_symtab_shndx();
+        writer.write_strtab();
+
+        // Write relocations.
+        for (index, section) in self.sections.iter().enumerate() {
+            if !section.relocations.is_empty() {
+                writer.write_align_relocation();
+                debug_assert_eq!(section_offsets[index].reloc_offset, writer.len());
+                for reloc in &section.relocations {
+                    let r_type = match self.architecture {
+                        Architecture::Aarch64 => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, RelocationEncoding::Generic, 64) => {
+                                elf::R_AARCH64_ABS64
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::Generic, 32) => {
+                                elf::R_AARCH64_ABS32
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::Generic, 16) => {
+                                elf::R_AARCH64_ABS16
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::Generic, 64) => {
+                                elf::R_AARCH64_PREL64
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::Generic, 32) => {
+                                elf::R_AARCH64_PREL32
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::Generic, 16) => {
+                                elf::R_AARCH64_PREL16
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::AArch64Call, 26)
+                            | (RelocationKind::PltRelative, RelocationEncoding::AArch64Call, 26) => {
+                                elf::R_AARCH64_CALL26
+                            }
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Aarch64_Ilp32 => {
+                            match (reloc.kind, reloc.encoding, reloc.size) {
+                                (RelocationKind::Absolute, RelocationEncoding::Generic, 32) => {
+                                    elf::R_AARCH64_P32_ABS32
+                                }
+                                (RelocationKind::Elf(x), _, _) => x,
+                                _ => {
+                                    return Err(Error(format!(
+                                        "unimplemented relocation {:?}",
+                                        reloc
+                                    )));
+                                }
+                            }
+                        }
+                        Architecture::Arm => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, _, 32) => elf::R_ARM_ABS32,
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Avr => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, _, 32) => elf::R_AVR_32,
+                            (RelocationKind::Absolute, _, 16) => elf::R_AVR_16,
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Bpf => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, _, 64) => elf::R_BPF_64_64,
+                            (RelocationKind::Absolute, _, 32) => elf::R_BPF_64_32,
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Csky => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, _, 32) => elf::R_CKCORE_ADDR32,
+                            (RelocationKind::Relative, RelocationEncoding::Generic, 32) => {
+                                elf::R_CKCORE_PCREL32
+                            }
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::I386 => match (reloc.kind, reloc.size) {
+                            (RelocationKind::Absolute, 32) => elf::R_386_32,
+                            (RelocationKind::Relative, 32) => elf::R_386_PC32,
+                            (RelocationKind::Got, 32) => elf::R_386_GOT32,
+                            (RelocationKind::PltRelative, 32) => elf::R_386_PLT32,
+                            (RelocationKind::GotBaseOffset, 32) => elf::R_386_GOTOFF,
+                            (RelocationKind::GotBaseRelative, 32) => elf::R_386_GOTPC,
+                            (RelocationKind::Absolute, 16) => elf::R_386_16,
+                            (RelocationKind::Relative, 16) => elf::R_386_PC16,
+                            (RelocationKind::Absolute, 8) => elf::R_386_8,
+                            (RelocationKind::Relative, 8) => elf::R_386_PC8,
+                            (RelocationKind::Elf(x), _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::X86_64 | Architecture::X86_64_X32 => {
+                            match (reloc.kind, reloc.encoding, reloc.size) {
+                                (RelocationKind::Absolute, RelocationEncoding::Generic, 64) => {
+                                    elf::R_X86_64_64
+                                }
+                                (RelocationKind::Relative, RelocationEncoding::X86Branch, 32) => {
+                                    elf::R_X86_64_PLT32
+                                }
+                                (RelocationKind::Relative, _, 32) => elf::R_X86_64_PC32,
+                                (RelocationKind::Got, _, 32) => elf::R_X86_64_GOT32,
+                                (RelocationKind::PltRelative, _, 32) => elf::R_X86_64_PLT32,
+                                (RelocationKind::GotRelative, _, 32) => elf::R_X86_64_GOTPCREL,
+                                (RelocationKind::Absolute, RelocationEncoding::Generic, 32) => {
+                                    elf::R_X86_64_32
+                                }
+                                (RelocationKind::Absolute, RelocationEncoding::X86Signed, 32) => {
+                                    elf::R_X86_64_32S
+                                }
+                                (RelocationKind::Absolute, _, 16) => elf::R_X86_64_16,
+                                (RelocationKind::Relative, _, 16) => elf::R_X86_64_PC16,
+                                (RelocationKind::Absolute, _, 8) => elf::R_X86_64_8,
+                                (RelocationKind::Relative, _, 8) => elf::R_X86_64_PC8,
+                                (RelocationKind::Elf(x), _, _) => x,
+                                _ => {
+                                    return Err(Error(format!(
+                                        "unimplemented relocation {:?}",
+                                        reloc
+                                    )));
+                                }
+                            }
+                        }
+                        Architecture::Hexagon => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, _, 32) => elf::R_HEX_32,
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::LoongArch64 => match (reloc.kind, reloc.encoding, reloc.size)
+                        {
+                            (RelocationKind::Absolute, _, 32) => elf::R_LARCH_32,
+                            (RelocationKind::Absolute, _, 64) => elf::R_LARCH_64,
+                            (RelocationKind::Relative, _, 32) => elf::R_LARCH_32_PCREL,
+                            (RelocationKind::Relative, _, 64) => elf::R_LARCH_64_PCREL,
+                            (RelocationKind::Relative, RelocationEncoding::LoongArchBranch, 16)
+                            | (
+                                RelocationKind::PltRelative,
+                                RelocationEncoding::LoongArchBranch,
+                                16,
+                            ) => elf::R_LARCH_B16,
+                            (RelocationKind::Relative, RelocationEncoding::LoongArchBranch, 21)
+                            | (
+                                RelocationKind::PltRelative,
+                                RelocationEncoding::LoongArchBranch,
+                                21,
+                            ) => elf::R_LARCH_B21,
+                            (RelocationKind::Relative, RelocationEncoding::LoongArchBranch, 26)
+                            | (
+                                RelocationKind::PltRelative,
+                                RelocationEncoding::LoongArchBranch,
+                                26,
+                            ) => elf::R_LARCH_B26,
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Mips | Architecture::Mips64 => {
+                            match (reloc.kind, reloc.encoding, reloc.size) {
+                                (RelocationKind::Absolute, _, 16) => elf::R_MIPS_16,
+                                (RelocationKind::Absolute, _, 32) => elf::R_MIPS_32,
+                                (RelocationKind::Absolute, _, 64) => elf::R_MIPS_64,
+                                (RelocationKind::Elf(x), _, _) => x,
+                                _ => {
+                                    return Err(Error(format!(
+                                        "unimplemented relocation {:?}",
+                                        reloc
+                                    )));
+                                }
+                            }
+                        }
+                        Architecture::Msp430 => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, _, 32) => elf::R_MSP430_32,
+                            (RelocationKind::Absolute, _, 16) => elf::R_MSP430_16_BYTE,
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::PowerPc => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, _, 32) => elf::R_PPC_ADDR32,
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::PowerPc64 => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, _, 32) => elf::R_PPC64_ADDR32,
+                            (RelocationKind::Absolute, _, 64) => elf::R_PPC64_ADDR64,
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Riscv32 | Architecture::Riscv64 => {
+                            match (reloc.kind, reloc.encoding, reloc.size) {
+                                (RelocationKind::Absolute, _, 32) => elf::R_RISCV_32,
+                                (RelocationKind::Absolute, _, 64) => elf::R_RISCV_64,
+                                (RelocationKind::Relative, RelocationEncoding::Generic, 32) => {
+                                    elf::R_RISCV_32_PCREL
+                                }
+                                (RelocationKind::Elf(x), _, _) => x,
+                                _ => {
+                                    return Err(Error(format!(
+                                        "unimplemented relocation {:?}",
+                                        reloc
+                                    )));
+                                }
+                            }
+                        }
+                        Architecture::S390x => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, RelocationEncoding::Generic, 8) => {
+                                elf::R_390_8
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::Generic, 16) => {
+                                elf::R_390_16
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::Generic, 32) => {
+                                elf::R_390_32
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::Generic, 64) => {
+                                elf::R_390_64
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::Generic, 16) => {
+                                elf::R_390_PC16
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::Generic, 32) => {
+                                elf::R_390_PC32
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::Generic, 64) => {
+                                elf::R_390_PC64
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::S390xDbl, 16) => {
+                                elf::R_390_PC16DBL
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::S390xDbl, 32) => {
+                                elf::R_390_PC32DBL
+                            }
+                            (RelocationKind::PltRelative, RelocationEncoding::S390xDbl, 16) => {
+                                elf::R_390_PLT16DBL
+                            }
+                            (RelocationKind::PltRelative, RelocationEncoding::S390xDbl, 32) => {
+                                elf::R_390_PLT32DBL
+                            }
+                            (RelocationKind::Got, RelocationEncoding::Generic, 16) => {
+                                elf::R_390_GOT16
+                            }
+                            (RelocationKind::Got, RelocationEncoding::Generic, 32) => {
+                                elf::R_390_GOT32
+                            }
+                            (RelocationKind::Got, RelocationEncoding::Generic, 64) => {
+                                elf::R_390_GOT64
+                            }
+                            (RelocationKind::GotRelative, RelocationEncoding::S390xDbl, 32) => {
+                                elf::R_390_GOTENT
+                            }
+                            (RelocationKind::GotBaseOffset, RelocationEncoding::Generic, 16) => {
+                                elf::R_390_GOTOFF16
+                            }
+                            (RelocationKind::GotBaseOffset, RelocationEncoding::Generic, 32) => {
+                                elf::R_390_GOTOFF32
+                            }
+                            (RelocationKind::GotBaseOffset, RelocationEncoding::Generic, 64) => {
+                                elf::R_390_GOTOFF64
+                            }
+                            (RelocationKind::GotBaseRelative, RelocationEncoding::Generic, 64) => {
+                                elf::R_390_GOTPC
+                            }
+                            (RelocationKind::GotBaseRelative, RelocationEncoding::S390xDbl, 32) => {
+                                elf::R_390_GOTPCDBL
+                            }
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Sbf => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, _, 64) => elf::R_SBF_64_64,
+                            (RelocationKind::Absolute, _, 32) => elf::R_SBF_64_32,
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Sharc => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, RelocationEncoding::SharcTypeA, 32) => {
+                                elf::R_SHARC_ADDR32_V3
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::Generic, 32) => {
+                                elf::R_SHARC_ADDR_VAR_V3
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::SharcTypeA, 24) => {
+                                elf::R_SHARC_PCRLONG_V3
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::SharcTypeA, 6) => {
+                                elf::R_SHARC_PCRSHORT_V3
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::SharcTypeB, 6) => {
+                                elf::R_SHARC_PCRSHORT_V3
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::Generic, 16) => {
+                                elf::R_SHARC_ADDR_VAR16_V3
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::SharcTypeA, 16) => {
+                                elf::R_SHARC_DATA16_V3
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::SharcTypeB, 16) => {
+                                elf::R_SHARC_DATA16_VISA_V3
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::SharcTypeA, 24) => {
+                                elf::R_SHARC_ADDR24_V3
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::SharcTypeA, 6) => {
+                                elf::R_SHARC_DATA6_V3
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::SharcTypeB, 6) => {
+                                elf::R_SHARC_DATA6_VISA_V3
+                            }
+                            (RelocationKind::Absolute, RelocationEncoding::SharcTypeB, 7) => {
+                                elf::R_SHARC_DATA7_VISA_V3
+                            }
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Sparc64 => match (reloc.kind, reloc.encoding, reloc.size) {
+                            // TODO: use R_SPARC_32/R_SPARC_64 if aligned.
+                            (RelocationKind::Absolute, _, 32) => elf::R_SPARC_UA32,
+                            (RelocationKind::Absolute, _, 64) => elf::R_SPARC_UA64,
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Xtensa => match (reloc.kind, reloc.encoding, reloc.size) {
+                            (RelocationKind::Absolute, _, 32) => elf::R_XTENSA_32,
+                            (RelocationKind::Relative, RelocationEncoding::Generic, 32) => {
+                                elf::R_XTENSA_32_PCREL
+                            }
+                            (RelocationKind::Elf(x), _, _) => x,
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        _ => {
+                            if let RelocationKind::Elf(x) = reloc.kind {
+                                x
+                            } else {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        }
+                    };
+                    let r_sym = symbol_offsets[reloc.symbol.0].index.0;
+                    writer.write_relocation(
+                        is_rela,
+                        &Rel {
+                            r_offset: reloc.offset,
+                            r_sym,
+                            r_type,
+                            r_addend: reloc.addend,
+                        },
+                    );
+                }
+            }
+        }
+
+        writer.write_shstrtab();
+
+        // Write section headers.
+        writer.write_null_section_header();
+
+        let symtab_index = writer.symtab_index();
+        for (comdat, comdat_offset) in self.comdats.iter().zip(comdat_offsets.iter()) {
+            writer.write_comdat_section_header(
+                comdat_offset.str_id,
+                symtab_index,
+                symbol_offsets[comdat.symbol.0].index,
+                comdat_offset.offset,
+                comdat.sections.len(),
+            );
+        }
+        for (index, section) in self.sections.iter().enumerate() {
+            let sh_type = match section.kind {
+                SectionKind::UninitializedData | SectionKind::UninitializedTls => elf::SHT_NOBITS,
+                SectionKind::Note => elf::SHT_NOTE,
+                SectionKind::Elf(sh_type) => sh_type,
+                _ => elf::SHT_PROGBITS,
+            };
+            let sh_flags = if let SectionFlags::Elf { sh_flags } = section.flags {
+                sh_flags
+            } else {
+                match section.kind {
+                    SectionKind::Text => elf::SHF_ALLOC | elf::SHF_EXECINSTR,
+                    SectionKind::Data | SectionKind::ReadOnlyDataWithRel => {
+                        elf::SHF_ALLOC | elf::SHF_WRITE
+                    }
+                    SectionKind::Tls => elf::SHF_ALLOC | elf::SHF_WRITE | elf::SHF_TLS,
+                    SectionKind::UninitializedData => elf::SHF_ALLOC | elf::SHF_WRITE,
+                    SectionKind::UninitializedTls => elf::SHF_ALLOC | elf::SHF_WRITE | elf::SHF_TLS,
+                    SectionKind::ReadOnlyData => elf::SHF_ALLOC,
+                    SectionKind::ReadOnlyString => {
+                        elf::SHF_ALLOC | elf::SHF_STRINGS | elf::SHF_MERGE
+                    }
+                    SectionKind::OtherString => elf::SHF_STRINGS | elf::SHF_MERGE,
+                    SectionKind::Other
+                    | SectionKind::Debug
+                    | SectionKind::Metadata
+                    | SectionKind::Linker
+                    | SectionKind::Note
+                    | SectionKind::Elf(_) => 0,
+                    SectionKind::Unknown | SectionKind::Common | SectionKind::TlsVariables => {
+                        return Err(Error(format!(
+                            "unimplemented section `{}` kind {:?}",
+                            section.name().unwrap_or(""),
+                            section.kind
+                        )));
+                    }
+                }
+                .into()
+            };
+            // TODO: not sure if this is correct, maybe user should determine this
+            let sh_entsize = match section.kind {
+                SectionKind::ReadOnlyString | SectionKind::OtherString => 1,
+                _ => 0,
+            };
+            writer.write_section_header(&SectionHeader {
+                name: Some(section_offsets[index].str_id),
+                sh_type,
+                sh_flags,
+                sh_addr: 0,
+                sh_offset: section_offsets[index].offset as u64,
+                sh_size: section.size,
+                sh_link: 0,
+                sh_info: 0,
+                sh_addralign: section.align,
+                sh_entsize,
+            });
+
+            if !section.relocations.is_empty() {
+                writer.write_relocation_section_header(
+                    section_offsets[index].reloc_str_id.unwrap(),
+                    section_offsets[index].index,
+                    symtab_index,
+                    section_offsets[index].reloc_offset,
+                    section.relocations.len(),
+                    is_rela,
+                );
+            }
+        }
+
+        writer.write_symtab_section_header(symtab_num_local);
+        writer.write_symtab_shndx_section_header();
+        writer.write_strtab_section_header();
+        writer.write_shstrtab_section_header();
+
+        debug_assert_eq!(writer.reserved_len(), writer.len());
+
+        Ok(())
+    }
+}