Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

1 files changed, 1095 insertions, 0 deletions

diff --git a/vendor/object/src/write/macho.rs b/vendor/object/src/write/macho.rs
new file mode 100644
index 0000000..1c61523
--- /dev/null
+++ b/vendor/object/src/write/macho.rs
@@ -0,0 +1,1095 @@
+use core::mem;
+
+use crate::endian::*;
+use crate::macho;
+use crate::write::string::*;
+use crate::write::util::*;
+use crate::write::*;
+use crate::AddressSize;
+
+#[derive(Default, Clone, Copy)]
+struct SectionOffsets {
+    index: usize,
+    offset: usize,
+    address: u64,
+    reloc_offset: usize,
+    reloc_count: usize,
+}
+
+#[derive(Default, Clone, Copy)]
+struct SymbolOffsets {
+    index: usize,
+    str_id: Option<StringId>,
+}
+
+/// The customizable portion of a [`macho::BuildVersionCommand`].
+#[derive(Debug, Default, Clone, Copy)]
+#[non_exhaustive] // May want to add the tool list?
+pub struct MachOBuildVersion {
+    /// One of the `PLATFORM_` constants (for example,
+    /// [`object::macho::PLATFORM_MACOS`](macho::PLATFORM_MACOS)).
+    pub platform: u32,
+    /// The minimum OS version, where `X.Y.Z` is encoded in nibbles as
+    /// `xxxx.yy.zz`.
+    pub minos: u32,
+    /// The SDK version as `X.Y.Z`, where `X.Y.Z` is encoded in nibbles as
+    /// `xxxx.yy.zz`.
+    pub sdk: u32,
+}
+
+impl MachOBuildVersion {
+    fn cmdsize(&self) -> u32 {
+        // Same size for both endianness, and we don't have `ntools`.
+        let sz = mem::size_of::<macho::BuildVersionCommand<Endianness>>();
+        debug_assert!(sz <= u32::MAX as usize);
+        sz as u32
+    }
+}
+
+// Public methods.
+impl<'a> Object<'a> {
+    /// Specify the Mach-O CPU subtype.
+    ///
+    /// Requires `feature = "macho"`.
+    #[inline]
+    pub fn set_macho_cpu_subtype(&mut self, cpu_subtype: u32) {
+        self.macho_cpu_subtype = Some(cpu_subtype);
+    }
+
+    /// Specify information for a Mach-O `LC_BUILD_VERSION` command.
+    ///
+    /// Requires `feature = "macho"`.
+    #[inline]
+    pub fn set_macho_build_version(&mut self, info: MachOBuildVersion) {
+        self.macho_build_version = Some(info);
+    }
+}
+
+// Private methods.
+impl<'a> Object<'a> {
+    pub(crate) fn macho_set_subsections_via_symbols(&mut self) {
+        let flags = match self.flags {
+            FileFlags::MachO { flags } => flags,
+            _ => 0,
+        };
+        self.flags = FileFlags::MachO {
+            flags: flags | macho::MH_SUBSECTIONS_VIA_SYMBOLS,
+        };
+    }
+
+    pub(crate) fn macho_segment_name(&self, segment: StandardSegment) -> &'static [u8] {
+        match segment {
+            StandardSegment::Text => &b"__TEXT"[..],
+            StandardSegment::Data => &b"__DATA"[..],
+            StandardSegment::Debug => &b"__DWARF"[..],
+        }
+    }
+
+    pub(crate) fn macho_section_info(
+        &self,
+        section: StandardSection,
+    ) -> (&'static [u8], &'static [u8], SectionKind, SectionFlags) {
+        match section {
+            StandardSection::Text => (
+                &b"__TEXT"[..],
+                &b"__text"[..],
+                SectionKind::Text,
+                SectionFlags::None,
+            ),
+            StandardSection::Data => (
+                &b"__DATA"[..],
+                &b"__data"[..],
+                SectionKind::Data,
+                SectionFlags::None,
+            ),
+            StandardSection::ReadOnlyData => (
+                &b"__TEXT"[..],
+                &b"__const"[..],
+                SectionKind::ReadOnlyData,
+                SectionFlags::None,
+            ),
+            StandardSection::ReadOnlyDataWithRel => (
+                &b"__DATA"[..],
+                &b"__const"[..],
+                SectionKind::ReadOnlyDataWithRel,
+                SectionFlags::None,
+            ),
+            StandardSection::ReadOnlyString => (
+                &b"__TEXT"[..],
+                &b"__cstring"[..],
+                SectionKind::ReadOnlyString,
+                SectionFlags::None,
+            ),
+            StandardSection::UninitializedData => (
+                &b"__DATA"[..],
+                &b"__bss"[..],
+                SectionKind::UninitializedData,
+                SectionFlags::None,
+            ),
+            StandardSection::Tls => (
+                &b"__DATA"[..],
+                &b"__thread_data"[..],
+                SectionKind::Tls,
+                SectionFlags::None,
+            ),
+            StandardSection::UninitializedTls => (
+                &b"__DATA"[..],
+                &b"__thread_bss"[..],
+                SectionKind::UninitializedTls,
+                SectionFlags::None,
+            ),
+            StandardSection::TlsVariables => (
+                &b"__DATA"[..],
+                &b"__thread_vars"[..],
+                SectionKind::TlsVariables,
+                SectionFlags::None,
+            ),
+            StandardSection::Common => (
+                &b"__DATA"[..],
+                &b"__common"[..],
+                SectionKind::Common,
+                SectionFlags::None,
+            ),
+            StandardSection::GnuProperty => {
+                // Unsupported section.
+                (&[], &[], SectionKind::Note, SectionFlags::None)
+            }
+        }
+    }
+
+    fn macho_tlv_bootstrap(&mut self) -> SymbolId {
+        match self.tlv_bootstrap {
+            Some(id) => id,
+            None => {
+                let id = self.add_symbol(Symbol {
+                    name: b"_tlv_bootstrap".to_vec(),
+                    value: 0,
+                    size: 0,
+                    kind: SymbolKind::Text,
+                    scope: SymbolScope::Dynamic,
+                    weak: false,
+                    section: SymbolSection::Undefined,
+                    flags: SymbolFlags::None,
+                });
+                self.tlv_bootstrap = Some(id);
+                id
+            }
+        }
+    }
+
+    /// Create the `__thread_vars` entry for a TLS variable.
+    ///
+    /// The symbol given by `symbol_id` will be updated to point to this entry.
+    ///
+    /// A new `SymbolId` will be returned. The caller must update this symbol
+    /// to point to the initializer.
+    ///
+    /// If `symbol_id` is not for a TLS variable, then it is returned unchanged.
+    pub(crate) fn macho_add_thread_var(&mut self, symbol_id: SymbolId) -> SymbolId {
+        let symbol = self.symbol_mut(symbol_id);
+        if symbol.kind != SymbolKind::Tls {
+            return symbol_id;
+        }
+
+        // Create the initializer symbol.
+        let mut name = symbol.name.clone();
+        name.extend_from_slice(b"$tlv$init");
+        let init_symbol_id = self.add_raw_symbol(Symbol {
+            name,
+            value: 0,
+            size: 0,
+            kind: SymbolKind::Tls,
+            scope: SymbolScope::Compilation,
+            weak: false,
+            section: SymbolSection::Undefined,
+            flags: SymbolFlags::None,
+        });
+
+        // Add the tlv entry.
+        // Three pointers in size:
+        //   - __tlv_bootstrap - used to make sure support exists
+        //   - spare pointer - used when mapped by the runtime
+        //   - pointer to symbol initializer
+        let section = self.section_id(StandardSection::TlsVariables);
+        let address_size = self.architecture.address_size().unwrap().bytes();
+        let size = u64::from(address_size) * 3;
+        let data = vec![0; size as usize];
+        let offset = self.append_section_data(section, &data, u64::from(address_size));
+
+        let tlv_bootstrap = self.macho_tlv_bootstrap();
+        self.add_relocation(
+            section,
+            Relocation {
+                offset,
+                size: address_size * 8,
+                kind: RelocationKind::Absolute,
+                encoding: RelocationEncoding::Generic,
+                symbol: tlv_bootstrap,
+                addend: 0,
+            },
+        )
+        .unwrap();
+        self.add_relocation(
+            section,
+            Relocation {
+                offset: offset + u64::from(address_size) * 2,
+                size: address_size * 8,
+                kind: RelocationKind::Absolute,
+                encoding: RelocationEncoding::Generic,
+                symbol: init_symbol_id,
+                addend: 0,
+            },
+        )
+        .unwrap();
+
+        // Update the symbol to point to the tlv.
+        let symbol = self.symbol_mut(symbol_id);
+        symbol.value = offset;
+        symbol.size = size;
+        symbol.section = SymbolSection::Section(section);
+
+        init_symbol_id
+    }
+
+    pub(crate) fn macho_fixup_relocation(&mut self, relocation: &mut Relocation) -> i64 {
+        let relative = match relocation.kind {
+            RelocationKind::Relative
+            | RelocationKind::GotRelative
+            | RelocationKind::PltRelative
+            | RelocationKind::MachO { relative: true, .. } => true,
+            _ => false,
+        };
+        if relative {
+            // For PC relative relocations on some architectures, the
+            // addend does not include the offset required due to the
+            // PC being different from the place of the relocation.
+            // This differs from other file formats, so adjust the
+            // addend here to account for this.
+            let pcrel_offset = match self.architecture {
+                Architecture::I386 => 4,
+                Architecture::X86_64 => match relocation.kind {
+                    RelocationKind::MachO {
+                        value: macho::X86_64_RELOC_SIGNED_1,
+                        ..
+                    } => 5,
+                    RelocationKind::MachO {
+                        value: macho::X86_64_RELOC_SIGNED_2,
+                        ..
+                    } => 6,
+                    RelocationKind::MachO {
+                        value: macho::X86_64_RELOC_SIGNED_4,
+                        ..
+                    } => 8,
+                    _ => 4,
+                },
+                // TODO: maybe missing support for some architectures and relocations
+                _ => 0,
+            };
+            relocation.addend += pcrel_offset;
+        }
+        // Aarch64 relocs of these sizes act as if they are double-word length
+        if self.architecture == Architecture::Aarch64 && matches!(relocation.size, 12 | 21 | 26) {
+            relocation.size = 32;
+        }
+        // Check for relocations that use an explicit addend.
+        if self.architecture == Architecture::Aarch64 {
+            if relocation.encoding == RelocationEncoding::AArch64Call {
+                return 0;
+            }
+            if let RelocationKind::MachO { value, .. } = relocation.kind {
+                match value {
+                    macho::ARM64_RELOC_BRANCH26
+                    | macho::ARM64_RELOC_PAGE21
+                    | macho::ARM64_RELOC_PAGEOFF12 => return 0,
+                    _ => {}
+                }
+            }
+        }
+        // Signify implicit addend.
+        let constant = relocation.addend;
+        relocation.addend = 0;
+        constant
+    }
+
+    pub(crate) fn macho_write(&self, buffer: &mut dyn WritableBuffer) -> Result<()> {
+        let address_size = self.architecture.address_size().unwrap();
+        let endian = self.endian;
+        let macho32 = MachO32 { endian };
+        let macho64 = MachO64 { endian };
+        let macho: &dyn MachO = match address_size {
+            AddressSize::U8 | AddressSize::U16 | AddressSize::U32 => &macho32,
+            AddressSize::U64 => &macho64,
+        };
+        let pointer_align = address_size.bytes() as usize;
+
+        // Calculate offsets of everything, and build strtab.
+        let mut offset = 0;
+
+        // Calculate size of Mach-O header.
+        offset += macho.mach_header_size();
+
+        // Calculate size of commands.
+        let mut ncmds = 0;
+        let command_offset = offset;
+
+        // Calculate size of segment command and section headers.
+        let segment_command_offset = offset;
+        let segment_command_len =
+            macho.segment_command_size() + self.sections.len() * macho.section_header_size();
+        offset += segment_command_len;
+        ncmds += 1;
+
+        // Calculate size of build version.
+        let build_version_offset = offset;
+        if let Some(version) = &self.macho_build_version {
+            offset += version.cmdsize() as usize;
+            ncmds += 1;
+        }
+
+        // Calculate size of symtab command.
+        let symtab_command_offset = offset;
+        let symtab_command_len = mem::size_of::<macho::SymtabCommand<Endianness>>();
+        offset += symtab_command_len;
+        ncmds += 1;
+
+        // Calculate size of dysymtab command.
+        let dysymtab_command_offset = offset;
+        let dysymtab_command_len = mem::size_of::<macho::DysymtabCommand<Endianness>>();
+        offset += dysymtab_command_len;
+        ncmds += 1;
+
+        let sizeofcmds = offset - command_offset;
+
+        // Calculate size of section data.
+        // Section data can immediately follow the load commands without any alignment padding.
+        let segment_file_offset = offset;
+        let mut section_offsets = vec![SectionOffsets::default(); self.sections.len()];
+        let mut address = 0;
+        for (index, section) in self.sections.iter().enumerate() {
+            section_offsets[index].index = 1 + index;
+            if !section.is_bss() {
+                address = align_u64(address, section.align);
+                section_offsets[index].address = address;
+                section_offsets[index].offset = segment_file_offset + address as usize;
+                address += section.size;
+            }
+        }
+        let segment_file_size = address as usize;
+        offset += address as usize;
+        for (index, section) in self.sections.iter().enumerate() {
+            if section.is_bss() {
+                debug_assert!(section.data.is_empty());
+                address = align_u64(address, section.align);
+                section_offsets[index].address = address;
+                address += section.size;
+            }
+        }
+
+        // Partition symbols and add symbol strings to strtab.
+        let mut strtab = StringTable::default();
+        let mut symbol_offsets = vec![SymbolOffsets::default(); self.symbols.len()];
+        let mut local_symbols = vec![];
+        let mut external_symbols = vec![];
+        let mut undefined_symbols = vec![];
+        for (index, symbol) in self.symbols.iter().enumerate() {
+            // The unified API allows creating symbols that we don't emit, so filter
+            // them out here.
+            //
+            // Since we don't actually emit the symbol kind, we validate it here too.
+            match symbol.kind {
+                SymbolKind::Text | SymbolKind::Data | SymbolKind::Tls | SymbolKind::Unknown => {}
+                SymbolKind::File | SymbolKind::Section => continue,
+                SymbolKind::Null | SymbolKind::Label => {
+                    return Err(Error(format!(
+                        "unimplemented symbol `{}` kind {:?}",
+                        symbol.name().unwrap_or(""),
+                        symbol.kind
+                    )));
+                }
+            }
+            if !symbol.name.is_empty() {
+                symbol_offsets[index].str_id = Some(strtab.add(&symbol.name));
+            }
+            if symbol.is_undefined() {
+                undefined_symbols.push(index);
+            } else if symbol.is_local() {
+                local_symbols.push(index);
+            } else {
+                external_symbols.push(index);
+            }
+        }
+
+        external_symbols.sort_by_key(|index| &*self.symbols[*index].name);
+        undefined_symbols.sort_by_key(|index| &*self.symbols[*index].name);
+
+        // Count symbols.
+        let mut nsyms = 0;
+        for index in local_symbols
+            .iter()
+            .copied()
+            .chain(external_symbols.iter().copied())
+            .chain(undefined_symbols.iter().copied())
+        {
+            symbol_offsets[index].index = nsyms;
+            nsyms += 1;
+        }
+
+        // Calculate size of relocations.
+        for (index, section) in self.sections.iter().enumerate() {
+            let count: usize = section
+                .relocations
+                .iter()
+                .map(|reloc| 1 + usize::from(reloc.addend != 0))
+                .sum();
+            if count != 0 {
+                offset = align(offset, pointer_align);
+                section_offsets[index].reloc_offset = offset;
+                section_offsets[index].reloc_count = count;
+                let len = count * mem::size_of::<macho::Relocation<Endianness>>();
+                offset += len;
+            }
+        }
+
+        // Calculate size of symtab.
+        offset = align(offset, pointer_align);
+        let symtab_offset = offset;
+        let symtab_len = nsyms * macho.nlist_size();
+        offset += symtab_len;
+
+        // Calculate size of strtab.
+        let strtab_offset = offset;
+        // Start with null name.
+        let mut strtab_data = vec![0];
+        strtab.write(1, &mut strtab_data);
+        write_align(&mut strtab_data, pointer_align);
+        offset += strtab_data.len();
+
+        // Start writing.
+        buffer
+            .reserve(offset)
+            .map_err(|_| Error(String::from("Cannot allocate buffer")))?;
+
+        // Write file header.
+        let (cputype, mut cpusubtype) = match (self.architecture, self.sub_architecture) {
+            (Architecture::Arm, None) => (macho::CPU_TYPE_ARM, macho::CPU_SUBTYPE_ARM_ALL),
+            (Architecture::Aarch64, None) => (macho::CPU_TYPE_ARM64, macho::CPU_SUBTYPE_ARM64_ALL),
+            (Architecture::Aarch64, Some(SubArchitecture::Arm64E)) => {
+                (macho::CPU_TYPE_ARM64, macho::CPU_SUBTYPE_ARM64E)
+            }
+            (Architecture::Aarch64_Ilp32, None) => {
+                (macho::CPU_TYPE_ARM64_32, macho::CPU_SUBTYPE_ARM64_32_V8)
+            }
+            (Architecture::I386, None) => (macho::CPU_TYPE_X86, macho::CPU_SUBTYPE_I386_ALL),
+            (Architecture::X86_64, None) => (macho::CPU_TYPE_X86_64, macho::CPU_SUBTYPE_X86_64_ALL),
+            (Architecture::PowerPc, None) => {
+                (macho::CPU_TYPE_POWERPC, macho::CPU_SUBTYPE_POWERPC_ALL)
+            }
+            (Architecture::PowerPc64, None) => {
+                (macho::CPU_TYPE_POWERPC64, macho::CPU_SUBTYPE_POWERPC_ALL)
+            }
+            _ => {
+                return Err(Error(format!(
+                    "unimplemented architecture {:?} with sub-architecture {:?}",
+                    self.architecture, self.sub_architecture
+                )));
+            }
+        };
+
+        if let Some(cpu_subtype) = self.macho_cpu_subtype {
+            cpusubtype = cpu_subtype;
+        }
+
+        let flags = match self.flags {
+            FileFlags::MachO { flags } => flags,
+            _ => 0,
+        };
+        macho.write_mach_header(
+            buffer,
+            MachHeader {
+                cputype,
+                cpusubtype,
+                filetype: macho::MH_OBJECT,
+                ncmds,
+                sizeofcmds: sizeofcmds as u32,
+                flags,
+            },
+        );
+
+        // Write segment command.
+        debug_assert_eq!(segment_command_offset, buffer.len());
+        macho.write_segment_command(
+            buffer,
+            SegmentCommand {
+                cmdsize: segment_command_len as u32,
+                segname: [0; 16],
+                vmaddr: 0,
+                vmsize: address,
+                fileoff: segment_file_offset as u64,
+                filesize: segment_file_size as u64,
+                maxprot: macho::VM_PROT_READ | macho::VM_PROT_WRITE | macho::VM_PROT_EXECUTE,
+                initprot: macho::VM_PROT_READ | macho::VM_PROT_WRITE | macho::VM_PROT_EXECUTE,
+                nsects: self.sections.len() as u32,
+                flags: 0,
+            },
+        );
+
+        // Write section headers.
+        for (index, section) in self.sections.iter().enumerate() {
+            let mut sectname = [0; 16];
+            sectname
+                .get_mut(..section.name.len())
+                .ok_or_else(|| {
+                    Error(format!(
+                        "section name `{}` is too long",
+                        section.name().unwrap_or(""),
+                    ))
+                })?
+                .copy_from_slice(&section.name);
+            let mut segname = [0; 16];
+            segname
+                .get_mut(..section.segment.len())
+                .ok_or_else(|| {
+                    Error(format!(
+                        "segment name `{}` is too long",
+                        section.segment().unwrap_or(""),
+                    ))
+                })?
+                .copy_from_slice(&section.segment);
+            let flags = if let SectionFlags::MachO { flags } = section.flags {
+                flags
+            } else {
+                match section.kind {
+                    SectionKind::Text => {
+                        macho::S_ATTR_PURE_INSTRUCTIONS | macho::S_ATTR_SOME_INSTRUCTIONS
+                    }
+                    SectionKind::Data => 0,
+                    SectionKind::ReadOnlyData | SectionKind::ReadOnlyDataWithRel => 0,
+                    SectionKind::ReadOnlyString => macho::S_CSTRING_LITERALS,
+                    SectionKind::UninitializedData | SectionKind::Common => macho::S_ZEROFILL,
+                    SectionKind::Tls => macho::S_THREAD_LOCAL_REGULAR,
+                    SectionKind::UninitializedTls => macho::S_THREAD_LOCAL_ZEROFILL,
+                    SectionKind::TlsVariables => macho::S_THREAD_LOCAL_VARIABLES,
+                    SectionKind::Debug => macho::S_ATTR_DEBUG,
+                    SectionKind::OtherString => macho::S_CSTRING_LITERALS,
+                    SectionKind::Other | SectionKind::Linker | SectionKind::Metadata => 0,
+                    SectionKind::Note | SectionKind::Unknown | SectionKind::Elf(_) => {
+                        return Err(Error(format!(
+                            "unimplemented section `{}` kind {:?}",
+                            section.name().unwrap_or(""),
+                            section.kind
+                        )));
+                    }
+                }
+            };
+            macho.write_section(
+                buffer,
+                SectionHeader {
+                    sectname,
+                    segname,
+                    addr: section_offsets[index].address,
+                    size: section.size,
+                    offset: section_offsets[index].offset as u32,
+                    align: section.align.trailing_zeros(),
+                    reloff: section_offsets[index].reloc_offset as u32,
+                    nreloc: section_offsets[index].reloc_count as u32,
+                    flags,
+                },
+            );
+        }
+
+        // Write build version.
+        if let Some(version) = &self.macho_build_version {
+            debug_assert_eq!(build_version_offset, buffer.len());
+            buffer.write(&macho::BuildVersionCommand {
+                cmd: U32::new(endian, macho::LC_BUILD_VERSION),
+                cmdsize: U32::new(endian, version.cmdsize()),
+                platform: U32::new(endian, version.platform),
+                minos: U32::new(endian, version.minos),
+                sdk: U32::new(endian, version.sdk),
+                ntools: U32::new(endian, 0),
+            });
+        }
+
+        // Write symtab command.
+        debug_assert_eq!(symtab_command_offset, buffer.len());
+        let symtab_command = macho::SymtabCommand {
+            cmd: U32::new(endian, macho::LC_SYMTAB),
+            cmdsize: U32::new(endian, symtab_command_len as u32),
+            symoff: U32::new(endian, symtab_offset as u32),
+            nsyms: U32::new(endian, nsyms as u32),
+            stroff: U32::new(endian, strtab_offset as u32),
+            strsize: U32::new(endian, strtab_data.len() as u32),
+        };
+        buffer.write(&symtab_command);
+
+        // Write dysymtab command.
+        debug_assert_eq!(dysymtab_command_offset, buffer.len());
+        let dysymtab_command = macho::DysymtabCommand {
+            cmd: U32::new(endian, macho::LC_DYSYMTAB),
+            cmdsize: U32::new(endian, dysymtab_command_len as u32),
+            ilocalsym: U32::new(endian, 0),
+            nlocalsym: U32::new(endian, local_symbols.len() as u32),
+            iextdefsym: U32::new(endian, local_symbols.len() as u32),
+            nextdefsym: U32::new(endian, external_symbols.len() as u32),
+            iundefsym: U32::new(
+                endian,
+                local_symbols.len() as u32 + external_symbols.len() as u32,
+            ),
+            nundefsym: U32::new(endian, undefined_symbols.len() as u32),
+            tocoff: U32::default(),
+            ntoc: U32::default(),
+            modtaboff: U32::default(),
+            nmodtab: U32::default(),
+            extrefsymoff: U32::default(),
+            nextrefsyms: U32::default(),
+            indirectsymoff: U32::default(),
+            nindirectsyms: U32::default(),
+            extreloff: U32::default(),
+            nextrel: U32::default(),
+            locreloff: U32::default(),
+            nlocrel: U32::default(),
+        };
+        buffer.write(&dysymtab_command);
+
+        // Write section data.
+        for (index, section) in self.sections.iter().enumerate() {
+            if !section.is_bss() {
+                buffer.resize(section_offsets[index].offset);
+                buffer.write_bytes(&section.data);
+            }
+        }
+        debug_assert_eq!(segment_file_offset + segment_file_size, buffer.len());
+
+        // Write relocations.
+        for (index, section) in self.sections.iter().enumerate() {
+            if !section.relocations.is_empty() {
+                write_align(buffer, pointer_align);
+                debug_assert_eq!(section_offsets[index].reloc_offset, buffer.len());
+                for reloc in &section.relocations {
+                    let r_length = match reloc.size {
+                        8 => 0,
+                        16 => 1,
+                        32 => 2,
+                        64 => 3,
+                        _ => return Err(Error(format!("unimplemented reloc size {:?}", reloc))),
+                    };
+
+                    // Write explicit addend.
+                    if reloc.addend != 0 {
+                        let r_type = match self.architecture {
+                            Architecture::Aarch64 | Architecture::Aarch64_Ilp32 => {
+                                macho::ARM64_RELOC_ADDEND
+                            }
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)))
+                            }
+                        };
+
+                        let reloc_info = macho::RelocationInfo {
+                            r_address: reloc.offset as u32,
+                            r_symbolnum: reloc.addend as u32,
+                            r_pcrel: false,
+                            r_length,
+                            r_extern: false,
+                            r_type,
+                        };
+                        buffer.write(&reloc_info.relocation(endian));
+                    }
+
+                    let r_extern;
+                    let r_symbolnum;
+                    let symbol = &self.symbols[reloc.symbol.0];
+                    if symbol.kind == SymbolKind::Section {
+                        r_symbolnum = section_offsets[symbol.section.id().unwrap().0].index as u32;
+                        r_extern = false;
+                    } else {
+                        r_symbolnum = symbol_offsets[reloc.symbol.0].index as u32;
+                        r_extern = true;
+                    }
+                    let (r_pcrel, r_type) = match self.architecture {
+                        Architecture::I386 => match reloc.kind {
+                            RelocationKind::Absolute => (false, macho::GENERIC_RELOC_VANILLA),
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::X86_64 => match (reloc.kind, reloc.encoding) {
+                            (RelocationKind::Absolute, RelocationEncoding::Generic) => {
+                                (false, macho::X86_64_RELOC_UNSIGNED)
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::Generic) => {
+                                (true, macho::X86_64_RELOC_SIGNED)
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::X86RipRelative) => {
+                                (true, macho::X86_64_RELOC_SIGNED)
+                            }
+                            (RelocationKind::Relative, RelocationEncoding::X86Branch) => {
+                                (true, macho::X86_64_RELOC_BRANCH)
+                            }
+                            (RelocationKind::PltRelative, RelocationEncoding::X86Branch) => {
+                                (true, macho::X86_64_RELOC_BRANCH)
+                            }
+                            (RelocationKind::GotRelative, RelocationEncoding::Generic) => {
+                                (true, macho::X86_64_RELOC_GOT)
+                            }
+                            (
+                                RelocationKind::GotRelative,
+                                RelocationEncoding::X86RipRelativeMovq,
+                            ) => (true, macho::X86_64_RELOC_GOT_LOAD),
+                            (RelocationKind::MachO { value, relative }, _) => (relative, value),
+                            _ => {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        },
+                        Architecture::Aarch64 | Architecture::Aarch64_Ilp32 => {
+                            match (reloc.kind, reloc.encoding) {
+                                (RelocationKind::Absolute, RelocationEncoding::Generic) => {
+                                    (false, macho::ARM64_RELOC_UNSIGNED)
+                                }
+                                (RelocationKind::Relative, RelocationEncoding::AArch64Call) => {
+                                    (true, macho::ARM64_RELOC_BRANCH26)
+                                }
+                                (
+                                    RelocationKind::MachO { value, relative },
+                                    RelocationEncoding::Generic,
+                                ) => (relative, value),
+                                _ => {
+                                    return Err(Error(format!(
+                                        "unimplemented relocation {:?}",
+                                        reloc
+                                    )));
+                                }
+                            }
+                        }
+                        _ => {
+                            if let RelocationKind::MachO { value, relative } = reloc.kind {
+                                (relative, value)
+                            } else {
+                                return Err(Error(format!("unimplemented relocation {:?}", reloc)));
+                            }
+                        }
+                    };
+                    let reloc_info = macho::RelocationInfo {
+                        r_address: reloc.offset as u32,
+                        r_symbolnum,
+                        r_pcrel,
+                        r_length,
+                        r_extern,
+                        r_type,
+                    };
+                    buffer.write(&reloc_info.relocation(endian));
+                }
+            }
+        }
+
+        // Write symtab.
+        write_align(buffer, pointer_align);
+        debug_assert_eq!(symtab_offset, buffer.len());
+        for index in local_symbols
+            .iter()
+            .copied()
+            .chain(external_symbols.iter().copied())
+            .chain(undefined_symbols.iter().copied())
+        {
+            let symbol = &self.symbols[index];
+            // TODO: N_STAB
+            let (mut n_type, n_sect) = match symbol.section {
+                SymbolSection::Undefined => (macho::N_UNDF | macho::N_EXT, 0),
+                SymbolSection::Absolute => (macho::N_ABS, 0),
+                SymbolSection::Section(id) => (macho::N_SECT, id.0 + 1),
+                SymbolSection::None | SymbolSection::Common => {
+                    return Err(Error(format!(
+                        "unimplemented symbol `{}` section {:?}",
+                        symbol.name().unwrap_or(""),
+                        symbol.section
+                    )));
+                }
+            };
+            match symbol.scope {
+                SymbolScope::Unknown | SymbolScope::Compilation => {}
+                SymbolScope::Linkage => {
+                    n_type |= macho::N_EXT | macho::N_PEXT;
+                }
+                SymbolScope::Dynamic => {
+                    n_type |= macho::N_EXT;
+                }
+            }
+
+            let n_desc = if let SymbolFlags::MachO { n_desc } = symbol.flags {
+                n_desc
+            } else {
+                let mut n_desc = 0;
+                if symbol.weak {
+                    if symbol.is_undefined() {
+                        n_desc |= macho::N_WEAK_REF;
+                    } else {
+                        n_desc |= macho::N_WEAK_DEF;
+                    }
+                }
+                n_desc
+            };
+
+            let n_value = match symbol.section.id() {
+                Some(section) => section_offsets[section.0].address + symbol.value,
+                None => symbol.value,
+            };
+
+            let n_strx = symbol_offsets[index]
+                .str_id
+                .map(|id| strtab.get_offset(id))
+                .unwrap_or(0);
+
+            macho.write_nlist(
+                buffer,
+                Nlist {
+                    n_strx: n_strx as u32,
+                    n_type,
+                    n_sect: n_sect as u8,
+                    n_desc,
+                    n_value,
+                },
+            );
+        }
+
+        // Write strtab.
+        debug_assert_eq!(strtab_offset, buffer.len());
+        buffer.write_bytes(&strtab_data);
+
+        debug_assert_eq!(offset, buffer.len());
+
+        Ok(())
+    }
+}
+
+struct MachHeader {
+    cputype: u32,
+    cpusubtype: u32,
+    filetype: u32,
+    ncmds: u32,
+    sizeofcmds: u32,
+    flags: u32,
+}
+
+struct SegmentCommand {
+    cmdsize: u32,
+    segname: [u8; 16],
+    vmaddr: u64,
+    vmsize: u64,
+    fileoff: u64,
+    filesize: u64,
+    maxprot: u32,
+    initprot: u32,
+    nsects: u32,
+    flags: u32,
+}
+
+pub struct SectionHeader {
+    sectname: [u8; 16],
+    segname: [u8; 16],
+    addr: u64,
+    size: u64,
+    offset: u32,
+    align: u32,
+    reloff: u32,
+    nreloc: u32,
+    flags: u32,
+}
+
+struct Nlist {
+    n_strx: u32,
+    n_type: u8,
+    n_sect: u8,
+    n_desc: u16,
+    n_value: u64,
+}
+
+trait MachO {
+    fn mach_header_size(&self) -> usize;
+    fn segment_command_size(&self) -> usize;
+    fn section_header_size(&self) -> usize;
+    fn nlist_size(&self) -> usize;
+    fn write_mach_header(&self, buffer: &mut dyn WritableBuffer, section: MachHeader);
+    fn write_segment_command(&self, buffer: &mut dyn WritableBuffer, segment: SegmentCommand);
+    fn write_section(&self, buffer: &mut dyn WritableBuffer, section: SectionHeader);
+    fn write_nlist(&self, buffer: &mut dyn WritableBuffer, nlist: Nlist);
+}
+
+struct MachO32<E> {
+    endian: E,
+}
+
+impl<E: Endian> MachO for MachO32<E> {
+    fn mach_header_size(&self) -> usize {
+        mem::size_of::<macho::MachHeader32<E>>()
+    }
+
+    fn segment_command_size(&self) -> usize {
+        mem::size_of::<macho::SegmentCommand32<E>>()
+    }
+
+    fn section_header_size(&self) -> usize {
+        mem::size_of::<macho::Section32<E>>()
+    }
+
+    fn nlist_size(&self) -> usize {
+        mem::size_of::<macho::Nlist32<E>>()
+    }
+
+    fn write_mach_header(&self, buffer: &mut dyn WritableBuffer, header: MachHeader) {
+        let endian = self.endian;
+        let magic = if endian.is_big_endian() {
+            macho::MH_MAGIC
+        } else {
+            macho::MH_CIGAM
+        };
+        let header = macho::MachHeader32 {
+            magic: U32::new(BigEndian, magic),
+            cputype: U32::new(endian, header.cputype),
+            cpusubtype: U32::new(endian, header.cpusubtype),
+            filetype: U32::new(endian, header.filetype),
+            ncmds: U32::new(endian, header.ncmds),
+            sizeofcmds: U32::new(endian, header.sizeofcmds),
+            flags: U32::new(endian, header.flags),
+        };
+        buffer.write(&header);
+    }
+
+    fn write_segment_command(&self, buffer: &mut dyn WritableBuffer, segment: SegmentCommand) {
+        let endian = self.endian;
+        let segment = macho::SegmentCommand32 {
+            cmd: U32::new(endian, macho::LC_SEGMENT),
+            cmdsize: U32::new(endian, segment.cmdsize),
+            segname: segment.segname,
+            vmaddr: U32::new(endian, segment.vmaddr as u32),
+            vmsize: U32::new(endian, segment.vmsize as u32),
+            fileoff: U32::new(endian, segment.fileoff as u32),
+            filesize: U32::new(endian, segment.filesize as u32),
+            maxprot: U32::new(endian, segment.maxprot),
+            initprot: U32::new(endian, segment.initprot),
+            nsects: U32::new(endian, segment.nsects),
+            flags: U32::new(endian, segment.flags),
+        };
+        buffer.write(&segment);
+    }
+
+    fn write_section(&self, buffer: &mut dyn WritableBuffer, section: SectionHeader) {
+        let endian = self.endian;
+        let section = macho::Section32 {
+            sectname: section.sectname,
+            segname: section.segname,
+            addr: U32::new(endian, section.addr as u32),
+            size: U32::new(endian, section.size as u32),
+            offset: U32::new(endian, section.offset),
+            align: U32::new(endian, section.align),
+            reloff: U32::new(endian, section.reloff),
+            nreloc: U32::new(endian, section.nreloc),
+            flags: U32::new(endian, section.flags),
+            reserved1: U32::default(),
+            reserved2: U32::default(),
+        };
+        buffer.write(&section);
+    }
+
+    fn write_nlist(&self, buffer: &mut dyn WritableBuffer, nlist: Nlist) {
+        let endian = self.endian;
+        let nlist = macho::Nlist32 {
+            n_strx: U32::new(endian, nlist.n_strx),
+            n_type: nlist.n_type,
+            n_sect: nlist.n_sect,
+            n_desc: U16::new(endian, nlist.n_desc),
+            n_value: U32::new(endian, nlist.n_value as u32),
+        };
+        buffer.write(&nlist);
+    }
+}
+
+struct MachO64<E> {
+    endian: E,
+}
+
+impl<E: Endian> MachO for MachO64<E> {
+    fn mach_header_size(&self) -> usize {
+        mem::size_of::<macho::MachHeader64<E>>()
+    }
+
+    fn segment_command_size(&self) -> usize {
+        mem::size_of::<macho::SegmentCommand64<E>>()
+    }
+
+    fn section_header_size(&self) -> usize {
+        mem::size_of::<macho::Section64<E>>()
+    }
+
+    fn nlist_size(&self) -> usize {
+        mem::size_of::<macho::Nlist64<E>>()
+    }
+
+    fn write_mach_header(&self, buffer: &mut dyn WritableBuffer, header: MachHeader) {
+        let endian = self.endian;
+        let magic = if endian.is_big_endian() {
+            macho::MH_MAGIC_64
+        } else {
+            macho::MH_CIGAM_64
+        };
+        let header = macho::MachHeader64 {
+            magic: U32::new(BigEndian, magic),
+            cputype: U32::new(endian, header.cputype),
+            cpusubtype: U32::new(endian, header.cpusubtype),
+            filetype: U32::new(endian, header.filetype),
+            ncmds: U32::new(endian, header.ncmds),
+            sizeofcmds: U32::new(endian, header.sizeofcmds),
+            flags: U32::new(endian, header.flags),
+            reserved: U32::default(),
+        };
+        buffer.write(&header);
+    }
+
+    fn write_segment_command(&self, buffer: &mut dyn WritableBuffer, segment: SegmentCommand) {
+        let endian = self.endian;
+        let segment = macho::SegmentCommand64 {
+            cmd: U32::new(endian, macho::LC_SEGMENT_64),
+            cmdsize: U32::new(endian, segment.cmdsize),
+            segname: segment.segname,
+            vmaddr: U64::new(endian, segment.vmaddr),
+            vmsize: U64::new(endian, segment.vmsize),
+            fileoff: U64::new(endian, segment.fileoff),
+            filesize: U64::new(endian, segment.filesize),
+            maxprot: U32::new(endian, segment.maxprot),
+            initprot: U32::new(endian, segment.initprot),
+            nsects: U32::new(endian, segment.nsects),
+            flags: U32::new(endian, segment.flags),
+        };
+        buffer.write(&segment);
+    }
+
+    fn write_section(&self, buffer: &mut dyn WritableBuffer, section: SectionHeader) {
+        let endian = self.endian;
+        let section = macho::Section64 {
+            sectname: section.sectname,
+            segname: section.segname,
+            addr: U64::new(endian, section.addr),
+            size: U64::new(endian, section.size),
+            offset: U32::new(endian, section.offset),
+            align: U32::new(endian, section.align),
+            reloff: U32::new(endian, section.reloff),
+            nreloc: U32::new(endian, section.nreloc),
+            flags: U32::new(endian, section.flags),
+            reserved1: U32::default(),
+            reserved2: U32::default(),
+            reserved3: U32::default(),
+        };
+        buffer.write(&section);
+    }
+
+    fn write_nlist(&self, buffer: &mut dyn WritableBuffer, nlist: Nlist) {
+        let endian = self.endian;
+        let nlist = macho::Nlist64 {
+            n_strx: U32::new(endian, nlist.n_strx),
+            n_type: nlist.n_type,
+            n_sect: nlist.n_sect,
+            n_desc: U16::new(endian, nlist.n_desc),
+            n_value: U64Bytes::new(endian, nlist.n_value),
+        };
+        buffer.write(&nlist);
+    }
+}