decomp-toolkit/src/obj/split.rs

use std::{cmp::min, collections::HashMap};

use anyhow::{anyhow, bail, ensure, Result};

use crate::obj::{
    ObjArchitecture, ObjInfo, ObjKind, ObjReloc, ObjSection, ObjSectionKind, ObjSymbol,
};

/// Split an executable object into relocatable objects.
pub fn split_obj(obj: &ObjInfo) -> Result<Vec<ObjInfo>> {
    ensure!(obj.kind == ObjKind::Executable, "Expected executable object");

    let mut objects: Vec<ObjInfo> = vec![];
    let mut object_symbols: Vec<Vec<Option<usize>>> = vec![];
    let mut name_to_obj: HashMap<String, usize> = HashMap::new();
    for unit in &obj.link_order {
        name_to_obj.insert(unit.clone(), objects.len());
        object_symbols.push(vec![None; obj.symbols.len()]);
        objects.push(ObjInfo {
            module_id: 0,
            kind: ObjKind::Relocatable,
            architecture: ObjArchitecture::PowerPc,
            name: unit.clone(),
            symbols: vec![],
            sections: vec![],
            entry: 0,
            sda2_base: None,
            sda_base: None,
            stack_address: None,
            stack_end: None,
            db_stack_addr: None,
            arena_lo: None,
            arena_hi: None,
            splits: Default::default(),
            named_sections: Default::default(),
            link_order: vec![],
            known_functions: Default::default(),
            unresolved_relocations: vec![],
        });
    }

    for (section_idx, section) in obj.sections.iter().enumerate() {
        let mut current_address = section.address as u32;
        let mut section_end = (section.address + section.size) as u32;
        // if matches!(section.name.as_str(), "extab" | "extabindex") {
        //     continue;
        // }
        // .ctors and .dtors end with a linker-generated null pointer,
        // adjust section size appropriately
        if matches!(section.name.as_str(), ".ctors" | ".dtors")
            && section.data[section.data.len() - 4..] == [0u8; 4]
        {
            section_end -= 4;
        }
        let mut file_iter = obj
            .splits
            .range(current_address..)
            .flat_map(|(addr, v)| v.iter().map(move |u| (addr, u)))
            .peekable();

        // Build address to relocation / address to symbol maps
        let relocations = section.build_relocation_map()?;
        let symbols = obj.build_symbol_map(section_idx)?;

        loop {
            if current_address >= section_end {
                break;
            }

            let (file_addr, unit) = match file_iter.next() {
                Some((&addr, unit)) => (addr, unit),
                None => bail!("No file found"),
            };
            ensure!(
                file_addr <= current_address,
                "Gap in files: {} @ {:#010X}, {} @ {:#010X}",
                section.name,
                section.address,
                unit,
                file_addr
            );
            let mut file_end = section_end;
            let mut dont_go_forward = false;
            if let Some(&(&next_addr, next_unit)) = file_iter.peek() {
                if file_addr == next_addr {
                    log::warn!("Duplicating {} in {unit} and {next_unit}", section.name);
                    dont_go_forward = true;
                    file_end = obj
                        .splits
                        .range(current_address + 1..)
                        .next()
                        .map(|(&addr, _)| addr)
                        .unwrap_or(section_end);
                } else {
                    file_end = min(next_addr, section_end);
                }
            }

            let file = name_to_obj
                .get(unit)
                .and_then(|&idx| objects.get_mut(idx))
                .ok_or_else(|| anyhow!("Unit '{unit}' not in link order"))?;
            let symbol_idxs = name_to_obj
                .get(unit)
                .and_then(|&idx| object_symbols.get_mut(idx))
                .ok_or_else(|| anyhow!("Unit '{unit}' not in link order"))?;

            // Calculate & verify section alignment
            let mut align = default_section_align(section);
            if current_address & (align as u32 - 1) != 0 {
                log::warn!(
                    "Alignment for {} {} expected {}, but starts at {:#010X}",
                    unit,
                    section.name,
                    align,
                    current_address
                );
                while align > 4 {
                    align /= 2;
                    if current_address & (align as u32 - 1) == 0 {
                        break;
                    }
                }
            }
            ensure!(
                current_address & (align as u32 - 1) == 0,
                "Invalid alignment for split: {} {} {:#010X}",
                unit,
                section.name,
                current_address
            );

            // Collect relocations; target_symbol will be updated later
            let out_relocations = relocations
                .range(current_address..file_end)
                .map(|(_, o)| ObjReloc {
                    kind: o.kind,
                    address: o.address - current_address as u64,
                    target_symbol: o.target_symbol,
                    addend: o.addend,
                })
                .collect();

            // Add section symbols
            let out_section_idx = file.sections.len();
            for &symbol_idx in symbols.range(current_address..file_end).flat_map(|(_, vec)| vec) {
                if symbol_idxs[symbol_idx].is_some() {
                    continue; // should never happen?
                }
                let symbol = &obj.symbols[symbol_idx];
                symbol_idxs[symbol_idx] = Some(file.symbols.len());
                file.symbols.push(ObjSymbol {
                    name: symbol.name.clone(),
                    demangled_name: symbol.demangled_name.clone(),
                    address: symbol.address - current_address as u64,
                    section: Some(out_section_idx),
                    size: symbol.size,
                    size_known: symbol.size_known,
                    flags: symbol.flags,
                    kind: symbol.kind,
                });
            }

            let data = match section.kind {
                ObjSectionKind::Bss => vec![],
                _ => section.data[(current_address as u64 - section.address) as usize
                    ..(file_end as u64 - section.address) as usize]
                    .to_vec(),
            };
            let name = if let Some(name) = obj.named_sections.get(&current_address) {
                name.clone()
            } else {
                section.name.clone()
            };
            file.sections.push(ObjSection {
                name,
                kind: section.kind,
                address: 0,
                size: file_end as u64 - current_address as u64,
                data,
                align,
                index: out_section_idx,
                elf_index: out_section_idx + 1,
                relocations: out_relocations,
                original_address: current_address as u64,
                file_offset: section.file_offset + (current_address as u64 - section.address),
                section_known: true,
            });

            if !dont_go_forward {
                current_address = file_end;
            }
        }
    }

    // Update relocations
    for (obj_idx, out_obj) in objects.iter_mut().enumerate() {
        let symbol_idxs = &mut object_symbols[obj_idx];
        for section in &mut out_obj.sections {
            for reloc in &mut section.relocations {
                match symbol_idxs[reloc.target_symbol] {
                    Some(out_sym_idx) => {
                        reloc.target_symbol = out_sym_idx;
                    }
                    None => {
                        // Extern
                        let out_sym_idx = out_obj.symbols.len();
                        let target_sym = &obj.symbols[reloc.target_symbol];
                        symbol_idxs[reloc.target_symbol] = Some(out_sym_idx);
                        out_obj.symbols.push(ObjSymbol {
                            name: target_sym.name.clone(),
                            demangled_name: target_sym.demangled_name.clone(),
                            ..Default::default()
                        });
                        reloc.target_symbol = out_sym_idx;
                        if section.name.as_str() == "extabindex" {
                            let (target_addr, target_unit) = obj
                                .splits
                                .range(..=target_sym.address as u32)
                                .map(|(addr, v)| (*addr, v.last().unwrap()))
                                .last()
                                .unwrap();
                            let target_section = &obj.section_at(target_addr)?.name;
                            log::warn!(
                                "Extern relocation @ {:#010X}\n\tSource object: {}:{:#010X} {}\n\tTarget object: {}:{:#010X} {}\n\tTarget symbol: {:#010X} {}\n",
                                reloc.address + section.original_address,
                                section.name,
                                section.original_address,
                                out_obj.name,
                                target_section,
                                target_addr,
                                target_unit,
                                target_sym.address,
                                target_sym.demangled_name.as_deref().unwrap_or(&target_sym.name),
                            );
                        }
                    }
                }
            }
        }
    }

    // Strip linker generated symbols
    for obj in &mut objects {
        for symbol in &mut obj.symbols {
            if is_skip_symbol(&symbol.name) {
                if symbol.section.is_some() {
                    log::debug!("Externing {:?} in {}", symbol, obj.name);
                    *symbol = ObjSymbol {
                        name: symbol.name.clone(),
                        demangled_name: symbol.demangled_name.clone(),
                        ..Default::default()
                    };
                }
            } else if is_linker_symbol(&symbol.name) {
                if let Some(section_idx) = symbol.section {
                    log::debug!("Skipping {:?} in {}", symbol, obj.name);
                    let section = &mut obj.sections[section_idx];
                    // TODO assuming end of file
                    section.size -= symbol.size;
                    section.data.truncate(section.data.len() - symbol.size as usize);
                    *symbol = ObjSymbol {
                        name: symbol.name.clone(),
                        demangled_name: symbol.demangled_name.clone(),
                        ..Default::default()
                    };
                }
            }
        }
    }

    Ok(objects)
}

/// mwld doesn't preserve the original section alignment values
fn default_section_align(section: &ObjSection) -> u64 {
    match section.kind {
        ObjSectionKind::Code => 4,
        _ => match section.name.as_str() {
            ".ctors" | ".dtors" | "extab" | "extabindex" => 4,
            _ => 8,
        },
    }
}

/// Linker-generated symbols to extern
#[inline]
fn is_skip_symbol(name: &str) -> bool {
    matches!(
        name,
        "_ctors"
            | "_dtors"
            | "_f_init"
            | "_f_init_rom"
            | "_e_init"
            | "_fextab"
            | "_fextab_rom"
            | "_eextab"
            | "_fextabindex"
            | "_fextabindex_rom"
            | "_eextabindex"
            | "_f_text"
            | "_f_text_rom"
            | "_e_text"
            | "_f_ctors"
            | "_f_ctors_rom"
            | "_e_ctors"
            | "_f_dtors"
            | "_f_dtors_rom"
            | "_e_dtors"
            | "_f_rodata"
            | "_f_rodata_rom"
            | "_e_rodata"
            | "_f_data"
            | "_f_data_rom"
            | "_e_data"
            | "_f_sdata"
            | "_f_sdata_rom"
            | "_e_sdata"
            | "_f_sbss"
            | "_f_sbss_rom"
            | "_e_sbss"
            | "_f_sdata2"
            | "_f_sdata2_rom"
            | "_e_sdata2"
            | "_f_sbss2"
            | "_f_sbss2_rom"
            | "_e_sbss2"
            | "_f_bss"
            | "_f_bss_rom"
            | "_e_bss"
            | "_f_stack"
            | "_f_stack_rom"
            | "_e_stack"
            | "_stack_addr"
            | "_stack_end"
            | "_db_stack_addr"
            | "_db_stack_end"
            | "_heap_addr"
            | "_heap_end"
            | "_nbfunctions"
            | "SIZEOF_HEADERS"
            | "_SDA_BASE_"
            | "_SDA2_BASE_"
            | "_ABS_SDA_BASE_"
            | "_ABS_SDA2_BASE_"
    )
}

/// Linker generated symbols to strip entirely
#[inline]
fn is_linker_symbol(name: &str) -> bool {
    matches!(
        name,
        "_eti_init_info" | "_rom_copy_info" | "_bss_init_info" | "_ctors$99" | "_dtors$99"
    )
}