xenia-rs/crates/xenia-analysis/src/func.rs

//! Function boundary detection via PPC prologue/epilogue pattern matching.
//!
//! Strategy (multi-pass):
//! 1. Identify all `bl` (branch-and-link) targets — these are call sites,
//!    hence very likely function entry points.
//! 2. Scan the save/restore GPR helper region and label it.
//! 3. For each candidate entry, look for prologue patterns:
//!      a) `mfspr rN, LR` (typically r0 or r12)
//!      b) `bl __savegprlr_NN`  (call into save stub)
//!      c) `stwu r1, -N(r1)`   (allocate stack frame)
//!    If a prologue is confirmed, record the function and its stack frame size.
//! 4. Walk forward from each function entry to find the epilogue:
//!      a) `blr`  (return)
//!      b) `b __restgprlr_NN` (tail-branch into restore stub which returns)
//!    Mark the function's end address.
//! 5. Detect leaf functions: `bl` targets that lack a prologue but eventually `blr`.

use std::collections::{HashMap, HashSet, BTreeMap};

/// Information about a detected function.
#[derive(Debug, Clone)]
pub struct FuncInfo {
    /// Absolute start address.
    pub start: u32,
    /// Absolute end address (exclusive — one past last instruction).
    pub end: u32,
    /// Stack frame size (0 if unknown / leaf).
    pub frame_size: u32,
    /// Number of saved GPRs (via __savegprlr helper), 0 if unknown.
    pub saved_gprs: u32,
    /// True if this is a leaf function (no bl, no frame setup).
    pub is_leaf: bool,
    /// True if this is a save/restore GPR helper stub.
    pub is_saverestore: bool,
}

/// Result of the function analysis pass.
pub struct FuncAnalysis {
    /// address → FuncInfo for every detected function, sorted by address.
    pub functions: BTreeMap<u32, FuncInfo>,
    /// Addresses in the save-GPR region (start of __savegprlr block).
    pub save_gpr_base: Option<u32>,
    /// Addresses in the restore-GPR region (start of __restgprlr block).
    pub restore_gpr_base: Option<u32>,
}

// ── Instruction field helpers ──────────────────────────────────────────────

fn op(instr: u32) -> u32 { (instr >> 26) & 0x3F }
fn bits(instr: u32, hi: u32, lo: u32) -> u32 {
    (instr >> (31 - hi)) & ((1 << (hi - lo + 1)) - 1)
}

fn is_mfspr_lr(instr: u32) -> Option<u32> {
    // mfspr rD, LR  →  opcode 31, xo=339, spr=8
    if op(instr) != 31 { return None; }
    let xo = bits(instr, 30, 21);
    if xo != 339 { return None; }
    let spr = (bits(instr, 20, 16) << 5) | bits(instr, 15, 11);
    if spr != 8 { return None; }
    Some(bits(instr, 10, 6)) // return rD
}

#[allow(dead_code)]
fn is_mtspr_lr(instr: u32) -> bool {
    // mtspr LR, rS  →  opcode 31, xo=467, spr=8
    if op(instr) != 31 { return false; }
    let xo = bits(instr, 30, 21);
    if xo != 467 { return false; }
    let spr = (bits(instr, 20, 16) << 5) | bits(instr, 15, 11);
    spr == 8
}

fn is_stwu_r1(instr: u32) -> Option<i32> {
    // stwu r1, d(r1)  →  opcode 37, rS=1, rA=1
    if op(instr) != 37 { return None; }
    let rs = bits(instr, 10, 6);
    let ra = bits(instr, 15, 11);
    if rs != 1 || ra != 1 { return None; }
    let d = ((instr & 0xFFFF) as i16) as i32;
    Some(d) // negative = frame allocation
}

fn is_blr(instr: u32) -> bool {
    instr == 0x4E800020
}

fn is_bctr(instr: u32) -> bool {
    instr == 0x4E800420
}

fn is_bl(instr: u32) -> Option<u32> {
    // bl target  →  opcode 18, LK=1, AA=0
    if op(instr) != 18 { return None; }
    if instr & 1 == 0 { return None; } // must have LK bit
    if instr & 2 != 0 { return None; } // not absolute
    // Return the signed offset
    let li = instr & 0x03FFFFFC;
    Some(li)
}

fn is_b(instr: u32) -> Option<u32> {
    // b target → opcode 18, LK=0, AA=0
    if op(instr) != 18 { return None; }
    if instr & 1 != 0 { return None; } // no LK bit
    if instr & 2 != 0 { return None; } // not absolute
    Some(instr & 0x03FFFFFC)
}

fn sign_ext26(val: u32) -> i32 {
    ((val << 6) as i32) >> 6
}

fn bl_target(instr: u32, addr: u32) -> Option<u32> {
    is_bl(instr).map(|off| addr.wrapping_add(sign_ext26(off) as u32))
}

fn b_target(instr: u32, addr: u32) -> Option<u32> {
    is_b(instr).map(|off| addr.wrapping_add(sign_ext26(off) as u32))
}

// ── Read instruction from PE ───────────────────────────────────────────────

fn read_instr(pe: &[u8], abs_addr: u32, image_base: u32) -> Option<u32> {
    let off = abs_addr.wrapping_sub(image_base) as usize;
    if off + 4 > pe.len() { return None; }
    Some(u32::from_be_bytes([pe[off], pe[off+1], pe[off+2], pe[off+3]]))
}

// ── Detect the save/restore GPR helper stubs ───────────────────────────────
//
// These are a well-known pattern emitted by the Xbox 360 linker.
// Save block: a cascade of `std rN, offset(r1)` for r14..r31 + `stw r12, -8(r1)` + `blr`
// Restore:    a cascade of `ld rN, offset(r1)` for r14..r31 + `lwz r12, -8(r1)` + `mtspr LR, r12` + `blr`
//
// We detect the save block by finding 18 consecutive `std rN, ...(r1)` instructions
// for r14 through r31.

fn find_saverestore_stubs(
    pe: &[u8],
    image_base: u32,
    code_ranges: &[(u32, u32)], // (abs_start, abs_end)
) -> (Option<u32>, Option<u32>) {
    let mut save_base = None;
    let mut restore_base = None;

    for &(start, end) in code_ranges {
        let mut addr = start;
        while addr + 4 * 18 < end {
            // Check if this is `std r14, ...(r1)` — opcode 62 (std), rS=14, rA=1
            let instr = match read_instr(pe, addr, image_base) { Some(i) => i, None => { addr += 4; continue; } };
            if op(instr) == 62 && bits(instr, 10, 6) == 14 && bits(instr, 15, 11) == 1 && (instr & 3) == 0 {
                // Verify it's a cascade: r14, r15, ..., r31
                let mut ok = true;
                for i in 0u32..18 {
                    let check = match read_instr(pe, addr + i * 4, image_base) { Some(c) => c, None => { ok = false; break; } };
                    if op(check) != 62 || bits(check, 10, 6) != 14 + i || bits(check, 15, 11) != 1 {
                        ok = false;
                        break;
                    }
                }
                if ok {
                    save_base = Some(addr);
                    // Restore block typically follows the save block
                    // After save: stw r12, -8(r1) + blr, then restore starts
                    let after_save = addr + 18 * 4 + 8; // skip stw r12 + blr
                    let check = read_instr(pe, after_save, image_base);
                    if let Some(c) = check {
                        // Should be `ld r14, ...(r1)` — opcode 58, rT=14, rA=1
                        if op(c) == 58 && bits(c, 10, 6) == 14 && bits(c, 15, 11) == 1 {
                            restore_base = Some(after_save);
                        }
                    }
                    break;
                }
            }
            addr += 4;
        }
        if save_base.is_some() { break; }
    }

    (save_base, restore_base)
}

// ── Main analysis ──────────────────────────────────────────────────────────

#[tracing::instrument(skip_all, fields(image_base = format_args!("{:#010x}", image_base), entry_point = format_args!("{:#010x}", entry_point)))]
pub fn analyze(
    pe: &[u8],
    image_base: u32,
    entry_point: u32,
    code_sections: &[(u32, u32, u32)], // (va_start, va_size, flags)
) -> FuncAnalysis {
    let started = std::time::Instant::now();
    let code_ranges: Vec<(u32, u32)> = code_sections.iter()
        .map(|(va, sz, _)| (image_base + va, image_base + va + sz))
        .collect();

    // 1. Find save/restore stubs
    let (save_base, restore_base) = find_saverestore_stubs(pe, image_base, &code_ranges);
    if let Some(sb) = save_base {
        tracing::debug!(addr = format_args!("{:#010x}", sb), "__savegprlr stub");
    }
    if let Some(rb) = restore_base {
        tracing::debug!(addr = format_args!("{:#010x}", rb), "__restgprlr stub");
    }

    // Set of addresses in the save/restore region (to exclude from function detection)
    let mut saverestore_addrs: HashSet<u32> = HashSet::new();
    if let Some(sb) = save_base {
        // Save block: 18 std + stw + blr = 20 instructions
        for i in 0..20 { saverestore_addrs.insert(sb + i * 4); }
    }
    if let Some(rb) = restore_base {
        // Restore block: 18 ld + lwz + mtspr + blr = 21 instructions
        for i in 0..21 { saverestore_addrs.insert(rb + i * 4); }
    }

    // 2. Collect all bl targets as candidate function entries
    let mut call_targets: HashSet<u32> = HashSet::new();
    call_targets.insert(entry_point);

    for &(start, end) in &code_ranges {
        let mut addr = start;
        while addr < end {
            if let Some(instr) = read_instr(pe, addr, image_base)
                && let Some(target) = bl_target(instr, addr) {
                    // Don't count calls into save/restore stubs as function entries
                    if !saverestore_addrs.contains(&target) {
                        call_targets.insert(target);
                    }
                }
            addr += 4;
        }
    }
    tracing::debug!(candidates = call_targets.len(), "bl targets collected");

    // 3. For each candidate, detect prologue and walk to epilogue
    let mut functions: BTreeMap<u32, FuncInfo> = BTreeMap::new();

    for &func_addr in &call_targets {
        if let Some(fi) = analyze_function(pe, image_base, func_addr, &code_ranges, save_base, restore_base) {
            functions.insert(func_addr, fi);
        }
    }

    // 4. Label save/restore stubs as special functions — one entry for the whole block
    if let Some(sb) = save_base {
        // The save block is one cascade: entry at each rN, falls through to blr
        // Treat as a single function with the first entry point
        functions.insert(sb, FuncInfo {
            start: sb,
            end: sb + 20 * 4, // 18 std + stw r12 + blr
            frame_size: 0,
            saved_gprs: 18,
            is_leaf: true,
            is_saverestore: true,
        });
    }
    if let Some(rb) = restore_base {
        functions.insert(rb, FuncInfo {
            start: rb,
            end: rb + 21 * 4, // 18 ld + lwz r12 + mtspr LR + blr
            frame_size: 0,
            saved_gprs: 18,
            is_leaf: true,
            is_saverestore: true,
        });
    }

    let elapsed_ms = started.elapsed().as_millis() as f64;
    metrics::histogram!("analysis.phase_ms", "phase" => "functions").record(elapsed_ms);
    tracing::info!(
        functions = functions.len(),
        elapsed_ms,
        "function detection complete"
    );

    FuncAnalysis {
        functions,
        save_gpr_base: save_base,
        restore_gpr_base: restore_base,
    }
}

/// Analyze a single function starting at `func_addr`.
fn analyze_function(
    pe: &[u8],
    image_base: u32,
    func_addr: u32,
    code_ranges: &[(u32, u32)],
    save_base: Option<u32>,
    restore_base: Option<u32>,
) -> Option<FuncInfo> {
    // Verify the address is within a code section
    let in_code = code_ranges.iter().any(|&(s, e)| func_addr >= s && func_addr < e);
    if !in_code { return None; }

    let instr0 = read_instr(pe, func_addr, image_base)?;

    let mut frame_size: u32 = 0;
    let mut saved_gprs: u32 = 0;
    let mut is_leaf = false;
    let mut prologue_len: u32 = 0;

    // Pattern A: mfspr rN, LR  [+ bl __savegprlr_NN]  + stwu r1, -N(r1)
    if let Some(_lr_reg) = is_mfspr_lr(instr0) {
        prologue_len = 4;
        let instr1 = read_instr(pe, func_addr + 4, image_base).unwrap_or(0);

        // Check if next is bl to save stub
        if let Some(target) = bl_target(instr1, func_addr + 4)
            && let Some(sb) = save_base
                && target >= sb && target < sb + 18 * 4 {
                    let idx = (target - sb) / 4;
                    saved_gprs = 18 - idx;
                    prologue_len = 8;
                }

        // Next should be stwu r1, -N(r1)
        let stwu_instr = read_instr(pe, func_addr + prologue_len, image_base).unwrap_or(0);
        if let Some(d) = is_stwu_r1(stwu_instr) {
            frame_size = (-d) as u32;
            prologue_len += 4;
        }
    }
    // Pattern B: stwu r1, -N(r1) without mfspr (rare but possible for leaf-ish functions)
    else if let Some(d) = is_stwu_r1(instr0) {
        frame_size = (-d) as u32;
        prologue_len = 4;
        is_leaf = true; // no LR save = likely leaf (or uses CTR)
    }
    // Pattern C: no prologue — leaf function, just code until blr
    else {
        is_leaf = true;
    }

    // Walk forward to find the end of the function
    let max_range = code_ranges.iter()
        .find(|&&(s, e)| func_addr >= s && func_addr < e)
        .map(|&(_, e)| e)
        .unwrap_or(func_addr + 0x100000);

    let mut end_addr = func_addr + 4;
    let mut addr = func_addr + prologue_len;
    let scan_limit = std::cmp::min(addr + 0x100000, max_range); // 1MB max function

    while addr < scan_limit {
        let instr = match read_instr(pe, addr, image_base) {
            Some(i) => i,
            None => break,
        };

        // Epilogue: blr
        if is_blr(instr) {
            end_addr = addr + 4;
            // Check if the instruction after blr looks like padding or another function
            // Sometimes there's trailing data after blr; we stop at the first blr
            // that isn't inside a branch-over pattern
            break;
        }

        // Epilogue: b __restgprlr_NN (tail branch into restore stub)
        if let Some(target) = b_target(instr, addr)
            && let Some(rb) = restore_base
                && target >= rb && target < rb + 18 * 4 {
                    end_addr = addr + 4;
                    break;
                }

        // Epilogue: bctr (indirect tail call — end of function)
        if is_bctr(instr) {
            end_addr = addr + 4;
            break;
        }

        addr += 4;
    }

    // If we didn't find any epilogue within a reasonable range, still emit
    // the function but mark end at the scan point
    if end_addr <= func_addr + 4 && prologue_len > 0 {
        end_addr = addr;
    }

    // Don't emit zero-size "functions" for addresses that are just data
    if end_addr <= func_addr + 4 && prologue_len == 0 {
        return None;
    }

    Some(FuncInfo {
        start: func_addr,
        end: end_addr,
        frame_size,
        saved_gprs,
        is_leaf,
        is_saverestore: false,
    })
}

// ── Label generation ───────────────────────────────────────────────────────

impl FuncAnalysis {
    /// Generate labels for all detected functions.
    /// Call targets with confirmed prologues get `sub_XXXXXXXX`.
    /// Save/restore entries get `__savegprlr_NN` / `__restgprlr_NN`.
    pub fn generate_labels(&self) -> HashMap<u32, String> {
        let mut labels = HashMap::new();

        for (&addr, fi) in &self.functions {
            if fi.is_saverestore {
                // Label the block start, plus individual register entry points
                if let Some(sb) = self.save_gpr_base
                    && addr == sb {
                        for i in 0u32..18 {
                            let reg = 14 + i;
                            labels.insert(sb + i * 4, format!("__savegprlr_{reg}"));
                        }
                        continue;
                    }
                if let Some(rb) = self.restore_gpr_base
                    && addr == rb {
                        for i in 0u32..18 {
                            let reg = 14 + i;
                            labels.insert(rb + i * 4, format!("__restgprlr_{reg}"));
                        }
                        continue;
                    }
            }
            labels.insert(addr, format!("sub_{addr:08X}"));
        }

        labels
    }

    /// Returns true if `addr` is the start of a detected function.
    pub fn is_function_start(&self, addr: u32) -> bool {
        self.functions.contains_key(&addr)
    }

    /// Get info for the function starting at `addr`.
    pub fn get(&self, addr: u32) -> Option<&FuncInfo> {
        self.functions.get(&addr)
    }
}