Sylpheed/crates/sylpheed-xex/src/pdata.rs

//! PE32 `.pdata` exception data parser for PowerPC Xbox 360 binaries.
//!
//! Each `RUNTIME_FUNCTION` entry is 8 bytes, big-endian on disk:
//! ```text
//!   word 0: BeginAddress (absolute VA, not RVA — Xbox 360 convention)
//!   word 1: packed metadata (read as a single big-endian u32; MSVC
//!           bit-field layout packs LSB-first):
//!     bits  0.. 7 (low 8) : prolog_length    (instruction count, dwords)
//!     bits  8..29 (mid 22): function_length  (instruction count, dwords)
//!     bit  30             : 32-bit code flag (always 1 on PPC)
//!     bit  31             : exception-handler-present flag
//! ```
//!
//! Reference: Microsoft PE32+ exception data spec (PowerPC RUNTIME_FUNCTION);
//! xenia-canary `src/xenia/cpu/xex_module.cc:1570-1587` (canary only reads
//! `BeginAddress`; the metadata layout above is the authoritative spec).
//!
//! `BeginAddress = 0` terminates the table early in some images (canary breaks
//! on this; we mirror).

use crate::pe::PeSection;

/// One parsed `RUNTIME_FUNCTION` entry.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct PdataEntry {
    /// Absolute VA of the function's first instruction.
    pub begin_address: u32,
    /// Function size in bytes (function_length_dwords * 4).
    pub function_length: u32,
    /// Prolog size in bytes (prolog_length_dwords * 4).
    pub prolog_length: u32,
    /// Raw 2-bit flags lifted from the packed word's top two bits, i.e.
    /// `(meta >> 30) & 3`. So **bit 0 mirrors packed bit 30 (32-bit-code, set
    /// on essentially every PPC entry) and bit 1 mirrors packed bit 31
    /// (exception handler registered)** — test `flags & 2` for "has EH".
    pub flags: u8,
}

impl PdataEntry {
    /// One-past-the-last instruction (exclusive).
    pub fn end_address(&self) -> u32 {
        self.begin_address.wrapping_add(self.function_length)
    }
}

/// Parse the `.pdata` section out of a decompressed PE image.
///
/// `pe` is the full image buffer (image_base-relative); `image_base` and the
/// `.pdata` section descriptor come from `sylpheed_xex::pe::parse_sections`.
/// Returns an empty vec if no `.pdata` section is present or it falls outside
/// the buffer — never an error (the caller already validated the section list).
pub fn parse_pdata(pe: &[u8], image_base: u32, sections: &[PeSection]) -> Vec<PdataEntry> {
    let pdata = match sections.iter().find(|s| s.name == ".pdata") {
        Some(s) => s,
        None => return Vec::new(),
    };

    let off = pdata.virtual_address as usize;
    let len = pdata.virtual_size as usize;
    if off.saturating_add(len) > pe.len() {
        return Vec::new();
    }

    // Each entry is 8 bytes; truncate any partial trailing entry.
    let n_entries = len / 8;
    let mut out = Vec::with_capacity(n_entries);

    for i in 0..n_entries {
        let p = off + i * 8;
        let begin = u32::from_be_bytes([pe[p], pe[p + 1], pe[p + 2], pe[p + 3]]);
        let meta = u32::from_be_bytes([pe[p + 4], pe[p + 5], pe[p + 6], pe[p + 7]]);

        // Sentinel: BeginAddress=0 marks early termination (canary `xex_module.cc:1583`).
        if begin == 0 {
            break;
        }

        let prolog_dwords = meta & 0xFF;
        let function_dwords = (meta >> 8) & 0x003F_FFFF;
        let flags = ((meta >> 30) & 0x3) as u8;

        out.push(PdataEntry {
            begin_address: begin,
            function_length: function_dwords * 4,
            prolog_length: prolog_dwords * 4,
            flags,
        });
    }

    // Sanity: drop any entry whose begin_address falls outside the image bounds.
    // Image high water = image_base + the largest virtual_address+virtual_size.
    let high = sections
        .iter()
        .map(|s| {
            image_base
                .wrapping_add(s.virtual_address)
                .wrapping_add(s.virtual_size)
        })
        .max()
        .unwrap_or(u32::MAX);
    out.retain(|e| e.begin_address >= image_base && e.begin_address < high);

    out
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::pe::PeSection;

    fn mk_pe(
        image_base: u32,
        text_va: u32,
        text_size: u32,
        pdata: &[(u32, u32)],
    ) -> (Vec<u8>, Vec<PeSection>) {
        // Build a synthetic PE image with .text and .pdata.
        // Layout: pdata at RVA 0x1000, .text at RVA 0x2000.
        let pdata_rva = 0x1000u32;
        let pdata_size = (pdata.len() * 8) as u32;
        let total = (text_va + text_size).max(pdata_rva + pdata_size) as usize;
        let mut buf = vec![0u8; total];

        for (i, &(begin, packed)) in pdata.iter().enumerate() {
            let p = pdata_rva as usize + i * 8;
            buf[p..p + 4].copy_from_slice(&begin.to_be_bytes());
            buf[p + 4..p + 8].copy_from_slice(&packed.to_be_bytes());
        }

        let sections = vec![
            PeSection {
                name: ".pdata".into(),
                virtual_address: pdata_rva,
                virtual_size: pdata_size,
                raw_offset: pdata_rva,
                raw_size: pdata_size,
                flags: 0x4000_0040, // INITIALIZED_DATA | READ
            },
            PeSection {
                name: ".text".into(),
                virtual_address: text_va,
                virtual_size: text_size,
                raw_offset: text_va,
                raw_size: text_size,
                flags: 0x6000_0020, // CODE | EXECUTE | READ
            },
        ];
        let _ = image_base; // image_base only matters for high-water bound
        (buf, sections)
    }

    /// Pack metadata in the on-disk layout: prolog in low 8 bits, function
    /// in next 22, flags in top 2.
    fn pack(prolog_dwords: u32, function_dwords: u32, flags: u32) -> u32 {
        ((flags & 0x3) << 30) | ((function_dwords & 0x3F_FFFF) << 8) | (prolog_dwords & 0xFF)
    }

    #[test]
    fn parses_simple_pdata() {
        // function at 0x82001000, 32 bytes long (8 dwords), 8-dword prolog (32 bytes).
        let packed = pack(8, 8, 0b01); // 32-bit-code flag set
        let (pe, sections) = mk_pe(0x8200_0000, 0x2000, 0x100, &[(0x8200_1000, packed)]);
        let entries = parse_pdata(&pe, 0x8200_0000, &sections);

        assert_eq!(entries.len(), 1);
        assert_eq!(entries[0].begin_address, 0x8200_1000);
        assert_eq!(entries[0].prolog_length, 32);
        assert_eq!(entries[0].function_length, 32);
        assert_eq!(entries[0].flags, 0b01);
        assert_eq!(entries[0].end_address(), 0x8200_1020);
    }

    #[test]
    fn stops_on_zero_sentinel() {
        let packed = pack(4, 4, 0b01);
        let entries = vec![
            (0x8200_1000, packed),
            (0u32, 0u32), // sentinel
            (0x8200_2000, packed),
        ];
        let (pe, sections) = mk_pe(0x8200_0000, 0x2000, 0x4000, &entries);
        let parsed = parse_pdata(&pe, 0x8200_0000, &sections);
        assert_eq!(parsed.len(), 1);
        assert_eq!(parsed[0].begin_address, 0x8200_1000);
    }

    #[test]
    fn drops_out_of_range_entries() {
        let packed = pack(4, 4, 0b01);
        let entries = vec![
            (0x8200_1000, packed),
            (0x4000_0000, packed), // outside image — drop
        ];
        let (pe, sections) = mk_pe(0x8200_0000, 0x2000, 0x100, &entries);
        let parsed = parse_pdata(&pe, 0x8200_0000, &sections);
        assert_eq!(parsed.len(), 1);
    }

    #[test]
    fn decodes_real_world_layout() {
        // Mimics a real-world entry: function_length 306 dwords (1224 bytes),
        // 0 prolog dwords, 32-bit-code flag set. Verify the bit-packed value
        // round-trips correctly through parse_pdata.
        let packed = pack(0, 306, 0b01);
        let begin = 0x8200_2000u32; // inside the synthetic .text region
        let (pe, sections) = mk_pe(0x8200_0000, 0x2000, 0x1000, &[(begin, packed)]);
        let entries = parse_pdata(&pe, 0x8200_0000, &sections);
        assert_eq!(entries.len(), 1);
        assert_eq!(entries[0].function_length, 306 * 4);
        assert_eq!(entries[0].prolog_length, 0);
        assert_eq!(entries[0].flags, 0b01);
        assert_eq!(entries[0].end_address(), begin + 1224);
    }

    #[test]
    fn returns_empty_when_no_pdata_section() {
        let sections = vec![PeSection {
            name: ".text".into(),
            virtual_address: 0x1000,
            virtual_size: 0x100,
            raw_offset: 0x1000,
            raw_size: 0x100,
            flags: 0x6000_0020,
        }];
        let pe = vec![0u8; 0x2000];
        assert!(parse_pdata(&pe, 0x8200_0000, &sections).is_empty());
    }
}