1 files changed, 283 insertions, 0 deletions

diff --git a/rsnix/src/load.rs b/rsnix/src/load.rs
new file mode 100644
index 0000000..cebca89
--- /dev/null
+++ b/rsnix/src/load.rs
@@ -0,0 +1,283 @@
+// ---------------------------------------------------------------------------
+// load — PE32+ executable loader (ADR 0006 Phase 2).
+//
+// Parses a PE32+ image read through the VFS, allocates identity-mapped
+// pages for it (the kernel runs identity-mapped, so "user" code lives at
+// its link address), applies base relocations, and returns the entry
+// point.  The spawn path (exec.rs glue in sched) builds an Exports table,
+// copies the argv block into the image's memory, and starts a task whose
+// trampoline calls entry(&Exports, argc, argv).
+//
+// Scope: what rustc/lld emits for a no_std UEFI-ish binary — DOS header,
+// COFF header, optional header PE32+, section table, .reloc base
+// relocations.  No imports, no TLS, no exceptions.
+// ---------------------------------------------------------------------------
+use crate::paging;
+
+/// Where binaries are loaded: above the heap, inside conventional RAM.
+/// The page allocator's span covers the conventional-memory range of the
+/// boot memory map; LOAD_BASE must sit inside it (heap ends ~0xbb6c000
+/// with 256 MiB guests; conventional RAM typically ends near 0x0FF00000).
+const LOAD_BASE: usize = 0x0C00_0000; // 192 MiB
+const LOAD_LIMIT: usize = 0x0F00_0000; // stop before top-of-RAM
+
+const PAGE_SIZE: usize = 4096;
+
+/// A loaded image: pages to free on exit + the entry point.
+pub struct Image {
+    /// First allocated page (free this..+page_count on exit).
+    pub base: usize,
+    pub page_count: usize,
+    pub entry: usize,
+}
+
+#[derive(Debug)]
+pub enum LoadError {
+    ReadFailed,
+    NotPe,
+    NotPe32Plus,
+    BadSectionTable,
+    NoEntryPoint,
+    AllocFailed,
+    MapFailed,
+    BadReloc,
+    TooBig,
+}
+
+// ---------------------------------------------------------------------------
+// PE file-format structures (packed reads via byte slices — no unaligned
+// struct pointer derefs).
+// ---------------------------------------------------------------------------
+
+fn u16_at(b: &[u8], off: usize) -> Option<u16> {
+    b.get(off..off + 2).map(|s| u16::from_le_bytes([s[0], s[1]]))
+}
+fn u32_at(b: &[u8], off: usize) -> Option<u32> {
+    b.get(off..off + 4)
+        .map(|s| u32::from_le_bytes([s[0], s[1], s[2], s[3]]))
+}
+fn u64_at(b: &[u8], off: usize) -> Option<u64> {
+    b.get(off..off + 8).map(|s| {
+        let mut t = [0u8; 8];
+        t.copy_from_slice(s);
+        u64::from_le_bytes(t)
+    })
+}
+
+const DOS_MAGIC: u16 = 0x5A4D; // "MZ"
+const PE_MAGIC: u32 = 0x0000_4550; // "PE\0\0"
+const OPT_PE32PLUS: u16 = 0x20B;
+const DIR_BASERELOC: usize = 5;
+
+/// Map an RVA to its raw file offset via the section table.
+fn rva_to_file(sections: &[Option<Section>], count: usize, rva: usize) -> Option<usize> {
+    for s in sections.iter().take(count).flatten() {
+        if rva >= s.virt_addr && rva < s.virt_addr + s.raw_size.max(s.virt_size) {
+            return Some(s.raw_ptr + (rva - s.virt_addr));
+        }
+    }
+    None
+}
+
+#[derive(Clone, Copy)]
+struct Section {
+    virt_addr: usize,
+    virt_size: usize,
+    raw_ptr: usize,
+    raw_size: usize,
+}
+
+/// Parse headers, apply relocations into `mem`, return the entry RVA.
+fn parse_and_relocate(img: &[u8], mem: usize) -> Result<usize, LoadError> {
+    // ---- DOS header ----
+    if u16_at(img, 0) != Some(DOS_MAGIC) {
+        return Err(LoadError::NotPe);
+    }
+    let e_lfanew = u32_at(img, 0x3C).ok_or(LoadError::NotPe)? as usize;
+
+    // ---- COFF header ----
+    if u32_at(img, e_lfanew) != Some(PE_MAGIC) {
+        return Err(LoadError::NotPe);
+    }
+    let coff = e_lfanew + 4;
+    let num_sections = u16_at(img, coff + 2).ok_or(LoadError::NotPe)? as usize;
+    let opt_size = u16_at(img, coff + 16).ok_or(LoadError::NotPe)? as usize;
+    if opt_size == 0 {
+        return Err(LoadError::NotPe);
+    }
+
+    // ---- Optional header (PE32+) ----
+    let opt = coff + 20;
+    if u16_at(img, opt) != Some(OPT_PE32PLUS) {
+        return Err(LoadError::NotPe32Plus);
+    }
+    let entry_rva = u32_at(img, opt + 16).ok_or(LoadError::NotPe32Plus)? as usize;
+    let image_base = u64_at(img, opt + 24).ok_or(LoadError::NotPe32Plus)? as usize;
+
+    let num_dirs = u32_at(img, opt + 108).ok_or(LoadError::NotPe32Plus)? as usize;
+    let dir_base = opt + 112;
+    let (reloc_rva, reloc_size) = if num_dirs > DIR_BASERELOC {
+        (
+            u32_at(img, dir_base + DIR_BASERELOC * 8).ok_or(LoadError::BadReloc)? as usize,
+            u32_at(img, dir_base + DIR_BASERELOC * 8 + 4).ok_or(LoadError::BadReloc)? as usize,
+        )
+    } else {
+        (0, 0)
+    };
+
+    // ---- Section table ----
+    let sect_tab = opt + opt_size;
+    let mut sections: [Option<Section>; 96] = [None; 96];
+    if num_sections > sections.len() {
+        return Err(LoadError::BadSectionTable);
+    }
+    for i in 0..num_sections {
+        let s = sect_tab + i * 40;
+        let virt_size = u32_at(img, s + 8).ok_or(LoadError::BadSectionTable)? as usize;
+        let virt_addr = u32_at(img, s + 12).ok_or(LoadError::BadSectionTable)? as usize;
+        let raw_size = u32_at(img, s + 16).ok_or(LoadError::BadSectionTable)? as usize;
+        let raw_ptr = u32_at(img, s + 20).ok_or(LoadError::BadSectionTable)? as usize;
+        sections[i] = Some(Section {
+            virt_addr,
+            virt_size,
+            raw_ptr,
+            raw_size,
+        });
+    }
+
+    // ---- Copy section contents ----
+    for s in sections.iter_mut().take(num_sections).flatten() {
+        let n = s.raw_size.min(s.virt_size);
+        if n == 0 {
+            continue;
+        }
+        let src = img.get(s.raw_ptr..s.raw_ptr + n).ok_or(LoadError::BadSectionTable)?;
+        unsafe {
+            let dst = (mem + s.virt_addr) as *mut u8;
+            core::ptr::copy_nonoverlapping(src.as_ptr(), dst, n);
+        }
+    }
+
+    // ---- Apply base relocations ----
+    if reloc_size > 0 && reloc_rva != 0 {
+        // The .reloc directory is an RVA; the section table maps it to a
+        // raw file offset.
+        let mut off = rva_to_file(&sections, num_sections, reloc_rva).ok_or(LoadError::BadReloc)?;
+        let end = off + reloc_size;
+        while off + 8 <= end {
+            let page_rva = u32_at(img, off).ok_or(LoadError::BadReloc)? as usize;
+            let block_size = u32_at(img, off + 4).ok_or(LoadError::BadReloc)? as usize;
+            if block_size < 8 || off + block_size > end {
+                break;
+            }
+            let entries = (block_size - 8) / 2;
+            for i in 0..entries {
+                let e = u16_at(img, off + 8 + i * 2).ok_or(LoadError::BadReloc)?;
+                let r#type = e >> 12;
+                let pos = e & 0xFFF;
+                if r#type == 0 {
+                    continue; // IMAGE_REL_BASED_ABSOLUTE — padding
+                }
+                let target = mem + page_rva + pos as usize;
+                match r#type {
+                    10 => {
+                        // DIR64: 8-bit image base delta
+                        unsafe {
+                            let p = target as *mut u64;
+                            let v = p.read_unaligned();
+                            p.write_unaligned(v.wrapping_add((mem as u64).wrapping_sub(image_base as u64)));
+                        }
+                    }
+                    _ => return Err(LoadError::BadReloc),
+                }
+            }
+            off += block_size;
+        }
+    }
+
+    Ok(entry_rva)
+}
+
+/// Load a PE32+ image from the given bytes.  Returns the loaded image
+/// (identity-mapped at LOAD_BASE+) with its entry point resolved.
+pub fn load_image(bytes: &[u8]) -> Result<Image, LoadError> {
+    if bytes.len() > 8 * 1024 * 1024 {
+        return Err(LoadError::TooBig);
+    }
+    // Quick header sanity before allocating.
+    if u16_at(bytes, 0) != Some(DOS_MAGIC) {
+        return Err(LoadError::NotPe);
+    }
+    let e_lfanew = u32_at(bytes, 0x3C).unwrap_or(0) as usize;
+    if u32_at(bytes, e_lfanew) != Some(PE_MAGIC) {
+        return Err(LoadError::NotPe);
+    }
+
+    let page_count = bytes.len().div_ceil(PAGE_SIZE);
+    // Allocate physical pages at a fixed window (identity mapping makes
+    // the link address = runtime address after relocation).
+    let base = crate::memory::alloc_pages_above(page_count, LOAD_BASE).ok_or(LoadError::AllocFailed)?;
+    if base >= LOAD_LIMIT {
+        crate::memory::free_pages(base, page_count);
+        return Err(LoadError::TooBig);
+    }
+    // Identity-map them user+writable+nx-default (relocations need write;
+    // we do not enforce W^X here — single-privilege-level kernel).
+    if !paging::map_range(base, page_count, paging::PAGE_USER | paging::PAGE_WRITABLE | paging::PAGE_NX) {
+        crate::memory::free_pages(base, page_count);
+        return Err(LoadError::MapFailed);
+    }
+
+    let entry_rva = match parse_and_relocate(bytes, base) {
+        Ok(e) => e,
+        Err(e) => {
+            crate::memory::free_pages(base, page_count);
+            return Err(e);
+        }
+    };
+    // Clear BSS tails: sections were copied raw-size bytes each; anything
+    // between raw_size and virt_size is zero per PE spec.  parse_and_relocate
+    // only copied min(raw,virt); zero-fill the remainder now.
+    zero_bss_tails(bytes, base);
+
+    Ok(Image {
+        base,
+        page_count,
+        entry: base + entry_rva,
+    })
+}
+
+/// Zero the part of each section between raw_size and virt_size (BSS).
+fn zero_bss_tails(img: &[u8], mem: usize) {
+    // Re-walk the section table minimally (headers are small).
+    let Some(e_lfanew) = u32_at(img, 0x3C) else { return };
+    let coff = e_lfanew as usize + 4;
+    let Some(num_sections) = u16_at(img, coff + 2) else { return };
+    let Some(opt_size) = u16_at(img, coff + 16) else { return };
+    let sect_tab = coff + 20 + opt_size as usize;
+    for i in 0..num_sections as usize {
+        let Some(virt_size) = u32_at(img, sect_tab + i * 40 + 8) else { return };
+        let Some(raw_size) = u32_at(img, sect_tab + i * 40 + 16) else { return };
+        let Some(virt_addr) = u32_at(img, sect_tab + i * 40 + 12) else { return };
+        if virt_size > raw_size {
+            unsafe {
+                core::ptr::write_bytes(
+                    (mem + virt_addr as usize + raw_size as usize) as *mut u8,
+                    0,
+                    virt_size as usize - raw_size as usize,
+                );
+            }
+        }
+    }
+}
+
+/// Free a previously loaded image.
+///
+/// The task that ran the image must be dead — no code may still execute
+/// from or reference these pages.
+pub unsafe fn unload_image(img: &Image) {
+    for i in 0..img.page_count {
+        let _ = paging::unmap_page(img.base + i * PAGE_SIZE);
+    }
+    crate::memory::free_pages(img.base, img.page_count);
+}