1 files changed, 129 insertions, 0 deletions

diff --git a/shell/src/lib.rs b/shell/src/lib.rs
index 175a2c7..0f5ac4b 100644
--- a/shell/src/lib.rs
+++ b/shell/src/lib.rs
@@ -716,6 +716,7 @@ write `{} <path> TIL <marker>`",
         "hello" => cmd_hello(&parsed),
         "info" => cmd_info(&parsed),
         "mem" => cmd_mem(&parsed),
+        "heapdbg" => cmd_heapdbg(&parsed),
         "mmap" => cmd_mmap(&parsed),
         "stress" => cmd_stress(&parsed),
         "date" => cmd_date(&parsed),
@@ -1571,6 +1572,134 @@ fn cmd_halt() -> ! {
     rsnix::power::halt()
 }
 
+/// Debug the crash-family: free-list state + the historical crash
+/// offset (heap+0x443e0) + the shadow block's header.  On the OptiPlex
+/// this shows whether the shadow span leaked into the free list and
+/// whether the probe region is zeroed/0xAA before any command runs.
+fn cmd_heapdbg(_p: &Parsed) {
+    let h = rsnix::memory::heap_stats();
+    term_println(&alloc::format!(
+        "heap: {:#x}..{:#x} cap={} MiB free={} KiB blocks={}",
+        h.heap_start,
+        h.heap_end,
+        h.heap_size / 1048576,
+        h.free_bytes / 1024,
+        h.free_blocks
+    ));
+    for l in rsnix::memory::freelist_lines(12) {
+        term_println(&l);
+    }
+    // fb vs heap overlap — OptiPlex crash hypothesis: the display's
+    // framebuffer may sit inside the heap region (GPU BAR not reserved in
+    // the EFI map), so display writes clobber live heap allocations.
+    if let Some((fb, fsz)) = rsnix::gop::framebuffer_region() {
+        let ov = h.heap_start < fb.saturating_add(fsz) && fb < h.heap_end;
+        term_println(&alloc::format!(
+            "fb {:#x} size={:#x} overlap-heap={}",
+            fb, fsz, ov
+        ));
+    }
+    let probe = h.heap_start.wrapping_add(0x443e0); // historical crash offset
+    match rsnix::memory::freelist_contains(probe) {
+        Some((b, s, off)) => term_println(&alloc::format!(
+            "probe {:#x} (+0x443e0) IN free blk {:#x} size={:#x} off={:#x}",
+            probe, b, s, off
+        )),
+        None => term_println(&alloc::format!("probe {:#x} (+0x443e0) NOT free", probe)),
+    }
+    let mut s = alloc::string::String::new();
+    unsafe {
+        for i in 0..8 {
+            if i > 0 {
+                s.push(' ');
+            }
+            let v = *(probe as *const u32).add(i);
+            s.push_str(&alloc::format!("{:08x}", v));
+        }
+    }
+    term_println(&alloc::format!("probe mem: {}", s));
+    // Scan the live shadow payload for 0x00aaaaaa words.  NOTE: this is
+    // the GRAY text color (rgb(170,170,170) = PALETTE[7] = fg 7), NOT a
+    // firmware scrub — the "0x00AAAAAA fill" in the OptiPlex crash dumps
+    // is just rendered text pixels.  The scan's real value: untouched
+    // shadow rows must be 0; non-zero far rows = out-of-bounds writes.
+    if let Some((b, size, _)) = rsnix::gop::shadow_block_state() {
+        let pay = b + 32;
+        let words = (size.saturating_sub(32)) / 4;
+        let mut n = 0u32;
+        let mut first: [usize; 8] = [0; 8];
+        let mut nf = 0usize;
+        unsafe {
+            let mut i = 0usize;
+            let cap = words.min(240_000); // bound the scan to avoid stalls
+            while i < cap {
+                let v = *(pay as *const u32).add(i);
+                if v == 0x00aa_aaaa {
+                    if nf < first.len() {
+                        first[nf] = i;
+                    }
+                    nf += 1;
+                    n += 1;
+                }
+                i += 1;
+            }
+        }
+        let mut fs = alloc::string::String::new();
+        for &f in first[..nf.min(8)].iter() {
+            fs.push_str(&alloc::format!("@{}(r{}c{}) ", f, f / 800, (f % 800) / 8));
+        }
+        term_println(&alloc::format!(
+            "shadow scan: {}w/{} ({}%) {}",
+            n,
+            words,
+            (n * 1000 / (words as u32).max(1)) / 10,
+            fs
+        ));
+        // Probe far rows (untouched by text) to check the init zeroing.
+        let mut d = alloc::string::String::new();
+        unsafe {
+            for (label, off) in [("r100", 80_000usize), ("r300", 240_000), ("r500", 400_000)] {
+                let w0 = *(pay as *const u32).add(off);
+                let w1 = *(pay as *const u32).add(off + 1);
+                d.push_str(&alloc::format!(" {}={:08x}{:08x}", label, w0, w1));
+            }
+        }
+        term_println(&alloc::format!("shadow far: {}", d));
+        // Underlying cell/rendered values at the first 0x00aaaaaa (gray
+        // text pixel) hit, if any: confirms the shadow word is the glyph
+        // pixel of a fg=7 cell (consistent) vs a shadow write outside
+        // the vt path (inconsistent).
+        if nf > 0 {
+            let f = first[0];
+            let tr = f / 800 / 16;
+            let tc = (f / 8) % 100;
+            let (rc, rr) = rsnix::vt::cell_raw(tr, tc);
+            term_println(&alloc::format!(
+                "shadow@{:x} cell={:08x} rendered={:08x}",
+                f, rc, rr
+            ));
+        }
+    }
+    match rsnix::gop::shadow_block_state() {
+        Some((b, size, free)) => {
+            term_println(&alloc::format!(
+                "shadow blk {:#x} size={:#x} free={}",
+                b,
+                size,
+                free
+            ));
+            match rsnix::memory::freelist_contains(b) {
+                Some((fb, fs, fo)) => term_println(&alloc::format!(
+                    "shadow base IN free list: blk {:#x} size={:#x} off={:#x}",
+                    fb, fs, fo
+                )),
+                None => term_println("shadow base NOT in free list"),
+            }
+        }
+        None => term_println("shadow: NONE (no-shadow mode)"),
+    }
+}
+
 fn cmd_date(p: &Parsed) {
     let t = rsnix::rtc::now();
     let mut pipe = Pipeline::new(&p.filters, &p.output);