v0.5.8: heap-free QR encoder + crash-dump QR on framebuffer

Real hardware has no serial console, so a kernel crash only leaves a
frozen screen.  Every dump_lines() report now also renders the crash
text as a scannable QR below the white-on-red band (photograph the
screen instead of relaying text).

- rsnix/src/qr.rs: from-scratch no_std/no_alloc byte-mode QR encoder
  (EC-L, v1..v40, .bss statics only — safe on the fault path):
  RS over GF(256), codeword interleave, zigzag placement, 8 masks with
  N1-N4 penalty auto-selection, format/version info.
- gop.rs: dump_qr() joins dump lines into a static buffer, truncates
  with '...' at the v40-L capacity, encodes, and renders centered
  black-on-white with a 4-module quiet zone.
- tools/qrcheck: host harness (embedds qr.rs) + qrcheck.py cross-check
  against segno's placement primitives.  Verified bit-exact: 12
  versions x 8 masks forced, plus auto-mask choice matches segno's
  penalty evaluation.  Caught 3 encoder bugs (multi-block interleave
  offsets, transposed version info, mask eval ordering).
- QEMU e2e: page-fault dump screendump decodes via zbarimg, content
  matches the serial log line-for-line.
- test-msg.sh and test-fault.sh both PASS; debug+release 0 warnings.

1 files changed, 58 insertions, 0 deletions

diff --git a/tools/qrcheck/src/main.rs b/tools/qrcheck/src/main.rs
new file mode 100644
index 0000000..d294485
--- /dev/null
+++ b/tools/qrcheck/src/main.rs
@@ -0,0 +1,58 @@
+//! Host-side cross-check tool for the kernel QR encoder.
+//!
+//! Usage: `qrcheck TEXT [VERSION] [MASK]`
+//!   - with VERSION+MASK: force both and dump the matrix (compared against
+//!     segno by `tools/qrcheck.py`);
+//!   - with neither: auto-pick version and best mask, print `v<ver> m<mask>`.
+//!
+//! Output: first line `v<N> m<N|999>`, then one line per matrix row of
+//! `#` (dark) / `.` (light).
+#![allow(static_mut_refs)]
+
+#[path = "../../../rsnix/src/qr.rs"]
+mod qr;
+
+fn main() {
+    let args: Vec<String> = std::env::args().collect();
+    if args.get(1).map(String::as_str) == Some("--raw") {
+        let text = args.get(2).map(String::as_str).unwrap_or("hello");
+        let version: usize = args.get(3).and_then(|s| s.parse().ok()).unwrap_or(0);
+        let v = if version > 0 {
+            qr::encode_at(text.as_bytes(), version, Some(0))
+        } else {
+            qr::encode(text.as_bytes())
+        };
+        if v == 0 {
+            eprintln!("FAIL");
+            std::process::exit(1);
+        }
+        for b in qr::codeword_stream() {
+            print!("{:02x}", b);
+        }
+        println!();
+        return;
+    }
+    let text = args.get(1).map(String::as_str).unwrap_or("hello world");
+    let version: usize = args.get(2).and_then(|s| s.parse().ok()).unwrap_or(0);
+    let mask: Option<usize> = args.get(3).and_then(|s| s.parse().ok());
+
+    let v = if version > 0 {
+        qr::encode_at(text.as_bytes(), version, mask)
+    } else {
+        qr::encode(text.as_bytes())
+    };
+    if v == 0 {
+        eprintln!("FAIL: cannot encode {} bytes at v{}", text.len(), version);
+        std::process::exit(1);
+    }
+    let size = qr::size();
+    let m = if let Some(m) = mask { m } else { qr::last_mask() };
+    println!("v{} m{}", v, m);
+    for y in 0..size {
+        let mut row = String::with_capacity(size);
+        for x in 0..size {
+            row.push(if qr::module(x, y) { '#' } else { '.' });
+        }
+        println!("{}", row);
+    }
+}