1 files changed, 15 insertions, 4 deletions
diff --git a/src/pardes/app.zig b/src/pardes/app.zig
index 1302556..8b43791 100644
--- a/src/pardes/app.zig
+++ b/src/pardes/app.zig
@@ -405,10 +405,21 @@ fn logFn(
 
 pub const panic = std.debug.FullPanic(panicImpl);
 
-fn panicImpl(msg: []const u8, _: ?usize) noreturn {
-    // The ROM path deliberately: a panic may BE the console writer failing, and `ets_printf` shares
-    // nothing with `uart.write` except the FIFO itself.
-    soc.rom.print("\r\nMARK PARDES_PANIC %s\r\n", .{msg.ptr});
+fn panicImpl(msg: []const u8, first_trace_addr: ?usize) noreturn {
+    // The fixed text goes out through the ROM deliberately: a panic may BE the console writer
+    // failing, and `ets_printf` shares nothing with `uart.write` except the FIFO itself.
+    //
+    // The MESSAGE does not, and that is a correction rather than a preference. `msg` is a Zig SLICE
+    // and `%s` reads until a NUL, so handing `msg.ptr` to printf prints the message and then
+    // whatever happens to sit after it in memory until a zero byte turns up. Literals get away with
+    // it; std's own panics do not, because they are formatted into a buffer - "index out of bounds:
+    // index 5, len 3" - and carry no terminator. `uart.write` takes a length.
+    soc.rom.print("\r\nMARK PARDES_PANIC ", .{});
+    uart.write(msg);
+    // The address is what makes it actionable: addr2line against the ELF in zig-out turns it into a
+    // source line, and without it a panic message names a KIND of failure with no way to find which
+    // one of them happened. Zero when the caller had no return address to give.
+    soc.rom.print("\r\nMARK PARDES_PANIC_AT 0x%08x\r\n", .{@as(u32, @truncate(first_trace_addr orelse 0))});
     while (true) {}
 }