From 7a30e902fcaa7e879d241517e9a5fcd289092a6e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20Balv=C3=ADn?= <opensource@petrbalvin.org>
Date: Sat, 29 Aug 2026 14:17:26 +0200
Subject: [PATCH] feat(debug): label coverage report for headless runs

---
 cmd/gasm/debug_linux.go | 57 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/cmd/gasm/debug_linux.go b/cmd/gasm/debug_linux.go
index a1b68b5..b73c4f6 100644
--- a/cmd/gasm/debug_linux.go
+++ b/cmd/gasm/debug_linux.go
@@ -37,6 +37,7 @@ REPL commands:
 	argsFile := fs.String("args", "", "file containing the ABI0 argument block")
 	bufSpec := fs.String("buf", "", "buffer specification: name:size:pattern[,name:size:pattern...] where pattern is zero, ones, seq, or hex")
 	script := fs.String("script", "", "run REPL commands from a file (one per line) and exit; '-' reads stdin")
+	cover := fs.Bool("cover", false, "run to completion with breakpoints on every label and report which blocks executed")
 	timeout := fs.Duration("timeout", 0, "kill the debuggee after this duration (e.g. 30s); for headless --script runs")
 	fs.Parse(args)
 
@@ -179,6 +180,62 @@ REPL commands:
 		srcLines = append(srcLines, debug.SourceLine{Offset: le.Offset, Line: le.Line})
 	}
 
+	// Coverage mode: pre-register a breakpoint on every label (the basic
+	// blocks of a hand-written kernel) and let the kernel run to completion.
+	// Each hit removes its breakpoint, so the final report lists exactly the
+	// labels execution reached — the fast answer to "did my test ever enter
+	// the tail loop / the negative branch?".
+	if *cover {
+		covered := map[string]bool{}
+		for _, l := range labels {
+			addr := sess.CodeBase() + uint64(fl.Offset) + uint64(l.Offset)
+			name := l.Name
+			if _, err := bm.SetWithCond(addr, name, nil); err != nil {
+				fmt.Fprintf(os.Stderr, "gasm debug: cover: %v\n", err)
+				return 1
+			}
+		}
+		fmt.Printf("gasm debug: coverage run over %d labels\n", len(labels))
+		for {
+			for _, bp := range bm.All() {
+				bm.Reinsert(bp.Addr)
+			}
+			// Remove the breakpoint the run is parked on, then continue.
+			regs, rerr := sess.GetRegs()
+			if rerr == nil {
+				if bp := bm.At(regs.GetPC()); bp != nil {
+					bm.Clear(bp.Addr)
+					covered[bp.Label] = true
+				}
+			}
+			if err := sess.Continue(); err != nil {
+				break // debuggee finished or died
+			}
+			if sess.Exited() {
+				break
+			}
+		}
+		var hit []string
+		var missed []string
+		for _, l := range labels {
+			if covered[l.Name] {
+				hit = append(hit, l.Name)
+			} else {
+				missed = append(missed, l.Name)
+			}
+		}
+		sort.Strings(hit)
+		sort.Strings(missed)
+		fmt.Printf("coverage: %d/%d labels reached\n", len(hit), len(labels))
+		for _, l := range hit {
+			fmt.Printf("  covered   %s\n", l)
+		}
+		for _, l := range missed {
+			fmt.Printf("  MISSED    %s\n", l)
+		}
+		return 0
+	}
+
 	// Headless mode: run the script through the normal command loop and
 	// exit.  The watchdog armed above covers launch, continue and step.
 	var in io.Reader = os.Stdin