From 2147d01c1a7daad7b56aa163b937c49c09387f48 Mon Sep 17 00:00:00 2001
From: Moses Narrow <36607567+0pcom@users.noreply.github.com>
Date: Thu, 13 Aug 2026 20:26:32 -0500
Subject: [PATCH] reflect: provide the linkname targets modern-go/reflect2
 expects
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reflect2 — pulled in by json-iterator, which plenty of dependency trees
carry — reaches into reflect's unexported runtime helpers by //go:linkname.
TinyGo's reflect has no such symbols, so linking any program that touches
that path fails with "undefined symbol: reflect.mapassign" and similar,
long after it has compiled.

These are matching symbols so such programs LINK. They panic if actually
exercised, and the file says so plainly: reflect2/jsoniter is not
functional under TinyGo, and encoding/json — which this reflect does
support — is the way to serialise. That is a deliberate trade. A link
error names a symbol nobody wrote and offers no way forward; a panic at
the one call that is genuinely unsupported names the thing you did.
---
 src/reflect/reflect2_linkname.go | 58 ++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 src/reflect/reflect2_linkname.go

diff --git a/src/reflect/reflect2_linkname.go b/src/reflect/reflect2_linkname.go
new file mode 100644
index 0000000000..d222b57c73
--- /dev/null
+++ b/src/reflect/reflect2_linkname.go
@@ -0,0 +1,58 @@
+package reflect
+
+// github.com/modern-go/reflect2 (used by github.com/json-iterator/go) reaches
+// into reflect's unexported runtime helpers via //go:linkname. TinyGo's reflect
+// does not implement these, so a program that links reflect2 fails at link time
+// with "undefined symbol: reflect.mapassign" etc. Provide matching symbols so
+// such programs LINK; they panic if actually exercised. reflect2/jsoniter is
+// therefore non-functional under TinyGo — callers should use encoding/json,
+// which TinyGo's reflect does support. See the skywire TinyGo build notes.
+
+import "unsafe"
+
+// sliceHeader mirrors reflect2's slice header ABI for typedslicecopy.
+type reflect2SliceHeader struct {
+	Data unsafe.Pointer
+	Len  int
+	Cap  int
+}
+
+//go:linkname reflect2_makemap reflect.makemap
+func reflect2_makemap(rtype unsafe.Pointer, cap int) unsafe.Pointer {
+	panic("reflect.makemap: reflect2/jsoniter is unsupported under TinyGo (use encoding/json)")
+}
+
+//go:linkname reflect2_unsafe_New reflect.unsafe_New
+func reflect2_unsafe_New(rtype unsafe.Pointer) unsafe.Pointer {
+	panic("reflect.unsafe_New: reflect2/jsoniter is unsupported under TinyGo (use encoding/json)")
+}
+
+//go:linkname reflect2_unsafe_NewArray reflect.unsafe_NewArray
+func reflect2_unsafe_NewArray(rtype unsafe.Pointer, length int) unsafe.Pointer {
+	panic("reflect.unsafe_NewArray: reflect2/jsoniter is unsupported under TinyGo (use encoding/json)")
+}
+
+//go:linkname reflect2_typedmemmove reflect.typedmemmove
+func reflect2_typedmemmove(rtype, dst, src unsafe.Pointer) {
+	panic("reflect.typedmemmove: reflect2/jsoniter is unsupported under TinyGo (use encoding/json)")
+}
+
+//go:linkname reflect2_typedslicecopy reflect.typedslicecopy
+func reflect2_typedslicecopy(elemType unsafe.Pointer, dst, src reflect2SliceHeader) int {
+	panic("reflect.typedslicecopy: reflect2/jsoniter is unsupported under TinyGo (use encoding/json)")
+}
+
+//go:linkname reflect2_mapassign reflect.mapassign
+func reflect2_mapassign(rtype, m, key, val unsafe.Pointer) {
+	panic("reflect.mapassign: reflect2/jsoniter is unsupported under TinyGo (use encoding/json)")
+}
+
+//go:linkname reflect2_mapiterinit reflect.mapiterinit
+func reflect2_mapiterinit(rtype, m, it unsafe.Pointer) {
+	panic("reflect.mapiterinit: reflect2/jsoniter is unsupported under TinyGo (use encoding/json)")
+}
+
+//go:linkname reflect2_mapiternext reflect.mapiternext
+func reflect2_mapiternext(it unsafe.Pointer) {
+	panic("reflect.mapiternext: reflect2/jsoniter is unsupported under TinyGo (use encoding/json)")
+}