common/autodata: autodata replacement which uses __attribute__((constructor))

This is a GCC extension, but avoids much other messiness.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/Makefile

@@ -1,6 +1,7 @@
 COMMON_SRC_NOGEN :=				\
 	common/addr.c				\
 	common/amount.c				\
+	common/autodata.c			\
 	common/base32.c				\
 	common/base64.c				\
 	common/bech32.c				\

common/autodata.c

@@ -0,0 +1,40 @@
+#include "config.h"
+#include <assert.h>
+#include <ccan/strmap/strmap.h>
+#include <common/autodata.h>
+
+struct typereg {
+	size_t num;
+	const void **ptrs;
+};
+
+static STRMAP(struct typereg *) typemap;
+
+void autodata_register_(const char *typename, const void *ptr)
+{
+	struct typereg *t;
+	assert(ptr);
+
+	t = strmap_get(&typemap, typename);
+	if (!t) {
+		t = malloc(sizeof(struct typereg));
+		t->num = 0;
+		t->ptrs = NULL;
+		strmap_add(&typemap, typename, t);
+	}
+
+	t->ptrs = realloc(t->ptrs, (t->num + 1) * sizeof(*t->ptrs));
+	t->ptrs[t->num] = ptr;
+	t->num++;
+}
+
+void *autodata_get_(const char *typename, size_t *nump)
+{
+	struct typereg *t = strmap_get(&typemap, typename);
+	if (!t) {
+		*nump = 0;
+		return NULL;
+	}
+	*nump = t->num;
+	return t->ptrs;
+}

common/autodata.h

@@ -0,0 +1,26 @@
+#ifndef LIGHTNING_COMMON_AUTODATA_H
+#define LIGHTNING_COMMON_AUTODATA_H
+#include "config.h"
+#include <ccan/compiler/compiler.h>
+#include <ccan/cppmagic/cppmagic.h>
+
+#define AUTODATA_TYPE(name, type)					\
+	static inline void register_autotype_##name(const type *t) {	\
+		autodata_register_(#name, t);				\
+	}								\
+	typedef type autodata_##name##_
+
+/* This uses GCC's constructor attribute */
+#define AUTODATA(name, ptr)						\
+	static __attribute__((constructor)) NEEDED			\
+	void CPPMAGIC_GLUE2(register_one_##name,__COUNTER__)(void) {	\
+		register_autotype_##name(ptr);				\
+	}
+
+#define autodata_get(name, nump)					\
+	((autodata_##name##_ **)autodata_get_(#name, (nump)))
+
+void autodata_register_(const char *typename, const void *ptr);
+void *autodata_get_(const char *typename, size_t *nump);
+
+#endif /* LIGHTNING_COMMON_AUTODATA_H */