Add some server entity code-crawling machinery

1 files changed, 105 insertions, 0 deletions

diff --git a/src/ent.c b/src/ent.c
index 4ab0379..8dcb1f1 100644
--- a/src/ent.c
+++ b/src/ent.c
@@ -14,6 +14,8 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include "con_.h"
+#include "dictmaptree.h"
 #include "engineapi.h"
 #include "errmsg.h"
 #include "feature.h"
@@ -22,6 +24,8 @@
 #include "intdefs.h"
 #include "mem.h"
 #include "vcall.h"
+#include "x86.h"
+#include "x86util.h"
 
 FEATURE()
 
@@ -45,7 +49,108 @@ void *ent_get(int idx) {
 	return e->ent_unknown;
 }
 
+struct CEntityFactory {
+	struct CEntityFactory_vtable {
+		void /*IServerNetworkable*/ *(*VCALLCONV Create)(
+				struct CEntityFactory *this, const char *name);
+		void (*VCALLCONV Destroy)(struct CEntityFactory *this,
+				void /*IServerNetworkable*/ *networkable);
+		usize (*VCALLCONV GetEntitySize)(struct CEntityFactory *this);
+	} *vtable;
+};
+
+struct CEntityFactoryDictionary {
+	void **vtable;
+	struct CUtlDict_p_ushort dict;
+};
+
+#ifdef _WIN32 // TODO(linux): this'll be different too, leaving out for now
+static struct CEntityFactoryDictionary *entfactorydict = 0;
+static inline bool find_entfactorydict(con_cmdcb dumpentityfactories_cb) {
+	const uchar *insns = (const uchar *)dumpentityfactories_cb;
+	for (const uchar *p = insns; p - insns < 64;) {
+		// the call to EntityFactoryDictionary() is inlined. that returns a
+		// static, which is lazy-inited (trivia: this was old MSVC, so it's not
+		// threadsafe like C++ requires nowadays). for some reason the init flag
+		// is set using OR, and then the instance is put in ECX to call the ctor
+		if (p[0] == X86_ORMRW && p[6] == X86_MOVECXI && p[11] == X86_CALL) {
+			entfactorydict = mem_loadptr(p + 7);
+			return true;
+		}
+		NEXT_INSN(p, "entity factory dictionary");
+	}
+	return false;
+}
+#endif
+
+const struct CEntityFactory *ent_getfactory(const char *name) {
+#ifdef _WIN32
+	if (entfactorydict) {
+		return CUtlDict_p_ushort_findval(&entfactorydict->dict, name);
+	}
+#endif
+	return 0;
+}
+
+typedef void (*VCALLCONV ctor_func)(void *);
+static inline ctor_func findctor(const struct CEntityFactory *factory,
+		const char *classname) {
+#ifdef _WIN32
+	const uchar *insns = (const uchar *)factory->vtable->Create;
+	// every Create() method follows the same pattern. after calling what is
+	// presumably operator new(), it copies the return value from EAX into ECX
+	// and then calls the constructor.
+	for (const uchar *p = insns; p - insns < 32;) {
+		if (p[0] == X86_MOVRMW && p[1] == 0xC8 && p[2] == X86_CALL) {
+			return (ctor_func)(p + 7 + mem_loadoffset(p + 3));
+		}
+		// duping NEXT_INSN macro here in the name of a nicer message
+		int len = x86_len(p);
+		if (len == -1) {
+			errmsg_errorx("unknown or invalid instruction looking for %s "
+					"constructor", classname);
+			return 0;
+		}
+		p += len;
+	}
+#else
+#warning TODO(linux): this will be different of course
+#endif
+	return 0;
+}
+
+void **ent_findvtable(const struct CEntityFactory *factory,
+		const char *classname) {
+#ifdef _WIN32
+	ctor_func ctor = findctor(factory, classname);
+	if (!ctor) return 0;
+	const uchar *insns = (const uchar *)ctor;
+	// the constructor itself should do *(void**)this = &vtable; almost right
+	// away, so look for the first immediate load into indirect register
+	for (const uchar *p = insns; p - insns < 24;) {
+		if (p[0] == X86_MOVMIW && (p[1] & 0xF8) == 0) return mem_loadptr(p + 2);
+		int len = x86_len(p);
+		if (len == -1) {
+			errmsg_errorx("unknown or invalid instruction looking for %s "
+					"vtable pointer", classname);
+			return 0;
+		}
+		p += len;
+	}
+#else
+#warning TODO(linux): this will be different of course
+#endif
+	return 0;
+}
+
 INIT {
+#ifdef _WIN32 // TODO(linux): above
+	struct con_cmd *dumpentityfactories = con_findcmd("dumpentityfactories");
+	if (!dumpentityfactories || !find_entfactorydict(dumpentityfactories->cb)) {
+		errmsg_warnx("server entity factories unavailable");
+	}
+#endif
+
 	// for PEntityOfEntIndex we don't really have to do any more init, we
 	// can just call the function later.
 	if (has_vtidx_PEntityOfEntIndex) return true;