support static-only systems

The iptables code supports a "no shared libs" mode where it can be used
without requiring dlfcn related functionality.  This adds similar support
to iproute2 so that it can easily be used on systems like nommu Linux (but
obviously with a few limitations -- no dynamic plugins).

Rather than modify every location that uses dlfcn.h, I hooked the dlfcn.h
header with stub functions when shared library support is disabled.  Then
symbol lookup is done via a local static lookup table (which is generated
automatically at build time) so that internal symbols can be found.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

Makefile

@@ -10,7 +10,12 @@ ARPDDIR=/var/lib/arpd
 # Path to db_185.h include
 DBM_INCLUDE:=$(ROOTDIR)/usr/include
 
+SHARED_LIBS = y
+
 DEFINES= -DRESOLVE_HOSTNAMES -DLIBDIR=\"$(LIBDIR)\"
+ifneq ($(SHARED_LIBS),y)
+DEFINES+= -DNO_SHARED_LIBS
+endif
 
 #options if you have a bind>=4.9.4 libresolv (or, maybe, glibc)
 LDLIBS=-lresolv

genl/Makefile

 GENLOBJ=genl.o
 
 include ../Config
+SHARED_LIBS ?= y
 
 GENLMODULES :=
 GENLMODULES += ctrl.o
@@ -9,8 +10,10 @@ GENLOBJ += $(GENLMODULES)
 
 GENLLIB :=
 
+ifeq ($(SHARED_LIBS),y)
 LDFLAGS += -Wl,-export-dynamic
 LDLIBS  += -lm -ldl
+endif
 
 all: genl
 
@@ -21,3 +24,15 @@ install: all
 
 clean:
 	rm -f $(GENLOBJ) $(GENLLIB) genl
+
+ifneq ($(SHARED_LIBS),y)
+
+genl: static-syms.o
+static-syms.o: static-syms.h
+static-syms.h: $(wildcard *.c)
+	files="$^" ; \
+	for s in `grep -B 3 '\<dlsym' $$files | sed -n '/snprintf/{s:.*"\([^"]*\)".*:\1:;s:%s::;p}'` ; do \
+		sed -n '/'$$s'[^ ]* =/{s:.* \([^ ]*'$$s'[^ ]*\) .*:extern char \1[] __attribute__((weak)); if (!strcmp(sym, "\1")) return \1;:;p}' $$files ; \
+	done > $@
+
+endif

genl/static-syms.c

+#include <string.h>
+void *_dlsym(const char *sym)
+{
+#include "static-syms.h"
+	return NULL;
+}

include/dlfcn.h

+/*
+ * Stub dlfcn implementation for systems that lack shared library support
+ * but obviously can still reference compiled-in symbols.
+ */
+
+#ifndef NO_SHARED_LIBS
+#include_next <dlfcn.h>
+#else
+
+#define RTLD_LAZY 0
+#define _FAKE_DLFCN_HDL (void *)0xbeefcafe
+
+static inline void *dlopen(const char *file, int flag)
+{
+	if (file == NULL)
+		return _FAKE_DLFCN_HDL;
+	else
+		return NULL;
+}
+
+extern void *_dlsym(const char *sym);
+static inline void *dlsym(void *handle, const char *sym)
+{
+	if (handle != _FAKE_DLFCN_HDL)
+		return NULL;
+	return _dlsym(sym);
+}
+
+static inline char *dlerror(void)
+{
+	return NULL;
+}
+
+static inline int dlclose(void *handle)
+{
+	return (handle == _FAKE_DLFCN_HDL) ? 0 : 1;
+}
+
+#endif

ip/Makefile

@@ -23,6 +23,20 @@ install: all
 clean:
 	rm -f $(ALLOBJ) $(TARGETS)
 
-LDLIBS += -ldl
+SHARED_LIBS ?= y
+ifeq ($(SHARED_LIBS),y)
 
+LDLIBS += -ldl
 LDFLAGS += -Wl,-export-dynamic
+
+else
+
+ip: static-syms.o
+static-syms.o: static-syms.h
+static-syms.h: $(wildcard *.c)
+	files="$^" ; \
+	for s in `grep -B 3 '\<dlsym' $$files | sed -n '/snprintf/{s:.*"\([^"]*\)".*:\1:;s:%s::;p}'` ; do \
+		sed -n '/'$$s'[^ ]* =/{s:.* \([^ ]*'$$s'[^ ]*\) .*:extern char \1[] __attribute__((weak)); if (!strcmp(sym, "\1")) return \1;:;p}' $$files ; \
+	done > $@
+
+endif

ip/static-syms.c

+#include <string.h>
+void *_dlsym(const char *sym)
+{
+#include "static-syms.h"
+	return NULL;
+}

tc/Makefile

@@ -3,6 +3,7 @@ TCOBJ= tc.o tc_qdisc.o tc_class.o tc_filter.o tc_util.o \
        m_ematch.o emp_ematch.yacc.o emp_ematch.lex.o
 
 include ../Config
+SHARED_LIBS ?= y
 
 TCMODULES :=
 TCMODULES += q_fifo.o
@@ -57,7 +58,12 @@ else
 endif
 
 TCOBJ += $(TCMODULES)
-LDLIBS += -L. -ltc -lm -ldl
+LDLIBS += -L. -ltc -lm
+
+ifeq ($(SHARED_LIBS),y)
+LDLIBS += -ldl
+LDFLAGS += -Wl,-export-dynamic
+endif
 
 TCLIB := tc_core.o
 TCLIB += tc_red.o
@@ -72,9 +78,6 @@ ifeq ($(TC_CONFIG_ATM),y)
   TCSO += q_atm.so
 endif
 
-
-LDFLAGS += -Wl,-export-dynamic
-
 YACC := bison
 LEX := flex
 
@@ -108,3 +111,15 @@ q_atm.so: q_atm.c
 
 %.lex.c: %.l
 	$(LEX) $(LEXFLAGS) -o$@ $<
+
+ifneq ($(SHARED_LIBS),y)
+
+tc: static-syms.o
+static-syms.o: static-syms.h
+static-syms.h: $(wildcard *.c)
+	files="$^" ; \
+	for s in `grep -B 3 '\<dlsym' $$files | sed -n '/snprintf/{s:.*"\([^"]*\)".*:\1:;s:%s::;p}'` ; do \
+		sed -n '/'$$s'[^ ]* =/{s:.* \([^ ]*'$$s'[^ ]*\) .*:extern char \1[] __attribute__((weak)); if (!strcmp(sym, "\1")) return \1;:;p}' $$files ; \
+	done > $@
+
+endif

tc/m_ipt.c

@@ -226,6 +226,10 @@ get_target_name(const char *name)
 	struct iptables_target *m;
 	char path[strlen(lib_dir) + sizeof ("/libipt_.so") + strlen(name)];
 
+#ifdef NO_SHARED_LIBS
+	return NULL;
+#endif
+
 	new_name = malloc(strlen(name) + 1);
 	lname = malloc(strlen(name) + 1);
 	if (new_name)

tc/static-syms.c

+#include <string.h>
+void *_dlsym(const char *sym)
+{
+#include "static-syms.h"
+	return NULL;
+}