build: replace weak symbols with a static library

Weak symbols were a nice idea, but they turned out not to be a good one.
Toolchain support is just too sparse, in particular llvm-gcc is totally
broken.

This patch uses a surprisingly low-tech approach: a static library.
Symbols in a static library are always overridden by symbols in an
object file.  Furthermore, if you place each function in a separate
source file, object files for unused functions will not be taken in.
This means that each function can use all the dependencies that it needs
(especially QAPI stuff such as error_setg).

Thus, all stubs are placed in separate object files and put together in
a static library.  The library then is linked to all programs.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Tested-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Tested-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

Makefile

@@ -157,6 +157,12 @@ version.o: $(SRC_PATH)/version.rc config-host.h
 	$(call quiet-command,$(WINDRES) -I. -o $@ $<,"  RC    $(TARGET_DIR)$@")
 
 version-obj-$(CONFIG_WIN32) += version.o
+
+######################################################################
+# Build library with stubs
+
+libqemustub.a: $(stub-obj-y)
+
 ######################################################################
 # Support building shared library libcacard
 
@@ -183,13 +189,13 @@ tools-obj-y = $(oslib-obj-y) $(trace-obj-y) qemu-tool.o qemu-timer.o \
 	main-loop.o iohandler.o error.o
 tools-obj-$(CONFIG_POSIX) += compatfd.o
 
-qemu-img$(EXESUF): qemu-img.o $(tools-obj-y) $(block-obj-y)
-qemu-nbd$(EXESUF): qemu-nbd.o $(tools-obj-y) $(block-obj-y)
-qemu-io$(EXESUF): qemu-io.o cmd.o $(tools-obj-y) $(block-obj-y)
+qemu-img$(EXESUF): qemu-img.o $(tools-obj-y) $(block-obj-y) libqemustub.a
+qemu-nbd$(EXESUF): qemu-nbd.o $(tools-obj-y) $(block-obj-y) libqemustub.a
+qemu-io$(EXESUF): qemu-io.o cmd.o $(tools-obj-y) $(block-obj-y) libqemustub.a
 
 qemu-bridge-helper$(EXESUF): qemu-bridge-helper.o
 
-vscclient$(EXESUF): $(libcacard-y) $(oslib-obj-y) $(trace-obj-y) libcacard/vscclient.o
+vscclient$(EXESUF): $(libcacard-y) $(oslib-obj-y) $(trace-obj-y) libcacard/vscclient.o libqemustub.a
 	$(call quiet-command,$(CC) $(LDFLAGS) -o $@ $^ $(libcacard_libs) $(LIBS),"  LINK  $@")
 
 fsdev/virtfs-proxy-helper$(EXESUF): fsdev/virtfs-proxy-helper.o fsdev/virtio-9p-marshal.o oslib-posix.o $(trace-obj-y)
@@ -232,7 +238,7 @@ $(SRC_PATH)/qapi-schema.json $(SRC_PATH)/scripts/qapi-commands.py $(qapi-py)
 QGALIB_GEN=$(addprefix qga/qapi-generated/, qga-qapi-types.h qga-qapi-visit.h qga-qmp-commands.h)
 $(qga-obj-y) qemu-ga.o: $(QGALIB_GEN)
 
-qemu-ga$(EXESUF): qemu-ga.o $(qga-obj-y) $(oslib-obj-y) $(trace-obj-y) $(qapi-obj-y) $(qobject-obj-y) $(version-obj-y)
+qemu-ga$(EXESUF): qemu-ga.o $(qga-obj-y) $(oslib-obj-y) $(trace-obj-y) $(qapi-obj-y) $(qobject-obj-y) $(version-obj-y) libqemustub.a
 
 QEMULIBS=libuser libdis libdis-user
 

Makefile.objs

+#######################################################################
+# Stub library, linked in tools
+stub-obj-y = stubs/
+
 #######################################################################
 # Target-independent parts used in system and user emulation
 universal-obj-y =
@@ -239,6 +243,7 @@ vl.o: QEMU_CFLAGS+=$(SDL_CFLAGS)
 QEMU_CFLAGS+=$(GLIB_CFLAGS)
 
 nested-vars += \
+	stub-obj-y \
 	qga-obj-y \
 	qom-obj-y \
 	qapi-obj-y \

Makefile.target

@@ -162,12 +162,12 @@ endif #CONFIG_LINUX_USER
 
 ifdef QEMU_PROGW
 # The linker builds a windows executable. Make also a console executable.
-$(QEMU_PROGW): $(all-obj-y)
+$(QEMU_PROGW): $(all-obj-y) ../libqemustub.a
 	$(call LINK,$^)
 $(QEMU_PROG): $(QEMU_PROGW)
 	$(call quiet-command,$(OBJCOPY) --subsystem console $(QEMU_PROGW) $(QEMU_PROG),"  GEN   $(TARGET_DIR)$(QEMU_PROG)")
 else
-$(QEMU_PROG): $(all-obj-y)
+$(QEMU_PROG): $(all-obj-y) ../libqemustub.a
 	$(call LINK,$^)
 endif
 

compiler.h

@@ -50,20 +50,9 @@
 #   define __printf__ __gnu_printf__
 #  endif
 # endif
-# if defined(__APPLE__)
-#  define QEMU_WEAK_ALIAS(newname, oldname) \
-        static typeof(oldname) weak_##newname __attribute__((unused, weakref(#oldname)))
-#  define QEMU_WEAK_REF(newname, oldname) (weak_##newname ? weak_##newname : oldname)
-# else
-#  define QEMU_WEAK_ALIAS(newname, oldname) \
-        typeof(oldname) newname __attribute__((weak, alias (#oldname)))
-#  define QEMU_WEAK_REF(newname, oldname) newname
-# endif
 #else
 #define GCC_ATTR /**/
 #define GCC_FMT_ATTR(n, m)
-#define QEMU_WEAK_ALIAS(newname, oldname) \
-        _Pragma("weak " #newname "=" #oldname)
 #endif
 
 #endif /* COMPILER_H */

osdep.c

@@ -54,38 +54,6 @@ static bool fips_enabled = false;
 
 static const char *qemu_version = QEMU_VERSION;
 
-static int default_fdset_get_fd(int64_t fdset_id, int flags)
-{
-    return -1;
-}
-QEMU_WEAK_ALIAS(monitor_fdset_get_fd, default_fdset_get_fd);
-#define monitor_fdset_get_fd \
-    QEMU_WEAK_REF(monitor_fdset_get_fd, default_fdset_get_fd)
-
-static int default_fdset_dup_fd_add(int64_t fdset_id, int dup_fd)
-{
-    return -1;
-}
-QEMU_WEAK_ALIAS(monitor_fdset_dup_fd_add, default_fdset_dup_fd_add);
-#define monitor_fdset_dup_fd_add \
-    QEMU_WEAK_REF(monitor_fdset_dup_fd_add, default_fdset_dup_fd_add)
-
-static int default_fdset_dup_fd_remove(int dup_fd)
-{
-    return -1;
-}
-QEMU_WEAK_ALIAS(monitor_fdset_dup_fd_remove, default_fdset_dup_fd_remove);
-#define monitor_fdset_dup_fd_remove \
-    QEMU_WEAK_REF(monitor_fdset_dup_fd_remove, default_fdset_dup_fd_remove)
-
-static int default_fdset_dup_fd_find(int dup_fd)
-{
-    return -1;
-}
-QEMU_WEAK_ALIAS(monitor_fdset_dup_fd_find, default_fdset_dup_fd_find);
-#define monitor_fdset_dup_fd_find \
-    QEMU_WEAK_REF(monitor_fdset_dup_fd_remove, default_fdset_dup_fd_find)
-
 int socket_set_cork(int fd, int v)
 {
 #if defined(SOL_TCP) && defined(TCP_CORK)

oslib-win32.c

@@ -32,13 +32,6 @@
 #include "trace.h"
 #include "qemu_socket.h"
 
-static void default_qemu_fd_register(int fd)
-{
-}
-QEMU_WEAK_ALIAS(qemu_fd_register, default_qemu_fd_register);
-#define qemu_fd_register \
-    QEMU_WEAK_REF(qemu_fd_register, default_qemu_fd_register)
-
 void *qemu_oom_check(void *ptr)
 {
     if (ptr == NULL) {

qemu-sockets.c

@@ -61,28 +61,6 @@ static QemuOptsList dummy_opts = {
     },
 };
 
-static int default_monitor_get_fd(Monitor *mon, const char *name, Error **errp)
-{
-    error_setg(errp, "only QEMU supports file descriptor passing");
-    return -1;
-}
-QEMU_WEAK_ALIAS(monitor_get_fd, default_monitor_get_fd);
-#define monitor_get_fd \
-    QEMU_WEAK_REF(monitor_get_fd, default_monitor_get_fd)
-
-static int default_qemu_set_fd_handler2(int fd,
-                                        IOCanReadHandler *fd_read_poll,
-                                        IOHandler *fd_read,
-                                        IOHandler *fd_write,
-                                        void *opaque)
-
-{
-    abort();
-}
-QEMU_WEAK_ALIAS(qemu_set_fd_handler2, default_qemu_set_fd_handler2);
-#define qemu_set_fd_handler2 \
-    QEMU_WEAK_REF(qemu_set_fd_handler2, default_qemu_set_fd_handler2)
-
 static int inet_getport(struct addrinfo *e)
 {
     struct sockaddr_in *i4;

qmp.c

@@ -471,15 +471,6 @@ DevicePropertyInfoList *qmp_device_list_properties(const char *typename,
     return prop_list;
 }
 
-static CpuDefinitionInfoList *default_arch_query_cpu_definitions(Error **errp)
-{
-    error_set(errp, QERR_NOT_SUPPORTED);
-    return NULL;
-}
-QEMU_WEAK_ALIAS(arch_query_cpu_definitions, default_arch_query_cpu_definitions);
-#define arch_query_cpu_definitions \
-    QEMU_WEAK_REF(arch_query_cpu_definitions, default_arch_query_cpu_definitions)
-
 CpuDefinitionInfoList *qmp_query_cpu_definitions(Error **errp)
 {
     return arch_query_cpu_definitions(errp);

rules.mak

@@ -31,7 +31,7 @@ endif
 %.o: %.m
 	$(call quiet-command,$(OBJCC) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) -c -o $@ $<,"  OBJC  $(TARGET_DIR)$@")
 
-LINK = $(call quiet-command,$(CC) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o $@ $(sort $(1)) $(LIBS),"  LINK  $(TARGET_DIR)$@")
+LINK = $(call quiet-command,$(CC) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o $@ $(sort $(filter %.o, $1)) $(filter-out %.o, $1) $(LIBS),"  LINK  $(TARGET_DIR)$@")
 
 %$(EXESUF): %.o
 	$(call LINK,$^)

stubs/Makefile.objs

+stub-obj-y += arch-query-cpu-def.o
+stub-obj-y += fdset-add-fd.o
+stub-obj-y += fdset-find-fd.o
+stub-obj-y += fdset-get-fd.o
+stub-obj-y += fdset-remove-fd.o
+stub-obj-y += get-fd.o
+stub-obj-y += set-fd-handler.o
+stub-obj-$(CONFIG_WIN32) += fd-register.o

stubs/arch-query-cpu-def.c

+#include "qemu-common.h"
+#include "arch_init.h"
+#include "qerror.h"
+
+CpuDefinitionInfoList *arch_query_cpu_definitions(Error **errp)
+{
+    error_set(errp, QERR_NOT_SUPPORTED);
+    return NULL;
+}

stubs/fd-register.c

+#include "qemu-common.h"
+#include "main-loop.h"
+
+void qemu_fd_register(int fd)
+{
+}

stubs/fdset-add-fd.c

+#include "qemu-common.h"
+#include "monitor.h"
+
+int monitor_fdset_dup_fd_add(int64_t fdset_id, int dup_fd)
+{
+    return -1;
+}

stubs/fdset-find-fd.c

+#include "qemu-common.h"
+#include "monitor.h"
+
+int monitor_fdset_dup_fd_find(int dup_fd)
+{
+    return -1;
+}

stubs/fdset-get-fd.c

+#include "qemu-common.h"
+#include "monitor.h"
+
+int monitor_fdset_get_fd(int64_t fdset_id, int flags)
+{
+    return -1;
+}

stubs/fdset-remove-fd.c

+#include "qemu-common.h"
+#include "monitor.h"
+
+int monitor_fdset_dup_fd_remove(int dupfd)
+{
+    return -1;
+}

stubs/get-fd.c

+#include "qemu-common.h"
+#include "monitor.h"
+
+int monitor_get_fd(Monitor *mon, const char *name, Error **errp)
+{
+    error_setg(errp, "only QEMU supports file descriptor passing");
+    return -1;
+}

stubs/set-fd-handler.c

+#include "qemu-common.h"
+#include "main-loop.h"
+
+int qemu_set_fd_handler2(int fd,
+                         IOCanReadHandler *fd_read_poll,
+                         IOHandler *fd_read,
+                         IOHandler *fd_write,
+                         void *opaque)
+{
+    abort();
+}