From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58867) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XOOzf-0001JS-GN for qemu-devel@nongnu.org; Mon, 01 Sep 2014 06:37:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XOOzY-0002Z2-Rh for qemu-devel@nongnu.org; Mon, 01 Sep 2014 06:37:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18984) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XOOzY-0002Yq-Ke for qemu-devel@nongnu.org; Mon, 01 Sep 2014 06:37:44 -0400 Message-ID: <54044C6F.2010202@redhat.com> Date: Mon, 01 Sep 2014 12:37:35 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1409567710-26217-1-git-send-email-famz@redhat.com> In-Reply-To: <1409567710-26217-1-git-send-email-famz@redhat.com> Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2] rules.mak: Fix DSO build by pulling in archive symbols List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng , qemu-devel@nongnu.org Cc: kwolf@redhat.com, Peter Maydell , Michael Tokarev , stefanha@redhat.com, hjl.tools@gmail.com Il 01/09/2014 12:35, Fam Zheng ha scritto: > This fixes an issue with module build system. block/iscsi.so is > currently broken: > > $ ~/build/last/qemu-img > Failed to open module: /home/fam/build/master/block-iscsi.so: > undefined symbol: qmp_query_uuid > qemu-img: Not enough arguments > Try 'qemu-img --help' for more information > > To fix this, we should (at least) let qemu-img link qmp_query_uuid from > libqemustub.a. (There are a few other symbols missing, as well.) > > This patch changes the linking rules to: > > 1) Build ".mo" with "ld -r -o $@ $^" for each ".so", and later build .so > with it. > > 2) Always build all the .mo before linking the executables. This is > achieved by adding those .mo files to the executables' "-y" > variables. > > 3) When linking an executable, those .mo files in its "-y" variables are > filtered out, and replaced by one or more -Wl,-u,$symbol flags. This > is done in the added macro "process-archive-undefs". > > These "-Wl,-u,$symbol" flags will force ld to pull in the function > definition from the archives when linking. > > Note that the .mo objects, that are actually meant to be linked in > the executables, are already expanded in unnest-vars, before the > linking command. So we are safe to simply filter out .mo for the > purpose of pulling undefined symbols. > > process-archive-undefs works as this: For each ".mo", find all the > undefined symbols in it, filter ones that are defined in the > archives. For each of these symbols, generate a "-Wl,-u,$symbol" in > the link command, and put them before archive names in the command > line. > > Suggested-by: H.J. Lu > Signed-off-by: Fam Zheng > --- > rules.mak | 43 ++++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 40 insertions(+), 3 deletions(-) > > diff --git a/rules.mak b/rules.mak > index ba2f4c1..1d73293 100644 > --- a/rules.mak > +++ b/rules.mak > @@ -22,6 +22,32 @@ QEMU_DGFLAGS += -MMD -MP -MT $@ -MF $(*D)/$(*F).d > # Same as -I$(SRC_PATH) -I., but for the nested source/object directories > QEMU_INCLUDES += -I$( > +WL_U := -Wl,-u, > +find-symbols = $(if $1, $(sort $(shell nm -P -g $1 | $2))) > +defined-symbols = $(call find-symbols,$1,awk '$$2!="U"{print $$1}') > +undefined-symbols = $(call find-symbols,$1,awk '$$2=="U"{print $$1}') > + > +# All the .mo objects in -m variables are also added into corresponding -y > +# variable in unnest-vars, but filtered out here, when LINK is called. > +# > +# The .mo objects are supposed to be linked as a DSO, for module build. So here > +# they are only used as a placeholders to generate those "archive undefined" > +# symbol options (-Wl,-u,$symbol_name), which are the archive functions > +# referenced by the code in the DSO. > +# > +# Also the presence in -y variables will also guarantee they are built before > +# linking executables that will load them. So we can look up symbol reference > +# in LINK. > +# > +# This is necessary because the exectuable itself may not use the function, in > +# which case the function would not be linked in. Then the DSO loading will > +# fail because of the missing symbol. > +process-archive-undefs = $(filter-out %.a %.mo,$1) \ > + $(addprefix $(WL_U), \ > + $(filter $(call defined-symbols,$(filter %.a, $1)), \ > + $(call undefined-symbols,$(filter %.mo,$1)))) \ > + $(filter %.a,$1) > + > extract-libs = $(strip $(foreach o,$1,$($o-libs))) > expand-objs = $(strip $(sort $(filter %.o,$1)) \ > $(foreach o,$(filter %.mo,$1),$($o-objs)) \ > @@ -38,7 +64,8 @@ LINKPROG = $(or $(CXX),$(CC)) > > ifeq ($(LIBTOOL),) > LINK = $(call quiet-command, $(LINKPROG) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o $@ \ > - $1 $(version-obj-y) $(call extract-libs,$1) $(LIBS)," LINK $(TARGET_DIR)$@") > + $(call process-archive-undefs, $1) \ > + $(version-obj-y) $(call extract-libs,$1) $(LIBS)," LINK $(TARGET_DIR)$@") > else > LIBTOOL += $(if $(V),,--quiet) > %.lo: %.c > @@ -50,7 +77,8 @@ LIBTOOL += $(if $(V),,--quiet) > > LINK = $(call quiet-command,\ > $(if $(filter %.lo %.la,$1),$(LIBTOOL) --mode=link --tag=CC \ > - )$(LINKPROG) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o $@ $1 \ > + )$(LINKPROG) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o $@ \ > + $(call process-archive-undefs, $1)\ > $(if $(filter %.lo %.la,$1),$(version-lobj-y),$(version-obj-y)) \ > $(if $(filter %.lo %.la,$1),$(LIBTOOLFLAGS)) \ > $(call extract-libs,$(1:.lo=.o)) $(LIBS),$(if $(filter %.lo %.la,$1),"lt LINK ", " LINK ")"$(TARGET_DIR)$@") > @@ -76,11 +104,17 @@ endif > > %$(DSOSUF): CFLAGS += -fPIC -DBUILD_DSO > %$(DSOSUF): LDFLAGS += $(LDFLAGS_SHARED) > -%$(DSOSUF): > +%$(DSOSUF): %.mo > $(call LINK,$^) > @# Copy to build root so modules can be loaded when program started without install > $(if $(findstring /,$@),$(call quiet-command,cp $@ $(subst /,-,$@), " CP $(subst /,-,$@)")) > > + > +LD_REL := $(CC) -nostdlib -Wl,-r > + > +%.mo: > + $(call quiet-command,$(LD_REL) -o $@ $^," LD -r $(TARGET_DIR)$@") > + > .PHONY: modules > modules: > > @@ -306,6 +340,9 @@ define unnest-vars > # For module build, build shared libraries during "make modules" > # For non-module build, add -m to -y > $(if $(CONFIG_MODULES), > + $(foreach o,$($v), > + $(eval $o: $($o-objs))) > + $(eval $(patsubst %-m,%-y,$v) += $($v)) > $(eval modules: $($v:%.mo=%$(DSOSUF))), > $(eval $(patsubst %-m,%-y,$v) += $(call expand-objs, $($v))))) > > Thanks, Reviewed-by: Paolo Bonzini