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[Qemu-devel] [PATCH v3] rules.mak: Fix DSO build by pulling in archive s
From: |
Fam Zheng |
Subject: |
[Qemu-devel] [PATCH v3] rules.mak: Fix DSO build by pulling in archive symbols |
Date: |
Tue, 2 Sep 2014 09:45:17 +0800 |
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 <address@hidden>
Signed-off-by: Fam Zheng <address@hidden>
---
v3: Add "2>/dev/null" for nm command.
Fix a few words in the comment.
---
rules.mak | 42 +++++++++++++++++++++++++++++++++++++++---
1 file changed, 39 insertions(+), 3 deletions(-)
diff --git a/rules.mak b/rules.mak
index ba2f4c1..24592ae 100644
--- a/rules.mak
+++ b/rules.mak
@@ -22,6 +22,31 @@ QEMU_DGFLAGS += -MMD -MP -MT $@ -MF $(*D)/$(*F).d
# Same as -I$(SRC_PATH) -I., but for the nested source/object directories
QEMU_INCLUDES += -I$(<D) -I$(@D)
+WL_U := -Wl,-u,
+find-symbols = $(if $1, $(sort $(shell nm -P -g $1 2>/dev/null | $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.
+#
+# The presence of module .mo names in -y variables will guarantee that they are
+# built before $(call LINK). So we can look up symbol reference in LINK.
+#
+# This function is necessary because the exectuable itself may not use the
+# function, in which case the function would not be linked, 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 +63,8 @@ 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 +76,8 @@ 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)$@")
@@ -76,11 +103,17 @@ endif
%$(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 +339,9 @@ 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)))))
--
2.1.0
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