This allows us to build any bundled plugins in the source tree.
Out-of-tree builds can call Makefile.plugins to build in their own
source tree:

  make -f $(QEMU_PATH)/trace/plugins/Makefile.plugins QEMU_SRC=$(QEMU_PATH)

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
---
 Makefile                       |  5 ++++-
 trace/Makefile.objs            | 24 ++++++++++++++++++++++++
 trace/plugins/Makefile.plugins | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 trace/plugins/Makefile.plugins

diff --git a/Makefile b/Makefile
index 1144d6e3ba..e04d1c5124 100644
--- a/Makefile
+++ b/Makefile
@@ -438,7 +438,7 @@ dummy := $(call unnest-vars,, \
 
 include $(SRC_PATH)/tests/Makefile.include
 
-all: $(DOCS) $(TOOLS) $(HELPERS-y) recurse-all modules
+all: $(DOCS) $(TOOLS) $(HELPERS-y) recurse-all modules plugins
 
 qemu-version.h: FORCE
 	$(call quiet-command, \
@@ -1091,6 +1091,9 @@ help:
 	@echo  '  all             - Build all'
 ifdef CONFIG_MODULES
 	@echo  '  modules         - Build all modules'
+endif
+ifdef CONFIG_TRACE_PLUGIN
+	@echo  '  plugins         - Build all plugins'
 endif
 	@echo  '  dir/file.o      - Build specified target only'
 	@echo  '  install         - Install QEMU, documentation and tools'
diff --git a/trace/Makefile.objs b/trace/Makefile.objs
index 4977f654a5..4f62022595 100644
--- a/trace/Makefile.objs
+++ b/trace/Makefile.objs
@@ -58,3 +58,27 @@ util-obj-$(CONFIG_TRACE_PLUGIN) += plugins.o
 util-obj-y += control.o
 target-obj-y += control-target.o
 util-obj-y += qmp.o
+
+######################################################################
+# Plugins
+ifdef CONFIG_TRACE_PLUGIN
+
+PLUGINS=$(dir $(wildcard $(SRC_PATH)/trace/plugins/*/.))
+
+.PHONY: plugins $(PLUGINS)
+
+plugins: $(PLUGINS)
+	$(info built all plugins $(PLUGINS))
+
+$(PLUGINS):
+	$(call quiet-command, 							\
+	   (cd $@ && $(MAKE) -f $(SRC_PATH)/trace/plugins/Makefile.plugins 	\
+				QEMU_SRC=$(SRC_PATH) 				\
+				BUILD_DIR=$(BUILD_DIR)/trace/plugins), 		\
+	"PLUGIN","in $@")
+
+else
+
+plugins:
+
+endif
diff --git a/trace/plugins/Makefile.plugins b/trace/plugins/Makefile.plugins
new file mode 100644
index 0000000000..0056d91c74
--- /dev/null
+++ b/trace/plugins/Makefile.plugins
@@ -0,0 +1,32 @@
+# -*- Mode: makefile -*-
+#
+# QEMU plugins
+#
+# This Makefile is used to build plugins for QEMU. Unlike the rest of
+# the object files we build we don't have visibility of QEMU's
+# internals. When called from the main makefile we build plugins into
+# BUILD_DIR/plugins otherwise where ever the Makefile was called from.
+# QEMU_SRC
+#
+
+BUILD_DIR ?= $(CURDIR)
+CC ?= cc
+
+ifndef QEMU_SRC
+$(error need to define QEMU_SRC for the build)
+endif
+
+GLIB_CFLAGS = $(shell pkg-config --cflags glib-2.0)
+CFLAGS = -I$(QEMU_SRC)/include/plugins $(GLIB_CFLAGS) -fno-PIE -fPIC -O3 -g
+LDFLAGS = $(shell pkg-config --libs glib-2.0) -shared
+
+SRC = $(wildcard *.c)
+PLUGINS = $(addprefix $(BUILD_DIR)/,$(SRC:.c=.so))
+
+$(BUILD_DIR)/%.so: %.c
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $<
+
+all: $(PLUGINS)
+
+clean:
+	rm -f $(PLUGIN_SO) $(PLUGIN_OBJ)
-- 
2.17.1

On 10/5/18 8:49 AM, Alex Bennée wrote:
> +GLIB_CFLAGS = $(shell pkg-config --cflags glib-2.0)
> +CFLAGS = -I$(QEMU_SRC)/include/plugins $(GLIB_CFLAGS) -fno-PIE -fPIC -O3 -g
> +LDFLAGS = $(shell pkg-config --libs glib-2.0) -shared

I'm not keen on defaulting to -O3.
I'd prefer if we passed up the flags from top-level, but I know you're also
trying to support out-of-tree builds.

Perhaps

CFLAGS ?= -O2 -g
QEMU_CFLAGS = $(CFLAGS) $(GLIB_CFLAGS) -I$(QEMU_SRC)/... -fno-PIE -fPIC

> +SRC = $(wildcard *.c)
> +PLUGINS = $(addprefix $(BUILD_DIR)/,$(SRC:.c=.so))
> +
> +$(BUILD_DIR)/%.so: %.c
> +	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $<
> +
> +all: $(PLUGINS)

Do you really want one plugin per source file rather than one plugin per
directory?  I think the latter makes more sense...

And of course you know the second thing people are going to want is to write
these plugins in C++...


r~

Richard Henderson <richard.henderson@linaro.org> writes:

> On 10/5/18 8:49 AM, Alex Bennée wrote:
>> +GLIB_CFLAGS = $(shell pkg-config --cflags glib-2.0)
>> +CFLAGS = -I$(QEMU_SRC)/include/plugins $(GLIB_CFLAGS) -fno-PIE -fPIC -O3 -g
>> +LDFLAGS = $(shell pkg-config --libs glib-2.0) -shared
>
> I'm not keen on defaulting to -O3.

Fair enough... I'll drop it down if not set...

> I'd prefer if we passed up the flags from top-level, but I know you're also
> trying to support out-of-tree builds.
>
> Perhaps
>
> CFLAGS ?= -O2 -g
> QEMU_CFLAGS = $(CFLAGS) $(GLIB_CFLAGS) -I$(QEMU_SRC)/... -fno-PIE -fPIC
>
>> +SRC = $(wildcard *.c)
>> +PLUGINS = $(addprefix $(BUILD_DIR)/,$(SRC:.c=.so))
>> +
>> +$(BUILD_DIR)/%.so: %.c
>> +	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $<
>> +
>> +all: $(PLUGINS)
>
> Do you really want one plugin per source file rather than one plugin per
> directory?  I think the latter makes more sense...
>
> And of course you know the second thing people are going to want is to write
> these plugins in C++...
>
>
> r~


--
Alex Bennée