[PATCH v6 1/6] Shared library support

From: Emese Revfy
Date: Thu Apr 07 2016 - 17:14:20 EST

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Infrastructure for building independent shared library targets.
This effectively also reverts commit 62e2210798ed38928ab24841e8b4878a
(Masahiro Yamada, kbuild: drop shared library support from Makefile.host).

Signed-off-by: Emese Revfy <re.emese@xxxxxxxxx>
---
Documentation/kbuild/makefiles.txt | 39 ++++++++++++++++-----
scripts/Makefile.build | 2 +-
scripts/Makefile.clean | 3 +-
scripts/Makefile.host | 70 +++++++++++++++++++++++++++++++++++++-
4 files changed, 103 insertions(+), 11 deletions(-)

diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt
index 13f888a..250729b 100644
--- a/Documentation/kbuild/makefiles.txt
+++ b/Documentation/kbuild/makefiles.txt
@@ -23,10 +23,11 @@ This document describes the Linux kernel Makefiles.
=== 4 Host Program support
--- 4.1 Simple Host Program
--- 4.2 Composite Host Programs
- --- 4.3 Using C++ for host programs
- --- 4.4 Controlling compiler options for host programs
- --- 4.5 When host programs are actually built
- --- 4.6 Using hostprogs-$(CONFIG_FOO)
+ --- 4.3 Defining shared libraries
+ --- 4.4 Using C++ for host programs
+ --- 4.5 Controlling compiler options for host programs
+ --- 4.6 When host programs are actually built
+ --- 4.7 Using hostprogs-$(CONFIG_FOO)

=== 5 Kbuild clean infrastructure

@@ -643,7 +644,29 @@ Both possibilities are described in the following.
Finally, the two .o files are linked to the executable, lxdialog.
Note: The syntax <executable>-y is not permitted for host-programs.

---- 4.3 Using C++ for host programs
+--- 4.3 Defining shared libraries
+
+ Objects with extension .so are considered shared libraries, and
+ will be compiled as position independent objects.
+ Kbuild provides support for shared libraries, but the usage
+ shall be restricted.
+ In the following example the libkconfig.so shared library is used
+ to link the executable conf.
+
+ Example:
+ #scripts/kconfig/Makefile
+ hostprogs-y := conf
+ conf-objs := conf.o libkconfig.so
+ libkconfig-objs := expr.o type.o
+
+ Shared libraries always require a corresponding -objs line, and
+ in the example above the shared library libkconfig is composed by
+ the two objects expr.o and type.o.
+ expr.o and type.o will be built as position independent code and
+ linked as a shared library libkconfig.so. C++ is not supported for
+ shared libraries.
+
+--- 4.4 Using C++ for host programs

kbuild offers support for host programs written in C++. This was
introduced solely to support kconfig, and is not recommended
@@ -666,7 +689,7 @@ Both possibilities are described in the following.
qconf-cxxobjs := qconf.o
qconf-objs := check.o

---- 4.4 Controlling compiler options for host programs
+--- 4.5 Controlling compiler options for host programs

When compiling host programs, it is possible to set specific flags.
The programs will always be compiled utilising $(HOSTCC) passed
@@ -694,7 +717,7 @@ Both possibilities are described in the following.
When linking qconf, it will be passed the extra option
"-L$(QTDIR)/lib".

---- 4.5 When host programs are actually built
+--- 4.6 When host programs are actually built

Kbuild will only build host-programs when they are referenced
as a prerequisite.
@@ -725,7 +748,7 @@ Both possibilities are described in the following.
This will tell kbuild to build lxdialog even if not referenced in
any rule.

---- 4.6 Using hostprogs-$(CONFIG_FOO)
+--- 4.7 Using hostprogs-$(CONFIG_FOO)

A typical pattern in a Kbuild file looks like this:

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index e1bc190..b2ce235 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -60,7 +60,7 @@ endif
endif

# Do not include host rules unless needed
-ifneq ($(hostprogs-y)$(hostprogs-m),)
+ifneq ($(hostprogs-y)$(hostprogs-m)$(hostlibs-y)$(hostlibs-m)$(hostcxxlibs-y)$(hostcxxlibs-m),)
include scripts/Makefile.host
endif

diff --git a/scripts/Makefile.clean b/scripts/Makefile.clean
index 55c96cb..e4e88ab 100644
--- a/scripts/Makefile.clean
+++ b/scripts/Makefile.clean
@@ -38,7 +38,8 @@ subdir-ymn := $(addprefix $(obj)/,$(subdir-ymn))
__clean-files := $(extra-y) $(extra-m) $(extra-) \
$(always) $(targets) $(clean-files) \
$(host-progs) \
- $(hostprogs-y) $(hostprogs-m) $(hostprogs-)
+ $(hostprogs-y) $(hostprogs-m) $(hostprogs-) \
+ $(hostlibs-y) $(hostlibs-m) $(hostlibs-)

__clean-files := $(filter-out $(no-clean-files), $(__clean-files))

diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index 133edfa..3439bd8 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -20,7 +20,25 @@
# Will compile qconf as a C++ program, and menu as a C program.
# They are linked as C++ code to the executable qconf

+# hostprogs-y := conf
+# conf-objs := conf.o libkconfig.so
+# libkconfig-objs := expr.o type.o
+# Will create a shared library named libkconfig.so that consists of
+# expr.o and type.o (they are both compiled as C code and the object files
+# are made as position independent code).
+# conf.c is compiled as a C program, and conf.o is linked together with
+# libkconfig.so as the executable conf.
+# Note: Shared libraries consisting of C++ files are not supported
+
+# hostcc-option
+# Usage: cflags-y += $(call hostcc-option,-march=winchip-c6,-march=i586)
+
+hostcc-option = $(call try-run,\
+ $(HOSTCC) $(HOSTCFLAGS) $(HOST_EXTRACFLAGS) $(1) -c -x c /dev/null -o "$$TMP",$(1),$(2))
+
__hostprogs := $(sort $(hostprogs-y) $(hostprogs-m))
+__hostlibs := $(sort $(hostlibs-y) $(hostlibs-m))
+__hostcxxlibs := $(sort $(hostcxxlibs-y) $(hostcxxlibs-m))

# C code
# Executables compiled from a single .c file
@@ -42,6 +60,18 @@ host-cxxmulti := $(foreach m,$(__hostprogs),$(if $($(m)-cxxobjs),$(m)))
# C++ Object (.o) files compiled from .cc files
host-cxxobjs := $(sort $(foreach m,$(host-cxxmulti),$($(m)-cxxobjs)))

+# Shared libaries (only .c supported)
+# Shared libraries (.so) - all .so files referenced in "xxx-objs"
+host-cshlib := $(sort $(filter %.so, $(__hostlibs)))
+host-cxxshlib := $(sort $(filter %.so, $(__hostcxxlibs)))
+# Remove .so files from "xxx-objs"
+host-cobjs := $(filter-out %.so,$(host-cobjs))
+host-cxxobjs := $(filter-out %.so,$(host-cxxobjs))
+
+# Object (.o) files used by the shared libaries
+host-cshobjs := $(sort $(foreach m,$(host-cshlib),$($(m:.so=-objs))))
+host-cxxshobjs := $(sort $(foreach m,$(host-cxxshlib),$($(m:.so=-objs))))
+
# output directory for programs/.o files
# hostprogs-y := tools/build may have been specified.
# Retrieve also directory of .o files from prog-objs or prog-cxxobjs notation
@@ -56,6 +86,10 @@ host-cmulti := $(addprefix $(obj)/,$(host-cmulti))
host-cobjs := $(addprefix $(obj)/,$(host-cobjs))
host-cxxmulti := $(addprefix $(obj)/,$(host-cxxmulti))
host-cxxobjs := $(addprefix $(obj)/,$(host-cxxobjs))
+host-cshlib := $(addprefix $(obj)/,$(host-cshlib))
+host-cxxshlib := $(addprefix $(obj)/,$(host-cxxshlib))
+host-cshobjs := $(addprefix $(obj)/,$(host-cshobjs))
+host-cxxshobjs := $(addprefix $(obj)/,$(host-cxxshobjs))
host-objdirs := $(addprefix $(obj)/,$(host-objdirs))

obj-dirs += $(host-objdirs)
@@ -124,5 +158,39 @@ quiet_cmd_host-cxxobjs = HOSTCXX $@
$(host-cxxobjs): $(obj)/%.o: $(src)/%.cc FORCE
$(call if_changed_dep,host-cxxobjs)

+# Compile .c file, create position independent .o file
+# host-cshobjs -> .o
+quiet_cmd_host-cshobjs = HOSTCC -fPIC $@
+ cmd_host-cshobjs = $(HOSTCC) $(hostc_flags) -fPIC -c -o $@ $<
+$(host-cshobjs): $(obj)/%.o: $(src)/%.c FORCE
+ $(call if_changed_dep,host-cshobjs)
+
+# Compile .c file, create position independent .o file
+# host-cxxshobjs -> .o
+quiet_cmd_host-cxxshobjs = HOSTCXX -fPIC $@
+ cmd_host-cxxshobjs = $(HOSTCXX) $(hostcxx_flags) -fPIC -c -o $@ $<
+$(host-cxxshobjs): $(obj)/%.o: $(src)/%.c FORCE
+ $(call if_changed_dep,host-cxxshobjs)
+
+# Link a shared library, based on position independent .o files
+# *.o -> .so shared library (host-cshlib)
+quiet_cmd_host-cshlib = HOSTLLD -shared $@
+ cmd_host-cshlib = $(HOSTCC) $(HOSTLDFLAGS) -shared -o $@ \
+ $(addprefix $(obj)/,$($(@F:.so=-objs))) \
+ $(HOST_LOADLIBES) $(HOSTLOADLIBES_$(@F))
+$(host-cshlib): FORCE
+ $(call if_changed,host-cshlib)
+$(call multi_depend, $(host-cshlib), .so, -objs -cshobjs)
+
+# Link a shared library, based on position independent .o files
+# *.o -> .so shared library (host-cxxshlib)
+quiet_cmd_host-cxxshlib = HOSTLLD -shared $@
+ cmd_host-cxxshlib = $(HOSTCXX) $(HOSTLDFLAGS) -shared -o $@ \
+ $(addprefix $(obj)/,$($(@F:.so=-objs))) \
+ $(HOST_LOADLIBES) $(HOSTLOADLIBES_$(@F))
+$(host-cxxshlib): FORCE
+ $(call if_changed,host-cxxshlib)
+$(call multi_depend, $(host-cxxshlib), .so, -objs -cxxshobjs)
+
targets += $(host-csingle) $(host-cmulti) $(host-cobjs)\
- $(host-cxxmulti) $(host-cxxobjs)
+ $(host-cxxmulti) $(host-cxxobjs) $(host-cshlib) $(host-cshobjs) $(host-cxxshlib) $(host-cxxshobjs)
--
2.4.1

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