linux-kernel - [RFC 01/19] kbuild: Fixes to rules for host-cshlib and host-cxxshlib

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Message-Id: <be2c361eac49ded2848b2a555b75e30cc3c24e71.1565676440.git-series.knut.omang@oracle.com>
Date:   Tue, 13 Aug 2019 08:09:16 +0200
From:   Knut Omang <knut.omang@...cle.com>
To:     linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shreyans Devendra Doshi <0xinfosect0r@...il.com>,
        Alan Maguire <alan.maguire@...cle.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Kevin Hilman <khilman@...libre.com>,
        Hidenori Yamaji <hidenori.yamaji@...y.com>,
        Frank Rowand <frowand.list@...il.com>,
        Timothy Bird <Tim.Bird@...y.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        "Theodore Ts'o" <tytso@....edu>, Daniel Vetter <daniel@...ll.ch>,
        Stephen Boyd <sboyd@...nel.org>,
        Knut Omang <knut.omang@...cle.com>
Subject: [RFC 01/19] kbuild: Fixes to rules for host-cshlib and host-cxxshlib

C++ libraries interfacing to C APIs might sometimes need some glue
logic more easily written in C.
Allow a C++ library to also contain 0 or more C objects.

Also fix rules for both C and C++ shared libraries:
- C++ shared libraries depended on .c instead of .cc files
- Rules were referenced as -objs instead of the intended
  -cobjs and -cxxobjs following the pattern from hostprogs*.

Signed-off-by: Knut Omang <knut.omang@...cle.com>
---
 scripts/Makefile.host | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index b6a54bd..4e9bb21 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -46,8 +46,10 @@ host-cxxmulti	:= $(foreach m,$(__hostprogs),$(if $($(m)-cxxobjs),$(m)))
 host-cxxobjs	:= $(sort $(foreach m,$(host-cxxmulti),$($(m)-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))))
+# Note: C++ libraries may contain both C and C++ objects, compiled differently:
+host-cshobjs	:= $(sort $(foreach m,$(host-cshlib),$($(m:.so=-cshobjs))))
+host-cshobjs	+= $(sort $(foreach m,$(host-cxxshlib),$($(m:.so=-cshobjs))))
+host-cxxshobjs	:= $(sort $(foreach m,$(host-cxxshlib),$($(m:.so=-cxxshobjs))))
 
 host-csingle	:= $(addprefix $(obj)/,$(host-csingle))
 host-cmulti	:= $(addprefix $(obj)/,$(host-cmulti))
@@ -130,14 +132,10 @@ quiet_cmd_host-cshobjs	= HOSTCC  -fPIC $@
 $(host-cshobjs): $(obj)/%.o: $(src)/%.c FORCE
 	$(call if_changed_dep,host-cshobjs)
 
-# Compile .c file, create position independent .o file
-# Note that plugin capable gcc versions can be either C or C++ based
-# therefore plugin source files have to be compilable in both C and C++ mode.
-# This is why a C++ compiler is invoked on a .c file.
-# host-cxxshobjs -> .o
+# Compile .cc (C++) file, create position independent .o file
 quiet_cmd_host-cxxshobjs	= HOSTCXX -fPIC $@
       cmd_host-cxxshobjs	= $(HOSTCXX) $(hostcxx_flags) -fPIC -c -o $@ $<
-$(host-cxxshobjs): $(obj)/%.o: $(src)/%.c FORCE
+$(host-cxxshobjs): $(obj)/%.o: $(src)/%.cc FORCE
 	$(call if_changed_dep,host-cxxshobjs)
 
 # Link a shared library, based on position independent .o files
@@ -154,7 +152,8 @@ $(call multi_depend, $(host-cshlib), .so, -objs)
 # *.o -> .so shared library (host-cxxshlib)
 quiet_cmd_host-cxxshlib	= HOSTLLD -shared $@
       cmd_host-cxxshlib	= $(HOSTCXX) $(KBUILD_HOSTLDFLAGS) -shared -o $@ \
-			  $(addprefix $(obj)/,$($(@F:.so=-objs))) \
+			  $(addprefix $(obj)/,$($(@F:.so=-cshobjs))) \
+			  $(addprefix $(obj)/,$($(@F:.so=-cxxshobjs))) \
 			  $(KBUILD_HOSTLDLIBS) $(HOSTLDLIBS_$(@F))
 $(host-cxxshlib): FORCE
 	$(call if_changed,host-cxxshlib)
-- 
git-series 0.9.1