[kernel-hardening] Re: [PATCH v5 1/5] Shared library support

Masahiro Yamada
2016-03-11T06:19:33Z

Hi Emese,

2016-03-07 8:03 GMT+09:00 Emese Revfy <re.emese@gmail.com>:
> 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@gmail.com>
> ---
> scripts/Makefile.build | 2 +-
> scripts/Makefile.clean | 3 ++-
> scripts/Makefile.host | 69 +++++++++++++++++++++++++++++++++++++++++++++++++-
> 3 files changed, 71 insertions(+), 3 deletions(-)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 130a452..bd2a31e 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..4d180d9 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

I do not see any use-case for the above.

This series adds cases for "foo.so" as a final target.

As an alternative, you can add needed build rules
into tools/gcc/Makefile, not scripts/Makefile.host

I guess these rule won't be used in other places.

> +# 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 +60,19 @@ 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, $(host-cobjs)))

useless.

> +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 +87,10 @@ 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 +159,37 @@ 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): $(obj)/%: $(host-cshobjs) FORCE
> + $(call if_changed,host-cshlib)

Could you use $(call multi-depend, ...)
if you need to handle multi-object please?

Please refer to commit c8589d1e9e01 and commit 97e3226e6e984c8.

But, I still do not see any gcc-plugin that is large enough
to be linked from multiple objects.

--
Best Regards
Masahiro Yamada