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Re: [PATCH v2 2/8] lib: collect library files in an archive

To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>
From: Julien Grall <julien@xxxxxxx>
Date: Wed, 18 Nov 2020 17:06:06 +0000
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
Delivery-date: Wed, 18 Nov 2020 17:06:15 +0000
List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

(+ Anthony)

Hi Jan,

On 23/10/2020 11:17, Jan Beulich wrote:

In order to (subsequently) drop odd things like CONFIG_NEEDS_LIST_SORT
just to avoid bloating binaries when only some arch-es and/or
configurations need generic library routines, combine objects under lib/
into an archive, which the linker then can pick the necessary objects
out of.

Note that we can't use thin archives just yet, until we've raised the
minimum required binutils version suitably.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
  xen/Rules.mk          | 33 +++++++++++++++++++++++++++------
  xen/arch/arm/Makefile |  6 +++---
  xen/arch/x86/Makefile |  8 ++++----
  xen/lib/Makefile      |  3 ++-

IIRC, Anthony worked on the build systems. If I am right, it would begood to get a review from him.

  4 files changed, 36 insertions(+), 14 deletions(-)

diff --git a/xen/Rules.mk b/xen/Rules.mk
index 333e19bec343..e59c7f213f77 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -41,12 +41,16 @@ ALL_OBJS-y               += $(BASEDIR)/xsm/built_in.o
  ALL_OBJS-y               += $(BASEDIR)/arch/$(TARGET_ARCH)/built_in.o
  ALL_OBJS-$(CONFIG_CRYPTO)   += $(BASEDIR)/crypto/built_in.o

+ALL_LIBS-y := $(BASEDIR)/lib/lib.a

+
  # Initialise some variables
+lib-y :=
  targets :=
  CFLAGS-y :=
  AFLAGS-y :=

ALL_OBJS := $(ALL_OBJS-y)

+ALL_LIBS := $(ALL_LIBS-y)

SPECIAL_DATA_SECTIONS := rodata $(foreach a,1 2 4 8 16, \

                                              $(foreach w,1 2 4, \
@@ -60,7 +64,14 @@ include Makefile
  # ---------------------------------------------------------------------------

quiet_cmd_ld = LD $@

-cmd_ld = $(LD) $(XEN_LDFLAGS) -r -o $@ $(real-prereqs)
+cmd_ld = $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter-out %.a,$(real-prereqs)) \
+               --start-group $(filter %.a,$(real-prereqs)) --end-group
+
+# Archive
+# ---------------------------------------------------------------------------
+
+quiet_cmd_ar = AR      $@
+cmd_ar = rm -f $@; $(AR) cPrs $@ $(real-prereqs)

# Objcopy

  # ---------------------------------------------------------------------------
@@ -86,6 +97,10 @@ obj-y    := $(patsubst %/, %/built_in.o, $(obj-y))
  # tell kbuild to descend
  subdir-obj-y := $(filter %/built_in.o, $(obj-y))

+# Libraries are always collected in one lib file.

+# Filter out objects already built-in
+lib-y := $(filter-out $(obj-y), $(sort $(lib-y)))
+
  $(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): CFLAGS-y += 
-DINIT_SECTIONS_ONLY

ifeq ($(CONFIG_COVERAGE),y)

@@ -129,19 +144,25 @@ include $(BASEDIR)/arch/$(TARGET_ARCH)/Rules.mk
  c_flags += $(CFLAGS-y)
  a_flags += $(CFLAGS-y) $(AFLAGS-y)

-built_in.o: $(obj-y) $(extra-y)

+built_in.o: $(obj-y) $(if $(strip $(lib-y)),lib.a) $(extra-y)
  ifeq ($(obj-y),)
        $(CC) $(c_flags) -c -x c /dev/null -o $@
  else
  ifeq ($(CONFIG_LTO),y)
-       $(LD_LTO) -r -o $@ $(filter-out $(extra-y),$^)
+       $(LD_LTO) -r -o $@ $(filter-out lib.a $(extra-y),$^)
  else
-       $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter-out $(extra-y),$^)
+       $(LD) $(XEN_LDFLAGS) -r -o $@ $(filter-out lib.a $(extra-y),$^)
  endif
  endif

+lib.a: $(lib-y) FORCE

+       $(call if_changed,ar)
+
  targets += built_in.o
-targets += $(filter-out $(subdir-obj-y), $(obj-y)) $(extra-y)
+ifneq ($(strip $(lib-y)),)
+targets += lib.a
+endif
+targets += $(filter-out $(subdir-obj-y), $(obj-y) $(lib-y)) $(extra-y)
  targets += $(MAKECMDGOALS)

built_in_bin.o: $(obj-bin-y) $(extra-y)

@@ -155,7 +176,7 @@ endif
  PHONY += FORCE
  FORCE:

-%/built_in.o: FORCE

+%/built_in.o %/lib.a: FORCE
        $(MAKE) -f $(BASEDIR)/Rules.mk -C $* built_in.o

%/built_in_bin.o: FORCE

diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
index 296c5e68bbc3..612a83b315c8 100644
--- a/xen/arch/arm/Makefile
+++ b/xen/arch/arm/Makefile
@@ -90,14 +90,14 @@ endif

ifeq ($(CONFIG_LTO),y)

  # Gather all LTO objects together
-prelink_lto.o: $(ALL_OBJS)
-       $(LD_LTO) -r -o $@ $^
+prelink_lto.o: $(ALL_OBJS) $(ALL_LIBS)
+       $(LD_LTO) -r -o $@ $(filter-out %.a,$^) --start-group $(filter %.a,$^) 
--end-group

# Link it with all the binary objects

  prelink.o: $(patsubst %/built_in.o,%/built_in_bin.o,$(ALL_OBJS)) prelink_lto.o
        $(call if_changed,ld)
  else
-prelink.o: $(ALL_OBJS) FORCE
+prelink.o: $(ALL_OBJS) $(ALL_LIBS) FORCE
        $(call if_changed,ld)
  endif

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile

index 9b368632fb43..8f2180485b2b 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -132,8 +132,8 @@ EFI_OBJS-$(XEN_BUILD_EFI) := efi/relocs-dummy.o

ifeq ($(CONFIG_LTO),y)

  # Gather all LTO objects together
-prelink_lto.o: $(ALL_OBJS)
-       $(LD_LTO) -r -o $@ $^
+prelink_lto.o: $(ALL_OBJS) $(ALL_LIBS)
+       $(LD_LTO) -r -o $@ $(filter-out %.a,$^) --start-group $(filter %.a,$^) 
--end-group

# Link it with all the binary objects

  prelink.o: $(patsubst %/built_in.o,%/built_in_bin.o,$(ALL_OBJS)) 
prelink_lto.o $(EFI_OBJS-y) FORCE
@@ -142,10 +142,10 @@ prelink.o: $(patsubst 
%/built_in.o,%/built_in_bin.o,$(ALL_OBJS)) prelink_lto.o $
  prelink-efi.o: $(patsubst %/built_in.o,%/built_in_bin.o,$(ALL_OBJS)) 
prelink_lto.o FORCE
        $(call if_changed,ld)
  else
-prelink.o: $(ALL_OBJS) $(EFI_OBJS-y) FORCE
+prelink.o: $(ALL_OBJS) $(ALL_LIBS) $(EFI_OBJS-y) FORCE
        $(call if_changed,ld)

-prelink-efi.o: $(ALL_OBJS) FORCE

+prelink-efi.o: $(ALL_OBJS) $(ALL_LIBS) FORCE
        $(call if_changed,ld)
  endif

diff --git a/xen/lib/Makefile b/xen/lib/Makefile

index 53b1da025e0d..b8814361d63e 100644
--- a/xen/lib/Makefile
+++ b/xen/lib/Makefile
@@ -1,2 +1,3 @@
-obj-y += ctype.o
  obj-$(CONFIG_X86) += x86/
+
+lib-y += ctype.o


May I ask why all the code movement by ctype was done after this patch?

Cheers,

--
Julien Grall

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