[PATCH 1/2] tinyconfig: enable CONFIG_LD_DEAD_CODE_DATA_ELIMINATION

[PATCH 1/2] tinyconfig: enable CONFIG_LD_DEAD_CODE_DATA_ELIMINATION

[Masahiro Yamada]

This CONFIG option, if supported by the architecture, helps reduce the
size of vmlinux.

For example, the size of vmlinux with ARCH=arm tinyconfig decreases as
follows:

   text	   data	    bss	    dec	    hex	filename
 631684	 104500	  18176	 754360	  b82b8	vmlinux.before
 455316	  93404	  15472	 564192	  89be0	vmlinux.after

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 kernel/configs/tiny.config | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/configs/tiny.config b/kernel/configs/tiny.config
index b753695c5a8f..5dd0f0a34a73 100644
--- a/kernel/configs/tiny.config
+++ b/kernel/configs/tiny.config
@@ -2,3 +2,4 @@ CONFIG_CC_OPTIMIZE_FOR_SIZE=y
 CONFIG_KERNEL_XZ=y
 CONFIG_SLUB=y
 CONFIG_SLUB_TINY=y
+CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y
-- 
2.43.0

[PATCH 2/2] kbuild: link lib-y objects to vmlinux forcibly even when CONFIG_MODULES=n

[Masahiro Yamada]

Since commit 7273ad2b08f8 ("kbuild: link lib-y objects to vmlinux
forcibly when CONFIG_MODULES=y"), all objects from lib-y have been
forcibly linked to vmlinux when CONFIG_MODULES=y.

To simplify future changes, this commit makes all objects from lib-y
be linked regardless of the CONFIG_MODULES setting.

Most use cases (CONFIG_MODULES=y) are not affected by this change.

The vmlinux size with ARCH=arm allnoconfig, where CONFIG_MODULES=n,
increases as follows:

   text    data     bss     dec     hex filename
1368644  835104  206288 2410036  24c634 vmlinux.before
1379440  837064  206288 2422792  24f808 vmlinux.after

We no longer benefit from using static libraries, but the impact is
mitigated by supporting CONFIG_LD_DEAD_CODE_DATA_ELIMINATION.

For example, the size of vmlinux remains almost the same with ARCH=arm
tinyconfig, where CONFIG_MODULES=n and
CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y.

   text    data     bss     dec     hex filename
 455316   93404   15472  564192   89be0 vmlinux.before
 455312   93404   15472  564188   89bdc vmlinux.after

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 Makefile | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index 682a8002b7a1..b8d94c7fe4af 100644
--- a/Makefile
+++ b/Makefile
@@ -1184,13 +1184,8 @@ export ARCH_LIB		:= $(filter %/, $(libs-y))
 export ARCH_DRIVERS	:= $(drivers-y) $(drivers-m)
 # Externally visible symbols (used by link-vmlinux.sh)
 
-KBUILD_VMLINUX_OBJS := ./built-in.a
-ifdef CONFIG_MODULES
-KBUILD_VMLINUX_OBJS += $(patsubst %/, %/lib.a, $(filter %/, $(libs-y)))
+KBUILD_VMLINUX_OBJS := built-in.a $(patsubst %/, %/lib.a, $(filter %/, $(libs-y)))
 KBUILD_VMLINUX_LIBS := $(filter-out %/, $(libs-y))
-else
-KBUILD_VMLINUX_LIBS := $(patsubst %/,%/lib.a, $(libs-y))
-endif
 
 export KBUILD_VMLINUX_LIBS
 export KBUILD_LDS          := arch/$(SRCARCH)/kernel/vmlinux.lds
-- 
2.43.0