[PATCH v3 1/1] Makefile: enable --gc-sections

[Kele Zhang]

The --gc-sections option enables the linker to perform garbage
collection of unreferenced code and data, thereby reducing the binary
size.

The -ffunction-sections option will place each function into a separate
section, so it is necessary to add .text.* to the linker script.

Signed-off-by: Kele Zhang <zhangcola2003 at gmail.com>
Signed-off-by: Yuan Tan <tanyuan at tinylab.org>
Signed-off-by: Zhangjin Wu <falcon at tinylab.org>
---
 Makefile             | 15 +++++++++------
 firmware/fw_base.ldS |  1 +
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/Makefile b/Makefile
index e5a0f19..30ba3b6 100644
--- a/Makefile
+++ b/Makefile
@@ -355,12 +355,7 @@ GENFLAGS	+=	$(libsbiutils-genflags-y)
 GENFLAGS	+=	$(platform-genflags-y)
 GENFLAGS	+=	$(firmware-genflags-y)
 
-CFLAGS		=	-g -Wall -Werror -ffreestanding -nostdlib -fno-stack-protector -fno-strict-aliasing
-ifneq ($(DEBUG),)
-CFLAGS		+=	-O0
-else
-CFLAGS		+=	-O2
-endif
+CFLAGS		=	-g -Wall -Werror -ffreestanding -nostdlib -fno-stack-protector -fno-strict-aliasing -ffunction-sections -fdata-sections
 CFLAGS		+=	-fno-omit-frame-pointer -fno-optimize-sibling-calls
 # Optionally supported flags
 ifeq ($(CC_SUPPORT_SAVE_RESTORE),y)
@@ -406,6 +401,7 @@ ASFLAGS		+=	$(firmware-asflags-y)
 ARFLAGS		=	rcs
 
 ELFFLAGS	+=	$(USE_LD_FLAG)
+ELFFLAGS	+=	-Wl,--gc-sections
 ifeq ($(OPENSBI_LD_EXCLUDE_LIBS),y)
 ELFFLAGS	+=	-Wl,--exclude-libs,ALL
 endif
@@ -424,6 +420,13 @@ MERGEFLAGS	+=	-m elf$(PLATFORM_RISCV_XLEN)lriscv
 
 DTSCPPFLAGS	=	$(CPPFLAGS) -nostdinc -nostdlib -fno-builtin -D__DTS__ -x assembler-with-cpp
 
+ifneq ($(DEBUG),)
+CFLAGS		+=	-O0
+ELFFLAGS	+=  -Wl,--print-gc-sections
+else
+CFLAGS		+=	-O2
+endif
+
 # Setup functions for compilation
 define dynamic_flags
 -I$(shell dirname $(2)) -D__OBJNAME__=$(subst -,_,$(shell basename $(1) .o))
diff --git a/firmware/fw_base.ldS b/firmware/fw_base.ldS
index fb47984..a33746a 100644
--- a/firmware/fw_base.ldS
+++ b/firmware/fw_base.ldS
@@ -20,6 +20,7 @@
 		PROVIDE(_text_start = .);
 		*(.entry)
 		*(.text)
+		*(.text.*)
 		. = ALIGN(8);
 		PROVIDE(_text_end = .);
 	}
-- 
2.43.0