Re: [PATCH u-boot 17/39] build: support building with Link Time Optimizations

On Tue, 9 Mar 2021 21:30:26 +0800 Bin Meng bmeng.cn@gmail.com wrote:

...

+config LTO

•   bool "Enable Link Time Optimizations"
  

•   depends on ARCH_SUPPORTS_LTO
  

•   default n  
  

nits: this line is not needed as the default value is n if omitted

This is for consistency. The other options in this file also use "default n"

...

+ifdef CONFIG_LTO

•   LTO_CFLAGS                      := -flto
  

•   LTO_FINAL_LDFLAGS               := -fwhole-program  
  

This one should not be necessary per my read of the GCC doc. Also in your patch, it is only used in the SPL build.

I shall do some tests.

...

+ifdef CONFIG_LTO +quiet_cmd_u-boot__ ?= LTO $@

•  cmd_u-boot__ ?=                                                          \
  

•           $(CC) -nostdlib -nostartfiles                                   \
  

•           $(LTO_FINAL_CFLAGS) $(c_flags)                                  \  
  

LTO_FINAL_CFLAGS is not defined anywhere. I guess you wanted to use LTO_FINAL_LDFLAGS?

THX, I forgot to change it here. We will see if this variable is needed (since it only contains -fwhole-program, which may be dropped)

...

•           $(KBUILD_LDFLAGS:%=-Wl,%) $(LDFLAGS_u-boot:%=-Wl,%) -o $@       \
  

•           -T u-boot.lds $(u-boot-init)                                    \
  

•           -Wl,--start-group -Wl,--whole-archive                           \  
  

--start-group should be dropped

Will test