[PATCH v2 1/1] Makefile: enable --gc-sections

[cola zhang]

Bin Meng <bmeng.cn at gmail.com> 于2024年9月1日周日 19:12写道：
>
> On Fri, Aug 30, 2024 at 4:12 AM Kele Zhang <zhangcola2003 at gmail.com> wrote:
> >
> > 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             | 5 +++--
> >  firmware/fw_base.ldS | 1 +
> >  2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index e5a0f19..44db5d4 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -355,9 +355,9 @@ GENFLAGS    +=      $(libsbiutils-genflags-y)
> >  GENFLAGS       +=      $(platform-genflags-y)
> >  GENFLAGS       +=      $(firmware-genflags-y)
> >
> > -CFLAGS         =       -g -Wall -Werror -ffreestanding -nostdlib -fno-stack-protector -fno-strict-aliasing
> > +CFLAGS         =       -g -Wall -Werror -ffreestanding -nostdlib -fno-stack-protector -fno-strict-aliasing -ffunction-sections -fdata-sections
> >  ifneq ($(DEBUG),)
> > -CFLAGS         +=      -O0
> > +CFLAGS         +=      -O0 -Wl,--print-gc-sections
>
> This should be put into the ELF flags too.

Are ELFflags the flags that take effect during linking?
-ffunction-sections -fdata-sections will take effect during compilation.
Enabling them will generate different .s files and will not affect the behavior
of the linker. So isn't it better to put them in cflags?

>
> >  else
> >  CFLAGS         +=      -O2
> >  endif
> > @@ -406,6 +406,7 @@ 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
> > 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 = .);
> >         }
>
> Regards,
> Bin