[PATCH v2 1/1] sandbox: eliminate unused functions from binaries

[Tom Rini]

On Mon, Oct 23, 2023 at 10:13:55AM -0700, Simon Glass wrote:
> Hi,
> 
> On Mon, 23 Oct 2023 at 10:03, Tom Rini <trini at konsulko.com> wrote:
> >
> > On Mon, Oct 23, 2023 at 01:37:27AM +0200, Heinrich Schuchardt wrote:
> > > The sandbox should closely mimic other architectures.
> > >
> > > Place each function or data in a separate section and let the linker
> > > eliminate unused ones. This will reduce the binary size.
> > >
> > > In the linker script mark that u_boot_sandbox_getopt are to be kept.
> > >
> > > Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> > > ---
> > > v2:
> > >       mark _u_boot_sandbox_getopt secitons a KEEP()
> > > ---
> > >  arch/sandbox/config.mk      | 4 +++-
> > >  arch/sandbox/cpu/u-boot.lds | 6 +++---
> > >  2 files changed, 6 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/arch/sandbox/config.mk b/arch/sandbox/config.mk
> > > index 2d184c5f65..c02f0229c2 100644
> > > --- a/arch/sandbox/config.mk
> > > +++ b/arch/sandbox/config.mk
> > > @@ -2,7 +2,7 @@
> > >  # Copyright (c) 2011 The Chromium OS Authors.
> > >
> > >  PLATFORM_CPPFLAGS += -D__SANDBOX__ -U_FORTIFY_SOURCE
> > > -PLATFORM_CPPFLAGS += -fPIC
> > > +PLATFORM_CPPFLAGS += -fPIC -ffunction-sections -fdata-sections
> > >  PLATFORM_LIBS += -lrt
> > >  SDL_CONFIG ?= sdl2-config
> > >
> > > @@ -26,6 +26,7 @@ cmd_u-boot__ = $(CC) -o $@ -Wl,-T u-boot.lds $(u-boot-init) \
> > >       $(KBUILD_LDFLAGS:%=-Wl,%) \
> > >       $(SANITIZERS) \
> > >       $(LTO_FINAL_LDFLAGS) \
> > > +     -Wl,--gc-section \
> > >       -Wl,--whole-archive \
> > >               $(u-boot-main) \
> > >               $(u-boot-keep-syms-lto) \
> > > @@ -37,6 +38,7 @@ cmd_u-boot-spl = (cd $(obj) && $(CC) -o $(SPL_BIN) -Wl,-T u-boot-spl.lds \
> > >       $(SANITIZERS) \
> > >       $(LTO_FINAL_LDFLAGS) \
> > >       $(patsubst $(obj)/%,%,$(u-boot-spl-init)) \
> > > +     -Wl,--gc-section \
> > >       -Wl,--whole-archive \
> > >               $(patsubst $(obj)/%,%,$(u-boot-spl-main)) \
> > >               $(patsubst $(obj)/%,%,$(u-boot-spl-platdata)) \
> >
> > There's already a call to --gc-sections for u-boot-spl on sandbox (in
> > the last line of the link command).  We should probably move the main
> > u-boot call there too, for consistency.
> 
> For the moment I really don't want this in sandbox. I think I explain
> that there is very little benefit in terms of size and it takes us
> away from how native apps are normally built. It also seems to mask
> problems in your CMDLINE series

This fixes problems with sandbox not acting like a proper U-Boot target.
It is not at all about size reduction, it's about being able to use
normal conventions in U-Boot.

-- 
Tom
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