[U-Boot] [PATCH 2/2] arm: config: enforce -fno-pic for SPL and normal U-Boot

[Tom Rini]

On Tue, Jul 04, 2017 at 01:09:36AM +0000, Peng Fan wrote:
> Hi Tom,
> 
> > -----Original Message-----
> > From: Tom Rini [mailto:trini at konsulko.com]
> > Sent: Tuesday, July 04, 2017 12:17 AM
> > To: Peng Fan <peng.fan at nxp.com>; Simon Glass <sjg at chromium.org>; Philipp
> > Tomsich <philipp.tomsich at theobroma-systems.com>
> > Cc: albert.u.boot at aribaud.net; u-boot at lists.denx.de
> > Subject: Re: [U-Boot] [PATCH 2/2] arm: config: enforce -fno-pic for SPL and
> > normal U-Boot
> > 
> > On Mon, Jul 03, 2017 at 09:14:08PM +0800, Peng Fan wrote:
> > 
> > > If not pass -fno-pic to toolchains, some toolchains may generate .got
> > > and .got.plt sections, but when generate binaries, we did not take
> > > .got and .got.plt into consideration, then SPL or normal U-Boot boot
> > > failure because image corrupted.
> > >
> > > Need to pass -fno-pic to disable generating .got and .got.plt
> > > sections.
> > >
> > > Signed-off-by: Peng Fan <peng.fan at nxp.com>
> > > Cc: Albert Aribaud <albert.u.boot at aribaud.net>
> > > Cc: Tom Rini <trini at konsulko.com>
> > > ---
> > >  arch/arm/config.mk | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/arm/config.mk b/arch/arm/config.mk index
> > > 1a77779..66ae403 100644
> > > --- a/arch/arm/config.mk
> > > +++ b/arch/arm/config.mk
> > > @@ -130,9 +130,10 @@ ALL-y += checkarmreloc  # instruction. Relocation
> > > is not supported for that case, so disable  # such usage by requiring
> > > word relocations.
> > >  PLATFORM_CPPFLAGS += $(call cc-option, -mword-relocations)
> > > -PLATFORM_CPPFLAGS += $(call cc-option, -fno-pic)  endif
> > >
> > > +PLATFORM_CPPFLAGS += $(call cc-option, -fno-pic)
> > > +
> > >  # limit ourselves to the sections we want in the .bin.
> > >  ifdef CONFIG_ARM64
> > >  OBJCOPYFLAGS += -j .text -j .secure_text -j .secure_data -j .rodata
> > > -j .data \
> > 
> > Something is "up" here and I need you to dig harder and perhaps see if we're
> > missing something in the linker scripts?  The very next line of context here is:
> >                 -j .u_boot_list -j .rela.dyn -j .got -j .got.plt
> > 
> > Meaning that we intentionally copy .got / .got.plt into the resulting binary.  And
> > I see that we took in 397d7d5a1be1 from you back in 2016 saying that we
> > needed this in SPL.  But 5a942a152776 put the got/got.plt sections (for 32bit
> > ARM) in intentionally as some relocations do need it.  And in 4b0d506ed3b4
> > Philipp seems to have seen the same problem you have, but fixed it with
> > adding got/got.plt to the sections list we copy in (the above hunk of context).
> 
> If pass -fno-pic to compiler, there will be no .got and .got.plt sections.
> The .got and .got.plt is usually used for dynamic link, such as linux "*.so" file.
> We need to pass -fno-pic to compiler to remove .got and .got.plt sections.

"Usually" isn't the same as "always" or "only".  And this reminded me
that we had to deal with e391b1e64b0b because yes, we're not making a
shared library but we do have position independent code.  So, in the
case of SPL, since we can get away with -fno-pic (and get some space
savings) that's just not true of U-Boot itself.  We're enforcing -fpic
on other architectures, so what exactly is going on with what you're
seeing?  Where would we need to be taking .got/.got.plt into
consideration and why would it be a bad thing to do so?  Thanks!

-- 
Tom
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