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

[Peng Fan]

> -----Original Message-----
> From: Tom Rini [mailto:trini at konsulko.com]
> Sent: Tuesday, July 04, 2017 10:47 AM
> To: Peng Fan <peng.fan at nxp.com>
> Cc: Simon Glass <sjg at chromium.org>; Philipp Tomsich
> <philipp.tomsich at theobroma-systems.com>; 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 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

>From https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html#Code-Gen-Options,
when -fpic is used for ARM, there will be GOT. The dynamic loader resolves the GOT entries
when the program starts (the dynamic loader is not part of GCC; it is part of the
operating system). 

> 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

For position independent code, but not making a shared library, we could use -fpie.

> 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

If not passing -fno-pic to gcc, the android toolchain will generate .got and .got.plt
section. I think these sections are for dynamic link, not for static link.

> would we need to be taking .got/.got.plt into consideration and why would it
> be a bad thing to do so?  Thanks!

We could keep .got and .got.plt, but personally I prefer use -fno-pic.
I think fpic is for shared library and fpie is for position independt code for static link.

Thanks,
Peng.

> 
> --
> Tom