[U-Boot] [PATCH] p2371-2180: Build position independent binary

[Thierry Reding <thierry.reding@gmail.com>]

On Tue, Mar 19, 2019 at 11:05:43AM -0600, Stephen Warren wrote:
> On 3/19/19 6:12 AM, Thierry Reding wrote:
> > On Mon, Mar 18, 2019 at 12:31:32PM -0600, Stephen Warren wrote:
> > > On 3/8/19 1:10 PM, Thierry Reding wrote:
> > > > From: Thierry Reding <treding@nvidia.com>
> > > > 
> > > > In order to support chainloading of U-Boot by an earlier bootloader,
> > > > make sure the binary is position independent, so that the earlier boot-
> > > > loader can relocate it if necessary.
> > > 
> > > Why not enable this for all 64-bit Tegra? They're all booted the exact same
> > > way at least with recent L4T builds.
> > 
> > Yeah, I think that would make sense.
> > 
> > > Also, U-Boot is typically linked to the address that cboot loads it to, and
> > > cboot typically always loads to precisely that address. I'm not sure why
> > > this patch is required.
> > 
> > I encountered this issue when I was trying to chainload U-Boot from
> > cboot on Jetson TX1. It seems like your above comment is no longer true,
> > though I suppose that could just mean that the link address for U-Boot
> > has become stale?
> 
> Looks like the upstream CONFIG_SYS_TEXT_BASE is indeed stale relative to the
> latest L4T builds:
> 
> Upstream:
> Jetson TX1: CONFIG_SYS_TEXT_BASE=0x80110000
> Jetson TX2: CONFIG_SYS_TEXT_BASE=0x80080000
> 
> L4T r32.1:
> Jetson TX1: #define CONFIG_SYS_TEXT_BASE    0x80080000
> Jetson TX2: #define CONFIG_SYS_TEXT_BASE    0x80080000

Okay, let me fix that up while at it. I think the 0x80110000 text base
was something that we cargo-culted from 32-bit ARM boards. I vaguely
recall that this might have been related to the SPL split in some way,
but I can't find anything to corroborate that.

> > > That said, it don't think it harms anything, so I'm fine with it being
> > > applied.
> > 
> > I suppose there's a bit of extra code to do the indirect jumps, but
> > overall U-Boot seems to work well and not noticeably slower if this is
> > enabled. Might be nice for extra flexibility and to avoid any surprises
> > if we ever end up loading U-Boot to a location other than where it was
> > liked to.
> > 
> > My understanding is that this could happen on Tegra186 if cboot detects
> > bad memory blocks in the area where U-Boot was meant to be loaded to. I
> > guess this doesn't apply to earlier chips, but perhaps it's good to have
> > it there for consistency anyway.
> 
> Yes, this could happen on Jetson TX2i at least.

Let me send out a proposal than makes all 64-bit Tegra builds position
independent and throws in the TEXT_BASE changes discussed above.

Thierry
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