On Wed, May 4, 2022 at 12:58 PM Stafford Horne <[email protected]> wrote:
>
> I have uploaded a diff I created here:
> https://gist.github.com/54334556f2907104cd12374872a0597c
>
> It shows the same output.
In hex_to_bin itself it seems to only be a difference due to some
register allocation (r19 and r3 switched around).
But then it gets inlined into hex2bin and there changes there seem to
be about instruction and basic block scheduling, so it's a lot harder
to see what's going on.
And a lot of constant changes, which honestly look just like code code
moved around by 16 bytes and offsets changed due to that.
So I doubt it's hex_to_bin() that is causing problems, I think it's
purely code movement. Which explains why adding a nop or a fake printk
fixes things.
Some alignment assumption that got broken?
Linus
On Wed, May 04, 2022 at 01:10:03PM -0700, Linus Torvalds wrote:
> On Wed, May 4, 2022 at 12:58 PM Stafford Horne <[email protected]> wrote:
> >
> > I have uploaded a diff I created here:
> > https://gist.github.com/54334556f2907104cd12374872a0597c
> >
> > It shows the same output.
>
> In hex_to_bin itself it seems to only be a difference due to some
> register allocation (r19 and r3 switched around).
>
> But then it gets inlined into hex2bin and there changes there seem to
> be about instruction and basic block scheduling, so it's a lot harder
> to see what's going on.
>
> And a lot of constant changes, which honestly look just like code code
> moved around by 16 bytes and offsets changed due to that.
>
> So I doubt it's hex_to_bin() that is causing problems, I think it's
> purely code movement. Which explains why adding a nop or a fake printk
> fixes things.
>
> Some alignment assumption that got broken?
This is what it looks like to me too. I will have to do a deep dive on what is
going on with this particular build combination as I can't figure out what it is
off the top of my head.
This test is using a gcc 11 compiler, I tried with my gcc 12 toolchain and the
issue cannot be reproduced.
- musl gcc 11 - https://musl.cc/or1k-linux-musl-cross.tgz
- openrisc gcc 12 - https://github.com/openrisc/or1k-gcc/releases/tag/or1k-12.0.1-20220210-20220304
But again the difference between the two compiler outputs is a lot of register
allocation and offsets changes. Its not easy to see anything that stands out.
I checked the change log for the openrisc specific changes from gcc 11 to gcc
12. Nothing seems to stand out, mcount profiler fix for PIC, a new large binary
link flag.
-Stafford