[U-Boot] [PATCH 2/7] HACK: rearrange link order for thumb

[Graeme Russ]

Hi Allen

On Tue, Jul 10, 2012 at 10:45 AM, Allen Martin <amartin at nvidia.com> wrote:
> On Sat, Jul 07, 2012 at 03:15:36AM -0700, Albert ARIBAUD wrote:
>> Hi Allen,
>>
>> On Fri, 6 Jul 2012 16:17:19 -0700, Allen Martin <amartin at nvidia.com> wrote:

[snip]

>> > And I forgot to mention, the code bloat from disabling the
>> > optimization is about 400 bytes (185136 -> 185540), so it's not bad,
>> > but it still seems a shame to disable all short branches because of
>> > one misoptimized one.

0.2% be my calcs

>>
>> Can this not be limited to compiling the object files which are known to be
>> sensitive to the problem?
>>
>
> I understand this issue fairly well now.  It's a known bug in the
> assembler that has already been fixed:
>
> http://sourceware.org/bugzilla/show_bug.cgi?id=12532
>
> It only impacts preembtable symbols, and since u-boot doesn't have any
> dynamic loadable objects it's only explictly defined weak symbols that
> should trigger the bug.
>
> I built a new toolchain with binutils 2.22 and verified the bug is no
> longer present there, and -fno-optimize-sibling-calls is the correct
> workaround for toolchains that do have the bug, so conditionally
> disabling the optimization for binutils < 2.22 seems like the right
> fix.
>
> I ran a quick scrub of the u-boot tree and there's 195 instances of
> __attribute__((weak)) spread across 123 source files, so I think just
> disabling optimization on the failing object files may be too fragile,
> as code movement could cause others to crop up.

Adding -fno-optimize-sibling-calls for binutils < 2.22 - 0.2% code size
increase for people using slightly older tools

Maintain the tweaking of a set of files - someone using binutils >= 2.22
adds __attribute__((weak)) to a single function and *BAM* three months
later someone complains that something broke

I vote option 1

I do wonder, though, if we should spit out warnings when applying
workaraounds for older tool-chains?

Regards,

Graeme