[OpenWrt-Devel] Broken GCC 4.9 (and 5.2) on ARM - asking for review/test

[Jonas Gorski]

Hi,

On Thu, Aug 20, 2015 at 11:40 AM, Dirk Neukirchen <dirkneukirchen at web.de> wrote:
> GCC 4.9 was marked BROKEN with r46089. Recently GCC 5.2 was added (marked as broken too)
>
> commit msg: " toolchain: mark gcc 4.9 as broken, it miscompiles some code especially on ARM"
>
> Looking through some GCC 5 serious regressions I found:
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65932
>
> I cannot replicate the ARM issue because of missing details and I dont have ARM hw where it occurs (arch: malta seems fine)
>  - but there was an open ticket from a dev on github regarding the boot problem, which might be a symptom of code miscompile
>
> https://github.com/wongsyrone/openwrt-1/issues/44
>
> According to his tests GCC4.9 and GCC5.2 now work with this 2 changes:
>
> adding -fno-ipa-sra to Kernel/CPU CFLAGS
>
> https://github.com/wongsyrone/openwrt-1/commit/35308f2435ec75192324d68817e7702e3b257e71
> https://github.com/wongsyrone/openwrt-1/commit/93c0a5173414cfa7684547de3c3a1f3dc4240383

Readin the bug ticket, it seems that

https://gcc.gnu.org/bugzilla/attachment.cgi?id=35775&action=diff

should fix the issue at the root cause, but with the "disadvantage" of
breaking some testcases relying on the (mis-?)behaviour, which sounds
like the "blocker" for this change.

So I wonder if adding that wouldn't be a better solution.


Jonas
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