[OpenWrt-Devel] [PATCH] ath79: switch to kernel 5.4

[Henrique de Moraes Holschuh]

On 12/05/2020 18:46, Hauke Mehrtens wrote:
> On 5/12/20 12:24 PM, Bjørn Mork wrote:
>> Hauke Mehrtens <hauke at hauke-m.de> writes:
>>
>>> I also get this problem with mainline kernel.
>>>
>>> See here for some more details:
>>> https://bugs.openwrt.org/index.php?do=details&task_id=2928
>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94506
>>
>> Hello,
>>
>> I wondered what the current state of this is?  Reading that GCC bug it
>> looks like all the results we've seen are just arbitrary, and either
>> triggering a latent bug or not.
>>
>> How do we proceed from there?
>>
>> FWIW, I just built current master (146e18af568a) with 5.4 kernel using
>> GCC 9.3.  And like others have reported, this booted just fine without
>> any other tricks.
>>
>> But it seems a bit too fragile for any release if it could break any
>> time we do a GCC or kernel update...
> 
> Hi,
> 
> I would prefer if we know the root cause, more code could be compiled
> wrong and just silently fail.

Here's a data point.   We *do* have a bug in the toolchain that causes 
it to generate broken binaries (maybe only the kernel?) in certain 
situations, and it is *not* new.

Since 18.06 (maybe earlier), I can 100% reproduce a broken image here 
that will crash-loop on boot on ar71xx *or* ath79 if I do the following 
steps:

0. Arch is ar71xx (18.06) or ath79 (19.07).   Target device tplink 
Archer C7v4 (MIPS 74kc).

1. Clean the toolchain and build tree so that it is going to be rebuilt 
from scratch
2. enable TARGET_OPTIONS using menuconfig
3. change CONFIG_TARGET_OPTIMIZATION, replace -mtune=24kc with -mtune=74kc

build.  The resulting image will crash-loop if installed.  Note: I did 
not try with the default options though.  I enable LuCi and a few other 
packages as built-in, etc.  If anyone fails to reproduce, I can send my 
standard .config.

DISABLE TARGET_OPTIONS (so that defaults are used), clean everything (so 
that the toolchain and all binaries will be rebuilt). rebuild, so that 
the toolchain is built without TARGET_OPTIONS.

it works.

Enable (2) and (3) again, do a new build, this time *not* rebuilding the 
toolchain.  i.e. only the kernel and packages are rebuilt with 
TARGET_OPTIONS enabled, and -mtune=74kc.

it works.


So, the problem seems to be on the toolchain build itself, that creates 
a faulty toolchain when TARGET_OPTIONS is active (I don't recall if it 
causes trouble if you just enable TARGET_OPTIONS but don't touch 
CONFIG_TARGET_OPTIONS, sorry).

-- 
Henrique de Moraes Holschuh