Re: OpenWrt/LEDE: dropbear & MIPS & gcc 7.1.0

[Syrone Wong]

Hi,

I think it's a bug in libtommath. Compiling both 2017.75 and 2017.75
with updated libtom*, the latter one works while the original one
doesn't. And for other parts, such as kernel, busybox, userspace
programs, etc. , all of them are working perfectly. That's the reason
why I think it isn't a compiler bug.

Sorry, since I cannot access the router, which means I cannot execute
any commands, it's not trivial to get the backtrace.

Based on Kevin's report,

> ssh -vvv' shows things hanging during the initial ECDH key exchange

it might be something wrong with key verification, I'm not sure about
it, totally wildly guess.

You may want to contact Kevin off-list to know how he finds the issue
resides in libtommath, I just follow his guess and replace libtom* to
verify his idea.

Kevin Darbyshire-Bryant 


Best Regards,
Syrone Wong

Re: OpenWrt/LEDE: dropbear & MIPS & gcc 7.1.0

[Matt Johnston]

Hi Syrone,

Updating libtom makes sense, it's on the todo list.

I'm curious if it's a bug in old libtommath or new gcc. In my experience 
differences between optimisation levels are more often problems with the 
compiler, but could be either.
If you could get a backtrace of a stuck "dbclient" built with gcc 7 it might be 
useful to see what's going on (and to know where to look in the libtommath 
commit log)

Cheers,
Matt

> On Thu 1/6/2017, at 2:28 pm, Syrone Wong  wrote:
> 
> Hi all,
> 
> Recently, I upgrade my LEDE toolchain to binutils 2.28 & GCC 7, notice
> I cannot SSH to router.
> 
> A more detailed description can be found
> (http://lists.infradead.org/pipermail/lede-dev/2017-May/007753.html),
> later, Kevin find it might related to libtommath
> (http://lists.infradead.org/pipermail/lede-dev/2017-May/007797.html).
> 
> Two possible solution:
> 
> i. change libtommath compilation flag from -Os to -O2:
> http://lists.infradead.org/pipermail/lede-dev/2017-May/007843.html
> 
> ii. update the bundled libtom* to latest:
> http://lists.infradead.org/pipermail/lede-dev/2017-May/007849.html
> 
> Please update the bundled libraries to latest, or help to find the root cause.
> 
> Thanks in advance
> 
> Best Regards,
> Syrone Wong

OpenWrt/LEDE: dropbear & MIPS & gcc 7.1.0

[Syrone Wong]

Hi all,

Recently, I upgrade my LEDE toolchain to binutils 2.28 & GCC 7, notice
I cannot SSH to router.

A more detailed description can be found
(http://lists.infradead.org/pipermail/lede-dev/2017-May/007753.html),
later, Kevin find it might related to libtommath
(http://lists.infradead.org/pipermail/lede-dev/2017-May/007797.html).

Two possible solution:

i. change libtommath compilation flag from -Os to -O2:
http://lists.infradead.org/pipermail/lede-dev/2017-May/007843.html

ii. update the bundled libtom* to latest:
http://lists.infradead.org/pipermail/lede-dev/2017-May/007849.html

Please update the bundled libraries to latest, or help to find the root cause.

Thanks in advance

Best Regards,
Syrone Wong