Re: [9front] 9Front Drawterm Code 139 Sig 11 SIGSEGV

[Dmad <dmadhatr@sdf.org>]

On Sat, 23 Sep 2023, Amavect wrote:

Was able to fix the memory issue with a tas.c function replacement 
yesterday, 
however, you may have found a way to fix the cpu bug message everyone has 
been getting from the 9front drawterm build.

> Date: Sat, 23 Sep 2023 23:44:32 -0500
> From: Amavect <amavect@gmail.com>
> Reply-To: 9front@9front.org
> To: 9front@9front.org
> Subject: Re: [9front] 9Front Drawterm Code 139 Sig 11 SIGSEGV
> 
> On Sat, Sep 23, 2023 at 6:24?PM Dmad <dmadhatr@sdf.org> wrote:
>> #3  0x0000000000226cdf in incref (r=0x0) at chan.c:57
> You have a null pointer dereference.
>
> Digging into this a bit,
> kern/chan.c:847: incref(&path->ref);
> ref is the first member of path, and path is not dereferenced,
> so the question is where c->path is set to null.
>
> A path of "./dev/label" results in namec()'s default case to be taken.
> kern/chan.c:1222: c = up->dot;
>
> up->dot appears to be defined in _syschdir().
> We know that chdir failed, so something happened.
> kern/sysfile:628:
> validaddr(name, 1, 0);
> c = namec(name, Atodir, 0, 0);
> cclose(up->dot);
> up->dot = c;
>
> Note that the validaddr() is a no-op macro on drawterm,
> but an actual function on 9front.
> If that would detect a problem, then maybe drawterm should have it.
> Perhaps someone else has a better idea of kernel internals,
> and how they parallel to drawterm.
>
>> Was not able to get a bt stack after compiling with additional CFLAGs
> Clearly a crash didn't happen with -O0.
> Were you able to login and start typing commands into drawterm?
>
> For fun, I installed FreeBSD on Qemu and compiled drawterm.
> No issues logging onto my server,
> but I don't know how to trigger a chdir failure.
>
> Thanks,
> Amavect
>
>

dmadhatr@sdf.org
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