[Openmcl-devel] freshly built wx86cl64.exe crashes on start

R. Matthew Emerson rme at acm.org
Fri Jan 6 14:20:58 PST 2023

> On Jan 6, 2023, at 2:01 PM, Bharat Shetty <bshetty at gmail.com> wrote:
> Is there some place we can get more details on the start up code/low address stuff in lisp-kernel, LAP, level-0 etc.? The info in the current and old ccl manual at trac is bit high level.

I think it would be best to figure out how to tell Windows to stop applying its disruptive protection settings rather than expend a lot of effort researching and possibly making a big CCL change that will, at best, result in the status quo but slightly worse.

I think it’s reasonable for a process to want to have control over its address space.  I would be surprised if Windows stops allowing that.

> On Thu, Jan 5, 2023 at 2:03 PM Bharat Shetty <bshetty at gmail.com> wrote:
> Unfortunately yes in low memory for now. But as I pointed earlier there might be issues with heap locations as well (windows handling FTH).
> Regards,
> Bharat
> On Thu, Jan 5, 2023 at 5:27 AM R. Matthew Emerson <rme at acm.org> wrote:
> > On Jan 4, 2023, at 3:15 PM, Bharat Shetty <bshetty at gmail.com> wrote:
> > 
> > Since two days wx86cl64.exe has been behaving erratically (both the version i downloaded and built using gccv4.7.1) it has been crashing randomly at startup and emacs is unable to start it with slime. I suspect this might be to do with some security patches installed. 
> > 
> > So I looked into the windows security controls. Turns out windows defender lets us configure "exploit protection setting" by configuring the following parameters
> >     • 
> > control flow guard CFG
> >     • Data Execution Prevention DEP
> >     • Mandatory ASLR (force randomisation for images - force relocation of images not compiled with Bottom-up ASLR ) -- off by default for now
> >     • Randomise memory allocation (Bottom-up ASLR) -- on by default
> >     • High Entropy ASLR - needs Bottom-up ASLR to be ON
> >     • validate execution chains (SEHOP)
> >     • validate heap integrity - terminate process when heap corruption os detected
> > 
> > I observed we can get wxcl8664 to run with 'Mandatory ASLR' and 'High Entropy ASLR' turned off and with all other options enabled. So even if gcc were to enable us to build non PIE position independant executable, it is just a matter of time before no-pie apps and ccl stops running on windows. 
> > 
> > The only way we can keep ccl running is making the code relocatable (PIE) at the earliest. The bright spot is it still runs on linux :) 
> The x86 port of CCL uses absolute addresses to reference code and other data in low memory. Is this what the problem is?
> Changing that would be a big hassle.

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