[cffi-devel] [Sbcl-devel] GC write-protected mappings vs. the OS kernel

[Samium Gromoff]

From: Samium Gromoff <_deepfire at feelingofgreen.ru>
> From: Juho Snellman <jsnell at iki.fi>
>> Samium Gromoff <_deepfire at feelingofgreen.ru> writes:
>> 
>>> Good day,
>>> 
>>> While debugging mysterious ioctl() failures in lh-usb on SBCL,
>>> I have discovered that using CFFI:WITH-POINTER-TO-VECTOR-DATA
>>> doesn't guarantee that the vector is in a writable region.
>> 
>> I thought we'd never write protect specialized raw arrays (either they
>> are in the nursery, or they're tenured into an unboxed region which
>> never get wpd). And passing generic arrays to ffi doesn't feel right.
>> What's the use case?
> 
> Array element type is (unsigned-byte 8), use case is shovelling
> data in/out a USB device using bulk transfers via ioctl().

A missing detail: while the vector is created in a live core all /seems/
to be well[1].  But when it comes from a dumped core, it gets a chance
(there doesn't appears to be a determinism there) of being in a
write-protected region.


regards,
  Samium Gromoff
--
1. It might be just that I didn't have enough statistics, as I'm working
mainly with cores of my own dumping.  Eh, hehe.


                                 _deepfire-at-feelingofgreen.ru
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