Memory-Mapped files and DWA compression
darby johnston <[email protected]> Tue, 30 Oct 2018 16:11:37 +0000 (UTC)
| Newsgroups | gmane.comp.video.openexr.devel |
|---|---|
| Message-ID | <[email protected]> |
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Hi all,
I was implementing memory-mapped loading of OpenEXR images for my viewer an=
d noticed a crash when loading DWA compressed files. Taking a look at the c=
ode it seems that DwaCompressor::uncompress() is writing to the const char =
* data that is passed to it:
int=20
DwaCompressor::uncompress
=C2=A0=C2=A0=C2=A0 (const char *inPtr,
=C2=A0=C2=A0=C2=A0=C2=A0 int inSize,
=C2=A0=C2=A0=C2=A0=C2=A0 IMATH_NAMESPACE::Box2i range,
=C2=A0=C2=A0=C2=A0=C2=A0 const char *&outPtr)
{=C2=A0=C2=A0=C2=A0 ...
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0Int64=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0 *dst =3D=C2=A0 (((Int64 *)inPtr) + i);
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 const char *src =3D (char *)(((I=
nt64 *)inPtr) + i);
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 Xdr::read<CharPtrIO> (src, *dst)=
;=C2=A0=C2=A0=C2=A0 ...
}
When the passed data is memory-mapped as read-only this causes a memory acc=
ess violation on Windows. Copying the data to a temporary buffer and then d=
oing the Xdr conversion fixes the issue; the performance difference should =
be negligible since this is only for some header data, probably less than 1=
00 bytes. If this seems like an OK change I've attached a patch or can also=
submit a git pull request.
Thanks, Darby
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<html><head></head><body><div class=3D"ydp72254857yahoo-style-wrap" style=
=3D"font-family:Helvetica Neue, Helvetica, Arial, sans-serif;font-size:13px=
;"><div id=3D"ydp72254857yiv0547984884"><div><div>Hi all,</div><div><br></d=
iv><div>I was implementing memory-mapped loading of OpenEXR images for my v=
iewer and noticed a crash when loading DWA compressed files. Taking a look =
at the code it seems that DwaCompressor::uncompress() is writing to the con=
st char * data that is passed to it:</div><div><span><br>int <br>DwaCompres=
sor::uncompress<br> (const char *inPtr,<br> &n=
bsp; int inSize,<br> IMATH_NAMESPACE::Box2i r=
ange,<br> const char *&outPtr)<br></span><div><=
span>{</span></div><div><span> ...<br></span></div><div><=
span> <span>Int64  =
; *dst =3D (((Int64 *)inPtr) + i);<br> &=
nbsp; const char *src =3D (char *)(((Int64 *)inPtr)=
+ i);<br><br></span></span><div><span><span> =
Xdr::read<CharPtrIO> (src, *dst);</span></span></div><di=
v> ...<br></div></div><div><div>}</div><div><br></div><di=
v>When the passed data is memory-mapped as read-only this causes a memory a=
ccess violation on Windows. Copying the data to a temporary buffer and then=
doing the Xdr conversion fixes the issue; the performance difference shoul=
d be negligible since this is only for some header data, probably less than=
100 bytes. If this seems like an OK change I've attached a patch or can al=
so submit a git pull request.</div><div><br></div><div><br></div><div>Thank=
s, Darby</div><div><br></div><span></span></div></div><div class=3D"ydp7225=
4857yiv0547984884ydpde2b8192yahoo-style-wrap" style=3D"font-family:Helvetic=
a Neue, Helvetica, Arial, sans-serif;font-size:13px;"></div></div></div></d=
iv></body></html>
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