xorg with i915kms crashes with GLSL compile failure when xsane starts

[tech-lists]

Hi,

I'm not sure whether this should go here or should I raise a bug or 
directly raise the issue with xorg?

This almost exact bug (xorg/i915kms) was patched/resolved in 2016 on
debian according to https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=834054
my issue is slightly different in that I'm using FreeBSD and it happens only 
when xsane starts and regardless of whether the scanner is even plugged in.

context:

12.0-STABLE r346338 GENERIC amd64

packages installed via pkg from default freebsd repos
nothing xorg related has been manually defined

drm-kmod-g20181126 (which has installed
drm-fbsd12.0-kmod-4.16.g20190305)
x11/xorg
x11/mate
graphics/xsane

The machine itself is quite old (c. 2010) but xorg/i915kms works fine on it
otherwise for stuff like firefox/libreoffice. It has 8GB ram and runs zfs. 
The crash happens shortly after xsane is started.

xorg error:

0:13(14): error: operands to arithmetic operators must be numeric
0:13(13): error: operands to arithmetic operators must be numeric

[  1338.766] Program source:
#define ATLAS_DIM_INV 0.000976562500000000
attribute vec2 primitive;
attribute vec2 source;
varying vec2 glyph_pos;
uniform vec2 fill_offset;
uniform vec2 fill_size_inv;
varying vec2 fill_pos;
uniform vec4 v_matrix;
void main() {
       gl_Position.xy = primitive.xy * v_matrix.xz + v_matrix.yw;
       gl_Position.zw = vec2(0.0,1.0);
       glyph_pos = source.xy * ATLAS_DIM_INV;
       fill_pos = (fill_offset + primitive.xy + pos) * fill_size_inv;
}
[  1338.766] (EE) 
Fatal server error:
[  1338.766] (EE) GLSL compile failure
[  1338.766] (EE) 
[  1338.766] (EE) 
Please consult the The X.Org Foundation support 
         at http://wiki.x.org
         for help.
[  1338.766] (EE) Please also check the log file at
"/var/log/Xorg.0.log" for additional information.
[  1338.767] (EE) 
[  1338.767] (II) AIGLX: Suspending AIGLX clients for VT switch
[  1338.772] (EE) Server terminated with error (1). Closing log file.

in the meantime I'm going to try building xorg/xsane from the ports

thanks,
-- 
J.
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