The following code segement is from sample_depth_texture from s_texture.c(6.4)
lines 2378-2380 or s_texfilter.c(6.5) line 2286-2288:

COMPUTE_NEAREST_TEXEL_LOCATION(tObj->WrapS, texcoords[i][0], width, col);
COMPUTE_NEAREST_TEXEL_LOCATION(tObj->WrapT, texcoords[i][1], height, row);
img->FetchTexelf(img, col, row, 0, &depthSample);

Depending on the wrap mode defined for the texture object, it is possible for
row or column to return from the COMPUTE_NEAREST_TEXEL_LOCATION as -1.  When
used in the fetch method, a segementation fault occurs.  (E.g.  This could occur
if CLAMP_TO_BORDER is selected as the wrap mode, depending on the input texture
coordinate.) 

It is recommended that the depthSample local variable be initialized during
instantiation, and the fetch method only be called if both row and col are
non-negative.

NOTE: This bug is also present in 6.5; however the reporting dialog does not
allow the report of errors for this version of Mesa yet.