[Mesa3d-dev] Unaligned traps in __indirect_glFrustum

[Mike A. H. <mh...@re...>]

I just recently recieved this bug report from an Alpha user.

Description of Problem:

The problem manifests itself in Mesa but this is really g_render.c
trouble so it belongs to X.

Various programs from "Mesa-demos" are consistently getting on Alpha
a number of "unaligned trap" errors.  Like this:

cubemap(16472): unaligned trap at 0000020000590334: 000002000002a03c 27 2
cubemap(16472): unaligned trap at 0000020000590344: 000002000002a044 27 3
cubemap(16472): unaligned trap at 0000020000590348: 000002000002a04c 27 4
cubemap(16472): unaligned trap at 0000020000590350: 000002000002a054 27 5

With Mesa-3.4.1 recompiled for debugging and run from a shell which
forces SIGBUS, instead of a fixup, on an unaligned trap 'gdb' reveals
this:

Starting program: /usr/bin/gears

Program received signal SIGBUS, Bus error.
__indirect_glFrustum (left=-1, right=1, bottom=-1, top=1, zNear=5, zFar=60)
    at g_render.c:2523
2523		__GLX_PUT_DOUBLE(12,right);


Starting program: /usr/bin/bounce

Program received signal SIGBUS, Bus error.
__indirect_glOrtho (left=-8.0000002384185791, right=8.0000002384185791,
    bottom=-6, top=6, zNear=-6, zFar=6) at g_render.c:2590
2590		__GLX_PUT_DOUBLE(12,right);


Starting program: /usr/bin/gamma

Program received signal SIGBUS, Bus error.
__indirect_glOrtho (left=-1, right=1, bottom=-1, top=1, zNear=-1, zFar=1)
    at g_render.c:2590
2590		__GLX_PUT_DOUBLE(12,right);

Starting program: /usr/bin/cubemap
GL_REFLECTION_MAP_ARB mode
keys:
  SPACE - toggle animation
  CURSOR KEYS - rotation
  m - toggle texgen reflection mode

Program received signal SIGBUS, Bus error.
__indirect_glFrustum (left=-2, right=2, bottom=-2, top=2, zNear=6, zFar=20)
    at g_render.c:2523
2523		__GLX_PUT_DOUBLE(12,right);

This is a backtrace for 'bounce'

#0  __indirect_glOrtho (left=-8.0000002384185791, right=8.0000002384185791,
    bottom=-6, top=6, zNear=-6, zFar=6) at g_render.c:2590
#1  0x20000412588 in glOrtho (left=-8.0000002384185791,
    right=8.0000002384185791, bottom=-6, top=6, nearval=-6, farval=6)
    at glapitemp.h:938
#2  0x120001a8c in reshape (width=5889, height=172080) at bounce.c:92
#3  0x200001409f8 in processWindowWorkList (window=0x120105170)
    at glut_event.c:1193
#4  0x20000140cc8 in __glutProcessWindowWorkLists () at glut_event.c:1328
#5  0x20000140d74 in glutMainLoop () at glut_event.c:1349
#6  0x120002240 in main (argc=1, argv=0x11ffff7b8) at bounce.c:218


and this is for 'cubemap'.

#0  __indirect_glFrustum (left=-2, right=2, bottom=-2, top=2, zNear=6,
zFar=20)
    at g_render.c:2523
#1  0x2000040fc08 in glFrustum (left=-2, right=2, bottom=-2, top=2,
nearval=6,
    farval=20) at glapitemp.h:513
#2  0x1200017a8 in reshape (width=300, height=300) at cubemap.c:144
#3  0x200001409f8 in processWindowWorkList (window=0x120104b40)
    at glut_event.c:1193
#4  0x20000140cc8 in __glutProcessWindowWorkLists () at glut_event.c:1328
#5  0x20000140d74 in glutMainLoop () at glut_event.c:1349
#6  0x120001cfc in main (argc=5889, argv=0x2000002a030) at cubemap.c:248

And this is the code in question, from __indirect_glFrustum, after macros
were expanded:

        *((INT16 *) (pc +  0 )) =   52   ;
	*((INT16 *) (pc +  2 )) = 175     ;
	*((FLOAT64 *) (pc +  4 )) =  left  ;
        *((FLOAT64 *) (pc +  12 )) =  right  ;
        *((FLOAT64 *) (pc +  20 )) =  bottom  ;
        *((FLOAT64 *) (pc +  28 )) =  top  ;
        *((FLOAT64 *) (pc +  36 )) =  zNear  ;
        *((FLOAT64 *) (pc +  44 )) =  zFar  ;


Unaligned access can be silent elsewhere but it is a performance drag on
any architecture.

   Michal
   mi...@ha...






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