Running "X -configure" (xorg 6.8.99.7) aborts with a segfault. Consequently, I
figured out that moving sisusb_driver.o (or .so) out of the way solves the problem.

After compiling a debugging version of xorg with shared libraries, I managed to
properly debug it:

ols-dell xc # gdb X
...
(gdb) run -configure
Starting program: /usr/bin/X -configure
...
Program received signal SIGSEGV, Segmentation fault.
0xb796164e in SISUSBProbe (drv=0x82a7a10, flags=1) at sisusb_driver.c:422
422            if((myminor = SiSUSBFindUSBDongle(devSections[i], minorArray,
numDevSections, &nameptr)) >= 0) {
(gdb) p devSections 
$1 = (GDevPtr *) 0x0

The cause is obvious -- dereferencing a NULL pointer.

Now, after some more debugging:

...
(gdb) break SISUSBProbe 
Breakpoint 1 at 0xb7961561: file sisusb_driver.c, line 361.
(gdb) run -configure
...
Breakpoint 1, SISUSBProbe (drv=0x82a7a10, flags=1) at sisusb_driver.c:361
361         Bool    foundScreen = FALSE;
(gdb) n
386         if((numDevSections = xf86MatchDevice(SISUSB_DRIVER_NAME,
&devSections)) <= 0) {
(gdb) p devSections 
$2 = (GDevPtr *) 0xb798d840
(gdb) step
xf86MatchDevice (drivername=0xb7973868 "sisusb", sectlist=0xbfffcac8) at
xf86Helper.c:1515
1515        GDevPtr       gdp, *pgdp = NULL;
(gdb) n
1519        if (sectlist)
(gdb) 
1520            *sectlist = NULL;
(gdb) 
1522        if (xf86DoProbe) return 1;
(gdb) 
1524        if (xf86DoConfigure && xf86DoConfigurePass1) return 1;
(gdb) p xf86DoConfigure
$3 = 1
(gdb) p xf86DoConfigurePass1 
$4 = 1
(gdb) n
1584    }
(gdb) 
SISUSBProbe (drv=0x82a7a10, flags=1) at sisusb_driver.c:406
406         if(!(minorArray = (int *)xalloc(numDevSections * sizeof(int)))) {
(gdb) p devSections 
$5 = (GDevPtr *) 0x0

# Now, we are back in SISUSBProbe, and xf86MatchDevice has returned 1
# (which is assigned to numDevSections) but it already NULL-ed the devSections
# pointer that was passed to it

(gdb) n
409         for(i = 0; i < numDevSections; i++) minorArray[i] = -1;
(gdb) 
412         if(!(devnameArray = (char **)xalloc(numDevSections * sizeof(char *)))) {
(gdb) 
420         numUsed = 0;
(gdb) 
421         for(i = 0; i < numDevSections; i++) {
(gdb) 
422            if((myminor = SiSUSBFindUSBDongle(devSections[i], minorArray,
numDevSections, &nameptr)) >= 0) {
(gdb) 

Program received signal SIGSEGV, Segmentation fault.
0xb796164e in SISUSBProbe (drv=0x82a7a10, flags=1) at sisusb_driver.c:422
422            if((myminor = SiSUSBFindUSBDongle(devSections[i], minorArray,
numDevSections, &nameptr)) >= 0) {
(gdb)

I don't know much about how xorg works, but from what I see, the xf86MatchDevice
function is a bit confusing:

- it returns 1 as in
    if (xf86DoConfigure && xf86DoConfigurePass1) return 1;
  but *sectlist == NULL at that point. So:
  -- return 1, *sectlist == NULL
- it returns 0 when it finds nothing in the config file, i.e.
  -- return 0, *sectlist == NULL
- it returns 1, if it finds exactly one entry in the config file, i.e.
  -- return 1, *sectlist == { some entry, NULL }
- According to the comments, the function *must* return
  -- 0 if nothing is found
  -- -1 on error
  -- the number of elements in *sectlist otherwise

I am guessing, those "return 1" statements are supposed to be "return -1"
instead? There is no other statement where the function can return -1 otherwise.

This bug is triggered by the sisusb driver, but I think that the driver is not
at fault and therefore I am not assignig it to Driver/SIS.