bug#52446: 28.0.90; Infinite loop in add_row_entry

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Po Lu <luangruo@yahoo.com>
>> Cc: 52446@debbugs.gnu.org
>> Date: Sun, 12 Dec 2021 15:36:30 +0800
>> 
>> >>     while (entry && !row_equal_p (entry->row, row, 1))
>> >> --->  entry = entry->next;
>> >> 
>> >> The problem seems to be that `entry' points to the same address as
>> >> `entry->next'.
>> 
>> > Are you sure?  This more-or-less "can't happen".  How did you see that
>> > this was the problem?
>> 
>> I did `p entry' and `p entry->next' in gdb.  Both pointed to the same
>> address.
>
> At which point in the code did you print those?

Inside the infinite loop.

> And what were the values of entry->row (you can display them with
> pgrowx)?

It prints the following text:

RIGHT: 54 glyphs
  0    0: CHAR[0x0] pos=-734003200 blev=0,btyp=UNDEF w=0 a+d=9216+-18611
  1    0: CHAR[0xec000000] pos=0 blev=0,btyp=UNDEF w=0 a+d=-7424+909 face=119 
vof=1
  2    0: CHAR[0x2500007f] pos=452984959 blev=0,btyp=UNDEF w=0 a+d=0+0
  3    0: CHAR[0x0] pos=-318766977 blev=0,btyp=UNDEF w=0 a+d=8704+0 face=1
  4    0:  pos=-1392508928 w=127 a+d=1280+-16534 face=828327 vof=-20 MB OVL [ ]
  5  127: CHAR[0x0] pos=805306368 blev=0,btyp=UNDEF w=0 a+d=0+0
  6  127: CHAR[0x30000000] pos=805306368 blev=0,btyp=UNDEF w=0 a+d=0+0
  7  127: CHAR[0x0] pos=0 blev=0,btyp=UNDEF w=0 a+d=12288+0
  8  127: CHAR[0x0] pos=0 blev=0,btyp=UNDEF w=0 a+d=0+0
  9  127: CHAR[0x0] pos=33554432 blev=0,btyp=UNDEF w=0 a+d=512+0
 10  127: CHAR[0x0] pos=0 blev=0,btyp=UNDEF w=0 a+d=12288+0
 11  127: CHAR[0x30000000] pos=2063597568 blev=0,btyp=UNDEF w=127 a+d=0+0
 12  254: CHAR[0x1000000] pos=0 blev=0,btyp=UNDEF w=0 a+d=-4096+743 vof=1
 13  254: CHAR[0x1000000] pos=16777216 blev=0,btyp=UNDEF w=0 a+d=256+0
 14  254: CHAR[0x0] pos=16777216 blev=0,btyp=UNDEF w=0 a+d=0+0
 15  254: CHAR[0x1000000] pos=0 blev=0,btyp=UNDEF w=0 a+d=-26624+11687 vof=1
 16  254: CHAR[0x0] pos=16777216 blev=0,btyp=UNDEF w=0 a+d=256+0
 17  254: CHAR[0x0] pos=0 blev=0,btyp=UNDEF w=0 a+d=0+0
 18  254:  pos=0 w=-1 a+d=-1+-1 vof=-1 MB PAD N/A OVL AVOID [ ]
 19  253: CHAR[0x0] pos=16777216 blev=0,btyp=UNDEF w=0 a+d=0+0
 20  253: CHAR[0x74000000] pos=0 blev=0,btyp=UNDEF w=0 a+d=0+0 face=655360
 21  253: CHAR[0x80000000] pos=-1929379713 blev=0,btyp=UNDEF w=0 a+d=0+16 
face=91794 vof=1
 22  253:  pos=0 w=0 a+d=-16384+-5898 face=655360 vof=-21 MB OVL [ ]
 23  253: CHAR[0xf000007f] pos=1560281088 blev=0,btyp=UNDEF w=0 
a+d=-19712+-19263
 24  253:  pos=33554432 w=0 a+d=-16384+-6069 face=655360 vof=-21 MB OVL [ ]
 25  253: CHAR[0x90000000] pos=-1258291200 blev=0,btyp=UNDEF w=0 a+d=8960+-19263
 26  253: CHAR[0xa400000] pos=-1543503872 blev=0,btyp=UNDEF w=0 
a+d=-16384+-17738 face=47798
 27  253: CHAR[0xa0000000] pos=-1006632960 blev=0,btyp=UNDEF w=0 a+d=9728+0 
face=46272
 28  253: CHAR[0x5000000] pos=-1879048192 blev=0,btyp=UNDEF w=0 
a+d=16384+-17736 face=47735
 29  253: CHAR[0x5000000] pos=171966464 blev=0,btyp=UNDEF w=0 a+d=32000+11690 
vof=1
 30  253: CHAR[0x6000000] pos=171966464 blev=0,btyp=UNDEF w=0 a+d=9472+26277 
vof=1
 31  253: CHAR[0xc0000000] pos=-268435456 blev=0,btyp=UNDEF w=127 a+d=0+0
 32  380: CHAR[0xd0000000] pos=33554559 blev=0,btyp=UNDEF w=0 a+d=12288+0
 33  380: CHAR[0xd0000000] pos=-805306368 blev=0,btyp=UNDEF w=0 a+d=-12288+245 
face=245
 34  380: CHAR[0xd0000000] pos=-805306368 blev=0,btyp=UNDEF w=0 a+d=-12288+245 
face=245
 35  380:  pos=-805306368 w=0 a+d=15104+-25445 face=245 vof=-20 MB OVL [ ]
 36  380: CHAR[0x0] pos=805306368 blev=0,btyp=UNDEF w=0 a+d=8448+0 face=724146
 37  380: CHAR[0x18000000] pos=553648128 blev=0,btyp=UNDEF w=-7102 a+d=22749+0
 38 -6722: CHAR[0x6f00006d] pos=0 blev=0,btyp=UNDEF w=0 a+d=8448+0 face=221549
 39 -6722: CHAR[0x2f000000] pos=553648243 blev=0,btyp=UNDEF w=25645 a+d=31073+0
 40 18923:  pos=1918986355 w=29801 a+d=97+28528 face=156265 vof=27693 N/A OVL 
AVOID [ ]
 41 48724: IMAGE[1] slice=8706,50290,47091,5475 pos=358856691 w=1 a+d=0+8706 
face=1 vof=-15246 PAD N/A OVL AVOID [ ]
 42 48725: IMAGE[0] slice=0,24832,0,0 pos=358856691 w=1 a+d=0+8706 face=1 
vof=-15246 PAD N/A OVL AVOID [ ]
 43 48726:  pos=-1811939201 w=0 a+d=0+25024 face=78033 vof=-36 MB OVL [ ]
 44 48726: CHAR[0xc0000000] pos=127 blev=0,btyp=UNDEF w=0 a+d=0+0
 45 48726: CHAR[0x0] pos=1073741824 blev=0,btyp=UNDEF w=0 a+d=0+11868 
face=77407 vof=1
 46 48726: CHAR[0xfd000000] pos=-251658240 blev=0,btyp=UNDEF w=0 a+d=0+0 
face=58281
 47 48726: CHAR[0x0] pos=0 blev=0,btyp=UNDEF w=0 a+d=0+0
 48 48726: CHAR[0x0] pos=16777216 blev=0,btyp=UNDEF w=0 a+d=0+0
 49 48726: CHAR[0x0] pos=0 blev=0,btyp=UNDEF w=0 a+d=0+0
 50 48726: CHAR[0x0] pos=0 blev=0,btyp=UNDEF w=0 a+d=0+0
 51 48726: CHAR[0x21000000] pos=553648128 blev=0,btyp=UNDEF w=0 a+d=0+0 
face=50249
 52 48726: CHAR[0x40000000] pos=1023422208 blev=0,btyp=UNDEF w=0 a+d=16640+0 
face=42283
 53 48726: CHAR[0x1000000] pos=1073741824 blev=0,btyp=UNDEF w=0 a+d=0+0 
face=69034 vof=1536

Does this make sense?  I think it's starting to smell like a memory
problem of sorts.