Re: segmentation failure plmerge / building libs back

[Riccardo Mottola]

Hi Richard,

sorry for the late answer, I was away without access to that specific 
computer.

Richard Frith-Macdonald wrote:
> I wouldn't say that.
> You can see that this is building a string from +initialize in NSBundle.m at 
> line 1180
> You can then look at the source and check that the format string looks correct 
> and the number of argument passed is correct.
> You can also look at where those two arguments come from, and see that they are 
> (most likely) to be literal/constant strings produced by the compiler.
>
> If this is using David's new ABI ... the problem might well be a bug in the new 
> code or (more likely) a mismatch between the layout the compiler is producing 
> and the library is expecting.

Well, it is libobjc2 "head" of git and I configured to use "ng" runtime, 
so it should be David's ABI.

> Anyway, it tells you that you can run the program under gdb, set a breakpoint 
> in +[NSBundle initialize] and look at exactly what's being passed to narrow 
> things down more.

As you suggested, I put a breakpoint in [NSBundle initialize]

I was able to step until 1180 and print put the variables and as you 
supposed they are string constants looking fine.

1180            gnustep_target_dir = [[NSString alloc] initWithFormat: 
@"%@-%@",
(gdb) p gnustep_target_cpu
$1 = (struct NSString *) 0xb7f59920 <.objc_str>
(gdb) p gnustep_target_os
$2 = (struct NSString *) 0xb7f5992c <.objc_str>
(gdb) po gnustep_target_cpu
ix86
(gdb) po gnustep_target_os
linux-gnu

however, as could be guessed, the next step fails
(gdb) n

Program received signal SIGSEGV, Segmentation fault.
0xb7b76294 in GSPrivateFormat (s=0xbfffdc34, format=0xbfffe45c,
    ap=0xbfffecc0 " 
\231\365\267,\231\365\267\204\237\365\267\210\221\365\314/\350\273\267\320\003\016\bP\032\275\267$\217\365\267\060\217\365\267\204\237\365\267P\220\365\267D\220\365\267\004r\"\b\016\b\324\267\030\217\365\267\360\217\365\267\344\217\365\267\330\217\365\267\314\217\365\267\300\217\365\267\264\217\365\267\f\217\365\267\250\217\365\267\234\217\365\267\220\217\365\267\204\217\365\267x\217\365\267`\217\365\267l\217\365\267T\217\365\267<\217\365\267\354\220\365\267\340\220\365\267\324\220\365\267\310\220\365\267\274\220\365\267\260\220\365\267\244\220\365\267\230\220\365\267\214\220\365\267 
\220\365\267\200\220\365\267\024\220\365\267t\220\365\267h\220\365\267\070\220\365\267,\220\365\267\374\217\365\267\\\220\365\267\314\235\365\267"..., 
locale=0x0) at GSFormat.m:1046
1046        for (; (size_t) nspecs_done < nspecs; ++nspecs_done)

I tried to setp into the string allocation and see where it fails and it 
appears here:

(gdb) s
Single stepping until exit from function objc_msgSend,
which has no line number information.
+[NSObject alloc] (self=0xb7bbe82f <+[NSBundle initialize]+15>, 
_cmd=0x80e03d0)
    at NSObject.m:1120
1120    + (id) alloc

(gdb) n
1122      return [self allocWithZone: NSDefaultMallocZone()];
(gdb) n

Program received signal SIGSEGV, Segmentation fault.

#0  0xb7b76294 in GSPrivateFormat (s=0xbfffdc34, format=0xbfffe45c,
    ap=0xbfffecc0 " 
\231\365\267,\231\365\267\204\237\365\267\210\221\365\267/\350\273\267\320\003\016\bP\032\275\267$\217\365\267\060\217\365\267\204\237\365\267P\220\365\267D\220\365\267\004r\"\b\016\b\324\267\030\217\365\267\360\217\365\267\344\217\365\267\330\217\365\267\314\217\365\267\300\217\365\267\264\217\365\267\f\217\365\267\250\217\365\267\234\217\365\267\220\217\365\267\204\217\365\267x\217\365\267`\217\365\267l\217\365\267T\217\365\267<\217\365\267\354\220\365\267\340\220\365\267\324\220\365\267\310\220\365\267\274\220\365\267\260\220\365\267\244\220\365\267\230\220\365\267\214\220\365\267 
\220\365\267\200\220\365\267\024\220\365\267t\220\365\267h\220\365\267\070\220\365\267,\220\365\267\374\217\365\267\\\220\365\267\314\235\365\267"..., 
locale=0x0) at GSFormat.m:1046
#1  0xb7b8c54e in -[GSPlaceholderString initWithFormat:locale:arguments:] (
    self=0x8171ab4, _cmd=0xb7f904e4 <.objc_selector_list+432>,
    format=0xb7f59194 <.objc_str.170>, locale=0x0,
    argList=0xbfffecc0 " 
\231\365\267,\231\365\267\204\237\365\267\210\221\365\267/\350\273\267\320\003\016\bP\032\275\267$\217\365\267\060\217\365\267\204\237\365\267P\220\365\267D\220\365\267\004r\"\b\016\b\324\267\030\217\365\267\360\217\365\267\344\217\365\267\330\217\365\267\314\217\365\267\300\217\365\267\264\217\365\267\f\217\365\267\250\217\365\267\234\217\365\267\220\217\365\267\204\217\365\267x\217\365\267`\217\365\267l\217\365\267T\217\365\267<\217\365\267\354\220\365\267\340\220\365\267\324\220\365\267\310\220\365\267\274\220\365\267\260\220\365\267\244\220\365\267\230\220\365\267\214\220\365\267 
\220\365\267\200\220\365\267\024\220\365\267t\220\365\267h\220\365\267\070\220\365\267,\220\365\267\374\
#2  0xb7ca9552 in -[NSString initWithFormat:] (self=<optimized out>,
    _cmd=<optimized out>, format=<optimized out>) at NSString.m:1366
#3  0xb7bbf0ac in +[NSBundle initialize] (self=<optimized out>,
    _cmd=<optimized out>) at NSBundle.m:1180
#4  0xb79da15c in objc_send_initialize ()
   from /System/Library/Libraries/libobjc.so.4.6
#5  0xb79e64d8 in slowMsgLookup ()
   from /System/Library/Libraries/libobjc.so.4.6
#6  0xb79ec5e1 in objc_msgSend () from 
/System/Library/Libraries/libobjc.so.4.6
#7  0xb7b665e0 in GSLanguageFromLocale (locale=<optimized out>)
    at GSLocale.m:264
#8  0xb7cdc51f in +[NSUserDefaults standardUserDefaults] (
    self=<optimized out>, _cmd=<optimized out>) at NSUserDefaults.m:995
#9  0xb7c08915 in -[NSDictionary writeToFile:atomically:] (
    self=<optimized out>, _cmd=<optimized out>, path=<optimized out>,
    useAuxiliaryFile=<optimized out>) at NSDictionary.m:1096
#10 0x080496e4 in main (argc=<optimized out>, argv=<optimized out>,
    env=<optimized out>) at plmerge.m:135

we are at
588      GSPrivateFormat(f, fmt, argList, locale);

I printed out f and fmt locale is 0x0

(gdb) p *f
$4 = {<> = {<> = {<> = {
        isa = 0x8098f00}, <No data fields>}, <No data fields>}, 
_contents = {
    u = 0x8098f00, c = 0x8098f00 "P\222\t\b`\267\017\b\255\225\324\267"},
  _count = 134844160, _flags = {wide = 0, owned = 0, unused = 0,
    hash = 8427760}, _capacity = 134844160, _zone = 0x8098f00}

(gdb) p *fmt
$6 = 37



Can we assume that NSObject's alloc (line 1122) passed successfully? Do 
you get any smarter? I don't...


Riccardo