Re: Cygwin 64 problem

[Ken Brown <kbrown@cornell.edu>]

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On 11/27/2016 11:02 AM, Ken Brown wrote:
> On 11/27/2016 9:03 AM, Girish Joglekar wrote:
>> Hi Ken,
>> Thank you for your reply on the Cygwin mailing list. I have created a
>> slightly smaller test example smaller than what I had created in Feb.
>> Attached is a tar file. After make insall if you run TEST.x and click
>> the Open button, it gives segmentation fault.
>> Hope you will be able to help.
>> Thank you.
>> Girish
> 
> Please keep the discussion on the mailing list so that people who might
> be able to help will see it.  I personally am not familiar with X11
> programming, so I'm not one of those people.
> 
> I do have a few comments, however:
> 
> 1. This may be slightly smaller than your previous program, but it is
> still *very* far from a small test case.  You really can't expect people
> to debug a program of this size for you.
> 
> 2. I suggest that you build with -Wall (as Marco already suggested in
> the earlier discussion) and fix all the compiler warnings.  I saw
> several that need attention (aside from the many "unused variable"
> warnings).  It wouldn't hurt to also use -Wextra.
> 
> 3. I also suggest that you use gdb to find out where the program is
> crashing and why.  You made a start on that in the discussion last
> March, but you didn't follow through.  (By the way, I recommend building
> without optimization; otherwise you may not be able to get accurate
> information about the crash from gdb.)
> 
> 4. If, after the steps above, you still think the crash is due to a
> Cygwin bug rather than a programming error, then try to extract from
> your program a test case as small as possible that reproduces the crash.

I've looked at this a little, and the crash occurs because of a bad value of a pointer to a font list.  I'm attaching an annotated transcript of a gdb session that illustrates this.  I didn't try to figure out where the bad pointer came from.

As a workaround, you can avoid the crash by removing from mosprshx.c all uses of spreadSheetFont, as in the following patch:

--- mosprshx.c~ 2016-11-27 08:46:12.000000000 -0500
+++ mosprshx.c  2016-11-29 14:58:23.114377500 -0500
@@ -29,8 +29,6 @@
    0x00, 0x7c, 0x07, 0x1e, 0x0f, 0x07, 0x9e, 0x03, 0xfc, 0x01, 0xf8, 0x00,
    0x70, 0x00, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00};
 
-static char *spreadSheetFont = "-adobe-courier-medium-r-normal--12-120-75-75-m-70-iso8859-1";
-
 #ifdef __STDC__
 static void mosprshCreateCheckMarkPixmap(Widget pushButton)
 #else
@@ -208,11 +206,6 @@
    if(isParentManaged)
       XtUnmanageChild(parentFM);
 
-   fromValue.addr = spreadSheetFont;
-   fromValue.size = utStringLength(fromValue.addr) + 1;
-   toValue.addr = NULL;
-   XtConvertAndStore(parentFM,XmRString,&fromValue,XmRFontList,&toValue);
-
    ac = 0;
    XtSetArg(al[ac],XmNuserData,(XtPointer)spreadSheetSize); ac++;
    spreadSheet = XmCreateForm(parentFM,"SpreadSheet",al,ac);
@@ -234,9 +227,6 @@
       XtSetArg(al[ac],XmNtraversalOn,FALSE); ac++;
    }
    XtSetArg(al[ac],XmNcolumns,longestFixedColumnSize+1); ac++;
-   if(toValue.addr) {
-      XtSetArg(al[ac],XmNfontList,*(unsigned int *)toValue.addr); ac++;
-   }
    for(i1=0 ; i1<nRows ; i1++) {
       sprintf(widgetName,"fixedColumnRow%d",i1);
       fixedColumnTF[i1] = XmCreateTextField(fixedColumn,widgetName,al,ac);
@@ -264,9 +254,6 @@
    if(cellSize > 0) {
       XtSetArg(al[ac],XmNcolumns,cellSize); ac++;
    }
-   if(toValue.addr) {
-      XtSetArg(al[ac],XmNfontList,*(unsigned int *)toValue.addr); ac++;
-   }
    for(j1=0 ; j1<nColumns ; j1++) {
       sprintf(widgetName,"fixedRowColumn%d",j1);
       fixedRowTF[j1] = XmCreateTextField(fixedRow,widgetName,al,ac);
@@ -294,9 +281,6 @@
             XtSetArg(al[ac],XmNcolumns,cellSize); ac++;
             XtSetArg(al[ac],XmNmaxLength,cellSize); ac++;
          }
-         if(toValue.addr) {
-            XtSetArg(al[ac],XmNfontList,*(unsigned int *)toValue.addr); ac++;
-         }
          sprintf(widgetName,"column%drow%d",j1,i1);
          variableRowAndColumnTF[loc] = XmCreateTextField(variableColumnFM[j1],widgetName,al,ac); loc++;
       }
@@ -886,15 +870,3 @@
       *nColumns = 0;
    }
 }
-
-
-#ifdef __STDC__
-char *moGetSpreadsheetFont()
-#else
-char *moGetSpreadsheetFont()
-#endif
-{
-   return(spreadSheetFont);
-}
-
-

Ken

[-- Attachment #2: gdb.txt --]
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Thread 1 "TEST.x" received signal SIGSEGV, Segmentation fault.
0x00000003fc68c4e5 in XmRenderTableCopy (table=0xaeeb0, tags=tags@entry=0x0, 
    tag_count=tag_count@entry=0)
    at /usr/src/debug/motif-2.3.6-1/lib/Xm/XmRenderT.c:1709
1709	  if (_XmRTDisplay(table))

[Crash here because the value of table is bogus.  See below.

+bt
#0  0x00000003fc68c4e5 in XmRenderTableCopy (table=0xaeeb0, 
    tags=tags@entry=0x0, tag_count=tag_count@entry=0)
    at /usr/src/debug/motif-2.3.6-1/lib/Xm/XmRenderT.c:1709
#1  0x00000003fc6831ba in XmFontListCopy (fontlist=<optimized out>)
    at /usr/src/debug/motif-2.3.6-1/lib/Xm/XmFontList.c:637
#2  0x00000003fc657920 in InitializeTextStruct (tf=tf@entry=0x6000af730)
    at /usr/src/debug/motif-2.3.6-1/lib/Xm/TextF.c:7295
#3  0x00000003fc657e67 in Initialize (request=request@entry=0x6000afb40, 
    new_w=new_w@entry=0x6000af730, args=args@entry=0xffffbd60, 
    num_args=num_args@entry=0xffffb320)
    at /usr/src/debug/motif-2.3.6-1/lib/Xm/TextF.c:7817
#4  0x00000003fc469bb1 in CallInitialize (
    class=0x3fc72c440 <xmTextFieldClassRec>, 
    req_widget=req_widget@entry=0x6000afb40, 
    new_widget=new_widget@entry=0x6000af730, args=args@entry=0xffffbd60, 
    num_args=num_args@entry=8) at /usr/src/debug/libXt-1.1.5-1/src/Create.c:226
#5  0x00000003fc46a65c in xtCreate (
    name=name@entry=0xffffb950 "fixedColumnRow0", class=class@entry=0x0, 
    widget_class=widget_class@entry=0x3fc72c440 <xmTextFieldClassRec>, 
    parent=0x1fc5dd590, parent@entry=0x6000af0d0, default_screen=0x600052780, 
    args=args@entry=0xffffbd60, num_args=num_args@entry=8, 
    typed_args=typed_args@entry=0x0, num_typed_args=num_typed_args@entry=0, 
    parent_constraint_class=0x3fc720dc0 <xmFormClassRec>, 
    post_proc=post_proc@entry=0x3fc469bf0 <widgetPostProc>)
    at /usr/src/debug/libXt-1.1.5-1/src/Create.c:416
#6  0x00000003fc46a906 in _XtCreateWidget (
    name=name@entry=0xffffb950 "fixedColumnRow0", 
    widget_class=widget_class@entry=0x3fc72c440 <xmTextFieldClassRec>, 
    parent=parent@entry=0x6000af0d0, args=args@entry=0xffffbd60, 
    num_args=num_args@entry=8, typed_args=typed_args@entry=0x0, 
    num_typed_args=num_typed_args@entry=0)
    at /usr/src/debug/libXt-1.1.5-1/src/Create.c:570
#7  0x00000003fc46abd9 in XtCreateWidget (name=0xffffb950 "fixedColumnRow0", 
    widget_class=0x3fc72c440 <xmTextFieldClassRec>, parent=0x6000af0d0, 
    args=0xffffbd60, num_args=8)
    at /usr/src/debug/libXt-1.1.5-1/src/Create.c:589
#8  0x00000003fc658a81 in XmCreateTextField (parent=<optimized out>, 
    name=<optimized out>, arglist=<optimized out>, argcount=<optimized out>)
    at /usr/src/debug/motif-2.3.6-1/lib/Xm/TextF.c:10645
#9  0x000000010040882d in mosprshCreateSpreadsheet (parentFM=0x6000acc60, 
    spreadSheetTitle=0x100421087 "Measuring Unit Specification", 
    rowNames=0x6000ab4f0, columnNames=0x6000ab4b0, cellSize=0, 
    mosprshCheckButtonCallback=0x0) at mosprshx.c:242
[...]

+p *table
$1 = (struct __XmRenderTableRec *) 0x56f700001ea1
+p *$
Cannot access memory at address 0x56f700001ea1
+f 2
#2  0x00000003fc657920 in InitializeTextStruct (tf=tf@entry=0x6000af730)
    at /usr/src/debug/motif-2.3.6-1/lib/Xm/TextF.c:7295
7295	     TextF_FontList(tf) = (XmFontList)XmFontListCopy(TextF_FontList(tf));
+p tf->text.font_list
$2 = (XmFontList) 0xaeeb0

[This is the bad pointer that was propagated to XmRenderTableCopy.  I
didn't chase down where it came from.]


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