>
> Try breaking the mallocs into separate lines to see which one fails:
>
> int errflag = 0;
> if (!(node = (struct node *)malloc(sizeof(struct node)))) {
> errflag = 1;
> } else {
> if (!(node->data = (struct symbol *)malloc(sizeof(struct
> symbol)))) {
> errflag = 2;
> }
> }
> if (errflag) {
> fprintf(stderr, "errflag=%d\n");
> fprintf(stderr, sym_tab_msg[MEMORY_ALLOCATION_FAILURE]);
> return FALSE;
> }
>
> If the first one sets errflag without a segfault in malloc, it would seem
> that your original compound statement tried to do the second malloc. The
> second malloc would certainly fail if the first malloc results in "node"
> being a null pointer, because it would try to set node->data. You can try
> to test this with:
The C language guarantees that with such AND logical expression, the 2nd
operand will not be executed unless the first operand has a logical value of
TRUE.
The real problem was that I was convinced that realloc(void*, size_t) does not
free the previously allocated area; and therefore have free it myself. That
was done much earlier then when malloc segfault since the error manifested
itself only when malloc had to run again.
>
> if (!((node = (struct node *)malloc(sizeof(struct node))) &&
> (fprintf (stderr, "should not get here\n")))) {
> }
>
>
> On Thu, 26 Jul 2001, Shaul Karl wrote:
>
> > > Have you tried to look at the value sizeof(struct node)? It might be too
> > > big.
> > > Otherwise, can you show us the backtrace in gdb.
> > >
> >
> >
> > gdb says sizeof(struct node) == 20. It is mostly a couple of pointers:
> >
> > struct node {
> > enum colors color;
> > struct node *left, *right, *parent;
> > void *data;
> > };
> >
> >
> > Breakpoint 1, insert_symbol (sym=0xbfffe25c) at symbols.c:197
> > 197 if (!((node = (struct node *)malloc(sizeof(struct node))) &&
> > (gdb) p sizeof(struct node)
> > $1 = 20
> > (gdb) c
> > Continuing.
> >
> > Program received signal SIGSEGV, Segmentation fault.
> > 0x400af19e in malloc () from /lib/libc.so.6
> > (gdb) bt
> > #0 0x400af19e in malloc () from /lib/libc.so.6
> > #1 0x400ae844 in malloc () from /lib/libc.so.6
> > #2 0x804c60a in insert_symbol (sym=0xbfffe25c) at symbols.c:197
> > #3 0x8048c6f in tmp_variable (tmp=0xbfffe398, sym_data=0xbfffe2ec)
> > at actions.c:115
> > #4 0x80497be in sym_for_const (tok=0xbfffe4f8, sym=0xbfffe398)
> > at actions.c:412
> > #5 0x804d55f in yyparse () at parser.y:216
> > #6 0x804ddd5 in translator (params=0xbffffb80) at parser.y:272
> > #7 0x804b08f in main (argc=1, argv=0xbffffc98) at main.c:195
> > #8 0x4005b2db in __libc_start_main () from /lib/libc.so.6
> > (gdb)
> >
> > I believe that malloc is called twice here due to line 198:
> >
> > if (!((node = (struct node *)malloc(sizeof(struct node))) &&
> > (node->data = malloc(sizeof(struct symbol))))) {
> >
> > and sizeof(struct symbol) is 52.
> >
> >
> >
> > > On [Thu, 26 Jul 2001 03:15:46 +0300], Shaul Karl <[EMAIL PROTECTED]>
> > > wrote:
> > > > Breakpoint 2, insert_symbol (sym=0xbfffe25c) at symbols.c:197
> > > > 197 if (!((node = (struct node *)malloc(sizeof(struct node)))
> > > > &&
> > > > (gdb) l 197
> > > > 192
> > > > 193 enum flag insert_symbol(struct symbol *sym)
> > > > 194 {
> > > > 195 struct node *node;
> > > > 196
> > > > 197 if (!((node = (struct node *)malloc(sizeof(struct node)))
> > > > &&
> > > > 198 (node->data = (struct symbol *)malloc(sizeof(struct
> > > > symbol))))) {
> > > > 199 fprintf(stderr, sym_tab_msg[MEMORY_ALLOCATION_FAILURE]);
> > > > 200 return FALSE;
> > > > 201 }
> > > > (gdb) n
> > > >
> > > > Program received signal SIGSEGV, Segmentation fault.
> > > > 0x400af19e in malloc () from /lib/libc.so.6
> > > > (gdb)
> > > >
> > > >
> > > > How can it be? If malloc can not allocate memory it should return a
> > > > NULL
> > > > pointer. How can it Seg fault?
> > > >
> > > > [03:09:45 16]$ free
> > > > total used free shared buffers
> > > > cached
> > > > Mem: 63584 60936 2648 31452 1344
> > > > 20472
> > > > -/+ buffers/cache: 39120 24464
> > > > Swap: 116924 52580 64344
> > > > [03:09:49 16]$
> > > >
> > > > Since all the memory is used and the machine is running for some time
> > > > now,
> > > > doesn't that precludes hardware problems?
> > > >
> > > > Obviously I am missing something.
> > > >
> > > >
> > > > --
> > > >
> > > > Shaul Karl <[EMAIL PROTECTED]>
> > > >
> > > >
> > > >
> > > > --
> > > > To UNSUBSCRIBE, email to [EMAIL PROTECTED]
> > > > with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
> > > >
> > >
> > > --
> > > Shao Zhang Tel: (02) 9209 4838
> > > Software Engineer Fax: (02) 9209 4992
> > > Redfern Broadband Networks (RBN) Mail: [EMAIL PROTECTED]
> > >
> > >
> > > --
> > > To UNSUBSCRIBE, email to [EMAIL PROTECTED]
> > > with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
> > >
> >
> > --
> >
> > Shaul Karl <[EMAIL PROTECTED]>
> >
> >
> >
> > --
> > To UNSUBSCRIBE, email to [EMAIL PROTECTED]
> > with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
> >
> >
>
> ...RickM...
>
--
Shaul Karl <[EMAIL PROTECTED]>
