Re: Minor off-by-one error in command_line_handler

[Daniel Jacobowitz <drow at mvista dot com>]

On Wed, Mar 27, 2002 at 12:01:07AM -0800, Jason Molenda wrote:
> The other problem is with the ALL_BLOCK_SYMBOLS macro.  It looks
> like this
> 
> /* Macro to loop through all symbols in a block BL.
>    i counts which symbol we are looking at, and sym points to the current
>    symbol.  */
> #define ALL_BLOCK_SYMBOLS(bl, i, sym)                   \
>         for ((i) = 0, (sym) = BLOCK_SYM ((bl), (i));    \
>              (i) < BLOCK_NSYMS ((bl));                  \
>              ++(i), (sym) = BLOCK_SYM ((bl), (i)))
> 
> Where the block structure (BL) ends with an array of pointers to
> symbols.  The third expression in the for statement increments the
> index variable and reads the address at the i'th element of the
> bl->sym[] array.
> 
> So when a block has 2 symbols, bl->sym[0] and bl->sym[1] contain
> values.  On the last evaluation of this loop, i is pre-incremented
> from 1 to 2 and the statement 'sym = bl->nsym[2]' is done - we're
> reading one element past the end of the array.
> 
> The invalid memory we just read is not used -- the conditional
> expression is then evaluated and the loop exits.  The only way
> I can see this causing a problem is on a system where reading
> that unallocated word of memory would cause a segfault.  Unless
> other people have heard complaints about gdb 5.1 doing so, I
> don't think this is worth worrying about. 

My fault (and after 5.1, I think).  This will cause errors with any
good memory checker, so I suppose it should be fixed.  This incurs a
little slowdown, but was the best way I could think of to do it... OK
to check in?


-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer

2002-03-29  Daniel Jacobowitz  <drow@mvista.com>

	* symtab.h (ALL_BLOCK_SYMBOLS): Don't dereference the pointer
	after the last symbol in a block.

Index: symtab.h
===================================================================
RCS file: /cvs/src/src/gdb/symtab.h,v
retrieving revision 1.29
diff -u -p -r1.29 symtab.h
--- symtab.h	2002/03/27 23:10:24	1.29
+++ symtab.h	2002/03/29 07:52:56
@@ -411,7 +411,9 @@ struct block
 #define ALL_BLOCK_SYMBOLS(bl, i, sym)			\
 	for ((i) = 0, (sym) = BLOCK_SYM ((bl), (i));	\
 	     (i) < BLOCK_NSYMS ((bl));			\
-	     ++(i), (sym) = BLOCK_SYM ((bl), (i)))
+	     ++(i), (sym) = ((i) < BLOCK_NSYMS ((bl)))	\
+			    ? BLOCK_SYM ((bl), (i))	\
+			    : NULL)
 
 /* Nonzero if symbols of block BL should be sorted alphabetically.
    Don't sort a block which corresponds to a function.  If we did the