bug#8211: uninitialized variable in detect_coding_iso_2022's end-of-composition code

bug#8211: uninitialized variable in detect_coding_iso_2022's end-of-composition code

[Paul Eggert]

I found this problem by compiling Emacs with GCC's -Wuninitialized flag.

The following code in the Emacs trunk src/coding.c's
detect_coding_iso_2022 function apparently uses an uninitialized variable:

           ...
           else if (c == '1')
             {
               /* End of composition.  */
               if (composition_count < 0
                   || composition_count > MAX_COMPOSITION_COMPONENTS)
                 /* Invalid */
                 break;
               composition_count = -1;
               found |= CATEGORY_MASK_ISO;
             }
           else
             ...

           /* We found a valid designation sequence for CHARSET.  */
           rejected |= CATEGORY_MASK_ISO_8BIT;
           if (SAFE_CHARSET_P (&coding_categories[coding_category_iso_7],
                               id))
             found |= CATEGORY_MASK_ISO_7;

The problem is that the "else if (c == '1')" branch does not initialize
the local variable "id", but the second "if" test uses that variable.

I plan to work around the uninitialized-variable problem by initializing
"id" to zero.  This will replace undefined behavior with defined behavior,
so it shouldn't introduce a new bug, but it probably doesn't fix the
bug in question, assuming there is one.  Could an expert in this
area please review this and come up with a real fix?

I'm CC'ing this to Kenichi Handa, who committed the code in question.

bug#8211: uninitialized variable in detect_coding_iso_2022's end-of-composition code

[Andreas Schwab]

Paul Eggert <eggert@cs.ucla.edu> writes:

> I found this problem by compiling Emacs with GCC's -Wuninitialized flag.
>
> The following code in the Emacs trunk src/coding.c's
> detect_coding_iso_2022 function apparently uses an uninitialized variable:
>
>           ...
>           else if (c == '1')
>             {
>               /* End of composition.  */
>               if (composition_count < 0
>                   || composition_count > MAX_COMPOSITION_COMPONENTS)
>                 /* Invalid */
>                 break;
>               composition_count = -1;
>               found |= CATEGORY_MASK_ISO;
>             }
>           else
>             ...
>
>           /* We found a valid designation sequence for CHARSET.  */
>           rejected |= CATEGORY_MASK_ISO_8BIT;
>           if (SAFE_CHARSET_P (&coding_categories[coding_category_iso_7],
>                               id))
>             found |= CATEGORY_MASK_ISO_7;
>
> The problem is that the "else if (c == '1')" branch does not initialize
> the local variable "id", but the second "if" test uses that variable.

I think it just lacks a break.  ESC '1' is not a designation sequence.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
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bug#8211: uninitialized variable in detect_coding_iso_2022's end-of-composition code

[Paul Eggert]

Kenichi Handa evidently fixed this old bug in 2011 after I filed it, so I'm closing the bug report now.