[PATCH] __vfscanf_internal: fix aliasing violation (bug 26690)

[Szabolcs Nagy]

The 10/01/2020 16:17, Andreas Schwab wrote:
> As noted in <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97264>, the cast
> in the call to the read_int function is an aliasing violation.  Change the
> type of local variable f to a pointer to unsigned, which allows to
> eliminate most casts while only adding three new ones.

this looks good to me.


> ---
>  stdio-common/vfscanf-internal.c | 22 +++++++++++-----------
>  1 file changed, 11 insertions(+), 11 deletions(-)
> 
> diff --git a/stdio-common/vfscanf-internal.c b/stdio-common/vfscanf-internal.c
> index 95b46dcbeb..3a323547f9 100644
> --- a/stdio-common/vfscanf-internal.c
> +++ b/stdio-common/vfscanf-internal.c
> @@ -277,7 +277,7 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>  #endif
>  {
>    va_list arg;
> -  const CHAR_T *f = format;
> +  const UCHAR_T *f = (const UCHAR_T *) format;
>    UCHAR_T fc;	/* Current character of the format.  */
>    WINT_T done = 0;	/* Assignments done.  */
>    size_t read_in = 0;	/* Chars read in.  */
> @@ -415,10 +415,11 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>  #endif
>  
>  #ifndef COMPILE_WSCANF
> -      if (!isascii ((unsigned char) *f))
> +      if (!isascii (*f))
>  	{
>  	  /* Non-ASCII, may be a multibyte.  */
> -	  int len = __mbrlen (f, strlen (f), &state);
> +	  int len = __mbrlen ((const char *) f, strlen ((const char *) f),
> +			      &state);
>  	  if (len > 0)
>  	    {
>  	      do
> @@ -426,7 +427,7 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>  		  c = inchar ();
>  		  if (__glibc_unlikely (c == EOF))
>  		    input_error ();
> -		  else if (c != (unsigned char) *f++)
> +		  else if (c != *f++)
>  		    {
>  		      ungetc_not_eof (c, s);
>  		      conv_error ();
> @@ -484,9 +485,9 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>        char_buffer_rewind (&charbuf);
>  
>        /* Check for a positional parameter specification.  */
> -      if (ISDIGIT ((UCHAR_T) *f))
> +      if (ISDIGIT (*f))
>  	{
> -	  argpos = read_int ((const UCHAR_T **) &f);
> +	  argpos = read_int (&f);
>  	  if (*f == L_('$'))
>  	    ++f;
>  	  else
> @@ -521,8 +522,8 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>  
>        /* Find the maximum field width.  */
>        width = 0;
> -      if (ISDIGIT ((UCHAR_T) *f))
> -	width = read_int ((const UCHAR_T **) &f);
> +      if (ISDIGIT (*f))
> +	width = read_int (&f);
>      got_width:
>        if (width == 0)
>  	width = -1;
> @@ -2522,12 +2523,11 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
>  	    }
>  
>  	  while ((fc = *f++) != '\0' && fc != ']')
> -	    if (fc == '-' && *f != '\0' && *f != ']'
> -		&& (unsigned char) f[-2] <= (unsigned char) *f)
> +	    if (fc == '-' && *f != '\0' && *f != ']' && f[-2] <= *f)
>  	      {
>  		/* Add all characters from the one before the '-'
>  		   up to (but not including) the next format char.  */
> -		for (fc = (unsigned char) f[-2]; fc < (unsigned char) *f; ++fc)
> +		for (fc = f[-2]; fc < *f; ++fc)
>  		  ((char *)charbuf.scratch.data)[fc] = 1;
>  	      }
>  	    else
> -- 
> 2.28.0
> 
> 
> -- 
> Andreas Schwab, SUSE Labs, schwab@suse.de
> GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
> "And now for something completely different."

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