Re: [RFC PATCH 6/6] utf8.c: avoid char overflow

[Beat Bolli <dev+git@xxxxxxxxx>]

Am 09.07.2018 16:48, schrieb Beat Bolli:
> Hi Dscho
>
> Am 09.07.2018 15:14, schrieb Johannes Schindelin:
> > Hi Beat,
> >
> > On Sun, 8 Jul 2018, Beat Bolli wrote:
> >
> > > In ISO C, char constants must be in the range -128..127. Change the 
> > > BOM
> > > constants to unsigned char to avoid overflow.
> > >
> > > Signed-off-by: Beat Bolli <dev+git@xxxxxxxxx>
> > > ---
> > >  utf8.c | 10 +++++-----
> > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/utf8.c b/utf8.c
> > > index d55e20c641..833ce00617 100644
> > > --- a/utf8.c
> > > +++ b/utf8.c
> > > @@ -561,15 +561,15 @@ char *reencode_string_len(const char *in, int 
> > > insz,
> > >  #endif
> > >
> > >  static int has_bom_prefix(const char *data, size_t len,
> > > -			  const char *bom, size_t bom_len)
> > > +			  const unsigned char *bom, size_t bom_len)
> > >  {
> > >  	return data && bom && (len >= bom_len) && !memcmp(data, bom, 
> > > bom_len);
> > >  }
> > >
> > > -static const char utf16_be_bom[] = {0xFE, 0xFF};
> > > -static const char utf16_le_bom[] = {0xFF, 0xFE};
> > > -static const char utf32_be_bom[] = {0x00, 0x00, 0xFE, 0xFF};
> > > -static const char utf32_le_bom[] = {0xFF, 0xFE, 0x00, 0x00};
> > > +static const unsigned char utf16_be_bom[] = {0xFE, 0xFF};
> > > +static const unsigned char utf16_le_bom[] = {0xFF, 0xFE};
> > > +static const unsigned char utf32_be_bom[] = {0x00, 0x00, 0xFE, 
> > > 0xFF};
> > > +static const unsigned char utf32_le_bom[] = {0xFF, 0xFE, 0x00, 
> > > 0x00};
> >
> > An alternative approach that might be easier to read (and avoids the
> > confusion arising from our use of (signed) chars for strings pretty 
> > much
> > everywhere):
> >
> > #define FE ((char)0xfe)
> > #define FF ((char)0xff)
> >
> > ...
>
> I have tried this first (without the macros, though), and thought it 
> looked
> really ugly. That's why I chose this solution. The usage is pretty 
> local and
> close to function has_bom_prefix().
>
> Would an explaining comment help?

I have found an even simpler solution. Use proper char literals.

I will put this into v2.

Regards,
Beat


diff --git a/utf8.c b/utf8.c
index d55e20c641..982217eec9 100644
--- a/utf8.c
+++ b/utf8.c
@@ -566,10 +566,10 @@ static int has_bom_prefix(const char *data, size_t 
len,
        return data && bom && (len >= bom_len) && !memcmp(data, bom, 
bom_len);
 }

-static const char utf16_be_bom[] = {0xFE, 0xFF};
-static const char utf16_le_bom[] = {0xFF, 0xFE};
-static const char utf32_be_bom[] = {0x00, 0x00, 0xFE, 0xFF};
-static const char utf32_le_bom[] = {0xFF, 0xFE, 0x00, 0x00};
+static const char utf16_be_bom[] = {'\xFE', '\xFF'};
+static const char utf16_le_bom[] = {'\xFF', '\xFE'};
+static const char utf32_be_bom[] = {'\0', '\0', '\xFE', '\xFF'};
+static const char utf32_le_bom[] = {'\xFF', '\xFE', '\0', '\0'};

 int has_prohibited_utf_bom(const char *enc, const char *data, size_t 
len)
 {