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Date: Wed, 28 Mar 2018 14:33:23 +0100
From: Jon Scobie <jon.scobie@...lsign.com>
To: musl@...ts.openwall.com
Subject: Re: Maybe not a bug but a possible omission?
Well, I definitely agree that instead of definitions like
#define INT64_MIN (-1-0x7fffffffffffffff)
we should have
#define INT64_MIN (-1 - INT64_C(0x7fffffffffffffff))
As for the WCHAR_MAX|MIN definitions, yes, swig should handle those. I'll
check the source and see about a patch for submission.
If the definitions above are what should be used, how do I go about getting
those updated?
Regards,
Jon.
*JON SCOBIE*
SENIOR SECURITY ENGINEER
+44 7894253988 <+44%7894253988>
www.callsign.com
On 28 March 2018 at 13:52, CodingMarkus <CodingMarkus@...auska.name> wrote:
>
>
> > On 2018-03-28, at 12:31, Jon Scobie <jon.scobie@...lsign.com> wrote:
> >
> > #define INT64_MIN (-1-0x7fffffffffffffff)
> >
> > the equivalent glibc definition is the equivalent of
> >
> > #define INT64_MIN (-1-0x7fffffffffffffffL)
>
> According to ISO-C 2011 standard (page 63):
>
> "The type of an integer constant is the first of the corresponding list in
> which its value can be represented.”
>
> And for constants that have no type suffix (no “L”, “LL”, “U”, “UL”,
> “ULL”), the “list” mentioned above contains the following types decimal
> values:
>
> int, long int, long long int
>
> and the following types of octal/hex values:
>
> int, unsigned int, long int, unsigned long int, long long int, unsigned
> long long int
>
> Thus the type is the first one of the three above that is big enough to
> represent a constant value.
>
> By using the suffix “L”, all that happens is that the type list is further
> limited down to:
>
> long int, long long int
>
> or for octal/hex values:
>
> long int, unsigned long int, long long int, unsigned long long int
>
> On most systems, only long int or long long int can represent
> "(-1-0x7fffffffffffffff)”, so either one will be the deferred type.
> Appending the suffix “L” would thus not make any difference, as it will not
> result in a different type. It only eliminates the type “int” from the list
> but I don’t know any system where the type int could represent such a big
> number, so int is never chosen to begin with.
>
> Personally I wonder about that definition in both libraries, I had
> expected it to be:
>
> #define INT64_MIN INT64_C(...)
>
> because that assures the type is pinned to whatever type int64_t maps on
> the system. After all the C standard also says about INT64_MIN the other
> defines:
>
> "Each instance of any defined macro shall be replaced by a constant
> expression suitable for use in #if preprocessing directives, and this
> expression shall have the same type as would an expression that is an
> object of the corresponding type converted according to the integer
> promotions.”
>
> So INT64_MIN should be the same type as int64_t is (that’s how I interpret
> the last part of that sentence) and that is not always guaranteed when
> defined as above, as when defined as above, a long int is enough to
> represent that type on a 64 bit system (on 64 bit systems, long is
> typically 64 bit already), whereas int64_t may as well be a long long int
> on such a system. At least PRI64d typically uses “lld” AFAIK and not “ld”,
> though I have not checked what musl or glibc uses for PRI64d on 64 bit
> systems.
>
> > The issue is that swig has no idea what type INT64_MAX is if you don't
> specifically state what it is so it treats it as a goint - which is not a
> long (or long long).
>
> If swig fails to correctly process valid C code, then this sounds like a
> bug that the swig developers should really fix. The type of a numeric
> constant is always exactly defined by the C standard, it’s never required
> to give an explicit type unless you want a “wider” type than would have
> been chosen automatically otherwise or you want to force a signed value to
> be an unsigned type. Every tool parsing, compiling or processing C code
> should know the type rules and should apply them the same way a C compiler
> would do it, shouldn’t it?
>
> Regards,
> Markus
>
>
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