This is a discussion on RE: OpenSSL breaks with gcc 4.2 - Openssl ; > x is still just a pointer to data - so it's the same > length in any case, all pointers to lvalues are the > same length in C. The only issue there is whether it's > aligned correctly ...
> x is still just a pointer to data - so it's the same
> length in any case, all pointers to lvalues are the
> same length in C. The only issue there is whether it's
> aligned correctly - that's the programmers problem.
Length is not the issue. There is no rule that says that two types must be
passed the same way just because they're the same length. For example, some
platforms may pass a 64-bit floating point number in a floating point
register but pass a 64-bit integer in an integer register.
All you can do is assume that it will work because it has always worked,
until it stops working.
> Mixing something like char *(*d2i)(), and char ** IS
> problematic, since those aren't guaranteed to be the
> same length but as far as I can remember OpenSSL doesn't
> do that.
If they are not the same length, it is not likely to work. That doesn't mean
it's legal if they are the same length.
> d2i is a function (prototype is unknown)
> but I've been told x is a pointer, &p is a pointer,
> len is long. There's nothing indeterminate about the
> size of any of those.
The issue is not size, it's type.
> C isn't a strongly typed language - there's no language
> requirement for an accurate function prototype or that
> the types of the arguments be correct - only that the
> size of them is correct.
You are correct, but that's not the issue. The issue is this simple -- if
you are going to call a function whose types you don't know (through a
prototype), you must cast each type you pass to the type the function
expects. End of story. OpenSSL does not do this. This is not valid C whether
or not the type sizes are the same.
> C is not the same language as C++, this instance should
> work with a C compiler - whether or not the compiler is
> passing the arguments via the stack or in registers.
Can you cite anything in the C standard that says this is allowed? As I
understand it, you must pass a function precisely the types it expects, or
use a prototype to force the compiler to cast them. Either way, the exact
type must be known where the call is compiled.
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