Re: [PATCH] newlib-stdint.h: Remove 32 bit longs

[Andrew Pinski <pinskia at gmail dot com>]

On Mon, Aug 22, 2016 at 9:09 AM, Andy Ross <andrew.j.ross@intel.com> wrote:
> The reproduction is straightforward.  Just build any cross gcc with
> --enable-newlib (e.g. the one in the Zephyr SDK) and compile this
> (on any 32 or 64 bit 2's complement architecture) with newlib's
> headers.
>
>     #include <stdint.h>
>
>     extern void takes_fmt(const char *fmt, ...)
>         __attribute__ ((format (printf, 1, 2)));
>
>     void foo()
>     {
>         int32_t x = 42;
>         takes_fmt("%d", x);
>     }
>
> The use of int32_t with the untyped format specifier produces the
> "expects argument of type ‘int’, but argument 2 has type ‘long int’"
> warning despite the fact that this platform (it's just an i586
> compiler!) is a standard ILP32 architecture.

Why do you think the above code does not have a bug in it?  int32_t is
long and changing it now is changing the ABI (especially for C++).
Before and after your patch take the following C++ program to see that
you just changed the ABI:
#include <stdint.h>

void f(int32_t a){}

>
> The reason for that is this bit in newlib's headers where they trust
> gcc if __INT32_TYPE__ is set:
>
>     https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;a=blob;f=newlib/libc/include/machine/_default_types.h;h=ffc646d9e3f5392a643f8b4ca203a3ad2a7627d8;hb=HEAD#l62
>
> And gcc, as seen by this patch, sets it to a long because it thinks
> that's what newlib *wants*.
>
> But if you look at the preprocessor code immediately following, newlib
> doesn't want that at all.  If it doesn't find __INT32_TYPE__, it will
> (see line 70) clearly choose a signed int, not a long.
>
> Newlib doesn't want that at all.  This just seems like some kind of
> historical mistake to me.  GCC's newlib "support" causes newlib code
> to emit warnings on benign code that is unwarned in AFAIK literally
> every other platform in existence.
>
> (And I understand the point about the PRI stuff in inttypes.h, which
> we're doing internally.  But that doesn't really address the bug in
> our SDK compiler.)

There is no bug in the compiler, just you misunderstanding that in32_t
can either be long or int and the reason why PRI were designed in the
first place.
I have fixed up many code which tries to use %d with int32_t inside
Cavium's simple-exec code and I don't see you can't do the same to
Zephyr (which is broken and not GCC/newlib).

Thanks,
Andrew

>
> Andy