linux-kernel - Re: [PATCH v2 3/7] selftests/nolibc: fix up compile warning with glibc on x86

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Message-Id: <20230529131536.80183-1-falcon@tinylab.org>
Date:   Mon, 29 May 2023 21:15:36 +0800
From:   Zhangjin Wu <falcon@...ylab.org>
To:     w@....eu
Cc:     arnd@...db.de, falcon@...ylab.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-riscv@...ts.infradead.org,
        thomas@...ch.de
Subject: Re: [PATCH v2 3/7] selftests/nolibc: fix up compile warning with glibc on x86_64

> On Mon, May 29, 2023 at 09:00:01PM +0800, Zhangjin Wu wrote:
> > Compiling nolibc-test.c with gcc on x86_64 got such warning:
> > 
> > tools/testing/selftests/nolibc/nolibc-test.c: In function 'expect_eq':
> > tools/testing/selftests/nolibc/nolibc-test.c:177:24: warning: format '%lld' expects argument of type 'long long int', but argument 2 has type 'uint64_t' {aka 'long unsigned int'} [-Wformat=]
> >   177 |  llen += printf(" = %lld ", expr);
> >       |                     ~~~^    ~~~~
> >       |                        |    |
> >       |                        |    uint64_t {aka long unsigned int}
> >       |                        long long int
> >       |                     %ld
> > 
> > It because that glibc defines uint64_t as "unsigned long int" when word
> > size (means sizeof(long)) is 64bit (see include/bits/types.h), but
> > nolibc directly use the 64bit "unsigned long long" (see
> > tools/include/nolibc/stdint.h), which is simpler, seems kernel uses it
> > too (include/uapi/asm-generic/int-ll64.h).
> > 
> > It is able to do like glibc, defining __WORDSIZE for all of platforms
> > and using "unsigned long int" to define uint64_t when __WORDSIZE is
> > 64bits, but here uses a simpler solution: nolibc always requires %lld to
> > match "unsigned long long", for others, only require %lld when word size
> > is 32bit.
> > 
> > Signed-off-by: Zhangjin Wu <falcon@...ylab.org>
> > ---
> >  tools/testing/selftests/nolibc/nolibc-test.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
> > index d417ca5d976f..7f9b716fd9b1 100644
> > --- a/tools/testing/selftests/nolibc/nolibc-test.c
> > +++ b/tools/testing/selftests/nolibc/nolibc-test.c
> > @@ -174,7 +174,11 @@ static int expect_eq(uint64_t expr, int llen, uint64_t val)
> >  {
> >  	int ret = !(expr == val);
> >  
> > +#if __SIZEOF_LONG__ == 4 || defined(NOLIBC)
> >  	llen += printf(" = %lld ", expr);
> > +#else
> > +	llen += printf(" = %ld ", expr);
> > +#endif
> >  	pad_spc(llen, 64, ret ? "[FAIL]\n" : " [OK]\n");
> >  	return ret;
> >  }
> 
> Please don't proceed like this. There's much easier to do here for a printf,
> just cast the expression to the type printf expects:
> 
> -  	llen += printf(" = %lld ", expr);
> +  	llen += printf(" = %lld ", (long long)expr);

Yes, this conversion is better, my method make things more complex ;-)

Thanks,
Zhangjin

> 
> Willy