From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <stephen@networkplumber.org>
Subject: Re: [PATCH] eal: remove variable length array
Date: Fri, 14 Dec 2018 10:36:03 -0800
Message-ID: <20181214103603.59336e0e@xeon-e3>
References: <20181214163827.9403-1-jeffrey.b.shaw@intel.com>
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To: Jeff Shaw <jeffrey.b.shaw@intel.com>
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On Fri, 14 Dec 2018 08:38:27 -0800
Jeff Shaw <jeffrey.b.shaw@intel.com> wrote:

> Compilers that do not support the C11 standard, or do not implement
> gcc extensions, may not support variable length arrays.
>=20
> The code prior to this commit produced the following warning when
> compiled with "-Wvla -std=3Dc90".
>=20
>   warning: ISO C90 forbids variable length array =E2=80=98array=E2=80=99 =
[-Wvla]
>=20
> This commit removes the variable length array from the PMD debug
> trace function by allocating memory dynamically on the stack using
> alloca().
>=20
> Signed-off-by: Jeff Shaw <jeffrey.b.shaw@intel.com>
> ---
>  lib/librte_eal/common/include/rte_dev.h | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
>=20
> diff --git a/lib/librte_eal/common/include/rte_dev.h b/lib/librte_eal/com=
mon/include/rte_dev.h
> index a9724dc91..af772872b 100644
> --- a/lib/librte_eal/common/include/rte_dev.h
> +++ b/lib/librte_eal/common/include/rte_dev.h
> @@ -47,22 +47,21 @@ __attribute__((format(printf, 2, 0)))
>  static inline void
>  rte_pmd_debug_trace(const char *func_name, const char *fmt, ...)
>  {
> +	char *buffer;
> +	int buf_len;
>  	va_list ap;
> =20
>  	va_start(ap, fmt);
> +	buf_len =3D vsnprintf(NULL, 0, fmt, ap) + 1;
> +	va_end(ap);
> =20
> -	{
> -		char buffer[vsnprintf(NULL, 0, fmt, ap) + 1];
> +	buffer =3D (char *)alloca(buf_len);

alloca is void * so cast is not necessary.

You might be able to skip the buffering step entirely by using rte_log
a little more creatively, see how other logging works.

But to go further since rte_pmd_debug_trace is not used anywhere in
current code base in DPDK, it should just be removed.