Re: [PATCH] exynos4210_gic: Suppress gcc9 format-truncation warnings - Philippe Mathieu-Daudé

From: "Philippe Mathieu-Daudé" <philmd@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>,
	i.mitsyanko@gmail.com, peter.maydell@linaro.org,
	Eric Blake <eblake@redhat.com>
Cc: qemu-arm@nongnu.org, qemu-devel@nongnu.org
Subject: Re: [PATCH] exynos4210_gic: Suppress gcc9 format-truncation warnings
Date: Fri, 4 Oct 2019 11:39:23 +0200	[thread overview]
Message-ID: <8a33744a-9ac5-4359-62d0-ccd9c9c43676@redhat.com> (raw)
In-Reply-To: <20191004025509.3012-1-david@gibson.dropbear.id.au>

On 10/4/19 4:55 AM, David Gibson wrote:
> exynos4210_gic_realize() prints the number of cpus into some temporary
> buffers, but it only allows 3 bytes space for it.  That's plenty - I'm
> pretty sure that existing machines will only ever set this value to 2
> (EXYNOS4210_NCPUS).  But the compiler can't really be expected to figure
> that out.
> 
> Some[*] gcc9 versions therefore emit -Wformat-truncation warnings.  Fix
> that by allowing more space in the temporary buffers - these are on stack
> very briefly before being essentially strdup()ed inside the memory region
> code, so there's not much cost to doing so.
> 
> [*] The bizarre thing here, is that I've long gotten these warnings
> compiling in a 32-bit x86 container as host - Fedora 30 with
> gcc-9.2.1-1.fc30.i686 - but it compiles just fine on my normal x86_64 host
> - Fedora 30 with and gcc-9.2.1-1.fc30.x86_64.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>   hw/intc/exynos4210_gic.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/intc/exynos4210_gic.c b/hw/intc/exynos4210_gic.c
> index a1b699b6ba..2e5e47f9ec 100644
> --- a/hw/intc/exynos4210_gic.c
> +++ b/hw/intc/exynos4210_gic.c
> @@ -290,8 +290,8 @@ static void exynos4210_gic_realize(DeviceState *dev, Error **errp)
>       SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
>       const char cpu_prefix[] = "exynos4210-gic-alias_cpu";
>       const char dist_prefix[] = "exynos4210-gic-alias_dist";
> -    char cpu_alias_name[sizeof(cpu_prefix) + 3];
> -    char dist_alias_name[sizeof(cpu_prefix) + 3];
> +    char cpu_alias_name[sizeof(cpu_prefix) + 10];
> +    char dist_alias_name[sizeof(cpu_prefix) + 10];

Hmm magic again... So GCC provides a new warning with no helpful 
definitions about how to clean this :(

We already have:
#define UUID_FMT_LEN 36

What about adding/using UINT32_FMT_LEN?

>       SysBusDevice *gicbusdev;
>       uint32_t i;
>   
> 