Re: [Qemu-devel] [PATCH] slirp: Gcc 9 -O3 fix

[Samuel Thibault <samuel.thibault@gnu.org>]

Hello,

Dr. David Alan Gilbert (git), le ven. 05 avril 2019 19:46:48 +0100, a ecrit:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Gcc 9 needs some convincing that sopreprbuf really is going to fill
> in iov in the call from soreadbuf, even though the failure case
> shouldn't happen; so swing the check around initialising the fields.

While I can understand that setting iov[0].iov_len may help a compiler,
I don't see why moving if (len <= 0) return 0; down?

> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  slirp/src/socket.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/slirp/src/socket.c b/slirp/src/socket.c
> index 4a3c935e25..4a2222a95f 100644
> --- a/slirp/src/socket.c
> +++ b/slirp/src/socket.c
> @@ -113,12 +113,14 @@ size_t sopreprbuf(struct socket *so, struct iovec *iov, int *np)
>  	DEBUG_CALL("sopreprbuf");
>  	DEBUG_ARG("so = %p", so);
>  
> -	if (len <= 0)
> -		return 0;
> -
>  	iov[0].iov_base = sb->sb_wptr;
> +        iov[0].iov_len = 0;
>          iov[1].iov_base = NULL;
>          iov[1].iov_len = 0;
> +
> +	if (len <= 0)
> +		return 0;
> +
>  	if (sb->sb_wptr < sb->sb_rptr) {
>  		iov[0].iov_len = sb->sb_rptr - sb->sb_wptr;
>  		/* Should never succeed, but... */
> -- 
> 2.21.0
> 

-- 
Samuel
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