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Re: [Qemu-devel] [PATCH 2/2] slirp: Don't mark struct ipq or struct ipas
From: |
Daniel P . Berrangé |
Subject: |
Re: [Qemu-devel] [PATCH 2/2] slirp: Don't mark struct ipq or struct ipasfrag as packed |
Date: |
Tue, 22 Jan 2019 18:55:15 +0000 |
User-agent: |
Mutt/1.10.1 (2018-07-13) |
On Tue, Jan 22, 2019 at 06:18:22PM +0000, Peter Maydell wrote:
> There is no reason to mark the struct ipq and struct ipasfrag as
> packed: they are naturally aligned anyway, and are not representing
> any on-the-wire packet format. Indeed they vary in size depending on
> the size of pointers on the host system, because the 'struct qlink'
> members include 'void *' fields.
>
> Dropping the 'packed' annotation fixes clang -Waddress-of-packed-member
> warnings and probably lets the compiler generate better code too.
>
> The only thing we do care about in the layout of the struct is
> that the frag_link matches up with the ipf_link of the struct
> ipasfrag, as documented in the comment on that struct; assert
> at build time that this is the case.
>
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> slirp/ip.h | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/slirp/ip.h b/slirp/ip.h
> index 243b6c8b249..20614f3b53e 100644
> --- a/slirp/ip.h
> +++ b/slirp/ip.h
Just here there's a misleading comment
* size 28 bytes
that should be purged
> @@ -217,7 +217,7 @@ struct ipq {
> uint8_t ipq_p; /* protocol of this fragment */
> uint16_t ipq_id; /* sequence id for reassembly */
> struct in_addr ipq_src,ipq_dst;
> -} QEMU_PACKED;
> +};
>
> /*
> * Ip header, when holding a fragment.
> @@ -227,7 +227,10 @@ struct ipq {
> struct ipasfrag {
> struct qlink ipf_link;
> struct ip ipf_ip;
> -} QEMU_PACKED;
> +};
> +
> +QEMU_BUILD_BUG_ON(offsetof(struct ipq, frag_link) !=
> + offsetof(struct ipasfrag, ipf_link));
>
> #define ipf_off ipf_ip.ip_off
> #define ipf_tos ipf_ip.ip_tos
Regards,
Daniel
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