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Re: [Qemu-devel] [PATCH] linux-user: correctly align types in thunking c
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] [PATCH] linux-user: correctly align types in thunking code |
Date: |
Fri, 11 May 2018 11:43:35 +0100 |
On 10 May 2018 at 21:59, Laurent Vivier <address@hidden> wrote:
> This is a follow up
> of patch:
>
> commit c2e3dee6e03527baf8698698cce76b1a3174969a
> Author: Laurent Vivier <address@hidden>
> Date: Sun Feb 13 23:37:34 2011 +0100
>
> linux-user: Define target alignment size
>
> In my case m68k aligns "int" on 2 not 4. You can check this with the
> following program:
>
> int main(void)
> {
> struct rtentry rt;
> printf("rt_pad1 %ld %zd\n", offsetof(struct rtentry, rt_pad1),
> sizeof(rt.rt_pad1));
> printf("rt_dst %ld %zd\n", offsetof(struct rtentry, rt_dst),
> sizeof(rt.rt_dst));
> printf("rt_gateway %ld %zd\n", offsetof(struct rtentry, rt_gateway),
> sizeof(rt.rt_gateway));
> printf("rt_genmask %ld %zd\n", offsetof(struct rtentry, rt_genmask),
> sizeof(rt.rt_genmask));
> printf("rt_flags %ld %zd\n", offsetof(struct rtentry, rt_flags),
> sizeof(rt.rt_flags));
> printf("rt_pad2 %ld %zd\n", offsetof(struct rtentry, rt_pad2),
> sizeof(rt.rt_pad2));
> printf("rt_pad3 %ld %zd\n", offsetof(struct rtentry, rt_pad3),
> sizeof(rt.rt_pad3));
> printf("rt_pad4 %ld %zd\n", offsetof(struct rtentry, rt_pad4),
> sizeof(rt.rt_pad4));
> printf("rt_metric %ld %zd\n", offsetof(struct rtentry, rt_metric),
> sizeof(rt.rt_metric));
> printf("rt_dev %ld %zd\n", offsetof(struct rtentry, rt_dev),
> sizeof(rt.rt_dev));
> printf("rt_mtu %ld %zd\n", offsetof(struct rtentry, rt_mtu),
> sizeof(rt.rt_mtu));
> printf("rt_window %ld %zd\n", offsetof(struct rtentry, rt_window),
> sizeof(rt.rt_window));
> printf("rt_irtt %ld %zd\n", offsetof(struct rtentry, rt_irtt),
> sizeof(rt.rt_irtt));
> }
>
> And result is :
>
> i386
>
> rt_pad1 0 4
> rt_dst 4 16
> rt_gateway 20 16
> rt_genmask 36 16
> rt_flags 52 2
> rt_pad2 54 2
> rt_pad3 56 4
> rt_pad4 62 2
> rt_metric 64 2
> rt_dev 68 4
> rt_mtu 72 4
> rt_window 76 4
> rt_irtt 80 2
>
> m68k
>
> rt_pad1 0 4
> rt_dst 4 16
> rt_gateway 20 16
> rt_genmask 36 16
> rt_flags 52 2
> rt_pad2 54 2
> rt_pad3 56 4
> rt_pad4 62 2
> rt_metric 64 2
> rt_dev 66 4
> rt_mtu 70 4
> rt_window 74 4
> rt_irtt 78 2
>
> This affects the "route" command :
>
> WITHOUT this patch:
>
> $ sudo route add -net default gw 10.0.3.1 window 1024 irtt 2 eth0
> $ netstat -nr
> Kernel IP routing table
> Destination Gateway Genmask Flags MSS Window irtt Iface
> 0.0.0.0 10.0.3.1 0.0.0.0 UG 0 67108866 32768
> eth0
> 10.0.3.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
>
> WITH this patch:
>
> $ sudo route add -net default gw 10.0.3.1 window 1024 irtt 2 eth0
> $ netstat -nr
> Kernel IP routing table
> Destination Gateway Genmask Flags MSS Window irtt Iface
> 0.0.0.0 10.0.3.1 0.0.0.0 UG 0 1024 2 eth0
> 10.0.3.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
>
> Signed-off-by: Laurent Vivier <address@hidden>
> ---
> include/exec/user/thunk.h | 22 +++++++++++++++++-----
> 1 file changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/include/exec/user/thunk.h b/include/exec/user/thunk.h
> index f19ef4b230..8f55b233b3 100644
> --- a/include/exec/user/thunk.h
> +++ b/include/exec/user/thunk.h
> @@ -149,20 +149,32 @@ static inline int thunk_type_align(const argtype
> *type_ptr, int is_host)
> case TYPE_CHAR:
> return 1;
> case TYPE_SHORT:
> - return 2;
> + if (is_host) {
> + return __alignof__(short);
> + } else {
> + return ABI_SHORT_ALIGNMENT;
> + }
> case TYPE_INT:
> - return 4;
> + if (is_host) {
> + return __alignof__(int);
> + } else {
> + return ABI_INT_ALIGNMENT;
> + }
> case TYPE_LONGLONG:
> case TYPE_ULONGLONG:
> - return 8;
> + if (is_host) {
> + return __alignof__(long long);
> + } else {
> + return ABI_LLONG_ALIGNMENT;
> + }
> case TYPE_LONG:
> case TYPE_ULONG:
> case TYPE_PTRVOID:
> case TYPE_PTR:
> if (is_host) {
> - return sizeof(void *);
> + return __alignof__(long);
> } else {
> - return TARGET_ABI_BITS / 8;
> + return ABI_LONG_ALIGNMENT;
> }
> break;
> case TYPE_OLDDEVT:
> --
This definitely looks like the right thing. As well as m68k,
this will also affect sh4 and i386 (where long long is 4
aligned but we were saying it should be 8 aligned) -- I wonder
if that fixes any bugs...
Reviewed-by: Peter Maydell <address@hidden>
thanks
-- PMM