Re: [Qemu-devel] [PULL] slirp: Fix issues with -mms-bitfields

[TeLeMan]

On Sun, Aug 21, 2011 at 04:00, Stefan Weil <address@hidden> wrote:
> Am 15.08.2011 08:39, schrieb Jan Kiszka:
>>
>> The following changes since commit
>> 3b6ffe50300f13240e1b46420ad05da1116df410:
>>
>> hw/scsi-bus.c: Fix use of uninitialised variable (2011-08-14 19:34:25
>> +0000)
>>
>> are available in the git repository at:
>> git://git.kiszka.org/qemu.git queues/slirp
>>
>> Jan Kiszka (1):
>> slirp: Fix bit field types in IP header structs
>>
>> slirp/ip.h | 8 ++++----
>> slirp/tcp.h | 4 ++--
>> 2 files changed, 6 insertions(+), 6 deletions(-)
>>
>> ---
>>
>> slirp: Fix bit field types in IP header structs
>>
>> -mms-bitfields prevents that the bitfields in current IP header structs
>> are packed into a single byte as it is required. Fix this by using
>> uint8_t as backing type.
>>
>> Signed-off-by: Jan Kiszka <address@hidden>
>> ---
>> slirp/ip.h | 8 ++++----
>> slirp/tcp.h | 4 ++--
>> 2 files changed, 6 insertions(+), 6 deletions(-)
>>
>> diff --git a/slirp/ip.h b/slirp/ip.h
>> index 48ea38e..72dbe9a 100644
>> --- a/slirp/ip.h
>> +++ b/slirp/ip.h
>> @@ -74,10 +74,10 @@ typedef uint32_t n_long; /* long as received from the
>> net */
>> */
>> struct ip {
>> #ifdef HOST_WORDS_BIGENDIAN
>> - u_int ip_v:4, /* version */
>> + uint8_t ip_v:4, /* version */
>> ip_hl:4; /* header length */
>> #else
>> - u_int ip_hl:4, /* header length */
>> + uint8_t ip_hl:4, /* header length */
>> ip_v:4; /* version */
>> #endif
>> uint8_t ip_tos; /* type of service */
>> @@ -140,10 +140,10 @@ struct ip_timestamp {
>> uint8_t ipt_len; /* size of structure (variable) */
>> uint8_t ipt_ptr; /* index of current entry */
>> #ifdef HOST_WORDS_BIGENDIAN
>> - u_int ipt_oflw:4, /* overflow counter */
>> + uint8_t ipt_oflw:4, /* overflow counter */
>> ipt_flg:4; /* flags, see below */
>> #else
>> - u_int ipt_flg:4, /* flags, see below */
>> + uint8_t ipt_flg:4, /* flags, see below */
>> ipt_oflw:4; /* overflow counter */
>> #endif
>> union ipt_timestamp {
>> diff --git a/slirp/tcp.h b/slirp/tcp.h
>> index 9d06836..b3817cb 100644
>> --- a/slirp/tcp.h
>> +++ b/slirp/tcp.h
>> @@ -51,10 +51,10 @@ struct tcphdr {
>> tcp_seq th_seq; /* sequence number */
>> tcp_seq th_ack; /* acknowledgement number */
>> #ifdef HOST_WORDS_BIGENDIAN
>> - u_int th_off:4, /* data offset */
>> + uint8_t th_off:4, /* data offset */
>> th_x2:4; /* (unused) */
>> #else
>> - u_int th_x2:4, /* (unused) */
>> + uint8_t th_x2:4, /* (unused) */
>> th_off:4; /* data offset */
>> #endif
>> uint8_t th_flags;
>
> Tested-by: Stefan Weil <address@hidden>
>
slirp is still broken on my mingw32. I used "#progma
pack(push,1)/#progma pack(pop)" to resolve this issue.

> There remain some issues with other packed structs
> which are obviously no longer packed with -mms-bitfields,
> for example those from bt.h, but slirp looks good with
> this patch.
>
> I used pahole (thanks Blue Swirl for this hint) and codiff
> to investigate and compare the structs with and without
> -mms-bitfields:
>
> * create qemu.exe (or any binary which you want)
> * convert it to elf format using objcopy -Oelf32-i386
>  (or the cross variant)
> * apply pahole -a to the resulting elf file
>  (without -a some structs are missing)
>
> Cheers,
> Stefan W.
>
>
>