Re: [Qemu-devel] [PATCH v5 4/8] linux-user: Split out preadv, pwritev, readv, writev, pread64, pwrite64

[Richard Henderson <richard.henderson@linaro.org>]

On 1/11/19 2:17 AM, Laurent Vivier wrote:
> On 19/12/2018 05:21, Richard Henderson wrote:
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>  linux-user/syscall-defs.h     |  14 ++++
>>  linux-user/syscall-file.inc.c | 124 ++++++++++++++++++++++++++++++++++
>>  linux-user/syscall.c          |  93 -------------------------
>>  linux-user/strace.list        |  18 -----
>>  4 files changed, 138 insertions(+), 111 deletions(-)
>>
> ...
>> diff --git a/linux-user/syscall-file.inc.c b/linux-user/syscall-file.inc.c
>> index 11e75044c1..410a763eee 100644
>> --- a/linux-user/syscall-file.inc.c
>> +++ b/linux-user/syscall-file.inc.c
>> @@ -315,6 +315,104 @@ SYSCALL_IMPL(openat)
> ...
>> +
>> +/*
>> + * Both preadv and pwritev merge args 4/5 into a 64-bit offset.
>> + * Moreover, the parts are *always* in little-endian order.
>> + */
>> +#if TARGET_ABI_BITS == 32
>> +SYSCALL_ARGS(preadv_pwritev)
>> +{
>> +    /* We have already assigned out[0-2].  */
>> +    abi_ulong lo = in[3], hi = in[4];
>> +    out[3] = ((hi << (TARGET_ABI_BITS - 1)) << 1) | lo;
>> +    return def;
>> +}
>> +#else
>> +#define args_preadv_pwritev NULL
>> +#endif
>> +
>> +/* Perform the inverse operation for the host.  */
>> +static inline void host_offset64_low_high(unsigned long *l, unsigned long *h,
>> +                                          uint64_t off)
>> +{
>> +    *l = off;
>> +    *h = (off >> (HOST_LONG_BITS - 1)) >> 1;
>> +}
> 
> 
> I have an error with preadv() on a 32bit target (powerpc, LTP test preadv02).
> 
> It works if I use:
> 
> static inline void host_offset64_low_high(unsigned long *hlow,
>                                           unsigned long *hhigh,
>                                           abi_ulong tlow,
>                                           abi_ulong thigh)
> {
>     uint64_t off = tlow |
>                    ((unsigned long long)thigh << TARGET_LONG_BITS / 2) <<
>                    TARGET_LONG_BITS / 2;
>     
>     *hlow = off;
>     *hhigh = (off >> HOST_LONG_BITS / 2) >> HOST_LONG_BITS / 2;
> }

This doesn't make any sense.  Where are "tlow" and "thigh" coming from?

I think the bug will be

 SYSCALL_ARGS(preadv_pwritev)
 {
     /* We have already assigned out[0-2].  */
     abi_ulong lo = in[3], hi = in[4];
-    out[3] = ((hi << (TARGET_ABI_BITS - 1)) << 1) | lo;
+    out[3] = (((uint64_t)hi << (TARGET_ABI_BITS - 1)) << 1) | lo;
     return def;
 }



r~