On 07.07.2017 15:46, Christian Borntraeger wrote:
> On 07/07/2017 12:26 PM, Thomas Huth wrote:
>> The upcoming netboot code will use the libc from SLOF. To be able
>> to still use s390-ccw.h there, the libc related functions in this
>> header have to be moved to a different location.
>> And while we're at it, remove the duplicate memcpy() function from
>> sclp.c.
>>
>> Signed-off-by: Thomas Huth <th...@redhat.com>
>
> one suggestion below, but
>
> Reviewed-by: Christian Borntraeger <borntrae...@de.ibm.com>
>
> for change and no change
>
> [...]
>> +static inline void *memcpy(void *s1, const void *s2, size_t n)
>> +{
>> + uint8_t *p1 = s1;
>> + const uint8_t *p2 = s2;
>> +
>> + while (n--) {
>> + p1[n] = p2[n];
>> + }
>> + return s1;
>> +}
>
> Not that it matters, and no idea if moving forward like in the for loop below
> might allow gcc to generate better code, but a for loop like below will be
> the
> same direction as the MVC instruction. Can you double check if this generates
> better code?
At least with my compiler version (old 4.8.1), the code looks pretty
similar. Backward loop:
1d8: a7 19 04 d1 lghi %r1,1233
1dc: e3 40 50 00 00 04 lg %r4,0(%r5)
1e2: e3 30 70 00 00 04 lg %r3,0(%r7)
1e8: a7 29 04 d2 lghi %r2,1234
1ec: 43 01 30 00 ic %r0,0(%r1,%r3)
1f0: a7 1b ff ff aghi %r1,-1
1f4: 42 01 40 01 stc %r0,1(%r1,%r4)
1f8: a7 27 ff fa brctg %r2,1ec <main+0x1ec>
Forward loop:
238: a7 19 00 00 lghi %r1,0
23c: e3 40 50 00 00 04 lg %r4,0(%r5)
242: e3 30 70 00 00 04 lg %r3,0(%r7)
248: a7 29 04 d2 lghi %r2,1234
24c: 43 01 30 00 ic %r0,0(%r1,%r3)
250: 42 01 40 00 stc %r0,0(%r1,%r4)
254: a7 1b 00 01 aghi %r1,1
258: a7 27 ff fa brctg %r2,24c <main+0x24c>
But I can switch to the for-loop version in my patch anyway, if you
prefer that.
Thomas
