Dan Horák wrote:
please, could some low-level s390 guru take a look at the atomic
primitives in libatomic_ops ? Are they correct, any improvements
possible, ...? I am trying to recommend this library as a universal
source of atomic primitives for user space instead of developing a
limited set for each project individually (and usually only for major
archs like i386/x86_64).
specifically the src/atomic_ops/sysdeps/gcc/s390.h file
I'm not sure the s390x version is correct.
Apparently (but I could be wrong), AO_t is pretty much guaranteed to be
a host architecture 'int'.
On s390x, an int is a 32 bit entity.
On s390x, the s390.h code performs a "CSG" - which acts upon 64 bit
registers, and the target memory address will be seen as a container for
a 64 bit value (basically storing a 64 bit value in a 32 bit container -
thus overshooting by 4 bytes).
The Compare and Swap instructions are as follow :
s390/32 bit : CS
s390x/32 bit : CS
s390/64 bit : CDS
s390x/64 bit : CSG or CDS
s390/128 bit : N/A
s390/128 bit : CDSG
See z/Architecture Principles of Operation - SA22-7832-07 (aka
dz9zr007.pdf) Page 7-66