Am 5/28/2024 um 7:58 PM schrieb Boqun Feng:
On Mon, May 27, 2024 at 03:40:13PM +0200, Jonas Oberhauser wrote:
Am 5/27/2024 um 3:28 PM schrieb Andrea Parri:
+ | smp_store_mb | W[once] ->po F[mb] |
I expect this one to be hard-coded in herd7 source code, but I cannot find
it. Can you give me a pointer?
smp_store_mb() is currently mapped to { __store{once}(X,V); __fence{mb}; } in
the .def file, so it's semantically equivalent to "WRITE_ONCE(); smp_mb();".
By the way, I experimented a little with these kind of mappings to see if we
can just explicitly encode the mapping there. E.g., I had an idea to use
{ __fence{mb-successful-rmw}; __cmpxchg{once}...;
__fence{mb-successful-rmw}; }
for defining (almost) the current mapping of cmpxchg explicitly.
But none of the changes I made were accepted by herd7.
Do you know how the syntax works?
This may not be trivial. Note that cmpxchg() is an expression (it has a
value), so in .def, we want to define it as an expression. However, the
C-like multiple-statement expression is not supported by herd parser, in
other words we want:
{
__fence{mb-successful-rmw};
int tmp = __cmpxchg{once}(...);
__fence{mb-successful-rmw};
tmp;
}
Oh, you're right. Then probably the rule I was violating is that
value-returning macros can not be defined with {} at all.
Given herd's other syntactic limitations, perhaps the best way would be
to introduce these macros as
x = cmpxchg(...) {
__fence{mb-successful-rmw};
x = __cmpxchg{once}(...);
__fence{mb-successful-rmw};
}
since I think x = M(...) is the only way we are allowed to use these
macros anyways.
