On 2020/1/7 6:00, Jim Wilson wrote:
On 1/2/20 7:33 PM, LIU Zhiwei wrote:
Until v0.7.1 specification, vector status is still not defined for
mstatus.
The v0.8 spec does define a VS bit in mstatus.
Yes, I will also support v0.8 spec after the v0.7.1 spec.
@@ -107,11 +112,6 @@ static int pmp(CPURISCVState *env, int csrno)
/* User Floating-Point CSRs */
static int read_fflags(CPURISCVState *env, int csrno, target_ulong
*val)
{
-#if !defined(CONFIG_USER_ONLY)
- if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
- return -1;
- }
-#endif
*val = riscv_cpu_get_fflags(env);
return 0;
}
This allows reads of fflags when it doesn't exist, and hence does not
make much sense. Instead of removing the code, you should add a check
for the vector extension, since the vector extension requires that
fcsr exist even if the base architecture doesn't include FP support.
Ideally this should use the VS bit, but if you don't have it then you
can just check to see if the vector extension was enabled as a command
line option.
I' sorry that there is some ambiguous here. The reason to remove these
code is that they are redundant, and has nothing to do with the vector
extension. I just delete them by hand.
As you can see, all float csr has a predicate function.
static int fs(CPURISCVState *env, int csrno)
{
#if !defined(CONFIG_USER_ONLY)
if (!env->debugger && !(env->mstatus & MSTATUS_FS)) {
return -1;
}
#endif
return 0;
}
The read or write function must be called after the predicate return 0.
So no need to check (!env->debugger && !(env->mstatus & MSTATUS_FS) again.
While the vector spec says that fcsr must exist, it doesn't specify
that the FP fields in fcsr are necessarily readable or writable when
there is no FP. It also doesn't specify whether the other FP related
shadows of fcsr exist, like fflags. This appears to have been left
unspecified. I don't think that you should be making fflags reads and
writes work for a target with vector but without float. I think it
would make more sense to have fcsr behave 3 different ways depending
on whether we have only F, only V, or both F and V. And then we can
support reads and writes of only the valid fields.
Thanks. Maybe I should just only loose the check condition for fcsr.
Best Regards,
Zhiwei
Jim
