reason:
svc call may trigger hardfault
Background
The origin of this issue is our desire to eliminate the function of storing
"regs" in g_current_regs and instead utilize (*running_task)->xcp.regs for storage.
The benefits of this approach include faster storage speed and
avoiding multiple accesses to g_current_regs during context switching,
thus ensuring that whether returning from an interrupt or an exception,
we consistently use this_task()->xcp.regs
Issue Encountered
However, when storing registers, we must ensure that (running_task)->xcp.regs is invalid
so that it can be safely overwritten.
According to the existing logic, the only scenario where (running_task)->xcp.regs
is valid is during restore_context. We must accurately identify this scenario.
Initially, we used the condition (running_task)==NULL for this purpose, but we deemed
this approach unsatisfactory as it did not align well with the actual logic.
(running_task) should not be NULL. Consequently, we adopted other arch-specific methods for judgment,
but due to special logic in some arch, the judgment was not accurate, leading to this issue.
Solution:
For armv6-m, we haven't found a more suitable solution, so we are sticking with (*running_task)==NULL.
For armv7-m/armv8-m, by removing support for primask, we can achieve accurate judgment.
PRIMASK is a design in armv6-m, that's why arm introduce BASEPRI from armv7-m.
It's wrong to provide this option for armv7-m/armv8-m arch.
Signed-off-by: hujun5 <hujun5@xiaomi.com>
