guberti opened a new issue, #13193:
URL: https://github.com/apache/tvm/issues/13193
Currently, we use the Corstone300 simulator to test our microTVM schedules.
The simulator is configured to model the Cortex-M7. However, we do not do any
fault handling, so when an exception (e.g. `UsageFault`) is thrown, the
simulator (and test) hang forever.
To prevent this, it would be nice to configure the simulator to report an
exception and terminate when a fault is thrown. Note that this issue is _not_
with the Corstone300 simulator (a real Cortex-M7 would also hang if configured
the same way), but rather with our usage of it.
----
### Long explanation
I recently spent three days tracking down a strange bug I encountered while
writing microTVM schedules for Arm Cortex-M. When I called the `tensorize`
function using the following function, the code ran to completion as expected
using the Corstone300 simulator:
```c
int func(int *output, int *tensor, int *kernel) {
int sum_0;
int a = tensor[0];
int b = tensor[1];
int c = kernel[0];
sum_0 = __builtin_arm_smlad(a, c, sum_0);
sum_0 = b + kernel[1] + sum_0;
output[0] = sum_0;
return 0;
}
```
However, tensorizing with the following code and running it in the
Corstone300 simulator made it hang forever without throwing an error:
```c
int func(int *output, int *tensor, int *kernel) {
int sum_0;
int a = tensor[0];
int b = tensor[1];
int c = kernel[0];
int d = kernel[1];
sum_0 = __builtin_arm_smlad(a, c, sum_0);
sum_0 = b + d + sum_0;
output[0] = sum_0;
return 0;
}
```
After some debugging, it turns out that when these chunks of code are
compiled with Arm GCC, different memory loading instructions are used
(specifically, the load doubleword instruction is used to load kernel memory in
the failing case, while two single word insturctions are used in the working
case).
As described in section 3.3.5 of the Cortex-M7 programmer's manual, this is
intended behavior - some, but not all memory instructions throw `UsageFault`
when an unaligned access is performed.
It would have saved me a ton of debugging time if the Corstone300 simulator
(and our tests) reported when an exception was thrown and failed the test
(instead of looping forever). Would love to see this change added!
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
