Previous linker versions had inserted some zero padding bytes
between the ELF headers and the first section, but LLD 14 does
not anymore.
Hard-coding the offset of the first section in ksupport.elf
manually isn't ideal; we should probably parse the ELF program
headers instead when first setting up the kernel CPU.
Receiving an empty string in an RPC call currently panics.
When `length` is zero, a call to the `alloc` function (as implemented in `artiq/firmware/runtime/session.rs`) returns a null pointer. Constructing a `CMutSlice` from a null pointer panics.
A `CMutSlice` consists of a pointer and the length. Rust's documentation of the `core::ptr` module states: "The canonical way to obtain a pointer that is valid for zero-sized accesses is `NonNull::dangling`."
This commits adds a check for the length of a string received in an RPC call. Only for lengths greater than zero a memory allocation is performed. For zero-length strings, a dangling pointer is used.
Test plan:
Invoke the following experiment, which returns an empty string over RPC:
```
class ReturnEmptyString(artiq.experiment.EnvExperiment):
def build(self):
self.core: Core = self.get_device("core")
@kernel
def run(self):
x = self.do_rpc()
print(x)
@rpc
def do_rpc(self) -> TStr:
return ""
```
Signed-off-by: Sven Over (Oxford Ionics) <sven.over@oxionics.com>
Also factors out duplicate code for (de)serializing
elements of lists and ndarrays, and replaces the rounding
calculations by the well-known, much faster power-of-two-only
bit-twiddling version.
GitHub: Fixes#1934.
Ported from:
M-Labs/artiq-zynq#162
This includes new API for exception handling, some refactoring to avoid
code duplication for exception structures, and modified protocols to
send nested exceptions and avoid string allocation.