24.8.2. m5ops instructions

There are few different possible instructions that can be used to implement identical m5ops:

All of those those methods are exposed through the gem5 m5 executable in-tree executable. You can select which method to use when calling the executable, e.g.:

m5 exit
# Same as the above.
m5 --inst exit
# The address is mandatory if not configured at build time.
m5 --addr 0x10010000 exit
m5 --semi exit

To make things simpler to understand, you can play around with our own minimized educational m5 subset:

The instructions used by ./c/m5ops.out are present in lkmc/m5ops.h in a very simple to understand and reuse inline assembly form.

To use that file, first rebuild m5ops.out with the m5ops instructions enabled and install it on the root filesystem:

./build-userland \
  --arch aarch64 \
  --force-rebuild \
  userland/c/m5ops.c \
;
./build-buildroot --arch aarch64

We don’t enable -DLKMC_M5OPS_ENABLE=1 by default on userland executables because we try to use a single image for both gem5, QEMU and native, and those instructions would break the latter two. We enable it in the Baremetal setup by default since we already have different images for QEMU and gem5 there.

Then, from inside gem5 Buildroot setup, test it out with:

# checkpoint
./c/m5ops.out c

# dumpstats
./c/m5ops.out d

# exit
./c/m5ops.out e

# dump resetstats
./c/m5ops.out r

In theory, the cleanest way to add m5ops to your benchmarks would be to do exactly what the m5 tool does:

However, I think it is usually not worth the trouble of hacking up the build system of the benchmark to do this, and I recommend just hardcoding in a few raw instructions here and there, and managing it with version control + sed.

Bibliography:

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