Add steps for testing the jit with arm64 architecture in docker

Author: TysonAndre

ext/opcache/jit/Dockerfile.arm64.example

@@ -0,0 +1,15 @@
+# Force this to build with arm64 even when the host architecture is different.
+# This requires that cross-compilation support be enabled with the steps in https://www.docker.com/blog/faster-multi-platform-builds-dockerfile-cross-compilation-guide/
+FROM --platform=arm64 ubuntu:20.04
+RUN apt-get update -y
+# DEBIAN_FRONTEND=noninteractive is needed to stop the tzdata installation from hanging.
+ENV DEBIAN_FRONTEND=noninteractive
+RUN apt-get install -y tzdata
+RUN apt-get install -y pkg-config build-essential autoconf bison re2c \
+                       libxml2-dev libsqlite3-dev
+
+ADD . /php-src/
+WORKDIR /php-src
+RUN ./buildconf
+# Compile a minimal debug build. --enable-debug adds runtime assertions and is slower than regular builds.
+RUN ./configure --enable-debug --disable-all --enable-opcache && make clean && make -j$(nproc)

ext/opcache/jit/README.md

@@ -114,3 +114,26 @@ make -j$(nproc)
 #### Running tests of the JIT on 32-bit builds
 
 See the section "Running tests of the JIT".
+
+### Testing the jit with arm64 on x86 computers
+
+https://www.docker.com/blog/faster-multi-platform-builds-dockerfile-cross-compilation-guide/
+may be useful for local development.
+
+Note that this is slower than compiling and testing natively.
+
+```
+# After following steps in https://www.docker.com/blog/faster-multi-platform-builds-dockerfile-cross-compilation-guide/
+cp .gitignore .dockerignore
+echo .git >> .dockerignore
+
+docker build --network=host -t php-src-arm64-example -f ext/opcache/jit/Dockerfile.arm64.example .
+docker run -it --rm php-src-arm64-example
+```
+
+Then, the docker image can be used to run tests with `make test`.
+For example, to test `ext/opcache` in parallel with the tracing JIT enabled:
+
+```
+docker run -it php-src-arms-example make test TESTS="-d opcache.jit_buffer_size=16M -d opcache.enable=1 -d opcache.enable_cli=1 -d opcache.protect_memory=1 -d opcache.jit=tracing --repeat 2 --show-diff -j$(nproc) ext/opcache"
+```