This is a PoC PHP 8 extension that demonstrates the observer API.
$ phpize \
&& ./configure \
--with-php-config=/path/to/php-config \
&& make
$ php -dextension=$(pwd)/modules/observer.so --ri=observerWhen INI setting observer.instrument=1, the observer extension will emit a message before and after every user land function call.
Execute via
$ /path/to/sapi/cli/php \
-d extension=$(pwd)/modules/observer.so \
-d observer.instrument=1 \
-r "function foo() {return 42;} var_dump(foo());"
[BEGIN foo()]
[END foo(): int]
int(42)