Hi Internals,
Currently PHP JIT only supports x86 and x86_64 CPUs on POSIX platforms and Windows.[1] With the
prevalence of PHP language and the notable
growth of ARM-based servers market, we believe JIT/arm64 would be in urgent need in the near future.
As an initial effort to enable PHP JIT/arm64, we (ARM) have supported the basic functionality, and
(partially) implemented the compilation for
several opcodes. Currently a number of simple JIT test cases from PHP test framework can be passed
on ARM-based machine. There are still a lot
of missing parts, such as hot loops, class/object/array operations, exception handling, etc, and we
will continue working on them.
We would like to share our work with you (See the draft patch https://github.com/shqking/php-src/commit/6aaf935).
Any feedback would be greatly appreciated, and please let we know if anyone wants to contribute to
this port.
Thanks,
Hao SUN
Email: hao.sun@arm.com<mailto:hao.sun@arm.com>
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Main updates:
1. JIT backend for AArch64
A new alternative, i.e. AArch64, was added while building PHP JIT. See the updates in the following
files. Note that we adopt capstone[2] for
disassembly on AArch64.
build/Makefile.global
ext/opcache/config.m4
ext/opcache/config.w32
ext/opcache/jit/Makefile.frag
ext/opcache/jit/zend_jit.c
ext/opcache/jit/zend_jit_vm_helpers.c
ext/opcache/jit/zend_jit_disasm_arm64.c
ext/opcache/jit/zend_jit_gdb.c
ext/opcache/jit/zend_jit_perf_dump.c
2. DynASM library
PHP JIT uses DynASM[3] (developed for LuaJIT project) to generate native code on the fly. We added
two useful but missing features, global label
reference and dynamic register names, into DynASM/arm64. See the updates in files:
ext/opcache/jit/dynasm/dasm_arm64.h
ext/opcache/jit/dynasm/dasm_arm64.lua
Note that these two features are available on DynASM/x86.
3. compilation for opcodes on AArch64
Our main work falls in the following files.
ext/opcache/jit/zend_jit_arm64.h
ext/opcache/jit/zend_jit_arm64.dasc
ext/opcache/jit/zend_jit_internal.h
Zend/zend_vm_opcodes.h
* AArch64 registers and calling conventions are defined.
* Instruction cache must be flushed for the JIT-ed code on AArch64. See macro JIT_CACHE_FLUSH in
file 'zend_jit_internal.h'.
* We have (partially) implemented the compilation for several opcodes, mainly for the function-based
JIT (with opcache.jit=1203). Currently,
test cases involving internal function call (e.g. var_dump), additions with integers/floating-point
numbers, integer overflows and simple
exception, can be supported now. See our newly added test cases under directory
'ext/opcache/tests/jit/arm64/'.
* Trace counter stubs are implemented for tracing JIT (with
opcache.jit=1255). See zend_jit_hybrid_trace_counter_stub() and zend_jit_hybrid_hot_trace_stub() in
file 'zend_jit_arm64.dasc'. Hot
functions can be recognized and compiled successfully. See the test case
'hot_func_002.phpt'.
How to build and test:
Our local test environment is an ARM-based server with Ubuntu 20.04 and GCC-10. We follow the
building commands as shown in the readme file [4].
Note that library capstone should be installed in advance.
We suggest running the JIT test cases using the following command. In our local test, 59 out of all
128 cases can be passed currently.
$ make test TESTS='-d opcache.jit=1203 ext/opcache/tests/jit/'
[1] https://wiki.php.net/rfc/jit
[2] https://www.capstone-engine.org/
[3] https://luajit.org/dynasm.html
[4] https://github.com/php/php-src