Awesome! Makes it even easier to spot and debug ARM bugs. Thanks Hannes
On Wed, Jan 29, 2014 at 7:42 PM, Jan de Mooij <jandemo...@gmail.com> wrote: > I just landed an ARM simulator for JIT code, imported from V8 (bug 959597 > [0]). > > This means if you build an x86 shell and pass --enable-arm-simulator > to configure, it will still compile an x86 shell but with the ARM JIT > backend for Baseline, Ion, Odin and YARR. When we enter JIT code, we > run it inside a simulator (interpreter) for ARM code. Note that this > only works with 32-bit builds (64-bit has a different Value format > etc). > > There are new JS_CODEGEN_* defines that you should use in most cases > for JIT backend stuff instead of JS_CPU_*. On real hardware there's no > difference but a simulator build will have JS_CPU_X86 and > JS_CODEGEN_ARM. > > Emulating an ARM processor may seem crazy and complicated, but the > simulator itself is < 3000 lines of code, most of it pretty > straight-forward and of course NPOTB (I'll try to get a Linux32 shell > build on TBPL so that we don't regress it). > > The code was imported from V8, with many changes to make it integrate > well with SpiderMonkey (style), mfbt etc. I added support for some > missing (float32) instructions, but other than that the code was very > stable and complete. It's also reasonably fast: an --enable-debug > --enable-optimize build can run jit-tests in 2-3 minutes on my laptop. > > The simulator is not useful for performance testing of course and is > not as reliable as real hardware, but for most changes it should be > sufficient. It also has some nice features like its own debugger so > that you can set breakpoints and disassemble code (I didn't import > V8's disassembler, instead we run llvm-mc), an icache checker and it > verifies JIT code does not modify callee-saved registers etc (this > caught a real bug, bug 964005 [1]). > > I hope this will make it easier for our JIT hackers and fuzzers to > improve/test our ARM backend. Thanks to V8 for the simulator code, to > Nicolas, Mike and Gerv for reviews and Douglas for many useful > suggestions and patches. > > Jan > > [0] https://bugzilla.mozilla.org/show_bug.cgi?id=959597 > [1] https://bugzilla.mozilla.org/show_bug.cgi?id=964005 > _______________________________________________ > dev-tech-js-engine-internals mailing list > dev-tech-js-engine-internals@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals > _______________________________________________ dev-tech-js-engine-internals mailing list dev-tech-js-engine-internals@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-tech-js-engine-internals
