840281 - OdinMonkey: x86 support

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Luke Wagner [:luke]]

The primary challenge here is that we can't use a global pinned register for the typed array, as we do on x64.  We also can't use the x64 "reserve 4GB so that out-of-bounds access never touches valid memory" trick because of the limited address space.  Baking in a constant isn't great because it means we'd have to clone/patch a module each time it was linked to a new global and it doesn't provide an efficient way to detect out-of-bounds (branching is measurably slow).  Instead, we'll use the x86 segmentation feature (like NaCL).  The main challenge is adding an entry to the LDT but, fortunately, NaCL is open-source:
  http://src.chromium.org/native_client/trunk/src/native_client/src/trusted/service_runtime/win/nacl_ldt.c

Comment 1

[Luke Wagner [:luke]]

Update: got the segment register scheme working on 32-bit OSX and passing the out-of-bounds torture tests:
http://hg.mozilla.org/users/lwagner_mozilla.com/odinmonkey/rev/57df8e4c52cc

Now just need to add the analogous calls for other Win/Linux, fill in the missing Asm(Load|Store)* nodes and the exit stubs.

Comment 2

[Luke Wagner [:luke]]

As of:
http://hg.mozilla.org/users/lwagner_mozilla.com/odinmonkey/rev/e2fd77ffd205
all the asm.js jit tests, emscripten shell tests pass and BananaBread runs in the browser.

I'll finish Windows on bug 840283.