552150 - JM: Dynamically generate trampolines

Status: RESOLVED INVALID

(Core :: JavaScript Engine, defect)

Description

[David Anderson [:dvander] - inactive, e-mail if emergency]

Right now our trampolines are inline assembly. We should probably dynamically generate them instead, This is advantageous for two reasons:

 - It's easier to make sure the code is correct across VMFrame adjustments, rather than static asserts w/ hardcoded offsets.
 - We can share code across similar operating systems/platforms (right now Windows/Linux x86 and x64 are very similar).
 - Easier to port x64, which has no inline assembly and thus requires using an external assembler.

Comment 1

[David Anderson [:dvander] - inactive, e-mail if emergency]

Right now I would like to call JaegerTrampoline() with an arbitrary inlineCallCount, but I can't because cx->fp's return address ends up as the trampoline return address. Luke pointed out I could fix this by having a second trampoline that uses "push ; jmp" instead of "call".

So there's another good reason to dynamically generate these things instead of having lots of duplication.

Comment 2

[Andrew Drake [:adrake]]

Groundwork has been laid for this in my patch for bug 570650. Unless someone really wants this to happen sooner, I was going to move over all the other trampolines after I finish the rest of the blockers for JaegerDebug.

Comment 3

[Sean Stangl [:sstangl]]

JM has been removed from the tree, replaced by Ion and Baseline. Ion's trampolines are dynamically generated.