[builtins] Make sure argument count is always valid for C++ builtins.

[builtins] Make sure argument count is always valid for C++ builtins.

When calling into C++ builtins, we need to make sure that the argument
count register contains the correct number of arguments, otherwise the
CEntryStub will not be able to leave the stack in the correct state.

R=ishell@chromium.org
BUG=v8:4413
LOG=n

Committed: https://crrev.com/9c8262f11e3d6359874a63f25a31c6ddfba3dc1c
Cr-Commit-Position: refs/heads/master@{#31120}

[Benedikt Meurer, 2015-10-06 07:43:20]

Hey Igor,

The fix I just mentioned.
Please take a look.

Thanks,
Benedikt

[Igor Sheludko, 2015-10-06 08:18:24]

lgtm with a nit:

https://codereview.chromium.org/1391543002/diff/1/src/x64/builtins-x64.cc
File src/x64/builtins-x64.cc (right):

https://codereview.chromium.org/1391543002/diff/1/src/x64/builtins-x64.cc#new...
src/x64/builtins-x64.cc:63: __ leap(rax, Operand(rbx, num_extra_args + 1));
You could probably do move(rax, rbx) here and then fall through instead of
jumping to done_argc. Same for Intel and MIPS* platforms.

[Benedikt Meurer, 2015-10-06 08:20:50]

https://codereview.chromium.org/1391543002/diff/1/src/x64/builtins-x64.cc
File src/x64/builtins-x64.cc (right):

https://codereview.chromium.org/1391543002/diff/1/src/x64/builtins-x64.cc#new...
src/x64/builtins-x64.cc:63: __ leap(rax, Operand(rbx, num_extra_args + 1));
I'll leave it this way for now. I like this approach better.

[Benedikt Meurer, 2015-10-06 08:21:55]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-10-06 08:22:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1391543002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1391543002/20001

[commit-bot: I haz the power, 2015-10-06 08:23:48]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-06 08:24:07]

Patchset 2 (id:??) landed as
https://crrev.com/9c8262f11e3d6359874a63f25a31c6ddfba3dc1c
Cr-Commit-Position: refs/heads/master@{#31120}