Bug 197732 – [JSC] Add CodeOffset, 32bit offset in JIT memory pool

• Status: NEW
• Component: JavaScriptCore

[Yusuke Suzuki]

We can just hold the offset in JIT code pool.

[Yusuke Suzuki]

(In reply to Yusuke Suzuki from comment #0)
> We can just hold the offset in JIT code pool.

We should have different types for (1) JIT code pointer and (2) C runtime pointer. And making (1) 32bit.

[Yusuke Suzuki]

Created attachment 369825 [details]
Patch

[EWS Watchlist]

Attachment 369825 [details] did not pass style-queue:


ERROR: Source/JavaScriptCore/jit/CodeOffset.h:47:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
ERROR: Source/JavaScriptCore/jit/CodeOffset.h:52:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
ERROR: Source/JavaScriptCore/jit/CodeOffset.h:54:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
Total errors found: 3 in 24 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[EWS Watchlist]

Comment on attachment 369825 [details]
Patch

Attachment 369825 [details] did not pass mac-debug-ews (mac):
Output: https://webkit-queues.webkit.org/results/12185748

Number of test failures exceeded the failure limit.

[EWS Watchlist]

Created attachment 369829 [details]
Archive of layout-test-results from ews114 for mac-highsierra

The attached test failures were seen while running run-webkit-tests on the mac-debug-ews.
Bot: ews114  Port: mac-highsierra  Platform: Mac OS X 10.13.6

[Yusuke Suzuki]

Created attachment 369906 [details]
Patch

[EWS Watchlist]

Attachment 369906 [details] did not pass style-queue:


ERROR: Source/JavaScriptCore/jit/CodeOffset.h:47:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
ERROR: Source/JavaScriptCore/jit/CodeOffset.h:52:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
ERROR: Source/JavaScriptCore/jit/CodeOffset.h:54:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
Total errors found: 3 in 24 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Yusuke Suzuki]

Created attachment 369919 [details]
Patch

[EWS Watchlist]

Attachment 369919 [details] did not pass style-queue:


ERROR: Source/JavaScriptCore/jit/CodeOffset.h:47:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
ERROR: Source/JavaScriptCore/jit/CodeOffset.h:52:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
ERROR: Source/JavaScriptCore/jit/CodeOffset.h:54:  Should have only a single space after a punctuation in a comment.  [whitespace/comments] [5]
Total errors found: 3 in 24 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[Yusuke Suzuki]

I think this should be definitely done. https://bugs.webkit.org/show_bug.cgi?id=186422 shows that Bag takes much memory.

6. WebKit BagNode_0x117c78000                                      30.0M      16.6M      16.6M         0K     195956      16.0M       575K      4%      30


This Bag is used by Watchpoint and JITIC things. And JITIC things include these CodeLocationLabel, and each takes 8bytes. If we use CodeOffset instead, it becomes 4bytes.

Furthermore, CodeOffset thing ensures that repatch only happens within 32bit range, this is further safer than having a pointer which can be read/write later.
I think the current patch is WIP. We should limit the source of CodeOffset and threading it in various places.