1911341 - AutoWritableJitCode has an almost unused constructor.

Status: RESOLVED FIXED

(Core :: JavaScript Engine: JIT, enhancement, P1)

Description

[Nicolas B. Pierron [:nbp]]

AutoWritableJitCode has a constructor which is given both an address and a size, and constructor which is given a JitCode which is only used by the Linker.
With Bug 1886557 intent to add data pages, we should remove the non-JitCode versions.

Comment 1

[Nicolas B. Pierron [:nbp]]

Attachment: Bug 1911341 - Only initialize AutoWritableJitCode with a JitCode.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/73cacb2035ea
Only initialize AutoWritableJitCode with a JitCode. r=jandem

Comment 3

[Serban Stanca [:SerbanS]]

Backed out for causing JitCode related mass failures.

• Backout link
• Push with failures

Please check multiple failure logs, as all failures are caused by this changeset.

Comment 4

[Nicolas B. Pierron [:nbp]]

The problem seen here is that AutoWrittableJitCode only mprotect the page as writable, but there is a rare case where the executable allocation is at the very end of a page, while all the code starting from JitCode::raw() is on another page.

This rare occasion causes the failure seen above, as the JitCodeHeader is not mapped as writable while the Linker attempts to write it.

Ideally this field should remain non writable after the Link phase, but given that in the majority of cases where AutoWritableJitCode is called, it would be, I do not see much risks in making it the default. Also, this would have to be addressed later on in the X-Only project.

I had this fixed in another patch, which apparently did not got merged into this one.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/1c7efc584c9c
Only initialize AutoWritableJitCode with a JitCode. r=jandem

Comment 6

[Serban Stanca [:SerbanS]]

Backed out for causing multiple failures.

• Backout link

---

• Push with failures - sm bustages
• Failure Log
• Failure line: TEST-UNEXPECTED-FAIL | js\src\jit-test\tests\gc\bug-1565272.js | Unknown (code 3221225477, args "--fuzzing-safe --ion-offthread-compile=off --ion-warmup-threshold=10 --ion-eager --ion-offthread-compile=off --more-compartments") [1.0 s]

---

• Push with failures - jit failures
• Failure Log
• Failure line: TEST-UNEXPECTED-FAIL | tests/jit-test/jit-test/tests/arrow-functions/params-default-2.js | (code 139, args "--baseline-eager --write-protect-code=off") [0.1 s]

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/b06adc0b8756
Only initialize AutoWritableJitCode with a JitCode. r=jandem

Comment 8

[Norisz Fay [:noriszfay]]

https://hg.mozilla.org/mozilla-central/rev/b06adc0b8756