commit 8f6dd1ad3a3462c46a2fb978efdf9995625ee6b4
author Nate Biggs <natebiggs@google.com> Fri Apr 19 06:03:01 2024 +0000
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Fri Apr 19 06:03:01 2024 +0000
tree d4d8562dee59ed360a866c1f8fa126c22a9117d0
parent de84385653631c6283b02f09fb1944f8d8dd3b17

[dart2js] Handle serialization offset address spaces larger than 2^29.

The dart2js binary serialization infrastructure only supports 30 bit integers with the "writeInt" method. The indexing infrastructure uses 1 of the bits to store locality information leaving 29 bits to encode the address space.

The recent dump info changes expanded the address space of some large programs beyond this 2^29 and is causing some serialization issues when trying to generate dump info.

The solution here is to check when an address is above 2^29 and instead encode the offset as a uint32. This will use 5 bytes for these large values (1 for the large offset indicator and 4 for the offset itself). By doing this we expand the address space to 2^32 which is more than enough to support larger programs.

An alternative would be to use some bits from the indicator and encode the rest in a separate 30-bit int. This would allow us to represent an address space closer to 2^60. But we would need to use an extra bit to differentiate the indicator and an actual offset. Which would reduce the base address space to 2^28 causing us to hit the more expensive 5-byte case earlier and increasing total write size. No known program is anywhere near the 2^32 address space size so the larger address space is not necessary.

Change-Id: Icbed2961099842ebf286b36314e8d6fab7389db4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/363541
Reviewed-by: Mayank Patke <fishythefish@google.com>
Commit-Queue: Nate Biggs <natebiggs@google.com>