After doing some more digging around in the code I found that if
V8_COMPRESS_POINTERS_IN_MULTIPLE_CAGES is defined then it will create a new
IsolateGroup and not use a global one. However in order for it to be
defined v8_enable_pointer_compression_shared_cage has to be set to false
and this leads back to mksnapshot crashing when it is. I tried also
disabling the shared ro heap with the option but it still crashes.
if (v8_enable_pointer_compression &&
!v8_enable_pointer_compression_shared_cage) {
defines += [ "V8_COMPRESS_POINTERS_IN_MULTIPLE_CAGES" ]
}
On Wednesday, January 1, 2025 at 3:08:12 PM UTC+8 Ronald Fenner wrote:
> I'm running into a checksum error when trying to load a custom snapshot
> during a unit test where it was created.
> Specifically this error
> # Fatal error in ../../src/heap/read-only-spaces.cc, line 96
> # Check failed: read_only_blob_checksum_ == snapshot_checksum
> (<unprintable> vs. 2723829699 <(272)%20382-9699>).
>
> I've dug into and found that it appears that an IsolateGroup is
> automatically created and any future isolates are loaded into this group
> fixing the readonly shared space checksum with the first startup data used.
>
> Subsequently when I tried to load the custom snapshot it's isolate gets
> put in this group and it's checksum no longer matches.
>
> I was able to substitute the custom startup, which for this test is just a
> recreation of the v8 snapshot no extras loaded into it, in as the v8
> startup blob and my core tests using it passed with no issue.
>
> I've tried to disable the Sandbox same error.
> Tried to disable the shared ro heap but this caused a torque static
> assertion about builtins
>
> Disabling both sandbox and shared ro heap cause mksnapshot to crash with
> # Fatal error in ../../src/diagnostics/objects-debug.cc, line 673
> # Check failed: HeapLayout::InAnySharedSpace(*this).
>
> I also tried to disable the shared pointer compression cage but this
> brought back mksnapshot crashing as in my other thread.
>
> Unfortunately other than creating a whole other app to run the unit test's
> checking the snapshot worked there doesn't seem to be a way around this as
> the IsolateGroup is not exposed to the public API for embedders and there
> seems to be no way to create a new one and associate it with an isolate
> during creation.
>
> I'm currently using 13.1.201.19 which is the currently stable release
> shipped in the current version of Chromium.
> This did work in 12.4.254.15 which is what i upgraded from and I'm pretty
> sure that the shared read only heap is a new feature added since then.
>
> It seems a little odd to assume that the startup data passed during
> isolate creation since it's a parameter of the create params wouldn't
> change though I know you all mainly base your use cases on Chromiums use of
> V8 and not what an embedder might do.
>
> Perhaps a fix is just to calculate a checksum when first creating the
> isolate for the startup data and if it matches use a group created for it.
> otherwise create a new one for that snapshot data, that or expose the
> IsolateGroup for the embedder to be able to create and associate with an
> isolate at creation like the cppheap.
>
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