RFR: 8365229: ARM32: c2i_no_clinit_check_entry assert failed after JDK-8364269 [v3]

[Andrew Dinn]

On Wed, 13 Aug 2025 13:43:52 GMT, Andrew Dinn <adinn at openjdk.org> wrote:

>> If you are curious, this is where Zero catches fire during build:
>> 
>> 
>> report_vm_error(...)
>> AdapterBlob::AdapterBlob()
>> AdapterBlob::create()
>> AdapterHandlerLibrary::generate_adapter_code()
>> AdapterHandlerLibrary::create_adapter()
>> AdapterHandlerLibrary::initialize()
>> SharedRuntime::init_adapter_library()
>> init_globals()
>> 
>> 
>> So we enter that path routinely, without any AOT features enabled...
>
> Ah, yikes, so we are actually creating an AdapterBlob here?
> 
> Oh dear, it seems we go on to do so at line 2849 in sharedRuntime.cpp.
> 
>     int entry_offset[AdapterBlob::ENTRY_COUNT];
>     assert(AdapterBlob::ENTRY_COUNT == 4, "sanity");
>     address i2c_entry = handler->get_i2c_entry();
>     entry_offset[0] = 0; // i2c_entry offset
>     entry_offset[1] = handler->get_c2i_entry() - i2c_entry;
>     entry_offset[2] = handler->get_c2i_unverified_entry() - i2c_entry;
>     entry_offset[3] = handler->get_c2i_no_clinit_check_entry() - i2c_entry;
> 
>     adapter_blob = AdapterBlob::create(&buffer, entry_offset); <== oops!
> 
> Ok, so we need to avoid doing that!
> 
> A fortiori, on Zero, because the result is broken even modulo the problme this patch is trying to fix. A few lines later we do this:
> 
>     handler->relocate(adapter_blob->content_begin());
> 
> What that does is compute a delta from the handler's first entry to the blob's start address and then apply that delta to all four addresses. So, that's not going to work.
> 
> We need to fix this in two places.
> 
> 1. we should bypass the blob create if we get back a buffer with length 0 i.e. if no code was generated -- that will fix Zero
> 2. We should tweak AdapterHandlerEntry::relocate() so that it only applies the delta when the corresponding entry address != nullptr -- that will fix arm32 i.e. will ensure that any attempt to use the invalid entry will be using a 0 address.

Correction - we just need to avoid creating the blob and checking the offsets when SharedRuntime::generate_i2c2i_adapters returns an empty code buffer. The nullptr checks are already in place in relocate.

Aleksey, are you ok to do that?

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PR Review Comment: https://git.openjdk.org/jdk/pull/26746#discussion_r2273621359