RFR: 8357060: [premain] assert(left >= right) failed: avoid underflow

[Ashutosh Mehra]

On Fri, 16 May 2025 15:56:48 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> This PR fixes a few things in the premain:
>> 1. When storing metadata in aot code cache, `AOTCacheAccess::delta_from_shared_address_base` was incorrectly using `SharedBaseAddress` for computing the offset. It should be using `MetaspaceShared::requested_base_address` because we convert the input address to the requested address.
>> 2. Fixing the above issue results in crash in C1 and C2 compiled code during production run because CompressedKlassPointer::base() value was hardcoded in the generated code. In mainline we emit relocation for `CompressedKlassPointer::base()`. This patch adds the same changes to premain. In addition to that, it also modifies `MacroAssembler::decode_and_move_klass_not_null` and `MacroAssembler::encode_and_move_klass_not_null` which are used by C2 compiled code.
>> 3. Fixing 2 reveals another problem when preload the code. `AOTCodeEntry::_method` can be invalid if the AOT Cache gets mapped to different address than the "requested" address, and can result in crash when accessing `AOTCodeEntry::_method` during preload. Fix is to store the offset of the `AOTCodeEntry::_method` and use the offset on load to get the correct Method pointer.
>> 4. While working on this issue, I realized archived `AOTCodeCache::compile_nmethod` is using archived nmethod to print the assembly. This results in crash as archived nmethod has some state cleaned up. Updated `AOTCodeCache::compile_nmethod` to fix this issue.
>
> src/hotspot/share/code/aotCodeCache.cpp line 1998:
> 
>> 1996:         continue;
>> 1997:       }
>> 1998:       Method* m = (Method*)((address)SharedBaseAddress + entry->method_offset());
> 
> Why not `MetaspaceShared::requested_base_address()` here?

Because when loading the AOT Cache, SharedBaseAddress is set to the mapped base address (in `MetaspaceShared::map_archives`). So it is fine to use it here.

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PR Review Comment: https://git.openjdk.org/leyden/pull/68#discussion_r2093328966