RFR: 8301703: java.base jdk.internal.foreign.abi.BindingSpecializer uses ASM to generate classes [v2]

[Adam Sotona]

On Fri, 31 Mar 2023 12:20:49 GMT, Adam Sotona <asotona at openjdk.org> wrote:

>> I believe that, in order to generate the actual bytecodes, the classfile API does a full verification pass (as it needs to infer the stackmap information). This leads me to believe that, yes, most (but probably all) errors would be detected simply by generating code. Maybe @asotona can clarify.
>
> Stackmap generator does not perform full verification, it only performs fast pass through the code and hits only errors preventing to construct valid stack maps (as for example stack underflow).
> Verifyier on the other hand does full verification similar to when the class is loaded.

Classfile API allows to pass-through complete class members or attributes, so resulting class might be invalid even the particular code and stack maps have been generated. 

This is brief list of verifications performed when `verify` is explicitly called:
- class version
- signatures
- instruction opcodes
- CP entries matching instructions (matching types, array dimensions limits, etc...)
- stack map frames and assignability between reference types
- flow control (branches, exception handlers, falling through code end, falling through initialised, etc..)
- exception tables (offsets, throwing Throwables, etc...)
- local variable tables 
- switches (low/high, number of keys, etc...)
- method calls (arguments, operands, constructor call target, constructors returning void, etc...)
- return values

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PR Review Comment: https://git.openjdk.org/jdk/pull/13247#discussion_r1154456627