RFR: 8314265: Fix -Wconversion warnings in miscellaneous runtime code [v2]

[Coleen Phillimore]

On Wed, 16 Aug 2023 12:30:18 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> According to the DWARF 4 spec, the discriminator is an unsigned integer (i.e. 32 bits). Also, the other fields like `isa or `column` are unsigned integer. I think we would be good to keep them as unsigned integer to follow the spec. 
>> 
>> `read_uleb128()` reads up to 8 bytes and just returns the result in a `uint64_t`. But sometimes, it should only read 1, 2, or 4 bytes. In that case, we additionally specify `check_size` to ensure that we can safely cast it. I guess we could change these calls to `read_uleb128()` to return a more precise type instead of relying on `check_size` passed in by a caller + casting the result in the caller.
>
> When we read the 64 bit values in the code, the values are 64 bits though.  So static_cast<> to narrow the result is more correct ?

This code:

      uint64_t isa;
      if (!_reader.read_uleb128(&isa, 4)) {
        // isa register is 4 bytes wide.
        return false;
      }
      _state->_isa = isa;  // only save 4 bytes

returns 64 bit of information into isa from this read_uleb128 call, even though it passes 4.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15233#discussion_r1295827701