RFR: 8357579: Compilation error: first argument in call to 'memset' is a pointer to non-trivially copyable type [v13]

[Ashutosh Mehra]

On Mon, 10 Nov 2025 07:24:50 GMT, Jan Kratochvil <jkratochvil at openjdk.org> wrote:

>> With clang-20 using --with-toolchain-type=clang resolveFieldEntry.cpp and resolveMethodEntry.cpp break the build with similar warnings like:
>> 
>> src/hotspot/share/oops/resolvedFieldEntry.cpp:49:10: error: first argument in call to 'memset' is a pointer to non-trivially copyable type 'ResolvedFieldEntry' [-Werror,-Wnontrivial-memcall]
>>    49 |   memset(this, 0, sizeof(*this));
>>       |          ^
>> src/hotspot/share/oops/resolvedFieldEntry.cpp:49:10: note: explicitly cast the pointer to silence this warning
>>    49 |   memset(this, 0, sizeof(*this));
>>       |          ^
>>       |          (void*)
>> 
>> The patch follows the suggested fix.
>
> Jan Kratochvil has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add Ioi Lam's comment

src/hotspot/share/oops/resolvedFieldEntry.cpp line 31:

> 29: STATIC_ASSERT(std::is_trivially_copyable_v<ResolvedFieldEntry> == true);
> 30: 
> 31: // Detect inadvertently introduced trailing padding.

Another way to detect padding (trailing or internal) could be to compare sizeof(ResolvedFieldEntry) against the sum up the size of all the elements. Something like:
`sizeofResolvedFieldEntry) == (sizeof(InstanceKlass*) + sizeof(int) + sizeof(u2) + ... + sizeof(_padding))`
It looks cumbersome but I think it is easy enough to update if a new field is added because the static assert will fail immediately.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26098#discussion_r2510917443