Make bt_field_blob_get_length return size_t instead of uint64_t

[kraj]

Fixes errors e.g.
| ../../git/src/cpp-common/bt2/field.hpp:1139:82: error: non-constant-expression cannot be narrowed from type 'std::uint64_t' (aka 'unsigned long long') to 'size_type' (aka 'unsigned int') in initializer list [-Wc++11-narrowing]
| 1139 | return {internal::CommonBlobFieldSpec::data(this->libObjPtr()), this->length()};
| | ^~~~~~~~~~~~~~
| ../../git/src/plugins/ctf/common/src/msg-iter.cpp:744:56: note: in instantiation of member function 'bt2::CommonBlobField<bt_field>::data' requested here
| 744 | std::memcpy(&this->_stackTopCurSubField().asBlob().data()[_mCurBlobFieldDataOffset],
| | ^
| ../../git/src/cpp-common/bt2/field.hpp:1139:82: note: insert an explicit cast to silence this issue
| 1139 | return {internal::CommonBlobFieldSpec::data(this->libObjPtr()), this->length()};
| | ^~~~~~~~~~~~~~
| | static_cast<size_type>( )

[eepp]

Thank you.

If you don't mind, could you create an issue on our official bug tracker instead? If you can't, I will.

May I also get your configure command line?

This specific fix isn't the right one. bt2::CommonBlobField::length() has every right to return std::uint64_t: it wraps a uint64_t-returning function. The constructor of bt2s::span expects std::size_t; that's where you want to cast this->length().

[kraj]

@eepp this issue happens when building for riscv32 targets using clang-20 compiler. I think it will also fail on other 32bit platforms too.

[kraj]

I do not have account on the bug tracker and creating new is sent to overlords for approval :)

[eepp]

In fact don't worry about the bug tracker, this is so simple we'll fix it now.

The patch is fine. The "right" cast is probably something like

typename bt2s::span<typename internal::CommonBlobFieldSpec<LibObjT>::Data>::size_type

(lol) but whatever.

However can you move this to a Gerrit change? You already have an account there.

[kraj]

done here - https://review.lttng.org/c/babeltrace/+/14316