Possible bug in binutils for MinGW-w64 related to linking weak symbols

[Fangrui Song]

On Thu, Mar 19, 2026 at 11:54 PM Martin Storsjö <martin@martin.st> wrote:
>
> On Thu, 19 Mar 2026, Fangrui Song wrote:
>
> > There is a distinction between weak definition and weak reference.
>
> Indeed; using a weak reference to access a potentially weak definition (as
> suggested above, by requiring the attribute to be used consistently on all
> declarations) seems both surprising and redundant. Plus that it is extra
> brittle due to relying on the linking order of the two object files,
> currently.
>
> If using a weak reference, the referencer should be ready to handle the
> case that there was no actual symbol present (the symbol resolving to
> absolute null), while the weak definition is for handling possibly two
> definitions of the same, with one giving way for the other.
>
> > The linker should allow a regular reference from foobar.o to resolve
> > to a weak definition (simulated with IMAGE_SYM_CLASS_WEAK_EXTERNAL
> > IMAGE_SYM_UNDEFINED symbol with an IMAGE_SYM_CLASS_EXTERNAL
> > IMAGE_SYM_ABSOLUTE auxiliary symbol
> > https://maskray.me/blog/2021-04-25-weak-symbol#pecoff).
>
> You've mixed up the quotes here.

Sorry for quoting the wrong part in my previous message.

> An IMAGE_SYM_CLASS_WEAK_EXTERNAL IMAGE_SYM_UNDEFINED symbol with an
> IMAGE_SYM_CLASS_EXTERNAL IMAGE_SYM_ABSOLUTE auxiliary symbol is used for
> weak references (with the absolute symbol used as the fallback null
> pointer, in case nothing else was found).
>
> An IMAGE_SYM_CLASS_WEAK_EXTERNAL IMAGE_SYM_UNDEFINED symbol with a defined
> IMAGE_SYM_CLASS_EXTERNAL symbol (for the actual function or data symbol)
> is used for weak definitions.

I've reviewed the two paragraphs on
https://maskray.me/blog/2021-04-25-weak-symbol#pecoff - they are
correct :)