Re: [PATCH v2 04/19] gendwarfksyms: Add support for type pointers

[Sami Tolvanen <samitolvanen@google.com>]

On Wed, Aug 28, 2024 at 04:15:03PM +0900, Masahiro Yamada wrote:
> On Wed, Aug 28, 2024 at 3:50 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > On Fri, Aug 16, 2024 at 2:39 AM Sami Tolvanen <samitolvanen@google.com> wrote:
> > >
> > > The compiler may choose not to emit type information in DWARF for
> > > external symbols. Clang, for example, does this for symbols not
> > > defined in the current TU.
> > >
> > > To provide a way to work around this issue, add support for
> > > __gendwarfksyms_ptr_<symbol> pointers that force the compiler to emit
> > > the necessary type information in DWARF also for the missing symbols.
> > >
> > > Example usage:
> > >
> > >   #define GENDWARFKSYMS_PTR(sym) \
> > >       static typeof(sym) *__gendwarfksyms_ptr_##sym __used  \
> > >           __section(".discard.gendwarfksyms") = &sym;
> > >
> > >   extern int external_symbol(void);
> > >   GENDWARFKSYMS_PTR(external_symbol);
> > >
> > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> >
> >
> >
> >
> > Commit ddb5cdbafaaad6b99d7007ae1740403124502d03
> > had a similar idea; it has a reference to each
> > export symbol, including the ones defined in different TUs,
> > but in assembly code.
> >
> > Didn't it suffice your need?
> >
> 
> 
> Presumably, this is an unfortunate duplication, but I do not have an
> idea to avoid it.
> 
> The symbol reference in assembly code works in *.S as well as *.c.
> 
> The C reference will pull-in the debug info, but it will not work in *.S

Correct. I'm not a huge fan of the extra reference either, but I don't
see a cleaner way to ensure we always have all the types in DWARF.

Sami