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

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Message-ID: <CAK7LNAQBO-VA8G9uumwH5m9idQofY1ZR+hnNfL7y4P3m16xFNQ@mail.gmail.com>
Date: Wed, 28 Aug 2024 16:15:03 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Luis Chamberlain <mcgrof@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Matthew Maurer <mmaurer@...gle.com>, 
	Alex Gaynor <alex.gaynor@...il.com>, Wedson Almeida Filho <wedsonaf@...il.com>, Gary Guo <gary@...yguo.net>, 
	Petr Pavlu <petr.pavlu@...e.com>, Neal Gompa <neal@...pa.dev>, Hector Martin <marcan@...can.st>, 
	Janne Grunau <j@...nau.net>, Asahi Linux <asahi@...ts.linux.dev>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-modules@...r.kernel.org, 
	rust-for-linux@...r.kernel.org
Subject: Re: [PATCH v2 04/19] gendwarfksyms: Add support for type pointers

On Wed, Aug 28, 2024 at 3:50 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> On Fri, Aug 16, 2024 at 2:39 AM Sami Tolvanen <samitolvanen@...gle.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@...gle.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





--
Best Regards
Masahiro Yamada