Re: [RFC PATCH v2 3/5] meson: Pass objects and dependencies to declare_dependency()

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 27/5/24 12:49, Paolo Bonzini wrote:
> From: Akihiko Odaki <akihiko.odaki@daynix.com>
> 
> We used to request declare_dependency() to link_whole static libraries.
> If a static library is a thin archive, GNU ld keeps all object files
> referenced by the archive open, and sometimes exceeds the open file limit.
> 
> Another problem with link_whole is that suboptimal handling of nested
> dependencies.
> 
> link_whole by itself does not propagate dependencies. In particular,
> gnutls, a dependency of crypto, is not propagated to its users, and we
> currently workaround the issue by declaring gnutls as a dependency for
> each crypto user.  On the other hand, if you write something like
> 
>    libfoo = static_library('foo', 'foo.c', dependencies: gnutls)
>    foo = declare_dependency(link_whole: libfoo)
> 
>    libbar = static_library('bar', 'bar.c', dependencies: foo)
>    bar = declare_dependency(link_whole: libbar, dependencies: foo)
>    executable('prog', sources: files('prog.c'), dependencies: [foo, bar])
> 
> hoping to propagate the gnutls dependency into bar.c, you'll see a
> linking failure for "prog", because the foo.c.o object file is included in
> libbar.a and therefore it is linked twice into "prog": once from libfoo.a
> and once from libbar.a.  Here Meson does not see the duplication, it
> just asks the linker to link all of libfoo.a and libbar.a into "prog".
> 
> Instead of using link_whole, extract objects included in static libraries
> and pass them to declare_dependency(); and then the dependencies can be
> added as well so that they are propagated, because object files on the
> linker command line are always deduplicated.
> 
> This requires Meson 1.1.0 or later.
> 
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> Message-ID: <20240524-objects-v1-1-07cbbe96166b@daynix.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   docs/devel/build-system.rst    |  3 ++-
>   meson.build                    | 44 +++++++++++++++++++---------------
>   gdbstub/meson.build            |  4 ++--
>   pythondeps.toml                |  2 +-
>   tcg/meson.build                |  6 +++--
>   tests/qtest/libqos/meson.build |  2 +-
>   6 files changed, 35 insertions(+), 26 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>