Re: [FFmpeg-devel] [PATCH v2 1/2] configure: don't force specific C++ standard library linking

[Timo Rothenpieler <timo@rothenpieler.org>]

On 06.09.2023 18:54, Kacper Michajlow wrote:
> On Wed, 6 Sept 2023 at 12:15, Timo Rothenpieler <timo@rothenpieler.org> wrote:
>>
>> On 06/09/2023 01:26, Kacper Michajłow wrote:
>>> Other C++ standard libraries exist. Also, this is not a proper way to
>>> link the standard library anyway. Instead when a C++ dependency is
>>> detected, switch to the C++ compiler driver to properly link everything.
>>>
>>> Signed-off-by: Kacper Michajłow <kasper93@gmail.com>
>>> ---
>>>    configure | 26 ++++++++++++++++++--------
>>>    1 file changed, 18 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/configure b/configure
>>> index bd7f7697c8..f3ff48586a 100755
>>> --- a/configure
>>> +++ b/configure
>>> @@ -3584,11 +3584,9 @@ bktr_indev_deps_any="dev_bktr_ioctl_bt848_h machine_ioctl_bt848_h dev_video_bktr
>>>    caca_outdev_deps="libcaca"
>>>    decklink_deps_any="libdl LoadLibrary"
>>>    decklink_indev_deps="decklink threads"
>>> -decklink_indev_extralibs="-lstdc++"
>>>    decklink_indev_suggest="libzvbi"
>>>    decklink_outdev_deps="decklink threads"
>>>    decklink_outdev_suggest="libklvanc"
>>> -decklink_outdev_extralibs="-lstdc++"
>>>    dshow_indev_deps="IBaseFilter"
>>>    dshow_indev_extralibs="-lpsapi -lole32 -lstrmiids -luuid -loleaut32 -lshlwapi"
>>>    fbdev_indev_deps="linux_fb_h"
>>> @@ -4984,6 +4982,18 @@ set_ccvars HOSTCC
>>>    test -n "$cc_type" && enable $cc_type ||
>>>        warn "Unknown C compiler $cc, unable to select optimal CFLAGS"
>>>
>>> +cxx_deps=(
>>> +    decklink
>>> +    libglslang
>>> +    libgme
>>> +    libopenmpt
>>> +    librubberband
>>> +    libsnappy
>>> +)
>>
>> Can't say I'm a fan of maintaining a random list in the middle of
>> configure, which manually contains all libs we think need libstdc++.
>>
>> This could for one change any time. But also, those dependenies might
>> have other dependencies, which when linking statically might need libstdc++.
>>
>> But in general, this seems extremely brittle and a maintenance nightmare.
> 
> Yes, that's the main problem. Linking static dependencies is an
> unsolved problem. We can discuss that, but wouldn't you agree that the
> proposed patch is an improvement over the current status quo? Forcing
> `-lstdc++` unconditionally, when some of the dependencies are enabled
> is way worse. The logic of maintaining the list does not change, it is
> just centralized in one place and properly switches linking language
> to C++ when needed, instead side-loading stdc++.

It's not really unsolved. The dependencies need to properly advertise 
their dependencies via pkg-config.
That only becomes an issue if we have some legacy manual detection that 
bypass pkg-config by default, or weird projects that don't supply 
pkg-config files.

> Good solution that would not require any maintenance is to switch to
> CXX always for linking.

Just test if linking with CC/LD fails, and if it does, test if it works 
with CXX, and if so, use CXX?
A bit crude, but at least does not cause a maintenance nightmare.
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