[libcamera-devel] build error with libunwind-14-dev

[Christian Rauch]

Hi Laurent,

Am 13.08.22 um 18:26 schrieb Laurent Pinchart:
> Hi Christian,
>
> On Sat, Aug 13, 2022 at 01:38:10PM +0200, Christian Rauch via libcamera-devel wrote:
>> Hello,
>>
>> tl;dr: On Ubuntu 22.04, "libunwind-14-dev" breaks the build process.
>>
>> When "libunwind-14-dev" is installed (sudo apt install libunwind-14-dev)
>> meson will report "Library libunwind found: YES" but ninja will fail
>> with "../src/libcamera/base/backtrace.cpp:26:10: fatal error:
>> libunwind.h: Datei oder Verzeichnis nicht gefunden
>> " (file not found).
>>
>> The header "libunwind.h" is indeed in multiple conflicting Ubuntu
>> packages, and the build only works with "libunwind-dev". All versioned
>> packages (libunwind-12-dev libunwind-13-dev, libunwind-14-dev) will show
>> the issue above.
>
> That's quite messy. It seems to be a distribution-specific issue, I'm
> tempted to say that Canonical should fix this.
>

I don't think it's a distribution issue. Looking at the meson.build I
can see that it only searches for the library
("cc.find_library('libunwind')") but not for the pkg-config file. I
think you are supposed to use "dependency('libunwind')" for this.

What happens is that meson finds the *.so file, sets "HAVE_UNWIND" but
then does not know where the header is, because it did not check the
*.pc file. If you compare the content of both packages:
- https://packages.ubuntu.com/jammy/amd64/libunwind-dev/filelist
- https://packages.ubuntu.com/jammy/amd64/libunwind-14-dev/filelist
you will see that both contain the "libunwind.so", which is why both
packages are exclusive, but only one contains a *.pc file.

In general, I believe that searching for build dependencies via
"find_library" is not correct. "find_library" only searches for the
library and not the headers.

Best,
Christian