Re: [RFC PATCH] meson.build: don't include libbpf in the common source set

[Paolo Bonzini <pbonzini@redhat.com>]

On 05/10/21 22:25, Richard Henderson wrote:
> On 10/5/21 12:27 PM, Paolo Bonzini wrote:
>> On 05/10/21 20:24, Alex Bennée wrote:
>>> This library is only needed for the softmmu targets and as such
>>> break static *-user builds where libbpf is detected and it tries to
>>> link it into the user binaries.
>>>
>>> Fixes: 46627f41b6 ("ebpf: Added eBPF RSS loader.")
>>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>> ---
>>>   meson.build | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/meson.build b/meson.build
>>> index 60f4f45165..d8bcf13b21 100644
>>> --- a/meson.build
>>> +++ b/meson.build
>>> @@ -2307,7 +2307,7 @@ subdir('bsd-user')
>>>   subdir('linux-user')
>>>   subdir('ebpf')
>>> -common_ss.add(libbpf)
>>> +softmmu_ss.add(libbpf)
>>
>> It should not be needed at all, since ebpf/meson.build has
>>
>> softmmu_ss.add(when: libbpf, if_true: files('ebpf_rss.c'), if_false: 
>> files('ebpf_rss-stub.c'))
>>
>> (which already adds libbpf if needed).
> 
> Ooo, magic side effects.  I'll note that the manual doesn't say that it 
> adds and dependencies from varnames_and_deps, only that it checks them.

Good point, it's in an example above:

# Include zlib.c if the zlib dependency was found, and link zlib
# in the executable
ss.add(when: zlib, if_true: files('zlib.c'))

Paolo