Re: [Qemu-devel] [RFC] configure script mistakenly detects static libraries

[Murilo Opsfelder Araujo <muriloo@linux.ibm.com>]

On 04/23/2018 01:16 PM, Peter Maydell wrote:
> On 23 April 2018 at 17:10, Murilo Opsfelder Araujo
> <muriloo@linux.ibm.com> wrote:
>> Hi, everyone!
>>
>> I'm facing an issue on how configure script detects static libraries and
>> would like to hear from community to find a common ground on how to
>> possibly fix it.
>>
>> Throughout configure, we use pkg-config command to verify if a library
>> is installed so qemu can be linked to it. This works fine when linking
>> qemu dynamically. However, configuring qemu with --static can mistakenly
>> detect a library that is actually not present on the system.
>>
>> For example, on Ubuntu Xenial, libcacard-dev package provides only
>> libcacard.so (not libcacard.a) and pkg-config reports success in both
>> cases:
>>
>>     $ pkg-config libcacard
>>     $ echo $?
>>     0
>>
>>     $ pkg-config --static libcacard
>>     $ echo $?
>>     0
>>
>> Since we use `pkg-config libcacard` to set smartcard=yes, this
>> mistakenly enables smartcard feature. This is acceptable with dynamic
>> linkage, but can be an issue with static linkage, where libcacard.a
>> doesn't exist on the system, resulting on a build error:
> 
> This seems to me to be an error in your distro's pkg-config information.
> If static linking against libcacard doesn't work, then
> "pkg-config --static libcacard" should fail.

I see in man(1) pkg-config that --static is merely used to compute
deeper dependency graph intended for static linking.

Since <package>.pc is present, pkg-config assumes the library exists and
--static is merely informational.

Do you think this should be reported to pkg-config project?

> Unfortunately IME the static linking support in distro-suppled
> pkgconfig files is rarely tested, so it's not uncommon for it to
> be broken.
> 
> From an upstream QEMU point of view, we primarily support --static
> for the benefit of the linux-user binaries, not for system emulation.
> So we care more if a "configure --disable-system --disable-tools --static"
> build doesn't work, than if the problem is only with features used
> by the system emulator binaries.

In this case, shouldn't we update configure script to emit a warning
message to user saying it's running a non-supported scenario when
--static is given without --disable-system and --disable-tools?

> thanks
> -- PMM
> 

Cheers
Murilo