On Mon, Apr 23, 2018 at 05:16:02PM +0100, Peter Maydell wrote: > On 23 April 2018 at 17:10, Murilo Opsfelder Araujo > <muri...@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.
IIUC, --static isn't actually proving that a static version of a library exists. Rather it just changes the logic for figuring out the dependancy graph & compiler/linker flags. So --static will always work fine even if only the .so is present, and no .a file exists. Similarly pkg-config without --static doesn't actually guarantee that a shared .so exists either - just tells you the flags you would need if it did exist. This works fine if you always build & ship static & shared versions of every library, but distros often ditch static builds of all but a handful of libraries, because of the ripple effect static linking has when security updates are issued. > 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. That reduces the 3rd party deps to essentially just your C library and glib2, which makes it more tractable from a security update POV. I would certainly not wish to see static linking of a system emulator which pulls in 150+ 3rd party libraries on my system ! Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
