Re: [Qemu-devel] [RFC] configure script mistakenly detects static libraries
On 04/23/2018 01:16 PM, Peter Maydell wrote: > On 23 April 2018 at 17:10, Murilo Opsfelder Araujo > 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 .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
Re: [Qemu-devel] [RFC] configure script mistakenly detects static libraries
On Mon, Apr 23, 2018 at 05:16:02PM +0100, Peter Maydell wrote: > On 23 April 2018 at 17:10, Murilo Opsfelder Araujo > 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 :|
Re: [Qemu-devel] [RFC] configure script mistakenly detects static libraries
On 23 April 2018 at 17:10, Murilo Opsfelder Araujo 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. 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. thanks -- PMM
[Qemu-devel] [RFC] configure script mistakenly detects static libraries
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:
$ ./configure --target-list=ppc64-softmmu --static && make -j$(nproc)
[...]
/usr/bin/ld: cannot find -lcacard
A workaround can be specifying --disable- for all missing
libraries.
One possible solution would be having a function, e.g. check_pkg_config,
that writes a C skeleton and tries to compile it using the desired
library, given as function parameter. Thus, compile_prog would return
success if library actually exists on the system. For example:
check_pkg_config() {
local_pkg_name=$1
local_cflags=$($pkg_config --cflags $local_pkg_name)
local_ldflags=$($pkg_config --libs $local_pkg_name)
write_c_skeleton
compile_prog "$local_cflags" "$local_ldflags"
}
That would work for both dynamic and static linkages. Then we could just
replace `$pkg_config ` by `check_pkg_config ` in the
configure script.
My approach might not be the best and only one, so I'd like to hear from
you what would be a reasoanble solution to fix this situation.
Cheers
Murilo
