How to add postgres library before compilation

[corvusrabus]

Hi,

I am trying to cross-compile from my x86 CPU to the target aarch64-unknown-linux-gnu and my code needs to be linked with libpq (the Postgres SQL library).
The error I get is: /usr/bin/ld: cannot find -lpq

I have tried multiple things already and none of them have worked. I think the biggest confusion for me is that the docker image that cross runs is an x86 image but the binary needs to be linked with an aarch64 version of libpq.

Any help would be greatly appreciated.

[Alexhuszagh]

See the wiki on working with external dependencies.

In this case, you'd likely want in Cross.toml:

[target.aarch64-unknown-linux-gnu]
pre-build = [
  "dpkg --add-architecture $CROSS_DEB_ARCH", 
  "apt-get update && apt-get --assume-yes install libpq-dev:$CROSS_DEB_ARCH"
]

And then it should just work.

[corvusrabus]

Hi Emil, thanks for helping as well. Your suggestion makes the bare-bones example I described above work!
In my actual project I get this error now:

/usr/bin/ld: skipping incompatible /usr/lib/aarch64-linux-gnu/libpq.so when searching for -lpq
/usr/bin/ld: skipping incompatible /usr/lib/aarch64-linux-gnu/libpq.a when searching for -lpq
/usr/bin/ld: cannot find -lpq
/usr/bin/ld: skipping incompatible /usr/lib/aarch64-linux-gnu/libgcc_s.so.1 when searching for libgcc_s.so.1
collect2: error: ld returned 1 exit status

I tried several times (with cargo cleans in between) with PKG_CONFIG_ALLOW_CROSS=1 and without PKG_CONFIG_ALLOW_CROSS

[Emilgardis]

Do you get that with Cross.toml containing

[target.aarch64-unknown-linux-gnu]
pre-build = [
  "dpkg --add-architecture $CROSS_DEB_ARCH", 
  "apt-get update && apt-get --assume-yes install libpq-dev:$CROSS_DEB_ARCH"
]

[corvusrabus]

Sorry that I didn't specify that. Yes, my Cross.toml contains that.

[Alexhuszagh]

@Emilgardis I'm pretty sure it's the same thing as discussed here, since it's using a proc macro and then running it on the x86_64 host. I'm trying to find a solution for proc macros just to confirm everything is done properly. The issue what I'm running into is proc macros are run on the host, so in this case, x86_64, but then the target they are compiled for is aarch64, and I'm not sure even if the code compilers if it is correct. I believe it is as long as it uses a shared library and then it requires the libql-dev:arm64 to run but not to compile, but I believe this will fail if it's a static library. I'm looking into this currently.

#605 (comment)

[Alexhuszagh]

Sorry that I didn't specify that. Yes, my Cross.toml contains that.

Ok we just discussed this in the matrix room: you will need both libpq-dev and libpq-dev:arm64, and we'll document this on the wiki shortly. The reason is the proc macro compiles for the host, but has no access to the final binary (only the TokenStream), so you will need it both for the host and the target.

[Alexhuszagh]

If you are using a procedural macro, you will need the dependencies for the proc macro on the host, and the dependencies for the post-expansion crate on the target. In this case, both are libpq-dev, so you will need libpq-dev and libpq-dev:arm64. We've now documented this on the wiki.

Let me know if this fixes the issue.

[corvusrabus]

Hi Alex. Unfortunately, the docker image won't build if I do what's written in the wiki. Apt complains that libpq-dev and libpq-dev:arm64 are conflicting packages. I have tried
[target.aarch64-unknown-linux-gnu] pre-build = [ "dpkg --add-architecture $CROSS_DEB_ARCH", "apt-get update && apt-get --assume-yes install libpq-dev:amd64 libpq-dev:$CROSS_DEB_ARCH" ]
and I get the following error from apt

#0 14.75 Some packages could not be installed. This may mean that you have
#0 14.75 requested an impossible situation or if you are using the unstable
#0 14.75 distribution that some required packages have not yet been created
#0 14.75 or been moved out of Incoming.
#0 14.75 The following information may help to resolve the situation:
#0 14.75
#0 14.75 The following packages have unmet dependencies:
#0 14.82 libpq-dev : Conflicts: libpq-dev:arm64 but 12.12-0ubuntu0.20.04.1 is to be installed
#0 14.82 libpq-dev:arm64 : Conflicts: libpq-dev but 12.12-0ubuntu0.20.04.1 is to be installed
#0 14.84 E: Unable to correct problems, you have held broken packages.

---

ERROR: failed to solve: executor failed running [/bin/sh -c eval "${CROSS_CMD}"]: exit code: 100

[Alexhuszagh]

Ah this is why:

• liqpq-dev:arm64
• liqpd-dev:amd64

There's a solution using apt download and dpkg -x, and is probably worth mentioning on the wiki. I'll try to get a working example. You will need to modify the include paths if you do. Specifically, all these files overlap:

/usr/bin/pg_config
/usr/include/postgresql/internal/c.h
/usr/include/postgresql/internal/libpq-int.h
/usr/include/postgresql/internal/libpq/pqcomm.h
/usr/include/postgresql/internal/port.h
/usr/include/postgresql/internal/postgres_fe.h
/usr/include/postgresql/internal/pqexpbuffer.h
/usr/include/postgresql/libpq-events.h
/usr/include/postgresql/libpq-fe.h
/usr/include/postgresql/libpq/libpq-fs.h
/usr/include/postgresql/pg_config.h
/usr/include/postgresql/pg_config_ext.h
/usr/include/postgresql/pg_config_manual.h
/usr/include/postgresql/pg_config_os.h
/usr/include/postgresql/postgres_ext.h
/usr/share/doc/libpq-dev/changelog.Debian.gz
/usr/share/doc/libpq-dev/copyright
/usr/share/man/man1/pg_config.1.gz

Installing them local to /usr/aarch64-linux-gnu should suffice, which would probably mean dpkg -x to some temp directory, then doing something like:

dirs=(bin lib include)
for dir in "${dirs[@]}"; do
    for f in "${td}/usr/${dir}"/*; do
        base=$(basename "${f}")
        cp -r "${f}" "${CROSS_SYSROOT}/${dir}/${base}"
    done
done

Note that this isn't tested code and might not work, but the general idea is there: install every aarch64 library to the cross sysroot, and every host library to the normal sysroot.

[Barugon]

See the wiki on working with external dependencies.

In this case, you'd likely want in Cross.toml:

[target.aarch64-unknown-linux-gnu]
pre-build = [
  "dpkg --add-architecture $CROSS_DEB_ARCH", 
  "apt-get update && apt-get --assume-yes install libpq-dev:$CROSS_DEB_ARCH"
]

And then it should just work.

Sweet! this totally solved my issue here, although I had to add some timezone stuff.

[target.aarch64-unknown-linux-gnu]
pre-build = [
  "dpkg --add-architecture $CROSS_DEB_ARCH",
  "ln -snf /usr/share/zoneinfo/America/Los_Angeles /etc/localtime && echo America/Los_Angeles > /etc/timezone",
  "apt-get update && apt-get --assume-yes install libgdal-dev:$CROSS_DEB_ARCH",
]

[Barugon]

Ah, I spoke too soon. The version of gdal I get is 2.6 but I need 3.6. 😞

[Emilgardis]

you'd have to install it yourself, ubuntu 18.04, 20.04 and 22.04 have <3.6

[Barugon]

Any suggestions for a base container?

[Emilgardis]

answered here