Cross-build not finding libraries

[GrantEdwards]

The handling of cross development appears to be fundamentally broken.

In my cmake toolchain file, I specify where the libraries are. When
building c-utility, it finds libssl, but not libcurl (which is in the
same directory).

Here's the content of deps/c-utility/build/error.txt:

/home/nextgen/toolchain/bin/../lib/gcc/arm-unknown-linux-uclibcgnueabi/4.6.3/../../../../arm-unknown-linux-uclibcgnueabi/bin/ld: cannot find -lcurl
collect2: ld returned 1 exit status
gmake[2]: *** [CMakeFiles/aziotsharedutil.dir/build.make:1138: libaziotsharedutil.so] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:68: CMakeFiles/aziotsharedutil.dir/all] Error 2
gmake: *** [Makefile:139: all] Error 2

And here's deps/c-utility/build/CMakeFiles/aziotsharedutil.dir/link.txt:

/home/nextgen/toolchain/bin/arm-linux-gcc -fPIC
-D_POSIX_C_SOURCE=200112L -fPIC -Werror -g -shared
-Wl,-soname,libaziotsharedutil.so -o libaziotsharedutil.so
CMakeFiles/aziotsharedutil.dir/src/base64.c.o
[...]
CMakeFiles/aziotsharedutil.dir/src/x509_openssl.c.o -lcurl
/home/nextgen/buildroot-new/output/host/usr/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib64/libssl.so
/home/nextgen/buildroot-new/output/host/usr/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib64/libcrypto.so
-lpthread -lm -luuid
-Wl,-rpath,/home/nextgen/buildroot-new/output/host/usr/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib64:

As you can see cmake found the ssl library files and specifed the full
path. But for the curl library (which is in the same location as ssl
library files), it just uses "-lcurl". That's broken.

I've tried setting CMAKE_EXE_LINKER_FLAGS, CMAKE_SHARED_LINKER_FLAGS,
CMAKE_C_FLAGS with "-L" options to specify the library directory, but
those settings are apparently ignored and never show up in
aziotsharedutil.dir/link.txt

How are you supposed to configure the location of library files when
doing cross development?

[damonbarry]

I agree this should be fixed. In our azure-c-shared-utility dependency, the root CMakeLists.txt file simply references curl, without doing a proper CMake find_package() first.

[damonbarry]

I submitted a pull request in the azure-c-shared-utility repo for this.

[GrantEdwards]

I've tried setting CMAKE_EXE_LINKER_FLAGS, CMAKE_SHARED_LINKER_FLAGS,
CMAKE_C_FLAGS with "-L" options to specify the library directory, but
those settings are apparently ignored and never show up in
aziotsharedutil.dir/link.txt

For future reference, you can specify compiler and linker flags in
your cmake toolchain to point to library locations, but there's a
trick to it:

SET(CMAKE_EXE_LINKER_FLAGS "-L<whatever>" CACHE STRING "" FORCE)
SET(CMAKE_SHARED_LINKER_FLAGS "-L<whatever>" CACHE STRING "" FORCE)
SET(CMAKE_C_FLAGS "-L<whatever>" CACHE STRING "" FORCE)

WARNING: This is pure cargo-cult cut-and-paste. I don't really understand what
those extra bits at the end are doing. But it works.