Ada library projects (built with GPRBuild) used in an external build system

[specing]

Would it be possible to have GPRBuild output -L, -l and potentially other gcc flags required for final linking an Ada library into an otherwise C/C++/whatever program that has an existing build system /= GPRBuild?

Additionally, I have tested a few option combinations mentioned in https://docs.adacore.com/gprbuild-docs/html/gprbuild_ug/gnat_project_manager.html#stand-alone-library-projects , but was unable to obtain a static library that would have no Ada dependencies (even if no with's are added, libgnat is always there). I'm not sure whether or not such a static library is obtainable, but it would make final linking trivial.

More info: https://github.com/mosteo/ada4cmake/issues/3

[t-14]

Would it be possible to have GPRBuild output -L, -l and potentially other gcc flags required for final linking an Ada library into an otherwise C/C++/whatever program that has an existing build system /= GPRBuild?

If we are talking of a static standalone library, you can use objcopy --dump-section to extract the section .GPR.linker_options of the partially linked file p__* inside the archive.

I'm not sure whether or not such a static library is obtainable

It's not obtainable unless it is not a SAL. Otherwise binder always adds libgnat dependency, so even if your own code doesn't depend on libgnat, bindfile does.

[specing]

Thank you, but I am having trouble finding this p* section (presumably pada_lib.o). With

library project Adalibtest is

   for Library_Name use "ada_lib";
   for Library_Kind use "static";
   --for Library_Kind use "relocatable";
   --for Library_Standalone use "encapsulated";
   for Library_Standalone use "standard";
   for Library_Interface use ("lib_test");  --  unit names

   for Library_Dir use "lib";
   for Object_Dir  use "obj";

   package Compiler is
      for Switches ("Ada") use ("-gnata", "-gnato", "-fstack-check");
   end Compiler;

end Adalibtest

there are only 2 files inside lib/libada_lib.a: b__ada_lib.o and lib_test.o as shown in objdump -s lib/libada_lib.a output. None of them has any section named .GPR.linker_options.

There is also no such section when Library_Standalone and Library_Interface are commented out.

GPRBuild version is GPRBUILD GPL 2017 (19940713) (x86_64-pc-linux-gnu) gcc version is gcc version 6.4.0

[t-14]

GPRBuild version is GPRBUILD GPL 2017

You need to build up-to-date gpr tools from this project.

[specing]

Is the _0 suffix in p__ada_lib_0.o: file format elf64-x86-64 reliable?

[t-14]

I don't think so. IIRC if there's a lot of objects we may resort to linking in several stages to workaround path length limitations, in which case the number won't be 0.

[specing]

Can a reliable method of determining -l and -L options be added?

[specing]

Potentially such that libraries are specified with their absolute path, so as to prevent wrong libraries being picked when other -L options are added from the parent build system.

[t-14]

Can a reliable method of determining -l and -L options be added?

Well we told you the method that gprbuild currently uses. That section is there for a reason. What do you need to be "added"?

[specing]

Thank you, I will first try using that method before complaining further.

By the way, I can only build a static library by using latest gprbuild + community2018 gcc. Using latest gprbuild + 6.4.0 (probably fsf) gcc results in:

[ 25%] Building library ada_lib...
Setup
   [mkdir]        object directory for project Adalibtest
   [mkdir]        library directory for project Adalibtest
Compile
   [Ada]          lib_test.adb
Build Libraries
   [gprlib]       ada_lib.lexch
   [bind SAL]     ada_lib
   [Ada]          b__ada_lib.adb
/usr/lib/gcc/x86_64-pc-linux-gnu/6.4.0/../../../../x86_64-pc-linux-gnu/bin/ld: -r and -pie may not be used together
collect2: error: ld returned 1 exit status
gprlib: call to linker driver /usr/bin/gcc failed
gprbuild: could not build library for project adalibtest

I don't know whether this is something that was already fixed or has to be fixed, but I'm putting it here for completeness.