[CMake] Link order (Ubuntu)

Discussion:

scrgiorgio

2018-11-06 00:52:58 UTC

i have the following CMakeList.txt:

add_library(ImpLib SHARED IMPORTED GLOBAL)
set_property(TARGET ImpLib APPEND PROPERTY INTERFACE_INCLUDE_DIRECTORIES
...)
set_target_properties(ImpLib PROPERTIES IMPORTED_LOCATION ...)

add_library(A SHARED)
# COMMENTED! A uses ImpLib but cannot link it because some third-party
executables requires 'run-time symbol resolution'
# target_link_libraries(A PUBLIC ImpLib )

add_library(B SHARED)
target_link_libraries(B PUBLIC A)
# COMMENTED! B uses ImpLib but cannot link it for the same previous reason
# target_link_libraries(B PUBLIC ImpLib )

# my executable requires ImpLib explicit/default cmake linking
add_executable(MyExe)
target_link_libraries(MyExe B)
target_link_libraries(MyExe ImpLib )

The CMake generated link order is (g++ -o .... ): "B;ImportedExtLib;A"
But in this way A cannot find symbols from ImpLib (at least using g++).

The right order is: "B;A;ImpLib"

I tried with "target_link_libraries(A INTERFACE ImpLib)" but then B will
link ImpLib

I tried "set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS}
-Wl,--start-group")" but sometimes it does not work.

is it doable? Can I force the right order?

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Bo Zhou

2018-11-06 01:16:05 UTC

Permalink

Hi

This is the classical issue of GNU toolchain for many years, usually super
painful when the program has to be linked with several static libraries.

One easy way to solve this issue is that you could specify the same library
for multiple times if the manual order really doesn't work well, then the
generated binary might have the complete symbols.

Thanks very much.

Post by scrgiorgio
add_library(ImpLib SHARED IMPORTED GLOBAL)
set_property(TARGET ImpLib APPEND PROPERTY INTERFACE_INCLUDE_DIRECTORIES
...)
set_target_properties(ImpLib PROPERTIES IMPORTED_LOCATION ...)
add_library(A SHARED)
# COMMENTED! A uses ImpLib but cannot link it because some third-party
executables requires 'run-time symbol resolution'
# target_link_libraries(A PUBLIC ImpLib )
add_library(B SHARED)
target_link_libraries(B PUBLIC A)
# COMMENTED! B uses ImpLib but cannot link it for the same previous reason
# target_link_libraries(B PUBLIC ImpLib )
# my executable requires ImpLib explicit/default cmake linking
add_executable(MyExe)
target_link_libraries(MyExe B)
target_link_libraries(MyExe ImpLib )
The CMake generated link order is (g++ -o .... ): "B;ImportedExtLib;A"
But in this way A cannot find symbols from ImpLib (at least using g++).
The right order is: "B;A;ImpLib"
I tried with "target_link_libraries(A INTERFACE ImpLib)" but then B will
link ImpLib
I tried "set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS}
-Wl,--start-group")" but sometimes it does not work.
is it doable? Can I force the right order?
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scrgiorgio

2018-11-06 13:24:37 UTC

Permalink

Thanks for the help,

trying this (or any combination):

target_link_libraries(MyExe B)
target_link_libraries(MyExe A )
target_link_libraries(MyExe ImpLib)

I get this order:

'B;...whatever...;A;ImpLib"

and the last past is causing the problem. Apparently there is no way to
change the right part (-Wl,--start-group -Wl,--end-groun sometimes work,
sometimes not).
Any advice?

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Robert Maynard

2018-11-06 13:29:33 UTC

Permalink

The target_link_libraries has a property called
LINK_INTERFACE_MULTIPLICITY that should help you out.
https://cmake.org/cmake/help/v3.13/command/target_link_libraries.html#cyclic-dependencies-of-static-libraries

Post by scrgiorgio
Thanks for the help,
target_link_libraries(MyExe B)
target_link_libraries(MyExe A )
target_link_libraries(MyExe ImpLib)
'B;...whatever...;A;ImpLib"
and the last past is causing the problem. Apparently there is no way to
change the right part (-Wl,--start-group -Wl,--end-groun sometimes work,
sometimes not).
Any advice?
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Giorgio Scorzelli

2018-11-06 13:51:08 UTC

Permalink

I read the docs about LINK_INTERFACE_MULTIPLICITY too.
But I'm not in the situation of a "cyclic dependency" so I 'm not sure if
it solve my problem.
In my case (with B A and ImpLib) what would be the syntax?

Il giorno mar 6 nov 2018 alle ore 06:30 Robert Maynard <

Post by Robert Maynard
The target_link_libraries has a property called
LINK_INTERFACE_MULTIPLICITY that should help you out.
https://cmake.org/cmake/help/v3.13/command/target_link_libraries.html#cyclic-dependencies-of-static-libraries

http://www.cmake.org/Wiki/CMake_FAQ

Post by scrgiorgio
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Post by scrgiorgio
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Robert Maynard

2018-11-06 13:59:21 UTC

Permalink

You have order dependent static libraries which can be solved by
constructing a cycle. As Bo stated by constructing the cycle
B;A;ImportedExtLib;B;A each library can see each other.

Looking at your original code example it looks like you are importing
the libraries as SHARED, but I think these are actually static
libraries and should be imported as such so that CMake does the
automatic cycle creation. In general CMake doesn't do cycle creation
for shared libraries as they are not link order dependent.

Post by Giorgio Scorzelli
I read the docs about LINK_INTERFACE_MULTIPLICITY too.
But I'm not in the situation of a "cyclic dependency" so I 'm not sure if it solve my problem.
In my case (with B A and ImpLib) what would be the syntax?

Giorgio Scorzelli

2018-11-06 14:19:17 UTC

Permalink

Thanks for you help.

They are really shared lib, not static. I know it sounds weird: it's a
python extension which must not link the ${PYTHON_LIBRARY} (according to
official docs; in fact If I do so I get a segmentation fault) but finally
in my executable,a sort of custom/home made ${PYTHON_EXECUTABLE}, I have
to link the ${PYTHON_LIBRARY}.

About the "B;A;ImportedExtLib;B;A" order. I agree too: it SHOULD work.
Let's say I do:

target_link_libraries(MyExe B A ImpLib)

in command line (make VERBOSE=1) I;m getting

g++ .... -o MyExe B A ImpLib A

The last "A" is coming from target_link_libraries(B PUBLIC A) and the
linker is complaining that this last "A" has undefined symbols.

Thanks.Giorgio.

Il giorno mar 6 nov 2018 alle ore 06:59 Robert Maynard <

Post by Robert Maynard
You have order dependent static libraries which can be solved by
constructing a cycle. As Bo stated by constructing the cycle
B;A;ImportedExtLib;B;A each library can see each other.
Looking at your original code example it looks like you are importing
the libraries as SHARED, but I think these are actually static
libraries and should be imported as such so that CMake does the
automatic cycle creation. In general CMake doesn't do cycle creation
for shared libraries as they are not link order dependent.

Post by Giorgio Scorzelli
I read the docs about LINK_INTERFACE_MULTIPLICITY too.
But I'm not in the situation of a "cyclic dependency" so I 'm not sure

if it solve my problem.

Post by Giorgio Scorzelli
In my case (with B A and ImpLib) what would be the syntax?
Il giorno mar 6 nov 2018 alle ore 06:30 Robert Maynard <

Post by Robert Maynard
The target_link_libraries has a property called
LINK_INTERFACE_MULTIPLICITY that should help you out.

https://cmake.org/cmake/help/v3.13/command/target_link_libraries.html#cyclic-dependencies-of-static-libraries