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digitalmars.D.learn - How may I tell dub where to find a C library for linking?

reply Pablo De =?UTF-8?B?TsOhcG9saQ==?= <nospam dev.null> writes:
Hi,

I was playing with the example in

https://github.com/MoritzMaxeiner/llvm-d/tree/master/examples/fibonacci

When I try to build it using dub, the linker cannot find the LLVM 
library

$ dub build
Performing "debug" build using /usr/bin/dmd for x86_64.
llvm-d 2.4.1: target for configuration "native-target" is up to 
date.
fibonacci ~master: building configuration "link-single"...
Linking...
/usr/bin/ld: cannot find -lLLVM
collect2: error: ld returned 1 exit status
Error: linker exited with status 1
/usr/bin/dmd failed with exit code 1.

On my system (Debian GNU/Linux 9, 64 bits) the library is in the 
directory /usr/lib/llvm-6.0/lib/

$ ls -l /usr/lib/llvm-6.0/lib/libLLVM.so
lrwxrwxrwx 1 root root 14 oct 24 19:44 
/usr/lib/llvm-6.0/lib/libLLVM.so -> libLLVM-6.0.so

But how am I supposed to tell dub this, so it passes this 
information to the linker??

I guess I should set "libs" in dubs.json

Off course I have tried to read the dub documentation (like 
https://code.dlang.org/package-format?lang=json) but it was not 
clear enough to me. Please note that this library cannot be find 
by pkgconfig.

Many thanks!
Pablo
Dec 09 2018
parent reply evilrat <evilrat666 gmail.com> writes:
On Monday, 10 December 2018 at 02:59:21 UTC, Pablo De Nápoli 
wrote:

 On my system (Debian GNU/Linux 9, 64 bits) the library is in 
 the directory /usr/lib/llvm-6.0/lib/

 $ ls -l /usr/lib/llvm-6.0/lib/libLLVM.so
 lrwxrwxrwx 1 root root 14 oct 24 19:44 
 /usr/lib/llvm-6.0/lib/libLLVM.so -> libLLVM-6.0.so

 But how am I supposed to tell dub this, so it passes this 
 information to the linker??

 I guess I should set "libs" in dubs.json


IIRC your guess is correct. "libs" is passed directly to linker 
and is the only way to do it, so you just do smth like this

    "libs" : ["-L/usr/lib/llvm-6.0/lib/", "libLLVM-6.0"]

note that this -L will be extended for linker as -L-L...
(also note that you can do platform specific way with 
"libs-windows", "libs-posix"? to pick proper paths per platform)

Though I'm not a linux pro and don't remember if linking to .so 
is same as linking import library, if this is not the case you 
just need to set RPATH or whatever it is so it can find dynamic 
lib.
Dec 09 2018
parent reply Pab De =?UTF-8?B?TsOhcG9saQ==?= <pdenapo nospam.null> writes:
On Monday, 10 December 2018 at 05:24:16 UTC, evilrat wrote:

 On Monday, 10 December 2018 at 02:59:21 UTC, Pablo De Nápoli 
 wrote:

 On my system (Debian GNU/Linux 9, 64 bits) the library is in 
 the directory /usr/lib/llvm-6.0/lib/

 $ ls -l /usr/lib/llvm-6.0/lib/libLLVM.so
 lrwxrwxrwx 1 root root 14 oct 24 19:44 
 /usr/lib/llvm-6.0/lib/libLLVM.so -> libLLVM-6.0.so

 But how am I supposed to tell dub this, so it passes this 
 information to the linker??

 I guess I should set "libs" in dubs.json


 IIRC your guess is correct. "libs" is passed directly to linker 
 and is the only way to do it, so you just do smth like this

    "libs" : ["-L/usr/lib/llvm-6.0/lib/", "libLLVM-6.0"]

 note that this -L will be extended for linker as -L-L...
 (also note that you can do platform specific way with 
 "libs-windows", "libs-posix"? to pick proper paths per platform)

 Though I'm not a linux pro and don't remember if linking to .so 
 is same as linking import library, if this is not the case you 
 just need to set RPATH or whatever it is so it can find dynamic 
 lib.


Many thanks but that didn't work,as I got the message

$ dub build
Performing "debug" build using /usr/bin/dmd for x86_64.
llvm-d 2.4.1: target for configuration "native-target" is up to 
date.
fibonacci ~master: building configuration "link-single"...
Linking...
/usr/bin/ld: cannot find -l-L/usr/lib/llvm-6.0/lib/
/usr/bin/ld: cannot find -llibLLVM-6.0
collect2: error: ld returned 1 exit status
Error: linker exited with status 1
/usr/bin/dmd failed with exit code 1.

The problem is that GNU ld expects the -L for specifying the 
search path, not -l

What actually did work was:

1) Setting the LD_LIBRARY_PATH environment variable with

export LD_LIBRARY_PATH=/usr/lib/llvm-6.0/lib/

and using

  "libs" : ["LLVM-6.0"]

in dub.json. (this is somewhat nasty, it would be nice to keep 
all the information together in dub.json)

Moreover, the information about the path for linking with LLVM 
can be obtained from the shell script llvconfig as

$llvm-config-6.0 --libs --ldflags
-L/usr/lib/llvm-6.0/lib
-lLLVM-6.0

It would be better not to hard-code this information in dub.json 
but I don't know if it possible to invoke a shell script with 
something like
$(llvm-config-6.0 --libs --ldflags) (as you would do in a 
Makefile)

This method used to be employed by many other libraries besides 
llvm (but many are migrating to pkgconfig).

Many thanks!)
Dec 10 2018
parent Mike Parker <aldacron gmail.com> writes:
On Monday, 10 December 2018 at 15:38:24 UTC, Pab De Nápoli wrote:



 1) Setting the LD_LIBRARY_PATH environment variable with

 export LD_LIBRARY_PATH=/usr/lib/llvm-6.0/lib/

 and using

  "libs" : ["LLVM-6.0"]

 in dub.json. (this is somewhat nasty, it would be nice to keep 
 all the information together in dub.json)

 Moreover, the information about the path for linking with LLVM 
 can be obtained from the shell script llvconfig as

 $llvm-config-6.0 --libs --ldflags
 -L/usr/lib/llvm-6.0/lib
 -lLLVM-6.0


If you do want to put it in the dub config, the -L option, and 
any linker options, can go in the "lflags" directive. "libs" is 
for libraries only.

"lflags": ["-L/usr/lib/llvm-6.0/lib"],
"libs": ["LLVM-6.0"]
Dec 10 2018