Re: XS linking problem

I just entered your example, and after a little fiddling, I was able to reproduce your error:

$ make
 . . . stuff elided . . .
Kbh.o: In function `XS_Kbh_send_string':
/Work/Perl/Perlmonks/XS_linking/Kbh.c:173: undefined reference to `sen
+d_string'
/Work/Perl/Perlmonks/XS_linking/Kbh.c:173:(.text+0xb3): relocation tru
+ncated to fit: R_X86_64_PC32 against undefined symbol `send_string'
collect2: error: ld returned 1 exit status
make: *** [Makefile:472: blib/arch/auto/Kbh/Kbh.dll] Error 1
[download]

I took a look at the object files it created and saw the following:

$ objdump.exe -t Kbh.o

Kbh.o:     file format pe-x86-64

SYMBOL TABLE:
[  0](sec -2)(fl 0x00)(ty   0)(scl 103) (nx 1) 0x0000000000000000 Kbh.
+c
File
[  2](sec  1)(fl 0x00)(ty  20)(scl   3) (nx 1) 0x0000000000000000 XS_K
+bh_send_string
AUX tagndx 0 ttlsiz 0x0 lnnos 0 next 0
   . . . elided . . .
[ 37](sec  0)(fl 0x00)(ty   0)(scl   2) (nx 0) 0x0000000000000000 __im
+p_PL_thr_key
[ 38](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x0000000000000000 pthr
+ead_getspecific
[ 39](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x0000000000000000 Perl
+_sv_2pv_flags
[ 40](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x0000000000000000 send
+_string
[ 41](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x0000000000000000 Perl
+_croak_xs_usage
[ 42](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x0000000000000000 Perl
+_xs_handshake
[ 43](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x0000000000000000 Perl
+_newXS_deffile
[ 44](sec  0)(fl 0x00)(ty  20)(scl   2) (nx 0) 0x0000000000000000 Perl
+_xs_boot_epilog

$ objdump.exe -t send_string.o

send_string.o:     file format pe-x86-64

SYMBOL TABLE:
[  0](sec -2)(fl 0x00)(ty   0)(scl 103) (nx 1) 0x0000000000000000 send
+_string.cpp
File
[  2](sec  1)(fl 0x00)(ty  20)(scl   2) (nx 1) 0x0000000000000000 _Z11
+send_stringPKc
AUX tagndx 0 ttlsiz 0x0 lnnos 0 next 0
   . . . elided . . .
[download]

As you can see, Kbh.o expects a symbol named "send_string", but send_string.o provides "_Z11send_stringPKc". The reason is that you put a .cpp suffix on your send_string source file, so gcc compiled it as a C++ program instead of C. C++ allows functions with the same name based on the argument types, and to do so and let the linker still work it does something called "name mangling" to add type information to the symbol name. So either alter the compiler flags to force gcc to compile it as a C program, or do what I did and simply rename send_string.cpp to send_string.c and give it a try. When I did so, it compiled and linked successfully:

$ make
cp lib/Kbh.pm blib/lib/Kbh.pm
cp Makefile.pl blib/lib/Makefile.pl
Running Mkbootstrap for Kbh ()
chmod 644 "Kbh.bs"
"/usr/bin/perl.exe" "/usr/lib/perl5/5.22/ExtUtils/xsubpp"  -typemap "/
+usr/lib/perl5/5.22/ExtUtils/typemap"  Kbh.xs > Kbh.xsc && mv Kbh.xsc 
+Kbh.c
gcc -c   -DPERL_USE_SAFE_PUTENV -D_GNU_SOURCE -U__STRICT_ANSI__ -ggdb 
+-O2 -pipe -Wimplicit-function-declaration -fdebug-prefix-map=/mnt/sha
+re/maint/perl.x86_64/build=/usr/src/debug/perl-5.22.4-1 -fdebug-prefi
+x-map=/mnt/share/maint/perl.x86_64/src/perl-5.22.4=/usr/src/debug/per
+l-5.22.4-1 -fwrapv -fno-strict-aliasing -fstack-protector-strong -D_F
+ORTIFY_SOURCE=2 -DUSEIMPORTLIB -O3   -DVERSION=\"0.01\" -DXS_VERSION=
+\"0.01\"  "-I/usr/lib/perl5/5.22/x86_64-cygwin-threads/CORE"   Kbh.c
gcc -c   -DPERL_USE_SAFE_PUTENV -D_GNU_SOURCE -U__STRICT_ANSI__ -ggdb 
+-O2 -pipe -Wimplicit-function-declaration -fdebug-prefix-map=/mnt/sha
+re/maint/perl.x86_64/build=/usr/src/debug/perl-5.22.4-1 -fdebug-prefi
+x-map=/mnt/share/maint/perl.x86_64/src/perl-5.22.4=/usr/src/debug/per
+l-5.22.4-1 -fwrapv -fno-strict-aliasing -fstack-protector-strong -D_F
+ORTIFY_SOURCE=2 -DUSEIMPORTLIB -O3   -DVERSION=\"0.01\" -DXS_VERSION=
+\"0.01\"  "-I/usr/lib/perl5/5.22/x86_64-cygwin-threads/CORE"   send_s
+tring.c
rm -f blib/arch/auto/Kbh/Kbh.dll
g++  --shared  -Wl,--enable-auto-import -Wl,--export-all-symbols -Wl,-
+-enable-auto-image-base -fstack-protector-strong Kbh.o send_string.o 
+ -o blib/arch/auto/Kbh/Kbh.dll         \
  /usr/lib/perl5/5.22/x86_64-cygwin-threads/CORE/cygperl5_22.dll      
+  \

chmod 755 blib/arch/auto/Kbh/Kbh.dll
"/usr/bin/perl.exe" -MExtUtils::Command::MM -e 'cp_nonempty' -- Kbh.bs
+ blib/arch/auto/Kbh/Kbh.bs 644
[download]

I've not done any XS coding before, which is why I tried to help--this way I could learn a little about it. When I originally tried to compile your program, it didn't like the wchar_t type, so I just changed all the "const wchar_t *" to "char *". Then I was able to essentially reproduce what you had.

$ cat Kbh.xs
#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"

#include "ppport.h"
#include "send_string.h"

MODULE = Kbh PACKAGE = Kbh

PROTOTYPES: DISABLE

void
send_string(s)
    const char * s

TYPEMAP: <<HERE
const char * T_PV
HERE

$ cat send_string.c
#include "send_string.h"
#include <stdio.h>
void send_string(const char* str) {
    puts(str);
}

$ cat send_string.h
void send_string(const char* str);

$ cat lib/Kbh.pm
package Kbh;
our $VERSION = '0.01';
require XSLoader;
XSLoader::load('Kbh', $VERSION);
1;

$ cat Makefile.pl
use ExtUtils::MakeMaker;
WriteMakefile (
    NAME=>'Kbh',
    VERSION_FROM =>'lib/Kbh.pm',
    OBJECT => 'Kbh.o send_string.o',
)


$ perl Makefile.pl
Generating a Unix-style Makefile
Writing Makefile for Kbh
Writing MYMETA.yml and MYMETA.json

$ make
cp Makefile.pl blib/lib/Makefile.pl
cp lib/Kbh.pm blib/lib/Kbh.pm
Running Mkbootstrap for Kbh ()
chmod 644 "Kbh.bs"
"/usr/bin/perl.exe" "/usr/lib/perl5/5.22/ExtUtils/xsubpp"  -typemap "/
+usr/lib/perl5/5.22/ExtUtils/typemap"  Kbh.xs > Kbh.xsc && mv Kbh.xsc 
+Kbh.c
gcc -c   -DPERL_USE_SAFE_PUTENV -D_GNU_SOURCE -U__STRICT_ANSI__ -ggdb 
+-O2 -pipe -Wimplicit-function-declaration -fdebug-prefix-map=/mnt/sha
+re/maint/perl.x86_64/build=/usr/src/debug/perl-5.22.4-1 -fdebug-prefi
+x-map=/mnt/share/maint/perl.x86_64/src/perl-5.22.4=/usr/src/debug/per
+l-5.22.4-1 -fwrapv -fno-strict-aliasing -fstack-protector-strong -D_F
+ORTIFY_SOURCE=2 -DUSEIMPORTLIB -O3   -DVERSION=\"0.01\" -DXS_VERSION=
+\"0.01\"  "-I/usr/lib/perl5/5.22/x86_64-cygwin-threads/CORE"   Kbh.c
gcc -c   -DPERL_USE_SAFE_PUTENV -D_GNU_SOURCE -U__STRICT_ANSI__ -ggdb 
+-O2 -pipe -Wimplicit-function-declaration -fdebug-prefix-map=/mnt/sha
+re/maint/perl.x86_64/build=/usr/src/debug/perl-5.22.4-1 -fdebug-prefi
+x-map=/mnt/share/maint/perl.x86_64/src/perl-5.22.4=/usr/src/debug/per
+l-5.22.4-1 -fwrapv -fno-strict-aliasing -fstack-protector-strong -D_F
+ORTIFY_SOURCE=2 -DUSEIMPORTLIB -O3   -DVERSION=\"0.01\" -DXS_VERSION=
+\"0.01\"  "-I/usr/lib/perl5/5.22/x86_64-cygwin-threads/CORE"   send_s
+tring.c
rm -f blib/arch/auto/Kbh/Kbh.dll
g++  --shared  -Wl,--enable-auto-import -Wl,--export-all-symbols -Wl,-
+-enable-auto-image-base -fstack-protector-strong Kbh.o send_string.o 
+ -o blib/arch/auto/Kbh/Kbh.dll  \
  /usr/lib/perl5/5.22/x86_64-cygwin-threads/CORE/cygperl5_22.dll      
+  \

chmod 755 blib/arch/auto/Kbh/Kbh.dll
"/usr/bin/perl.exe" -MExtUtils::Command::MM -e 'cp_nonempty' -- Kbh.bs
+ blib/arch/auto/Kbh/Kbh.bs 644
[download]

...roboticus

When your only tool is a hammer, all problems look like your thumb.

Comment on Re: XS linking problem Select or Download Code

Replies are listed 'Best First'.
Re^2: XS linking problem by frazap (Monk) on Sep 21, 2017 at 07:53 UTC
Thanks a lot for the use objdump on the object file and for the explanation ! I saw that there is a ExtUtils::XSpp module but it use build.pl instead of make and I have no experience with this. I will translate my cpp code in c François	[reply]
Re^3: XS linking problem by GrandFather (Saint) on Sep 23, 2017 at 22:12 UTC
No need to stoop that low! Instead prefix the functions you want to have C linkage with `extern "C"`: `extern "C" void send_string (const wchar_t * str);` [download] If you are forward declaring the function in a header you don't need to provide the extern declaration in the definition. Now you can provide a C API and still have the power of C++ to go forth and conquer the world. Premature optimization is the root of all job security	[reply] [d/l] [select]