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Jun 17th, 2009
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g++ - linking error - undefined reference to <func_name>

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Hi,

I have 3 seperate make file where,
1st one generates a static library libCanOpen.a,
(using ""ar -r ")
2nd one creates a dynamically linkable library libPixyCANopen.so
(using "g++ -Wall -fPIC -shared")
and the 3rd one creates the executable by linking it to libPixyCANopen.so.

The 1st two makefiles build without a single warning (-Wall is used)
The last Makefile is generating linking error like the following:

C++ Syntax (Toggle Plain Text)
  1.  
  2. ../lib/libPixyCANopen.so: undefined reference to `coTimerPulse'
  3. ../lib/libPixyCANopen.so: undefined reference to `releaseTimer'

nm command shows that the corresponding object names are mangled (e.g. _Z12releaseTimerv), Using extern "C" in the header file did not remove it.

But, I am using g++ for every compilation, so I think the mangling should not matter.

Any suggestion is appreciated.

Thanks,
Anirban
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Re: g++ - linking error - undefined reference to <func_name>

> nm command shows that the corresponding object names are mangled (e.g. _Z12releaseTimerv),
Try adding the extern "C" to the implementation of those functions as well.

> Using extern "C" in the header file did not remove it.
But it did make it so that the users of that function did get the unmangled name.
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Re: g++ - linking error - undefined reference to <func_name>

Thanks .. that did help ..

There is only one linking error now, it's an extern variable .. the problem is same .. "undefined reference to <var_name>" ..

Need to share this variable .. that means I have to keep that extern stuff .. but, how?
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Re: g++ - linking error - undefined reference to <func_name>

Click to Expand / Collapse  Quote originally posted by anirbanjoy ...
Thanks .. that did help ..

There is only one linking error now, it's an extern variable .. the problem is same .. "undefined reference to <var_name>" ..

Need to share this variable .. that means I have to keep that extern stuff .. but, how?
The short answer to that one is that you should not have public access to the variable, access should be wrapped within get/set methods.

And you shouldn't have to worry about name-mangling, declaring functions as extern C isn't necessary. What do your makefiles look like?
Last edited by Stinomus; Jun 17th, 2009 at 7:21 pm.
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Re: g++ - linking error - undefined reference to <func_name>

It's shouldn't be necessary to use extern,
generally you have access to all the public variables and function in the symboltable, but only the externed are required to have the same signature, from version to version.
This is atleast how it should be.

http://people.redhat.com/drepper/dsohowto.pdf

try doing a ldd on your compiled files to see if anything is missing
Last edited by monkey_king; Jun 17th, 2009 at 10:51 pm.
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Jun 18th, 2009
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Re: g++ - linking error - undefined reference to <func_name>

This was my assumption too. As I am using g++ for all the cmpilation, extern "C" stuff does not seem logical. however, here are the outputs of 3 Makefiles in order:

Makefile #1
C++ Syntax (Toggle Plain Text)
  1. root:/tmp/trunk/CANopenStack/source# make CC=g++
  2. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o access_o.o access_o.c
  3. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o cmsmain.o cmsmain.c
  4. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o nmt.o nmt.c
  5. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o cmscodec.o cmscodec.c
  6. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o sdoserv.o sdoserv.c
  7. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o sdoclien.o sdoclien.c
  8. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o sdomain.o sdomain.c
  9. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o sdo.o sdo.c
  10. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o emerg.o emerg.c
  11. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o lme.o lme.c
  12. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o pdo.o pdo.c
  13. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o set_com.o set_com.c
  14. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o sync.o sync.c
  15. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o utility.o utility.c
  16. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o time.o time.c
  17. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o timer.o timer.c
  18. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o nmterr.o nmterr.c
  19. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o nmt_s.o nmt_s.c
  20. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o led.o led.c
  21. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o co_debug.o co_debug.c
  22. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o heartbt.o heartbt.c
  23. g++ -Wall -I/tmp/trunk/PIXYapi/include -I/tmp/trunk/PIXYapi -I../include -I. -I/tmp/trunk/CANdriver/include   -c -o slave_ut.o slave_ut.c
  24. ar -r ./lib/libCanOpen.a access_o.o cmsmain.o nmt.o cmscodec.o sdoserv.o sdoclien.o sdomain.o sdo.o emerg.o lme.o pdo.o set_com.o sync.o utility.o time.o timer.o nmterr.o nmt_s.o led.o co_debug.o heartbt.o slave_ut.o
  25. ar: creating ./lib/libCanOpen.a

Makefile #2
C++ Syntax (Toggle Plain Text)
  1. root:/tmp/trunk/PIXYapi# make CC=g++
  2. g++ -Wall -fPIC -shared -DNO_RT -I. -I./include -I../CANopenStack/include -I../CANdriver/include   -c -o ../CANdriver/src/can_p_l.o ../CANdriver/src/can_p_l.c
  3. g++ -Wall -fPIC -shared -DNO_RT -I. -I./include -I../CANopenStack/include -I../CANdriver/include   -c -o ../CANdriver/src/cpu_generic.o ../CANdriver/src/cpu_generic.c
  4. g++ -Wall -fPIC -shared -DNO_RT -I. -I./include -I../CANopenStack/include -I../CANdriver/include   -c -o ../CANdriver/src/cdriver.o ../CANdriver/src/cdriver.c
  5. g++ -Wall -fPIC -shared -DNO_RT -I. -I./include -I../CANopenStack/include -I../CANdriver/include   -c -o ../CANdriver/src/cpu.o ../CANdriver/src/cpu.c
  6. g++ -Wall -fPIC -shared -DNO_RT -I. -I./include -I../CANopenStack/include -I../CANdriver/include   -c -o co_init.o co_init.c
  7. g++ -Wall -fPIC -shared -DNO_RT -I. -I./include -I../CANopenStack/include -I../CANdriver/include   -c -o nmtslave.o nmtslave.c
  8. g++ -Wall -fPIC -shared -DNO_RT -I. -I./include -I../CANopenStack/include -I../CANdriver/include   -c -o objects.o objects.c
  9. g++ -Wall -fPIC -shared -DNO_RT -I. -I./include -I../CANopenStack/include -I../CANdriver/include   -c -o usr_301.o usr_301.c
  10. g++ -Wall -fPIC -shared -DNO_RT -I. -I./include -I../CANopenStack/include -I../CANdriver/include   -c -o PixyCANopen.o PixyCANopen.c
  11. g++ -Wall -fPIC -shared -DNO_RT -I. -I./include -I../CANopenStack/include -I../CANdriver/include -shared -o lib/libPixyCANopen.so ../CANdriver/src/can_p_l.o ../CANdriver/src/cpu_generic.o ../CANdriver/src/cdriver.o ../CANdriver/src/cpu.o co_init.o nmtslave.o objects.o usr_301.o PixyCANopen.o -L../CANopenStack/source/lib/ -L./lib -lpcan -lCanOpen -lh8com

Makefile #3

C++ Syntax (Toggle Plain Text)
  1. root:/tmp/trunk/PIXYapi/test# make
  2. g++ -g -Wall -DNO_RT -I../include/ -I../ -I../../CANopenStack/include/ -I../../CANdriver/include/ -I../CANopenStack/source   -c -o src/main.o src/main.cpp
  3. g++ -g -Wall -DNO_RT -I../include/ -I../ -I../../CANopenStack/include/ -I../../CANdriver/include/ -I../CANopenStack/source -L../lib -lPixyCANopen -o ApiTest src/main.o 
  4. ../lib/libPixyCANopen.so: undefined reference to `coTimerPulse'
  5.  

Existence of coTimerPulse in code is:
C++ Syntax (Toggle Plain Text)
  1. root:/tmp/trunk# grep -nR "coTimerPulse" *
  2. CANdriver/src/.svn/text-base/cpu_generic.c.svn-base:164:VOLATILE UNSIGNED16 CO_CONST coTimerPulse = CONFIG_TIMER_INC; /**< length of 1 tick / unit 100us */
  3. CANdriver/src/cpu_generic.c:169:UNSIGNED16 CO_CONST coTimerPulse = CONFIG_TIMER_INC; /**< length of 1 tick / unit 100us */
  4. CANopenStack/include/co_drv.h:149:extern UNSIGNED16 coTimerPulse;
  5. CANopenStack/include/co_drv.h:151:extern UNSIGNED16 CO_CONST coTimerPulse;
  6. Binary file CANopenStack/source/timer.o matches
  7. CANopenStack/source/lme.c:533:    GL_VAR(coTimerPulse) = CONFIG_TIMER_INC;
  8. Binary file CANopenStack/source/lib/libCanOpen.a matches
  9. CANopenStack/source/globvars.c:261://UNSIGNED16 coTimerPulse;
  10. CANopenStack/source/timer.c:565:    if (timerVal > ((UNSIGNED32)GL_VAR(coTimerPulse) << 15))  {
  11. CANopenStack/source/timer.c:573:    if ((timerVal + pTimer->restTime) <= GL_VAR(coTimerPulse))  {
  12. CANopenStack/source/timer.c:580:        pTimer->endTime = tVal / GL_VAR(coTimerPulse);
  13. CANopenStack/source/timer.c:582:        pTimer->endTime = (UNSIGNED16)(tVal / GL_VAR(coTimerPulse));
  14. CANopenStack/source/timer.c:585:        pTimer->restTime = (UNSIGNED16)(tVal % GL_VAR(coTimerPulse));
  15. CANopenStack/source/timer.c:744:        retVal = addTimerEvent(pTimer, pTimer->endTime * GL_VAR(coTimerPulse),
  16. CANopenStack/source/timer.c:829:    ticks = timerVal / GL_VAR(coTimerPulse);
  17. CANopenStack/source/timer.c:831:    if ((ticks * GL_VAR(coTimerPulse)) < timerVal)  {
  18. GL_VAR(coTimerPulse) = CONFIG_TIMER_INC;
  19. Binary file PIXYapi/test/lib/libPixyCANopen.so matches
  20. Binary file PIXYapi/lib/libPixyCANopen.so matches

Click to Expand / Collapse  Quote originally posted by monkey_king ...
It's shouldn't be necessary to use extern,
generally you have access to all the public variables and function in the symboltable, but only the externed are required to have the same signature, from version to version.
This is atleast how it should be.

http://people.redhat.com/drepper/dsohowto.pdf

try doing a ldd on your compiled files to see if anything is missing
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Jun 18th, 2009
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Re: g++ - linking error - undefined reference to <func_name>

Could you try doing a
'ldd libPixyCANopen.so'
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Re: g++ - linking error - undefined reference to <func_name>

root:/tmp/trunk/PIXYapi/lib# ldd libPixyCANopen.so
libpcan.so.0 => /usr/lib/libpcan.so.0 (0x00138000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x0013b000)
libm.so.6 => /lib/libm.so.6 (0x0021c000)
libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x00241000)
libc.so.6 => /lib/libc.so.6 (0x0024c000)
/lib/ld-linux.so.2 (0xb7f07000)$

I removed the extern variable and now the linking problem is gone .. but still I will keep trying to remove the extern "C" completely from my code.

Click to Expand / Collapse  Quote originally posted by monkey_king ...
Could you try doing a
'ldd libPixyCANopen.so'
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