"relocation R_X86_64_32 against `.bss' can not be used when making a shared..." error

aryan1 · 01-20-2010, 09:04 AM

Hi All,

I am getting "relocation R_X86_64_32 against `.bss' can not be used when making a shared object; recompile with -fPIC" error when compiling a shared object with optimization option -O2 enabled using GNU GCC:

First, I compile a static library, which is used by the shared object, as follows:

Code:

g++  -g -O2 -c common/src/packet-class-registry.cc
ar  -cvq libclassreg.a common/src/packet-class-registry.o

Below is how I compile the shared object, which uses libclassreg.a:

Code:

g++  -g -O2 -fPIC -c packet-v4.cc -o packet-v4.o 
gcc  -shared -Wl,-soname,libv4.so.1 -o libv4.so.1.0 packet-v4.o -Lcommon/lib -Lconf/configLib/lib -lclassreg -lNsConf 
/usr/bin/ld: common/lib/libclassreg.a(packet-class-registry.o): relocation R_X86_64_32 against `.bss' can not be used when making a shared object; recompile with -fPIC
common/lib/libclassreg.a: could not read symbols: Bad value
collect2: ld returned 1 exit status
make: *** [libv4.so] Error 1

Is this a problem regarding the order of compiler options ? (-O2 appears before -fPIC)

Or is it something else ?

Thanks.

johnsfine · 01-20-2010, 09:19 AM

In that situation, you need -fPIC when compiling the code that goes into the .a file, not just when compiling the main code of the .so file.

So the first g++ command you quoted above also needs -fPIC

aryan1 · 01-20-2010, 01:39 PM

Quote:

Originally Posted by johnsfine

In that situation, you need -fPIC when compiling the code that goes into the .a file, not just when compiling the main code of the .so file.

So the first g++ command you quoted above also needs -fPIC

Is the side-effect of not using -fPIC when compiling a static library which goes into a shared object platform-dependent ?

I am asking this since the way of compilation denoted in my first thread works "without" any problem on two different machines. That is, -fPIC is not used to compile .a file, which is linked into a shared object. However, on another machine, the same compilation fails.

johnsfine · 01-20-2010, 01:47 PM

Quote:

Originally Posted by aryan1

Is the side-effect of not using -fPIC when compiling a static library which goes into a shared object platform-dependent ?

Yes. I assumed we were just talking about x86_64.

I don't have as good an understanding of this question on any other platform.

aryan1 · 01-20-2010, 02:03 PM

Quote:

Originally Posted by johnsfine

Yes. I assumed we were just talking about x86_64.

Sorry. I am also talking about x86. By "different platforms", I meant different machines.

Let me clarify my question. The way of compilation above succeeded in one x86 machine, but it failed on another x86 machine.

So how come does the lack of -fPIC usage cause an error on one x86 machine, but not on another x86 ?

The one where the compilation fails is a 64-bit machine. I am not sure about the other one.

And, does the usage of g++ and gcc together like above work all the times ?

johnsfine · 01-20-2010, 03:13 PM

Quote:

Originally Posted by aryan1

Sorry. I am also talking about x86. By "different platforms", I meant different machines.

By different platforms, I meant things like x86 vs. x86_64.

Quote:

So how come does the lack of -fPIC usage cause an error on one x86 machine, but not on another x86 ?

It failed on x86_64. I don't know what would happen on x86 without that -fPIC option when building the .a.

The fact that x86_64 hardware can run your choice of x86 or x86_64 architecture, does not make x86 and x86_64 the same "platform".

Quote:

The one where the compilation fails is a 64-bit machine. I am not sure about the other one.

32 bit is x86 architecture.

Maybe there is a machine specific difference in the way g++ is installed to make -fPIC the default on one system, so you don't need to specify it. That is unlikely, but not impossible.

More likely, the relevant difference is x86 (32 bit) vs. x86_64.

Quote:

And, does the usage of g++ and gcc together like above work all the times ?

g++ and gcc are very similar front ends to the same compile and link tools. When compiling the choice of command g++ vs. gcc determines whether the compiler is expecting C++ or C code. But when linking (as you seem to be in your use of GCC) I don't know of anything different that the gcc command would do compared to a g++ command.

aryan1 · 01-21-2010, 01:00 AM

Quote:

Originally Posted by johnsfine

More likely, the relevant difference is x86 (32 bit) vs. x86_64.

I agree.

I found out that the machine where the compilation without -fPIC option succeeds has an 32-bit OS. On the other hand, the other one where it fails is x86_64 with an 64-bit OS.

As a general principle, is it OK if I make -fPIC part of all of my CFLAGS settings ?

johnsfine · 01-21-2010, 08:26 AM

I'm pretty sure -fPIC will work OK outside of shared libraries, but it may generate code that is less efficient and also harder to debug.

I would suggest not making -fPIC always part of the CFLAGS.