Date: Fri, 30 Mar 2007 20:14:39 -0800 From: Garrett Cooper <youshi10@u.washington.edu> To: freebsd-hackers@freebsd.org Subject: Re: Thread local storage not working with -fPIC and shared objects Message-ID: <460DE02F.5020202@u.washington.edu> In-Reply-To: <200703310426.23953.pieter@degoeje.nl> References: <200703310426.23953.pieter@degoeje.nl>
next in thread | previous in thread | raw e-mail | index | archive | help
Pieter de Goeje wrote:
> Hello List,
>
> I have these files:
> --- loader.cpp ---
> #include <stdio.h>
> #include "tls.h"
>
> int main() {
> tls = 0;
> printf("%d\n", tls);
> }
>
> --- tls.cpp ---
> #include "tls.h"
> int __thread tls;
>
> --- tls.h ---
> extern __thread int tls;
>
> When I compile them like this:
> c++ -fPIC -o tls.so tls.cpp -shared
> c++ -fPIC -o loader loader.cpp tls.so
>
> And run the resulting program, I get:
> pyotr@nox:~/projects/misc/tls> ./loader
> /libexec/ld-elf.so.1: ./loader: Unsupported relocation type 37 in non-PLT
> relocations
>
> When I omit -fPIC, it runs fine. But I need fPIC for the shared object on
> amd64 arch. I've tried it on Linux/i386 (gcc 4.1) and it ran fine (with
> fPIC).
>
> Much to my surprise however, a particularly large application I'm working on
> did compile & run on FreeBSD/amd64 using -fpic (lowercase) and gcc 4.3.
> Trying -fpic on FreeBSD/i386 resulted in failure.
>
> FYI, I need tls to work because I'm using OpenMP's tls (#pragma omp
> threadprivate()) support in gcc 4.3.
>
> The workaround I found on FreeBSD/amd64 was linking the main executable
> with -fno-PIC, or building everything with -fpic. (both workarounds didn't
> work on FreeBSD/i386)
>
> I would be grateful if someone could shed some light on this.
>
> Regards,
> Pieter de Goeje
Pieter,
Did you know that -fPIC and -fpic aren't the same? From
<http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Code-Gen-Options.html#Code-Gen-Options>:
|-fpic|
Generate position-independent code (PIC) suitable for use in a
shared library, if supported for the target machine. Such code
accesses all constant addresses through a global offset table (GOT).
The dynamic loader resolves the GOT entries when the program starts
(the dynamic loader is not part of GCC; it is part of the operating
system). If the GOT size for the linked executable exceeds a
machine-specific maximum size, you get an error message from the
linker indicating that -fpic does not work; in that case, recompile
with -fPIC instead. (These maximums are 8k on the SPARC and 32k on
the m68k and RS/6000. The 386 has no such limit.)
Position-independent code requires special support, and therefore
works only on certain machines. For the 386, GCC supports PIC for
System V but not for the Sun 386i. Code generated for the IBM
RS/6000 is always position-independent.
|-fPIC|
If supported for the target machine, emit position-independent code,
suitable for dynamic linking and avoiding any limit on the size of
the global offset table. This option makes a difference on the m68k,
PowerPC and SPARC.
Position-independent code requires special support, and therefore
works only on certain machines.
Cheers,
-Garrett
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?460DE02F.5020202>