I see the following behavior when compiling an OpenMP program: $ cat omp.c
extern void omp_set_num_threads (int); #define NT 4 int main() { omp_set_num_threads(NT); return(0); } $ gcc --version gcc (GCC) 4.2.0 20070514 (rpm:4) Copyright (C) 2007 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. $ gcc -static -fopenmp omp.c -lc /usr/lib/../lib64/libpthread.a(lockfile.o)(.text+0xb0): In function `__flockfile': /usr/src/packages/BUILD/glibc-2.3/linuxthreads/lockfile.c:29: multiple definition of `_IO_flockfile' /usr/lib/../lib64/libc.a(flockfile.o)(.text+0x0):../linuxthreads/sysdeps/pthread/flockfile.c:30: first defined here /usr/bin/ld: Warning: size of symbol `_IO_flockfile' changed from 24 in /usr/lib/../lib64/libc.a(flockfile.o) to 12 in /usr/lib/../lib64/libc.a(flockfile.o) /usr/lib/../lib64/libpthread.a(lockfile.o)(.text+0xb0): In function `__flockfile': /usr/src/packages/BUILD/glibc-2.3/linuxthreads/lockfile.c:29: multiple definition of `__flockfile' /usr/lib/../lib64/libc.a(flockfile.o)(.text+0x0):../linuxthreads/sysdeps/pthread/flockfile.c:30: first defined here /usr/bin/ld: Warning: size of symbol `__flockfile' changed from 24 in /usr/lib/../lib64/libc.a(flockfile.o) to 12 in /usr/lib/../lib64/libc.a(flockfile.o) /usr/lib/../lib64/libpthread.a(lockfile.o)(.text+0xa0): In function `__funlockfile': /usr/src/packages/BUILD/glibc-2.3/linuxthreads/lockfile.c:39: multiple definition of `_IO_funlockfile' /usr/lib/../lib64/libc.a(funlockfile.o)(.text+0x0):../linuxthreads/sysdeps/pthread/funlockfile.c:30: first defined here /usr/bin/ld: Warning: size of symbol `_IO_funlockfile' changed from 24 in /usr/lib/../lib64/libc.a(funlockfile.o) to 12 in /usr/lib/../lib64/libc.a(funlockfile.o) /usr/lib/../lib64/libpthread.a(lockfile.o)(.text+0xa0): In function `__funlockfile': /usr/src/packages/BUILD/glibc-2.3/linuxthreads/lockfile.c:39: multiple definition of `__funlockfile' /usr/lib/../lib64/libc.a(funlockfile.o)(.text+0x0):../linuxthreads/sysdeps/pthread/funlockfile.c:30: first defined here /usr/bin/ld: Warning: size of symbol `__funlockfile' changed from 24 in /usr/lib/../lib64/libc.a(funlockfile.o) to 12 in /usr/lib/../lib64/libc.a(funlockfile.o)collect2: ld returned 1 exit status $ Problem does NOT occur if I don't include '-lc'. I don't quite understand why this is a factor, since gcc automatically specifies '-lc' when linking the program. Please enlighten me as to why adding this to the command line causes the error. Here is the version of Linux I am using: $ uname -a Linux guppy2 2.6.5-7.286-ss #6 SMP Wed Jul 11 14:28:20 PDT 2007 x86_64 x86_64 x86_64 GNU/Linux $ cat /etc/SuSE-release SUSE LINUX Enterprise Server 9 (x86_64) VERSION = 9 PATCHLEVEL = 2 $ I am building a program for the Cray XT3, so static libraries must be used. -- Summary: Multiple definitions of __flockfile when compiling an openMP program Product: gcc Version: 4.2.0 Status: UNCONFIRMED Severity: major Priority: P3 Component: c AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: geir at cray dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32799