The pthread library has changed the size of some data structures, such as sem_t, but the major version number on the shared library was not incremented. Hence, old RH 5.1 binaries that use semaphores segfault on RH 6.0. Lack of backward compatibility is a disaster, since it makes upgrading machines much harder.
Do you have example code that breaks between glibc 2.0 and glibc 2.1?
Reply from the e-mail message: Here is the sem_t structure definition from the include files of Red Hat 5.1. It's defined in /usr/include/semaphorebits.h. typedef struct { long int sem_status; int sem_spinlock; } sem_t; Here is the Red Hat 6.0 version, from file /usr/include/semaphore.h. typedef struct { struct { long int status; int spinlock; } __sem_lock; int __sem_value; _pthread_descr __sem_waiting; } sem_t; You'll notice that the second structure is larger than the first. When a Red Hat 5.1 program runs on Red Hat 6.0 and calls sem_init, the function modifies memory off the end of the space the program allocated for the sem_t object. Since the size of the data structure changed, the shared object should have been versioned, so that old programs got the older version of sem_init. Is this enough explanation? All of the real applications that break in my environment are GUI tools. If needed I could write a test program demonstrating the problem. bob
Fixed in glibc-2.1.2-1