Hello there, I'm experiencing some weird problems with a multi-threaded application I'm working on: A function which uses nothing but a single input value, a few constants and a couple of floating point operations returns wrong results from time to time. The application uses multiple threads, and we're suspecting that the FPU state isn't properly saved and restored when switching between threads within a process.
I've written a trivial test program which can be used to reproduce the issue (see below). In theory the program should run forever, but in UML it aborts after just a few seconds. I have observed the issue both with kernel 2.6.28.8 and Busybox/uclibc and with the demo kernel 2.6.24-rc7 and the Fedora10 image from the UML home page. The problem does not happen with kernel 2.6.23.1. We're suspecting that the problem has been introduced by the patch [1] to stop saving the process FP state which has been applied just before 2.6.24-rc1. Regards, Ingo [1] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=42daba316557e597a90a730f61c762602b7f0e0c ====================================================================== #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <pthread.h> static double my_abs(double d) { return (d >= 0) ? d : -d; } static void *fp_test_thread_func(void *arg) { volatile double value1 = *(double *)arg; volatile double value2 = *(double *)arg; while (1) { if (my_abs(value1 - value2) > 0.0001) { fprintf(stderr, "Inconsistent values: %lf, %lf\n", value1, value2); abort(); } } return NULL; } #define NUM_THREADS 2 int main(void) { pthread_t threads[NUM_THREADS]; int i; for (i = 0; i < NUM_THREADS; i++) { double startval = i; pthread_create(&threads[i], NULL, fp_test_thread_func, &startval); } while (1) pause(); return 0; } ------------------------------------------------------------------------------ This SF.net email is sponsored by: High Quality Requirements in a Collaborative Environment. Download a free trial of Rational Requirements Composer Now! http://p.sf.net/sfu/www-ibm-com _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
