Bug 69496
| Summary: | strange floating point exceptions in trivial C programs | ||
|---|---|---|---|
| Product: | [Retired] Red Hat Linux | Reporter: | Need Real Name <komarek> |
| Component: | gcc | Assignee: | Jakub Jelinek <jakub> |
| Status: | CLOSED NOTABUG | QA Contact: | Brian Brock <bbrock> |
| Severity: | high | Docs Contact: | |
| Priority: | medium | ||
| Version: | 7.1 | CC: | komarek |
| Target Milestone: | --- | ||
| Target Release: | --- | ||
| Hardware: | alpha | ||
| OS: | Linux | ||
| Whiteboard: | |||
| Fixed In Version: | Doc Type: | Bug Fix | |
| Doc Text: | Story Points: | --- | |
| Clone Of: | Environment: | ||
| Last Closed: | 2002-07-22 21:07:45 UTC | Type: | --- |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | |
| Embargoed: | |||
Have you tried -mieee? Nope, we haven't. Things appear work properly when we do. I apologize for wasting your bug time on us lusers. I only wish we had wasted your time in January instead of waiting until July. ;-) |
From Bugzilla Helper: User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.0) Gecko/20020618 Description of problem: It is possible to write a trivial C program which causes a floating point exception using one summation. Version-Release number of selected component (if applicable): How reproducible: Always Steps to Reproduce: Compile and link these programs with "gcc -o foo foo.c". I've tried many other optimization and debug settings, with no change in results. This C code works correctly: #include <stdio.h> int main(void) { printf("sum=%g\n", 1.21678e-308 + 1.07381e-308); return 0; } This C code dies with a floating point exception: #include <stdio.h> int main(void) { double hi, lo, sum; hi = 1.21678e-308; lo = 1.07381e-308; sum = (hi + lo); /* Produces bad result. */ printf( "sum=%g\n", sum); /* Dies here. */ return 0; } Actual Results: The first program works correctly. The second does not. Expected Results: Both should have worked correctly. =-) Additional info: For both of these programs, compiling with Compaq's ccc produces underflow warnings but the executable works correctly (no fp exceptions and prints the expected "sum=2.29059e-308". gcc2.96 fails, as does gcc3.1 (built from sources). We've messed with this on 3 Alpha machines. Two have dual 667MHz 21264 cpus (DS-20 clones from Microway, 4MB cache), and one is a single cpu Compaq ES-40 (8MB cache). We've fought with and tried to work around this for quite a while, and have finally distilled it to this form. Any help (workarounds, bug fixes, etc) would be greatly appreciated, as this has cost us a lot of time. I'd be happy to provide assembly dumps or run experiments as needed.