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    SubjectRe: bug in redhat gcc 2.96
    This bug is fixed in gcc-2.96-82 and higher, as per
    http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=37054. I've posted
    gcc-2.96-84.src.rpm at your enterprise ftp folder.

    --jeremy


    Jim Wright wrote:
    >
    > We believe we have found a bug in gcc. We have been trying to track
    > down why the .../drivers/scsi/sym53c8xx.c driver oopses with a divide
    > by zero when initializing at line 5265, which reads:
    >
    > period = (4 * div_10M[0] + np->clock_khz - 1) / np->clock_khz;
    >
    > We believe the bug is that gcc is generating incorrect code for this:
    >
    > if (f1 < 55000) f1 = 40000;
    > else f1 = 80000;
    >
    > Here is the test code to demonstrate this:
    >
    > % cat bug.c
    > int main (int argc, char *argv[])
    > {
    > unsigned f1;
    >
    > f1 = (unsigned)argc;
    >
    > if (f1 < 5) {
    > f1 = 4;
    > } else {
    > f1 = 8;
    > }
    > exit (f1);
    > }
    >
    > And here are commands to exhibit the problem.
    >
    > % for i in 0 1 2 3 4 5 6 ; do ln bug.c bug$i.c ; done
    > % for i in 0 1 2 3 4 5 6 ; do gcc -save-temps -O$i -o bug$i bug$i.c ; done
    > % for i in 0 1 2 3 4 5 6 ; do ./bug$i 1 2 ; echo $? ; done
    > % for i in 0 1 2 3 4 5 6 ; do ./bug$i 1 2 3 4 5 6 7 ; echo $? ; done
    >
    > The level 0 optimization assembly code appears correct. For level 1 and
    > above, the compiler emits a long-subtract-with-borrow statement which
    > leaves EAX either 0 filled or 1 filled, based on the carry flag.
    >
    > As this is with Red Hat's version of gcc, I'm not sending
    > this to the gcc folks. RPMs of gcc with this problem
    > include gcc-2.96-69 and gcc-2.96-81. This has been logged
    > as http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=39764.
    > Any suggestions for a way to cope with this? We have a
    > customer who's system fails due to this.
    >
    > --
    > Jim Wright Software Engineer Penguin Computing
    > jwright@penguincomputing.com v:415-358-2609 f:415-358-2646
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