Public bug reported:
== Comment: #0 - Alexander Efremkin <[email protected]> - 2016-02-17
12:18:14 ==
With a C program sets FPE handler and triggers an FPE exception, it expects
that machine-dependent context data, which is passed to the handler, will
contain sensible values.
In this scenario, however, FPC register was zero and contained no DXC
(Data-Exception Code) indication:
#include <stdio.h>
#include <string.h>
#include <signal.h>
void trapFunction() {
asm volatile ("lhi %r1,0\n\t"
"cit %r1,0,8\n\t");
}
static void sigFPE_handler(int signal, siginfo_t *info, void *context) {
ucontext_t *uc = context;
mcontext_t mc = uc->uc_mcontext;
fpregset_t fpregs = mc.fpregs;
unsigned int fpc = fpregs.fpc;
printf("received signal!\n");
printf("fpc: %08x\n", fpc );
}
int main() {
struct sigaction action;
memset(&action, '\0', sizeof(action));
printf("registering signal handler\n");
action.sa_flags |= SA_SIGINFO;
action.sa_sigaction = sigFPE_handler;
if (sigaction(SIGFPE, &action, NULL))
printf("error calling sigaction\n");
printf("firing trap\n");
trapFunction();
return 0;
}
This program prints "fpc: 00000000", but the expected output is "fpc:
0000ff00"..
The IBM Java team has encountered test failures around the use of trap
instructions; Linux on z Distribution Test reproduced the issue on the
following system:
z13 LPAR
Ubuntu 16.04
Kernel 4.4.0-4-generic
gcc (Ubuntu 5.3.1-8ubuntu2) 5.3.1 20160205
libc6 2.21-0ubuntu5
Also, similar issue has been found during test of SIMD (vector)
instructions, FPC contents was also zero, whereas it expected at least
an exception mask and vector-defined DXC.
** Affects: ubuntu
Importance: Undecided
Assignee: Skipper Bug Screeners (skipper-screen-team)
Status: New
** Tags: architecture-s39064 bugnameltc-137317 severity-critical
targetmilestone-inin1604
** Tags added: architecture-s39064 bugnameltc-137317 severity-critical
targetmilestone-inin1604
** Changed in: ubuntu
Assignee: (unassigned) => Skipper Bug Screeners (skipper-screen-team)
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https://bugs.launchpad.net/bugs/1548414
Title:
Floating-point exception handler receives empty Data-Exception Code in
Floating Point Control register
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