I'm getting SIGILL on a call to sched_getcpu:
gcc 6.3.0 201700221 (Ubuntu 6.3.0-8ubuntu1) and libc6:ppc64el 2.24-7ubuntu2
$ cat example.c
#define _GNU_SOURCE
#include <sched.h>
int main(void)
{
return sched_getcpu();
}
gcc -g example.c -o example
./example
Illegal instruction
$ gdb ./example
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Reading symbols from ./example...done.
(gdb) run
Starting program: /home/king/example
Program received signal SIGILL, Illegal instruction.
__kernel_getcpu ()
at /build/linux-mMU5bT/linux-4.10.0/arch/powerpc/kernel/vdso64/getcpu.S:32
32 /build/linux-mMU5bT/linux-4.10.0/arch/powerpc/kernel/vdso64/getcpu.S: No such file or directory.
(gdb) where
#0 __kernel_getcpu ()
at /build/linux-mMU5bT/linux-4.10.0/arch/powerpc/kernel/vdso64/getcpu.S:32
#1 0x00003fffb7ea08e8 in sched_getcpu ()
at ../sysdeps/unix/sysv/linux/sched_getcpu.c:32
#2 0x00000000200007f0 in main () at example.c:7
Hi Colin, what system is this on?
The failing instruction should be a read of SPRG3:
│0x3fffb7f807c8 <__kernel_getcpu> mfspr r5,259
which should be fine to execute in userspace. There was a NUMA_BALANCING bug around that time where we'd end up mapping the vdso no execute, but I don't think Ubuntu is enabling that feature.