rcutorture’s init segfaults in ppc64le VM

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Dear Linux folks,


On the POWER8 server IBM S822LC running Ubuntu 21.10, building Linux 5.17-rc2+ with rcutorture tests

    $ tools/testing/selftests/rcutorture/bin/torture.sh --duration 10

the built init

    $ file tools/testing/selftests/rcutorture/initrd/init
tools/testing/selftests/rcutorture/initrd/init: ELF 64-bit LSB executable, 64-bit PowerPC or cisco 7500, version 1 (SYSV), statically linked, BuildID[sha1]=0ded0e45649184a296f30d611f7a03cc51ecb616, for GNU/Linux 3.10.0, stripped

segfaults in QEMU. From one of the log files


/dev/shm/linux/tools/testing/selftests/rcutorture/res/2022.02.01-21.52.37-torture/results-rcutorture/TREE03/console.log

    [    1.119803][    T1] Run /init as init process
[ 1.122011][ T1] init[1]: segfault (11) at f0656d90 nip 10000a18 lr 0 code 1 in init[10000000+d0000] [ 1.124863][ T1] init[1]: code: 2c2903e7 f9210030 4081ff84 4bffff58 00000000 01000000 00000580 3c40100f [ 1.128823][ T1] init[1]: code: 38427c00 7c290b78 782106e4 38000000 <f821ff81> 7c0803a6 f8010000 e9028010

Executing the init, which just seems to be an endless loop, from userspace work:

    $ strace ./tools/testing/selftests/rcutorture/initrd/init
execve("./tools/testing/selftests/rcutorture/initrd/init", ["./tools/testing/selftests/rcutor"...], 0x7ffffdb9e860 /* 31 vars */) = 0
    brk(NULL)                               = 0x1001d940000
    brk(0x1001d940b98)                      = 0x1001d940b98
    set_tid_address(0x1001d9400d0)          = 2890832
    set_robust_list(0x1001d9400e0, 24)      = 0
uname({sysname="Linux", nodename="flughafenberlinbrandenburgwillybrandt.molgen.mpg.de", ...}) = 0 prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0 readlink("/proc/self/exe", "/dev/shm/linux/tools/testing/sel"..., 4096) = 61
    getrandom("\xf1\x30\x4c\x9e\x82\x8d\x26\xd7", 8, GRND_NONBLOCK) = 8
    brk(0x1001d970b98)                      = 0x1001d970b98
    brk(0x1001d980000)                      = 0x1001d980000
    mprotect(0x100e0000, 65536, PROT_READ)  = 0
clock_nanosleep(CLOCK_REALTIME, 0, {tv_sec=1, tv_nsec=0}, 0x7ffffb22c8a8) = 0 clock_nanosleep(CLOCK_REALTIME, 0, {tv_sec=1, tv_nsec=0}, 0x7ffffb22c8a8) = 0 clock_nanosleep(CLOCK_REALTIME, 0, {tv_sec=1, tv_nsec=0}, ^C{tv_sec=0, tv_nsec=872674044}) = ? ERESTART_RESTARTBLOCK (Interrupted by signal)
    strace: Process 2890832 detached

Any ideas, what `mkinitrd.sh` [2] should do differently?

```
cat > init.c << '___EOF___'
#ifndef NOLIBC
#include <unistd.h>
#include <sys/time.h>
#endif

volatile unsigned long delaycount;

int main(int argc, int argv[])
{
	int i;
	struct timeval tv;
	struct timeval tvb;

	for (;;) {
		sleep(1);
		/* Need some userspace time. */
		if (gettimeofday(&tvb, NULL))
			continue;
		do {
			for (i = 0; i < 1000 * 100; i++)
				delaycount = i * i;
			if (gettimeofday(&tv, NULL))
				break;
			tv.tv_sec -= tvb.tv_sec;
			if (tv.tv_sec > 1)
				break;
			tv.tv_usec += tv.tv_sec * 1000 * 1000;
			tv.tv_usec -= tvb.tv_usec;
		} while (tv.tv_usec < 1000);
	}
	return 0;
}
___EOF___

# build using nolibc on supported archs (smaller executable) and fall
# back to regular glibc on other ones.
if echo -e "#if __x86_64__||__i386__||__i486__||__i586__||__i686__" \
           "||__ARM_EABI__||__aarch64__\nyes\n#endif" \
   | ${CROSS_COMPILE}gcc -E -nostdlib -xc - \
   | grep -q '^yes'; then
	# architecture supported by nolibc
        ${CROSS_COMPILE}gcc -fno-asynchronous-unwind-tables -fno-ident \
		-nostdlib -include ../../../../include/nolibc/nolibc.h \
		-s -static -Os -o init init.c -lgcc
else
	${CROSS_COMPILE}gcc -s -static -Os -o init init.c
fi
```


Kind regards,

Paul


[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/rcutorture/doc/initrd.txt [2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/rcutorture/bin/mkinitrd.sh



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