rpi-5.6.y -- vdso version of clock_gettime is wrong, syscall is correct #3579
Description
Is this the right place for my bug report?
I believe so. With default Raspbian kernel and userland, the program produces correct output. Building 5.6 kernel following https://www.raspberrypi.org/documentation/linux/kernel/building.md and booting the result, the program produces erratic output.
Describe the bug
The VDSO version of clock_gettime( CLOCK_REALTIME, ts ); produces erratic, incorrect output. The syscall version works fine.
To reproduce
Boot a stock raspberry pi 4b rev 1.2 with https://downloads.raspberrypi.org/raspbian_lite_latest (2020-02-13) and run apt-get update and apt-get upgrade.
Build the kernel:
sudo apt install git bc bison flex libssl-dev make
git clone --depth=1 --branch rpi-5.6.y https://github.com/raspberrypi/linux
cd linux
mkdir ../build
make O=../build bcm2711_defconfig
make O=../build -j4
sudo cp ../build/arch/arm/boot/zImage /boot/kernel7l.img
sudo reboot
Now build the program with MUSL libc (I used musl-cross-make)
#include <stdio.h>
#include <unistd.h>
#include <time.h>
#include <syscall.h>
int main(int argc, char**argv) {
struct timespec ts_sc[1];
struct timespec ts_vd[1];
syscall(SYS_clock_gettime64, CLOCK_REALTIME, ts_sc);
clock_gettime(CLOCK_REALTIME, ts_vd); // musl will use vdso here
printf(
"vd: %lld %lld (%llx %llx)\n"
"sc: %lld %lld (%llx %llx)\n",
(long long) ts_vd->tv_sec, (long long) ts_vd->tv_nsec,
(long long) ts_vd->tv_sec, (long long) ts_vd->tv_nsec,
(long long) ts_sc->tv_sec, (long long) ts_sc->tv_nsec,
(long long) ts_sc->tv_sec, (long long) ts_sc->tv_nsec
);
}Expected behaviour
The time in seconds (first column) should increase by about 1 per second. This should happen for both rows, VDSO and syscall.
$ ./mix
vd: 1587861652 218823486 (5ea4d894 d0afb3e)
sc: 1587861652 218784111 (5ea4d894 d0a616f)
$ ./mix
vd: 1587861652 838336559 (5ea4d894 31f8002f)
sc: 1587861652 838282913 (5ea4d894 31f72ea1)
$ ./mix
vd: 1587861653 427229788 (5ea4d895 1977025c)
sc: 1587861653 427190569 (5ea4d895 19766929)
$ ./mix
vd: 1587861654 20806558 (5ea4d896 13d7b9e)
sc: 1587861654 20748798 (5ea4d896 13c99fe)
$ ./mix
vd: 1587861654 589989110 (5ea4d896 232a84f6)
sc: 1587861654 589934787 (5ea4d896 2329b0c3)
Actual behaviour
The seconds column for VDSO is erratic. The seconds column for syscall increases by about 1 per second.
$ ./mix
vd: 1602382300 871248665 (5f8269dc 33ee3319)
sc: 1587861514 880693130 (5ea4d80a 347e4f8a)
$ ./mix
vd: 1592986975 290581759 (5ef30d5f 1151ecff)
sc: 1587861515 313451055 (5ea4d80b 12aee22f)
$ ./mix
vd: 1600536634 931908777 (5f66403a 378bcca9)
sc: 1587861515 766646428 (5ea4d80b 2db2189c)
$ ./mix
vd: 1591309079 582261861 (5ed97317 22b49c65)
sc: 1587861516 220063133 (5ea4d80c d1de59d)
System
Copy and paste the results of the raspinfo command in to this section. Alternatively, copy and paste a pastebin link, or add answers to the following questions:
- Which model of Raspberry Pi?
$ dmesg | grep Rasp
[ 0.000000] OF: fdt: Machine model: Raspberry Pi 4 Model B Rev 1.2- Which OS and version (
cat /etc/rpi-issue)?
$ cat /etc/rpi-issue
Raspberry Pi reference 2020-02-13
Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 5f884374b6ac6e155330c58caa1fb7249b8badf1, stage2- Which firmware version (
vcgencmd version)?
From the 5.6 kernel:
$ vcgencmd version
VCHI initialization failed
From stock kernel:
$ vcgencmd version
Feb 12 2020 12:36:21
Copyright (c) 2012 Broadcom
version c3c8dbdf147686fb0c3f32aece709d0653368810 (clean) (release) (start)
- Which kernel version (
uname -a)?
uname -a
Linux raspberrypi 5.6.4-v7l+ #1 SMP Sat Apr 25 19:34:29 EDT 2020 armv7l GNU/LinuxLogs
Let me know if you want anything else.
Additional context
Related problem report at richfelker/musl-cross-make#96