Re: [QEMU] Question regarding user mode support for ARM syscalls

[Alistair Francis]

On Tue, Nov 3, 2020 at 3:03 AM Lukasz Majewski <lukma@denx.de> wrote:
>
> Dear Qemu Community,

Hey Lukasz,

+ QEMU Dev Mailing list
+ Laurent

>
> I would like to ask you for some advice regarding the usage of
> arm-linux-user/qemu-arm user space program simulation.
>
> Background:
> -----------
>
> I'm looking for a way to efficiently test y2038 in-glibc solution for
> 32 bit architectures (e.g. ARM).
>
> For now I do use qemu-system-arm (part of Yocto/OE), which I'm using to
> run Linux kernel 5.1, glibc under test and Y2038 tests. It works [1].
>
> Problem:
> --------
>
> I would like to test cross-compiled tests (which are built from glibc
> sources) without the need to run the emulated system with
> qemu-system-arm.
>
> I've come across the "QEMU user mode", which would execute the
> cross-compiled test (with already cross-compiled glibc via -L switch)
> and just return exit status code. This sounds appealing.

As another advantage it is much, much faster at running the glibc tests.

>
> As fair as I've read - QEMU user mode emulates ARM syscalls.
>
> During test execution (single qemu user mode process) I would need to
> adjust date with clock_settime64 syscall and then execute other
> syscalls if needed.
>
>
> Please correct me if I'm wrong:
> - It looks like qemu-arm doesn't have switch which would allow it to
>   set time offset (to e.g. year 2039 - something similar to
>   qemu-system-arm -rtc=).
>
> - As of 5.1 qemu version there is no support for syscalls supporting 64
>   bit time on 32 bit architectures (e.g. clock_settime64 and friends
>   from [2]).

There is some support in the current master, for example
__NR_futex_time64 is supported.

I started to add some support for RV32 once it was merged into glibc.

>
> For my example program [3] statically build for testing (it works with
> qemu-system-arm):
>
> ~/work/qemu-arm-tests-program$
> ../qemu-5.1.0-arm/arm-linux-user/qemu-arm -L
> ~/work/yocto/y2038/build/tmp/armv7at2hf-neon-poky-linux-gnueabi/y2038-glibc/2.30+git999-r0/image/opt
> -strace ./cst
>
> 17746 brk(NULL) = 0x00074000
> 17746 brk(0x000748a8) = 0x000748a8
> 17746 uname(0x40800370) = 0
> 17746 readlink("/proc/self/exe",0x407ff488,4096) = 43
> 17746 brk(0x000958a8) = 0x000958a8
> 17746 brk(0x00096000) = 0x00096000
> 17746 mprotect(0x00070000,8192,PROT_READ) = 0
> 17746statx(1,"",AT_EMPTY_PATH|AT_NO_AUTOMOUNT,STATX_BASIC_STATS,0x407ffd70)
> = 0
> 17746 Unknown syscall 404 --> is the syscall number of clock_settime64

clock_settime64 is supported in master QEMU.

>
> 17746 dup(2) = 3
> 17746 fcntl64(3,F_GETFL) = 2
> 17746statx(3,"",AT_EMPTY_PATH|AT_NO_AUTOMOUNT,STATX_BASIC_STATS,0x407ff8e8)
> = 0 ERR
>
> Questions:
> ----------
>
> 1. Is there any plan to add support for emulating syscalls supporting
> 64 bit time on 32 bit architectures [2]?

I would like to have RV32 supported, but it's a low priority for me. I
expect it's something that will eventually happen though.

>
> 2. Provide QEMU user space switch to adjust its time (i.e. add some
> offset to in-fly emulated time syscalls - like clock_settime64) when it
> is started?

That I'm not sure about. I assume just running date/clock_settime64
from a script wouldn't work with the glibc test framework?

Alistair

>
>
> Thanks in advance for your help and reply.
>
>
> Links:
> [1] - https://github.com/lmajewski/meta-y2038/
> [2] -
> https://elixir.bootlin.com/linux/latest/source/arch/arm/tools/syscall.tbl#L419
>
> [3]:
> Example program:
> cat <<- EOF >> clock_settime_test.c
> #include <stdio.h>
> #include <time.h>
>
> int main (int argc, char **argv)
> {
>         struct timespec tv;
>         int ret;
>
>         tv.tv_sec = 0x7FFFFFFF;
>         tv.tv_sec += 61;
>         tv.tv_nsec = 0;
>
>         printf("clock_settime test program: ");
>         ret = clock_settime(CLOCK_REALTIME, &tv);
>         if (!ret)
>                 printf("OK\n");
>         else
>                 perror("ERR\n");
>
>         return 0;
> }
> EOF
>
> Build the test program:
> gcc -Wall -ggdb -D_TIME_BITS=64 -D_FILE_OFFSET_BITS=64 -I/opt/include
> -I/opt/usr/include -L/opt/usr/lib \ -Wl,-rpath=/opt/lib
> -Wl,--dynamic-linker=/opt/lib/ld-linux.so.2 clock_settime_test.c -o cst
> -static
>
>
>
> Best regards,
>
> Lukasz Majewski
>
> --
>
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
> Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@denx.de