[Qemu-devel] [Bug 1754038] Re: ARM M: Systick first wrap delayed (qemu-timers/icount prb?)

[Antoine]

I finally implemented a workaround to correct the problem:

in cpus.c : qemu_start_warp_timer(), in the "if (deadline > 0) { ... }"
part, I added:

        CPUState *cpu;
        CPU_FOREACH(cpu) {
            atomic_mb_set(&cpu->exit_request, 1);
        }

I do not understand more than 5% of the code I am messing up, so this
hack is probably broken...

Then I tested a bit more the code with different testcases... and I
found a new bug when writing a reload value smaller than the current
counter (the counter will then read as 0). It is due to this piece of
code in armv7m_systick.c : systick_read() :

        /* The interrupt in triggered when the timer reaches zero.
           However the counter is not reloaded until the next clock
           tick.  This is a hack to return zero during the first tick.  */
        if (val > s->reload) {
            val = 0;
        }

Well this is not really a prb for me with normal code, and it looks like
under control, but I can open another bug if needed.

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https://bugs.launchpad.net/bugs/1754038

Title:
  ARM M: Systick first wrap delayed (qemu-timers/icount prb?)

Status in QEMU:
  New

Bug description:
  When running this kind of code with qemu:

  static void SysTickISR(void)
  {
        printf("SysTick\n");
  }

  void main()
  {
        volatile int i, j;
        printf("setup timer\n");
        *(uint32_t*) 0xE000E014 = 0x8FFFFF; //reload value
        *(uint32_t*) 0xE000E018 = 0;        //force reload
        *(uint32_t*) 0xE000E010 = 7;        //cpu clk + ISR + enable 

        for (j = 0; j < 0x100; j++) {
                for (i = 0; i < 0x100000; i++)
                        ;
                printf("cnt %08x  -- %8x\n", *(uint32_t*) 0xE000E018, 
*(uint32_t*)0xE000E010);
        }
  }

  I get the following output (comments added after '#'):

  setup timer
  cnt 007cccca  --        7
  cnt 006998a2  --        7
  cnt 00566479  --        7
  cnt 0043304f  --        7
  cnt 002ffc26  --        7
  cnt 001cc7fd  --        7
  cnt 000993d5  --        7
  cnt 00000000  --        7  <--- problem here, systick should wrap and raise 
isr
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  cnt 00000000  --        7
  SysTick                     <--- delayed isr occuring here
  cnt 000986e0  --    10007
  SysTick
  cnt 00865290  --    10007   <---- then running fine as long as regs not 
modified
  cnt 00731e51  --        7
  cnt 005fea27  --        7
  cnt 004cb5ff  --        7
  cnt 003981d6  --        7
  cnt 00264dad  --        7
  cnt 00131984  --        7
  SysTick
  cnt 008fe545  --    10007
  cnt 007cb106  --        7
  cnt 00697cdd  --        7
  cnt 005648b4  --        7
  cnt 0043148b  --        7
  cnt 002fe061  --        7
  cnt 001cac38  --        7
  cnt 00097810  --        7
  SysTick
  cnt 008643d6  --    10007
  cnt 00730f97  --        7
  cnt 005fdb6d  --        7
  cnt 004ca745  --        7
  cnt 0039731c  --        7
  cnt 00263ef3  --        7
  cnt 00130aca  --        7
  SysTick
  cnt 008fd68b  --    10007
  cnt 007ca24c  --        7
  cnt 00696e23  --        7
  cnt 005639fa  --        7
  cnt 004305d1  --        7
  cnt 002fd1a8  --        7
  cnt 001c9d7f  --        7
  cnt 00096956  --        7
  SysTick
  cnt 0086351d  --    10007
  cnt 007300dd  --        7
  cnt 005fccb4  --        7
  cnt 004c988c  --        7
  cnt 00396463  --        7
  cnt 00263039  --        7
  cnt 0012fc10  --        7
  [...]

  Command line and version:
  qemu-system-arm -M lm3s6965evb -nographic -kernel hello.bin -monitor stdio 
-serial file:/dev/pts/6 -icount 4 -cpu cortex-m4
  QEMU 2.11.50

  I am compiling from git repo, head is:
  commit f32408f3b472a088467474ab152be3b6285b2d7b
  Author: Daniel P. Berrangé <address@hidden>
  Date:   Tue Mar 6 13:43:17 2018 +0000

  Config options:
  ./configure --target-list=arm-softmmu --enable-debug --disable-slirp 
--enable-tcg-interpreter --disable-blobs --disable-docs --disable-guest-agent 
--disable-gnutls --disable-nettle --disable-gcrypt --disable-sdl --disable-gtk 
--disable-vnc --disable-virtfs --disable-mpath --disable-xen --disable-brlapi 
--disable-curl --disable-bluez --disable-kvm --disable-hax --disable-hvf 
--disable-whpx --disable-rdma --disable-vde --disable-netmap 
--disable-linux-aio --disable-cap-ng --disable-attr --disable-vhost-net 
--disable-spice --disable-rbd --disable-libiscsi --disable-libnfs 
--disable-smartcard --disable-libusb --disable-live-block-migration 
--disable-usb-redir --disable-lzo --disable-snappy --disable-bzip2 
--disable-seccomp --disable-glusterfs --disable-tpm --disable-libssh2 
--disable-numa --disable-libxml2 --disable-tcmalloc --disable-jemalloc 
--disable-replication --disable-vhost-vsock --disable-opengl 
--disable-virglrenderer --disable-xfsctl --disable-qom-cast-debug 
--disable-vxhs --disable-crypto-afalg --disable-vhost-user --disable-capstone 
--disable-pie --extra-cflags=-mtune=native

  
  Not working with git tag 2.10.0 (almost same config)

  Working with stock qemu-arm 2.5.0 from Ubuntu 16.04.

  I started investigating, though I am not familiar with qemu code and I
  could see that the execution is not geting out of
  qemu_tcg_rr_cpu_thread_fn() 'while' loop and timers are not triggered
  because the values in cpu->icount_extra or cpu->icount_budget are not
  to modified accordingly after the timer is set (host side) when the
  systick register is written (target side).

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