[Qemu-devel] [Bug 657006] Re: arm v7M - svc insn doesn't trigger PendSV handler

[Mark Phillips]

I have been experimenting with Sebastian's patches mentioned earlier
(http://git.rtems.org/rtems/tree/c/src/lib/libbsp/arm/lm3s69xx?id=e1ebfebf1bffe3e7731ac529409bd2576285467b)
and think I have found another major issue:-(

My reading of the ARM documentation is that the SVC opcode should perform a 
synchronous exception.
It doesn't, the calling code continues to execute asynchronously.

This means that

1) When the execption handler runs, it will not be able to find the SVC 
argument (because the PC in the execption frame will not allow it to locate the 
SVC call
2) Code will be incorrectly executed. For example code after an OS suspend call 
will be executed before the thread is suspended and resumed....

Cheers
Mark

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/657006

Title:
  arm v7M - svc insn doesn't trigger PendSV handler

Status in QEMU:
  New

Bug description:
  The svc instruction doesn't work as expected.

  -> qemu 0.13.0 rc1 (git)

  Test : demo with freeRTOS (for example
  FreeRTOS-6.0.5/Demo/CORTEX_LM3S811_GCC) with the card lm3s811evb.

  If we start the scheduler, it will call that function (__attribute__
  (( naked ))) :

  void vPortStartFirstTask( void )

  {

          __asm volatile(

                                          " ldr r0, =0xE000ED08   \n" /*
  Use the NVIC offset register to locate the stack. */

                                          " ldr r0, [r0]
  \n"

                                          " ldr r0, [r0]
  \n"

                                          " msr msp, r0
  \n" /* Set the msp back to the start of the stack. */

                                          " svc 0
  \n" /* System call to start first task. */

                                  );

  }

  The 4 first lines in asm work fine. The scv 0 call will rise the right 
interrupt in qemu (line 151, in arm_gic.c, best_irq = 15). However, it will 
never call the PendSV Handler (xPortPendSVHandler here). This function is 
recorded in the nvic vector.
  Next, (after the svc), the processor will execute the line after in code 
(this is a naked function) so the next function written after 
vPortStartFirstTask in the code.

  
  command line :
  console 1 : qemu-system-arm -M lm3s6965evb -kernel gcc/RTOSDemo.axf -s -S
  console 2 : arm-none-eabi-gdb -ex "target remote localhost:1234" 
gcc/RTOSDemo.axf

  arm-none-eabi from 
http://www.codesourcery.com/sgpp/lite/arm/portal/release1294
  Same error with another project with arm-elf

  processor : arm cortex m3

  host : gentoo (2.6.35-r9) (without kqemu)

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/657006/+subscriptions