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

[Mark Phillips]

I have put together a test program and tried against a vanila copy of
qemu 1.1.1

The SVC wil be completely masked unless I apply patch 0002-target-arm-
Disable-priority_mask-feature.patch, which hacks arm_gic.c to initialise
the gic priority_mask to 0x100 instead of 0xf0. There doesn't appear to
be anyway to write to the gix priority_mask from arm code - maybe it
should be linked to the ARM Cortex BASEPRI?

Anyway the test code indicates execution does continue after the SVC
call before the exception is handled.

Where would you like me to upload/send the test code?

Cheers
Mark

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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)

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