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

[Oleksiy Bondarenko]

>From the manual 
>DDI0403C_arm_architecture_v7m_reference_manual_errata_markup_2_0.pdf
A6.7.97 POP
Pop Multiple Registers loads a subset (or possibly all) of the general-purpose 
registers R0-R12 and the PC
or the LR from the stack.
If the registers loaded include the PC, the word loaded for the PC is treated 
as an address or an exception
return value and a branch occurs. Bit<0> complies with the ARM architecture 
interworking rules for
branches to Thumb state execution and must be 1. If bit<0> is 0, a UsageFault 
exception occurs.


And even more if we will look into  Yiu, Joseph. The definitive guide to the 
ARM Cortex-M3 / Joseph Yiu.
chapter 9 Interrupt behavior we will see how actually processor pushes data and 
in real I thin it does not uses pop and push instructions, we just simulate 
real behavior with this instructions.

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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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