Thanks for clarification. Now I understood what you there talking about PopStack pseudocode function.
(4) It is entirely possible that hardware implementations to date ignore the lsbit in this situation. That doesn't mean that software which relies on this UNPREDICTABLE behaviour is not buggy. It seams true because I have used a lot of different cortex m3 micros and none of them does not refused to execute such task stack initialization. I have just looked in Micrium uCOS III sources and in there there is the same usage of THUMB pointer to init PC. My point that in production there is a lot of code that does not care about this PREDICTABLE behavior and in my case I just want to run firmware without recompile and changes as it is. And for those who want this it is better at least to mention this behavior in comments or some there else , and maybe this will save a lot of time. -- 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