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[Bug 1923861] Re: Hardfault when accessing FPSCR register

From: ml-0
Subject: [Bug 1923861] Re: Hardfault when accessing FPSCR register
Date: Thu, 15 Apr 2021 16:44:58 -0000

Command line is
qemu-system-arm -machine mps3-an547 -nographic -kernel test.elf -semihosting 
-semihosting-config enable=on,target=native

Binary is attached. It does

int main(int argc, char* argv[])
    SCB->NSACR |= (3U << 10U);                /* enable Non-secure access to 
CP10 and CP11 coprocessors */

    SCB->CPACR |= ((3U << 10U*2U) |           /* enable CP10 Full Access */
                   (3U << 11U*2U)  );         /* enable CP11 Full Access */

//   enable DL branch cache
    #define CCR      (*((volatile unsigned int *)0xE000ED14))
    #define CCR_DL   (1 << 19)
      CCR |= CCR_DL;

   uint32_t result;
    __asm volatile ("VMRS %0, fpscr" : "=r" (result) );           // <-- NOCP 
    printf("fpscr = 0x%08lx\r\n", result);
    __asm volatile ("VMRS %0, mvfr0" : "=r" (result) );
    printf("mvfr0 = 0x%08lx\r\n", result);
    __asm volatile ("VMRS %0, mvfr1" : "=r" (result) );
    printf("mvfr1 = 0x%08lx\r\n", result);
    __asm volatile ("VMRS %0, mvfr2" : "=r" (result) );
    printf("mvfr2 = 0x%08lx\r\n", result);


Thank you for your help!

** Attachment added: "test.elf"

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  Hardfault when accessing FPSCR register

Status in QEMU:

Bug description:
  QEMU release version: v6.0.0-rc2

  command line:
  qemu-system-arm -machine mps3-an547 -nographic -kernel <my_project>.elf 
-semihosting -semihosting-config enable=on,target=native

  host operating system: Linux ISCNR90TMR1S 5.4.72-microsoft-standard-
  WSL2 #1 SMP Wed Oct 28 23:40:43 UTC 2020 x86_64 x86_64 x86_64

  guest operating system: none (bare metal)

  I am simulating embedded firmware for a Cortex-M55 device, using MPS3-AN547 
machine. In the startup code I am accessing the FPSCR core register:

      unsigned int fpscr =__get_FPSCR();
      fpscr = fpscr & (~FPU_FPDSCR_AHP_Msk);

  where the register access functions __get_FPSCR() and
  __set_FPSCR(fpscr) are taken from CMSIS_5 at

  I observe hardfaults upon __get_FPSCR() and __set_FPSCR(fpscr). The
  same startup code works fine on the Arm Corstone-300 FVP (MPS3-AN547).

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