Hi Dongxu,

As you can see, the arm_monitor_vector uses PC-relative addressing so that the code can be moved around in memory.  I think ldr pc, =smc_handler breaks this. Also, please set the NS bit in SCR to 1 before returning.

To reserve a memory region for the monitor-mode code and data, I suggest you modify the avail_p_regs[] in kernel/include/plat/imx6/plat/machine/hardware.h file. See the kernel/include/plat/tk1/plat/machine/hardware.h as an example.



From: Dongxu Ji <jidongxu1993@gmail.com>
Sent: Wednesday, August 29, 2018 12:02 AM
To: devel@sel4.systems; Shen, Yanyan (Data61, Kensington NSW)
Subject: Fwd: [seL4] SMC in seL4
Hi  Yanyan,
1. It doesn't set the NS bit to 1 in SCR(I just want it to return without do anything). The arm_monitor_vector and the smc_handler():

    ldr pc, [pc, #28]
    ldr pc, [pc, #24]
    ldr pc, =smc_handler
    ldr pc, [pc, #16]
    ldr pc, [pc, #12]
    ldr pc, [pc, #8]
    ldr pc, [pc, #4]
    ldr pc, [pc, #0]

    movs pc, lr

2. I didn't do any extra work other than the boot log:

ELF-loader started on CPU: ARM Ltd. Cortex-A9 r2p10                             
ELF-loading image 'kernel'                                                      
ELF-loading image 'sel4test-driver'                                             
Enabling MMU and paging                                                         
Jumping to kernel-image entry point...

3. The initialization operations in platform_init.c:
set sp:
#define MONITOR_MODE        (0x16)
#define MON_VECTOR_START    (0x11000000)
#define VECTOR_BASE     0x11000000
#define STACK_TOP       (VECTOR_BASE + (1 << 12) - 0x10)

asm volatile ( "mrs r1, cpsr\n\t"
                      "cps %0\n\t"
                      "mov sp, %1\n\t"
                      "msr cpsr, r1\n\t"                 

copy monitor mode vector to MON_VECTOR_START  and write into MVBAR: 
uint32_t size = arm_monitor_vector_end - arm_monitor_vector;
    printf("Copy monitor mode vector from %x to %x size %x\n", (arm_monitor_vector), MON_VECTOR_START, size);
    memcpy((void *)MON_VECTOR_START, (void *)(arm_monitor_vector), size);
        asm volatile ("dmb\n isb\n");
        asm volatile ("mcr p15, 0, %0, c12, c0, 1"::"r"(MON_VECTOR_START));

I enter into SVC mode by software interrupt and call the function smc():
                  asm (".arch_extension sec\n");
     asm volatile ("stmfd    sp!, {r3-r11, lr}\n\t"
                   "smc #0\n"
                   "ldmfd    sp!, {r3-r11, pc}");

and then the problem arises.

Thank you,
Dongxu Ji

<Yanyan.Shen@data61.csiro.au> 于2018年8月28日周二 下午8:30写道:


The smc_handle() in monitor.S, it does nothing but "movs pc, lr".
Does it set the NS bit to 1 in SCR?

Also, what did you do to ensure that 0x11000000 is not used by the kernel?

Could you share the code (if possible) so that I could better understand the problem. 


From: Devel <devel-bounces@sel4.systems> on behalf of 冀东旭 <jidongxu1993@gmail.com>
Sent: Tuesday, August 28, 2018 1:02 PM
To: devel@sel4.systems
Subject: [seL4] SMC in seL4
I'm porting sel4 to imx6q sabrelite as the trusted OS in trustzone.  I initialize the monitor mode by setting the sp to  STACK_TOP and copying arm_monitor_vector to MON_VECTOR_START according to the functions "install_monitor_hook()" and "switch_to_mon_mode()" in "platform_init.c".
#define VECTOR_BASE     0x11000000(addr is not used by the seL4 kernel)
#define STACK_TOP       (VECTOR_BASE + (1 << 12) - 0x10)
#define MON_VECTOR_START    0x11000000(The VECTOR_BASE is the same as MON_VECTOR_START)
The smc_handle() in monitor.S, it does nothing but "movs pc, lr".  After calling smc in SVC mode, it hangs without any log.  If I comment the "smc #0", it can return the caller successfully in usr mode.
    stmfd    sp!, {r3-r11, lr}
    smc #0
    ldmfd    sp!, {r3-r11, pc}
Is the sp in monitor mode appropriate? Or I need to do something else in initialization operations?  What's wrong with it?  Do you have any ideas?
Thank you!
Dongxu Ji