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Non-secure call Secure used SG instruction cause Hard Fault

Thomas Coding

I tried to switch between secure and non-secure on M33. Based on the qemu mps2-an521 platform, with sau configured, the security can be switched to the non-secure state, and then I tried to switch to the secure state through the SG instruction, but it failed.

memory layout：

0x0200_0000 - 0x003F_FFFF (non-secure)

0x1000_0000 - 0x100F_FFFF (secure)

0x1010_0000 - 0x101F_FFFF (non-secure callable)

SAU config:

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SAU->RBAR = 0x10100000;
SAU->RLAR = 0x101FFFE3;
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

NSC code:

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.thumb_func
.section NSC,"aw"
.globl nsc_call
nsc_call:
sg
nop
nop
nop
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

secure ld：

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NSC (0x10100000):
{
*nsc*(.text*)
} > RAM
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

non-secure caller code:

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ldr r0, =0x10100001;
bx r0
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

When the line of code 'bx r0' is executed, it will enter the secure world hard fault. 

Any reason why this is occurring? I don’t know how to continue. 

Thanks for any clues or suggestions.

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