Incorrect epilogue code in __attribute__((cmse_nonsecure_entry)) function

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Mit freundlichen Grüßen / Best regards

Steffen Wolfer

--
Dipl.-Inform. Steffen Wolfer
Software Engineer Embedded Systems

WEISS ROBOTICS GmbH & Co. KG
Karl-Heinrich-Käferle-Str. 8
D-71640 Ludwigsburg, Germany

Phone: +49 7141 94702-22
Fax: +49 7141 94702-99
http://www.weiss-robotics.com

Sitz der Gesellschaft: Ludwigsburg
Registergericht Stuttgart, HRA725006

Pers. haftende Gesellschafterin:
Weiss Robotics Verwaltungs-GmbH, Sitz Ludwigsburg
Registergericht Stuttgart, HRB73310
Geschäftsführer: Dr. Karsten Weiß

Public bug reported:

Pertinent bug report info:

- GCC version: 9-2020-q2
- CPU: Arm Cortex-M23
- Optimization level: Os

---------

Checking the following non-secure callable (NSC) function with Os,

```C
int __attribute__((cmse_nonsecure_entry))
foo(int a)
{
    return a + 1;
}
```

Compiled assembly code:

```ASM
                  foo:
0x000004E8 3001 ADDS r0,#1
0x000004EA 0001 MOVS r1,r0
0x000004EC 0002 MOVS r2,r0
0x000004EE 0003 MOVS r3,r0
0x000004F0 4680 MOV r8,r0
0x000004F2 4681 MOV r9,r0
0x000004F4 4682 MOV r10,r0
0x000004F6 4683 MOV r11,r0
0x000004F8 4684 MOV r12,r0
0x000004FA F38E8800 MSR APSR_nzcvq,lr ; formerly CPSR_f
0x000004FE 4774 BXNS lr
```

According to Arm's "ARMv8-M Security Extensions: Requirements on
Development Tools", on return from an entry function, restore all
callee-saved registers (here r8~r12) as mandated by [AAPCS], rather than
clear them.

** Affects: gcc-arm-embedded
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1903018

Title:
  Incorrect epilogue code in __attribute__((cmse_nonsecure_entry))
  function

Status in GNU Arm Embedded Toolchain:
  New

Bug description:
  Pertinent bug report info:

  - GCC version: 9-2020-q2
  - CPU: Arm Cortex-M23
  - Optimization level: Os

  ---------

  Checking the following non-secure callable (NSC) function with Os,

  ```C
  int __attribute__((cmse_nonsecure_entry))
  foo(int a)
  {
      return a + 1;
  }
  ```

  Compiled assembly code:

  ```ASM
                    foo:
  0x000004E8 3001 ADDS r0,#1
  0x000004EA 0001 MOVS r1,r0
  0x000004EC 0002 MOVS r2,r0
  0x000004EE 0003 MOVS r3,r0
  0x000004F0 4680 MOV r8,r0
  0x000004F2 4681 MOV r9,r0
  0x000004F4 4682 MOV r10,r0
  0x000004F6 4683 MOV r11,r0
  0x000004F8 4684 MOV r12,r0
  0x000004FA F38E8800 MSR APSR_nzcvq,lr ; formerly CPSR_f
  0x000004FE 4774 BXNS lr
  ```

  According to Arm's "ARMv8-M Security Extensions: Requirements on
  Develop...

Hi,

I believe this is the one addressing the reported bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95646

/K

Thanks. Yes, 95646 is addressing it.