Caller Function Did Not Keep R3

Hi,

I have a "test_fun1()" function call to a inline ASM "test_fun2()". I found that the caller, "test_fun1()" did not keep the R3 before jump to "test_fun2()", which cause the result of the  "test_fun1()" is not correct (inline ASM "test_fun2()" use R3).

The same code works fine with Keil MDK-ARM. It also works when I change the Core from M3 to M0. 

Does the "test_fun2()" have any problem/violation?

I will be appreciated if anyone can give some suggestions. Thanks.

Following are some information and the code (It has some differences from the original application code, I create a simple ASM version to reproduces the issue). 

Sincerely,

Weiting

Caller_R3_source_code.zip

GNU Arm Version: 9 2020-q2-update (gcc-arm-none-eabi-9-2020-q2-update-win32.exe)

ARM_CORE = cortex-m0
ARCH_OPTION = -mcpu=$(ARM_CORE) -mthumb -mthumb-interwork
C_OPTION = -gdwarf-2 -MD -Wall -Os -mapcs-frame -ffunction-sections -fdata-sections
L_OPTION = -Wl,-Map=$(TARGET_NAME).map -Wl,--gc-sections --specs=nano.specs

main.c

int result;

int main(void)
{
  extern int test_fun1(int a, int b, int c, int d);
  extern int gTest;

  result = test_fun1(1, 2, 3, 4);

  if (gTest != 4)
  {
    while (1); // R3 Error here
  }

  while (1) // OK
  {

  }
}

test.c

void test_fun2(int a, int b, int c);

int gTest = 0;

int test_fun1(int a, int b, int c, int d)
{
  int uStart;

  uStart = gTest;
  if (a > 0)
  {
    test_fun2(uStart, uStart + c, 5);
  }

  uStart += d;
  gTest = uStart;

  return 1;
}

#if defined (__CC_ARM)
__asm void test_fun2(int a, int b, int c)
{
  PUSH {R4-R6, LR}
  MOV R4, R0
  LDR R3, =0x1234
  ADD R1, R1, R3
  POP {R4-R6, PC}
}
#endif

#if defined (__GNUC__)
void test_fun2(int a, int b, int c)
{
  __asm volatile("PUSH {R4-R6, LR}");
  __asm volatile("MOV R4, R0");
  __asm volatile("LDR R3, =0x1234");
  __asm volatile("ADD R1, R1, R3");
  __asm volatile("POP {R4-R6, PC}");
}
#endif

disasm.txt

    $t
    main
        0x00000198:    b508        ..      PUSH     {r3,lr}
        0x0000019a:    2203        ."      MOVS     r2,#3
        0x0000019c:    2304        .#      MOVS     r3,#4
        0x0000019e:    2102        .!      MOVS     r1,#2
        0x000001a0:    2001        .       MOVS     r0,#1
        0x000001a2:    f000f815    ....    BL       test_fun1 ; 0x1d0
        0x000001a6:    4b04        .K      LDR      r3,[pc,#16] ; [0x1b8] = 0x20000020
        0x000001a8:    6018        .`      STR      r0,[r3,#0]
        0x000001aa:    4b04        .K      LDR      r3,[pc,#16] ; [0x1bc] = 0x2000001c
        0x000001ac:    681b        .h      LDR      r3,[r3,#0]
        0x000001ae:    2b04        .+      CMP      r3,#4
        0x000001b0:    d000        ..      BEQ      0x1b4 ; main + 28
        0x000001b2:    e7fe        ..      B        0x1b2 ; main + 26
        0x000001b4:    e7fe        ..      B        0x1b4 ; main + 28
        0x000001b6:    bf00        ..      NOP      
    $d
        0x000001b8:    20000020     ..     DCD    536870944
        0x000001bc:    2000001c    ...     DCD    536870940
    $t
    test_fun2
        0x000001c0:    b570        p.      PUSH     {r4-r6,lr}
        0x000001c2:    4604        .F      MOV      r4,r0
        0x000001c4:    f2412334    A.4#    MOV      r3,#0x1234
        0x000001c8:    4419        .D      ADD      r1,r1,r3
        0x000001ca:    bd70        p.      POP      {r4-r6,pc}
        0x000001cc:    4770        pG      BX       lr
        0x000001ce:    0000        ..      MOVS     r0,r0
    $t
    test_fun1
        0x000001d0:    b538        8.      PUSH     {r3-r5,lr}
        0x000001d2:    4d07        .M      LDR      r5,[pc,#28] ; [0x1f0] = 0x2000001c
        0x000001d4:    2800        .(      CMP      r0,#0
        0x000001d6:    4611        .F      MOV      r1,r2
        0x000001d8:    682c        ,h      LDR      r4,[r5,#0]
        0x000001da:    dd04        ..      BLE      0x1e6 ; test_fun1 + 22
        0x000001dc:    2205        ."      MOVS     r2,#5
        0x000001de:    4620         F      MOV      r0,r4
        0x000001e0:    4421        !D      ADD      r1,r1,r4
        0x000001e2:    f7ffffed    ....    BL       test_fun2 ; 0x1c0
        0x000001e6:    441c        .D      ADD      r4,r4,r3
        0x000001e8:    2001        .       MOVS     r0,#1
        0x000001ea:    602c        ,`      STR      r4,[r5,#0]
        0x000001ec:    bd38        8.      POP      {r3-r5,pc}
        0x000001ee:    bf00        ..      NOP      
    $d
        0x000001f0:    2000001c    ...     DCD    536870940