使用通过寄存器传递的参数的地址, 作为支持调用其他函数

#include <stdint.h>

uint32_t arg = 0x12345678;

uint32_t getArgVal0( uint32_t * arg)
{
  return *arg;
}

uint32_t getArgVal( uint32_t arg)
{
  return getArgVal0( &arg );
}

uint32_t * getArgPtr( uint32_t arg)
{
  return &arg;
}

int main( void )
{
  arg = (uint32_t)getArgVal( arg);        // OK 
  arg = (uint32_t)getArgPtr( arg);        // ERROR
}

 

getArgVal0:
   0x200050d0: 0x6800         LDR       R0, [R0]
   0x200050d2: 0x4770         BX        LR
getArgVal:
   0x200050d4: 0xb501         PUSH      {R0, LR}
   0x200050d6: 0xa800         ADD       R0, SP, #0x0　　　　　　　; Push Arg to Stack, use Address of Stack as argument pass to getArgVal0()　　　
   0x200050d8: 0xf7ff 0xfffa  BL        getArgVal0              ; 0x200050d0
   0x200050dc: 0xbd02         POP       {R1, PC}
getArgPtr:
   0x200050de: 0xb401         PUSH      {R0}
   0x200050e0: 0xa800         ADD       R0, SP, #0x0　　　　　　　; Push Arg to Stack, Return Address of Stack　
   0x200050e2: 0xb001         ADD       SP, SP, #0x4
   0x200050e4: 0x4770         BX        LR
main:
   0x200050e8: 0x481b         LDR.N     R0, ??DataTable1_1      ; arg
   0x200050ea: 0x6800         LDR       R0, [R0]
   0x200050ec: 0xf7ff 0xfff2  BL        getArgVal               ; 0x200050d4
   0x200050f0: 0x4919         LDR.N     R1, ??DataTable1_1      ; arg
   0x200050f2: 0x6008         STR       R0, [R1]
   0x200050f4: 0x4818         LDR.N     R0, ??DataTable1_1      ; arg
   0x200050f6: 0x6800         LDR       R0, [R0]
   0x200050f8: 0xf7ff 0xfff1  BL        getArgPtr               ; 0x200050de
   0x200050fc: 0x4916         LDR.N     R1, ??DataTable1_1      ; arg
   0x200050fe: 0x6008         STR       R0, [R1]                ; R0 is Address in Stack, NOT global