#include "ARMCFunctions.h"

MMFLOAT doubleit(MMFLOAT *c){
 return *c *2.0;
}
__attribute__((noinline)) void getFPC(void *a, void *b, volatile unsigned int *c)
   {
       *c = (unsigned int) (__builtin_return_address (0) - (b -a) - 1) ;      
   }

void p_string(const char *s){
  volatile unsigned int libAddr ;
  getFPC(0,&&getFPCLab,&libAddr) ;
  getFPCLab: { }
  unsigned char  * testData    = (unsigned char *)((void *)s + libAddr);
  MMPrintString(testData);
}
void p_int(int a,int base){
  char b[64];
  IntToStr(b,a,base);
  MMPrintString(b);
}
void p_float(float a,int m, int n, char c){
// m is the nbr of chars before the decimal point
// n is the nbr chars after the point
// ch is the leading pad char
  char b[14];
  FloatToStr(b,a, m, n ,c);
  MMPrintString(b);
}

void foo(void) {
//    char s[] = "_Hello World\r\n";
//    s[0] = 13;
//    MMPrintString(s);  
}

typedef void (*function_t)(void);

void main(long long int *c, MMFLOAT *b){
  volatile unsigned int libAddr ;
  getFPC(0,&&getFPCLab,&libAddr) ;
  getFPCLab: { }
  static const char crlf[]="\r\n";
  static const char s1[]="First variable = ";
  static const char s2[]="Second variable = ";
 p_string(s1); p_int(*c,10); p_string(crlf);
 p_string(s2); p_float(doubleit(b),4,2,' '); p_string(crlf);

 foo();

 // *** Hangs if this is uncommented. ***
 function_t fptr = &foo;
 fptr();
}

test.c: In function 'main':
test.c:55:3: error: called object 'fptr' is not a function or function pointer
  55 |   fptr();
     |   ^~~~
test.c:54:10: note: declared here
  54 |   void (*fptr) = foo;

void (*fptr)(void);     // equivalent to void (*fptr)();
fptr = foo;             // equivalent to fptr = &foo;
fptr();

// Declare fptr to be a pointer to a function with 0 args and no return value.

void (*fptr)(void);

// Assign the address of a function to 'fptr'.
// fptr = foo;
// fptr = &foo;
// and possibly even
// fptr = *foo;
// fptr = ***** foo;
// are all treated the same, see https://stackoverflow.com/questions/16917043/do-function-pointers-need-an-ampersand

fptr = foo;

// Call foo via the pointer:

fptr();

#include "ARMCFunctions.h"

void p_int(int a,int base){
  char b[64];
  IntToStr(b,a,base);
  MMPrintString(b);
}

void foo(void) {
 putConsole('*'); putConsole('\r'); putConsole('\n');  
}

void main(long long int *c, MMFLOAT *b){
 putConsole('a'); putConsole('\r'); putConsole('\n');
 foo();
 putConsole('b'); putConsole('\r'); putConsole('\n');
 void (*fptr)(void);
 putConsole('c'); putConsole('\r'); putConsole('\n');
 fptr = &foo; // <--- hangs here, how is that even possible?
 putConsole('d'); putConsole('\r'); putConsole('\n');
}

#include "ARMCFunctions.h"

void p_int(int a,int base){
 char b[64];
 IntToStr(b,a,base);
 MMPrintString(b);
}

void GetRetAdd(unsigned int* padd)
{
// get return address in foo
*padd = (unsigned int)  __builtin_return_address (0);
}

void foo(unsigned int* padd, char cInitAdd) {
if(cInitAdd){ // initialise the address
GetRetAdd(padd);
}
else{ // what you really want to do in foo()
putConsole('*'); putConsole('\r'); putConsole('\n');  
}
}

void main(long long int *c, MMFLOAT *b){
unsigned int* padd = 0;
void (*fptr)(unsigned int* , char );
putConsole('a'); putConsole('\r'); putConsole('\n');
foo(padd,1); // *** initialise address
putConsole('b'); putConsole('\r'); putConsole('\n');
*padd -= 24; // *** 24 = number of bytes from calling GetRetAdd() in foo to foo's entry
// so now data in padd points to foo
fptr = (void (*)(unsigned int* , char )) *padd; // *** set pointer
putConsole('c'); putConsole('\r'); putConsole('\n');
fptr(padd,0);  // call foo via function pointer to do real stuff
putConsole('d'); putConsole('\r'); putConsole('\n');
fptr(padd,0);  // just to prove it works  again!
putConsole('e'); putConsole('\r'); putConsole('\n');
}

15: **** void foo(unsigned int* padd, char cInitAdd) {
130               .loc 1 15 45
131               .cfi_startproc
132               @ args = 0, pretend = 0, frame = 8
133               @ frame_needed = 1, uses_anonymous_args = 0
134 0000 80B5     push {r7, lr}
135               .cfi_def_cfa_offset 8
136               .cfi_offset 7, -8
137               .cfi_offset 14, -4
138 0002 82B0     sub sp, sp, #8
139               .cfi_def_cfa_offset 16
140 0004 00AF     add r7, sp, #0
141               .cfi_def_cfa_register 7
142 0006 7860     str r0, [r7, #4]
143 0008 0B46     mov r3, r1
144 000a FB70     strb r3, [r7, #3]
 16                     if(cInitAdd==1){ // initialise the address
145               .loc 1 16 4
146 000c FB78     ldrb r3, [r7, #3] @ zero_extendqisi2
147 000e 012B     cmp r3, #1
148 0010 03D1     bne .L6
 17:                  GetRetAdd(padd);
149               .loc 1 17 3
150 0012 7868     ldr r0, [r7, #4]
151 0014 FFF7FEFF bl GetRetAdd(PLT)