stack memory layout in C

Question

I try to verify my understand of the stack memory layout in C by compiling following code and inspect the address in gdb. I only record the least significant digits, the higher ones are the same. The outputs are generated by using the

print \u &a

Here is a simple test code:

void test(int a,int b)
{
  int c = a;
  int d = b;
  printf("%d,%d\n",c,d);
}

int main()
{
  int x = 1;
  int y = 2;
  test(x,y);
  return 0;
}

If I look at the test function frame, I have following results,

&b: 6808 &a: 6812

&c: 6824 &d: 6828

$rbp: 6832 (frame pointer).

I am confused. Shouldn't function parameters sit at higher memory address with respect to the local variables. Can someone explain this in detail please?

Edit:
If I print the memory out like:

printf("&a:%p,&b:%p\n",(&a),(&b));
printf("&c:%p,&d:%p\n",(&c),(&d));

I got

&a:0x7fff4737687c,&b:0x7fff47376878
&c:0x7fff47376888,&d:0x7fff4737688c

It turns to be in b a c d order. There is a 8 byte gap between end of a and beginning c. I guess it shall be the return address?

Some stacks grow upward, others downward. Depends on the system. — dandan78, Oct 10 '14 at 07:49
Your code and results would make more sense if you actually printed the address of the variable in the code, e.g. `printf("%p, %p\n", &a, &b);` inside `test()`. — unwind, Oct 10 '14 at 07:50
@RaymondChen ... [unless there are too many to be passed through registers](http://msdn.microsoft.com/en-us/library/zthk2dkh.aspx) — Andreas Fester, Oct 10 '14 at 08:17
On which architecture are you working? The stack is different on each one. — fuz, Oct 10 '14 at 09:54
The wikipedia page is actually not that bad. It describes the general case and points out the the actual layout of stack frames is machine dependant. http://en.wikipedia.org/wiki/Call_stack — Klas Lindbäck, Oct 10 '14 at 10:08
C does not even require the stack to exist, much less specify its layout. — n. m. could be an AI, Jun 18 '23 at 08:18

score 0 · Answer 1 · edited May 23 '17 at 12:20

0

As per the flow of a function, first arguments are allocated and then the internal arguments. Your concern is based on the presumption that stack grows upwards (which is not necessary).

Please follow the below link for more understanding: Does stack grow upward or downward?

edited May 23 '17 at 12:20

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answered Oct 10 '14 at 10:53

thepace

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stack memory layout in C

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