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BSD 2.11 - man page for stack (bsd section 5)

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STACK(5)										 STACK(5)

NAME
       stack -	2.10BSD PDP-11 C stack frame conventions

DESCRIPTION
       The standard C stack frame layout:

	      ------------------
	      |...nth argument |	      push arguments in reverse order
	      ------------------
	      |second argument |
	      ------------------
	      | first argument |
	      ------------------	      JSR PC,*$_FOO
	      | return address |
	      ------------------	      JSR R5,CSV
	      |  old R5 value  | <-----
	      ------------------      |
	      |previous overlay|      |
	      |     number     |      |
	      ------------------      |
	      |       r4       |      |
	      ------------------      |
	      |       r3       |      |
	      ------------------      |
	      |       r2       |      |
	      ------------------      |
	      | first local var|      | This is the top of the stack
	      ------------------      | when the called routine ``starts''
	      |     routine    |      |
	      |    allocates   |      |
	      |     storage    |      |       SUB $n,SP
	      |    temporary   |      |
	      ------------------      |
	      | push arguments |      |
	      | of next routine|      |
	      ------------------      |       JSR PC,*$_BAR
	      | return address |      |
	      ------------------      |       JSR R5,CSV
	      | old R5 value---+-------
	      ------------------      ^
	      |previous overlay|      |
	      |     number     |      |
	      ------------------      |
	      | r4/43/r2/...   |      |
	      ------------------
	      | and so on..... |

       The stack pushes downward through memory addresses.  Overlay numbers saved in non-overlaid
       objects are always zero, but the simplification of not having to  maintain  two	different
       stack  frame formats more than outweighs the extra few micro seconds (less than four) nec-
       essary to save the zero ...

       Functions returning integers leave their return value in R0; functions returning  floating
       constants  use  FR0; functions returning longs leave return values in R1/R0 (R0 high word,
       R1 low); functions returning structures leave a pointer to bss storage (one chunk of which
       is  allocated for each such routine) in R0, and the caller will copy from that bss storage
       to the local destination.

       Local variables are allocated in such a way that they are referred to as ``-N(R5)'', argu-
       ments  are  referred  to  as ``+N(R5)''; arguments start at 4(R5), the first integer local
       declared will be at -10(R5).

       The SP normally points at the first word available for parameter pushing.  A function tak-
       ing only single word as a parameter can be called simply by moving the parameter into (SP)
       and calling the function, without having to clean the parameter off the stack  on  return.
       Any  parameters passed after the first (actually "Nth") must be pushed before the call and
       cleaned off afterwards.	If the function has no local variables and calls no functions, it
       will allocate no stack and the word labelled ``first local var'' will be unused.

       It is important to note that routines know how many arguments they pass to a function, and
       will adjust the stack accordingly after a function returns.

NOTE
       This stack frame format is the same as that used by overlaid objects in 2.9BSD.

AUTHOR
       John F. Woods, MIT Concouse Computer Center

3rd Berkeley Distribution								 STACK(5)
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