who called a C routine - get it from the stack frame

[Gregory Smith]

In article <961 at cuuxb.UUCP> wbp at cuuxb.UUCP (Walt Pesch) writes:
>In article <810 at hropus.UUCP> jgy at hropus.UUCP writes:
>>Can anyone help me with the following problem:  I'm looking for a few 
>>lines of C or assembly code which can be used at the top of a function 
>>to get the address of the function which called it.  I can then map
>>this address to the calling functions name using "nm".
>
>Oh, well, you asked!  Time to get down into the mud...  For System V,
>the following dirty trick should work:
>
>When defining the actual function, which is normally passed "n" 
>variables, define the function to have "n+1" variables.  By the nature 
>of the stack frame, the "n+1"'th variable will contain the program
>address for returning.

Not on anything I've seen. The n+1'th parameter will be part of the caller's
auto or temp space.

What you need is the 'zeroth' parameter:

foo(a,b)
any a,b;
{	char **klugepointer =( (char **)&a) -1;

This sets klugepointer to an address one 'char *' lower than the address of
the first parameter - this will point to the return address on many machines.
More directly:
	char *retadress = ( (char**) &a )[-1];
This return address will be somewhere within the calling routine.
You can use that to find the caller's name. If you can look at the
next stack frame down, you can find the address to return from the
caller. This will allow you to locate the subroutine call which activated
the caller. The caller's start address will be contained in this
instruction ( or can be calculated from it ). This is assuming that
the caller was normally called, of course. There may be >1 type of
call instruction. If these are of different lengths, you cannot determine
the beginning of the instruction given the address of the next instruction
(i.e. the return address).

You will need a 3B2 machine-language reference and some sample 
assembler output from cc to complete this fearsome, grisly mission
if you choose to accept it. Of course, don't expect it to port to
a different compiler, let alone a different machine.

-- 
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Greg Smith     University of Toronto      UUCP: ..utzoo!utcsri!greg
Have vAX, will hack...