Re: mprof and new systems..

Julian Elischer wrote:
> mprof is a memory allocation profiler.
> 
> as part of what it does it reads the stack for a call graph.
> 
> it finds the current frame  pointer from the address of a variable on
> the stack
> and then from that traces back to previous return addresses.
> 
> however there is a catch, at least on i386..
> 
> with -O2 the variable is 4 bytes below the fp and
> without it it is 12 bytes below.
> so it has to know how it was compiled to get it right.
> 
> in addition, with -O2 it seems that the address of the variable
> may actually be wring if the optimiser never bothers to
> have the variable actually saved.
> 
> 
> one possibility would be to use #asm to just give the value of %ebp

but I don't know how to do that..

> 
> currently it does:
> 
> 
> 
> findretaddr()
> {
>   int first_var;
>   u_int *fp
>   u_int *retptr
> 
> 
>   fp = ((char *)(&first_var)) + 4;  /* needs to be 12 if no -O2 */
>   retptr = ((char *)fp) + 4;
>   prev_fp = *fp;
> 
>   [...]
> 
> 
> }
> 
> Anyone with ideas as to how to make the port act reliably?
> 
> mprof is really cool but thos probelm makes it hard to use.
> you have ot make sure you compile the library itself without -O
> and change the code..
> 
> why it needs to be 12 is unknown  the compiler seems to want
> to push extra regs before savinghte frame pointer.

here's a littel test program that demonsteates how good mprof is
(when it works)

however if you compile mprof with O2 as it is by default I think,
it just crashes.
no -O allows it to work but you have to fix the 4 to 12 in the 
mprof_???.h file.
this seems a bit less tham 'predictable'

#include <stdio.h>
#include <stdlib.h>

typedef struct A
{
     char c[300];
} A;

void foo2()
{
     void * ptr = malloc(1024);
     *(char *)ptr = 'a';
}
void foo1()
{
     void * ptr = malloc(1024);
     struct A *p = malloc(sizeof(struct A));
     p->c[0] = 'b';
     *(char *)ptr = 'a';
     foo2();
}
void foo()
{
     int first_local;
     first_local=10;
     void * ptr = malloc(1024);
     *(char *)ptr = 'a';
     foo1();
     foo2();
}
int main(int argc, char**argv)
{
     void *ptr = malloc(1024);
     free(ptr);
     foo();
     foo2();

     return(0);
}

> 
> 
> 
> 
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