[Bug translator/1133] support .callees probe pattern extension

["jlebon at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=1133

--- Comment #5 from Jonathan Lebon <jlebon at redhat dot com> ---
(In reply to Jonathan Lebon from comment #4)
> What the new DW_TAG_call_site DIE does give us however is a way of listing
> callees of a DW_TAG_subprogram. So, we could use them to support
> .callees("") by retrieving the address from the DIEs of all target functions.

I've implemented this feature on my branch jlebon/callee. I've opted for the
'.callee' suffix instead of callees to be more in line with other components
that allow a string arg to filter results, such as 'function', 'label', etc...
If desired, we can also add a .callees as a shorthand for .callee("*").

The branch also includes a 'temp' dir with some sample programs on which to
test it. For example:

$ cd temp
$ cat simple.c
// gcc -o simple simple.c -g -O

__attribute__((noinline))
int func(int a, int b) {
   return a + b;
}

int main(void) {
   int a = 1;
   a = func(a, a);
   return a;
}

$ gcc -o simple simple.c -g -O
$ stap -L 'process("simple").function("main").callee("*")'
process("/home/yyz/jlebon/codebase/systemtap/systemtap/temp/simple").function("func@/home/yyz/jlebon/codebase/systemtap/systemtap/temp/simple.c:4")
$a:int $b:int
$ 
$ 
$ 
$ cat inlined.c
// gcc -o inlined inlined.c -g -O

__attribute__((noinline))
int foo(int a, int b) {
   return a % b;
}

__attribute__((always_inline))
int func(int a, int b) {
   int c, d, e;
   c = a + b;
   d = a * b;
   e = foo(c, d);
   return e - 1;
}

int main(void) {
   int a = 1;
   a = func(a, a);
   return a;
}

$ gcc -o inlined inlined.c -g -O -w
$ stap -L 'process("inlined").function("main").callee("*")'
process("/home/yyz/jlebon/codebase/systemtap/systemtap/temp/inlined").function("func@/home/yyz/jlebon/codebase/systemtap/systemtap/temp/inlined.c:9")
$b:int $a:int
$ stap -L 'process("inlined").function("func").callee("*")'
process("/home/yyz/jlebon/codebase/systemtap/systemtap/temp/inlined").function("foo@/home/yyz/jlebon/codebase/systemtap/systemtap/temp/inlined.c:4")
$a:int $b:int
$ 

Callee functions defined externally are also supported:

$ cat extern.c
// gcc -o extern extern.c extern2.c -g -O

long int fn2 (long int, long int, long int);
long int fn4 (long int *i, long int j);

long int
fn3 (long int x, long int (*fn4) (long int *, long int))
{
  long int v, w, w2, z;
  w = (*fn4) (&w2, x);
  v = (*fn4) (&w2, x);
  z = fn2 (1, v + 1, w);
  {
    int v1 = v + 4;
    z += fn2 (w, v * 2, x);
  }
  return z;
}

int main(void) {
  long int a = 1;
  a = fn3(a, &fn4);
  return a - 5;
}

$ cat extern2.c
// gcc -o extern extern.c extern2.c -g -O

long int
fn2 (long int a, long int b, long int c)
{
  long int q = 2 * a;
  return q + 5;
}

long int fn4 (long int *i, long int j) {
  return *i << j;
}

$ gcc -o extern extern.c extern2.c -g -O
$ stap -L 'process("extern").function("main").callee("*")'
process("/home/yyz/jlebon/codebase/systemtap/systemtap/temp/extern").function("fn3@/home/yyz/jlebon/codebase/systemtap/systemtap/temp/extern.c:7")
$x:long int $fn4:void* $w2:long int
$ 
$ stap -L 'process("extern").function("fn3").callee("*")'
process("/home/yyz/jlebon/codebase/systemtap/systemtap/temp/extern").function("fn2@/home/yyz/jlebon/codebase/systemtap/systemtap/temp/extern2.c:4")
$a:long int $b:long int $c:long int $q:long int
$ 

> Note however that call site DIEs are not guaranteed to be emitted for all
> call sites (DW_TAG_subprogram attributes such as DW_AT_all_call_sites could
> be examined to determine if they're all there, if it matters to us).

Unfortunately, there is a slight issue here as well. DW_AT_all_call_sites only
guarantees that all tail calls and normal calls have a corresponding
DW_TAG_call_site DIE, but it makes no guarantee regarding inlined functions. In
other words, we have no way of determining whether callee("*") truly caught
every call possible.

The DWARF issue (see [1] in comment 4) does have a new flag to that effect,
DW_AT_all_source_call_sites, which, if present, indicates that all inlines,
normal, and tail calls are present. Until this is implemented in gcc, we can
make no guarantee on whether callee("*") is completely thorough.

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