discussion about registering task_finder in user space probing

[Wenji Huang <wenji dot huang at oracle dot com>]

Hi,

I found our task_finder embedded in each stap_uprob_spec even it is 
same. That will cause many times registering similar task_finder. For 
example,

$stap -p4 -vve 'probe 
process("/home/wjhuang/Download/git-1.5.6/git*").function("xmalloc"){}'

The generated C code is like,
[snip]
static struct stap_uprobe_spec {
  struct stap_task_finder_target finder;
  unsigned long address;
  const char *pathname;
  const char *pp;
  void (*ph) (struct context*);
  unsigned return_p:1;
} stap_uprobe_specs [] = {
  { .finder = { .pathname="/home/wjhuang/Download/git-1.5.6/git", }, 
.address=(unsigned long)0x804b180ULL, 
.pp="process(\"/home/wjhuang/Download/git-1.5.6/git\").function(\"xmalloc@/home/wjhuang/Download/git-1.5.6/git-compat-util.h:256\")", 
.ph=&probe_1383, },
  { .finder = { .pathname="/home/wjhuang/Download/git-1.5.6/git", }, 
.address=(unsigned long)0x804b9cfULL, 
.pp="process(\"/home/wjhuang/Download/git-1.5.6/git\").function(\"xmalloc@/home/wjhuang/Download/git-1.5.6/git-compat-util.h:256\")", 
.ph=&probe_1383, },
  { .finder = { .pathname="/home/wjhuang/Download/git-1.5.6/git", }, 
.address=(unsigned long)0x804c05cULL, 
.pp="process(\"/home/wjhuang/Download/git-1.5.6/git\").function(\"xmalloc@/home/wjhuang/Download/git-1.5.6/git-compat-util.h:256\")", 
.ph=&probe_1383, },
  { .finder = { .pathname="/home/wjhuang/Download/git-1.5.6/git", }, 
.address=(unsigned long)0x804c3b0ULL, 
.pp="process(\"/home/wjhuang/Download/git-1.5.6/git\").function(\"xmalloc\")", 
.ph=&probe_1383, },
[snip]
  for (i=0; i<220; i++) {
    struct stap_uprobe_spec *sups = & stap_uprobe_specs[i];
    probe_point = sups->pp;
    if (sups->finder.pathname) sups->finder.callback = & 
stap_uprobe_process_found;
    else if (sups->pathname) sups->finder.vm_callback = & 
stap_uprobe_vmchange_found;
    rc = stap_register_task_finder_target (& sups->finder);
    if (rc) break;
  }
[snip]

So we will have 220 times registering similar task_finder. I think
the probe point is irrelevant to task_finder. Can we just keep only one 
and invoke callbacks to register all the stap_uprobes[i] once interested 
process found?

Regards,
Wenji