Let query_module abort early for simple matches

query_module was already returning DW_CB_ABORT when a simple match was
found, but dwflpp::iterate_over_modules was ignoring that and instead
forcing the module loop to restart.  The only way out of the loop was
with the pending_interrupts flag, which is only for signalled
interrupts.

Now iterate_over_modules will only attempt the dwfl_getmodules loop
once, since that loop will only abort if the CB returns DW_CB_ABORT.
Then query_module is also modified to return ABORT if pending_interrupts
is flagged.

My trusty test, stap -l syscall.*, is nearly 2x faster with this change.
Empirically, I found that the kernel object is always the first "module"
returned, so the syscall probepoints always gets to short-circuit the
loop right away.

1 files changed, 2 insertions, 7 deletions

diff --git a/dwflpp.cxx b/dwflpp.cxx
index 3af26053..1a589771 100644
--- a/dwflpp.cxx
+++ b/dwflpp.cxx
@@ -397,13 +397,8 @@ dwflpp::iterate_over_modules(int (* callback)(Dwfl_Module *, void **,
                                               void *),
                              base_query *data)
 {
-  ptrdiff_t off = 0;
-  do
-    {
-      if (pending_interrupts) return;
-      off = dwfl_getmodules (dwfl, callback, data, off);
-    }
-  while (off > 0);
+  dwfl_getmodules (dwfl, callback, data, 0);
+
   // Don't complain if we exited dwfl_getmodules early.
   // This could be a $target variable error that will be
   // reported soon anyway.