From: Josh Stone <jistone@redhat.com>
Date: Thu, 11 Dec 2014 02:33:34 +0000 (-0800)
Subject: libdw: optimize dwarf_hasattr to just look at abbrev
X-Git-Tag: elfutils-0.161~47
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=64e44dfc9420940d238e5fdad4fadce3c1f5f05e;p=thirdparty%2Felfutils.git

libdw: optimize dwarf_hasattr to just look at abbrev

To just check the presence of an attribute, we only need to look at the
abbreviation data.  This optimization avoids reading over die data at all,
except possibly just to get the abbrev code.

Signed-off-by: Josh Stone <jistone@redhat.com>
---

diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index 0d3150b91..90c080926 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,7 @@
+2014-12-10  Josh Stone  <jistone@redhat.com>
+
+	* dwarf_hasattr.c (dwarf_hasattr): Just walk abbrev for presence.
+
 2014-12-10  Josh Stone  <jistone@redhat.com>
 
 	* libdwP.h (__libdw_dieabbrev): New die->abbrev lookup function.
diff --git a/libdw/dwarf_hasattr.c b/libdw/dwarf_hasattr.c
index fb7e1d5ed..6ed1a98cb 100644
--- a/libdw/dwarf_hasattr.c
+++ b/libdw/dwarf_hasattr.c
@@ -43,10 +43,44 @@ dwarf_hasattr (die, search_name)
   if (die == NULL)
     return 0;
 
-  /* Search for the attribute with the given name.  */
-  unsigned int code;
-  unsigned char *addr = __libdw_find_attr (die, search_name, &code, NULL);
+  /* Find the abbreviation entry.  */
+  Dwarf_Abbrev *abbrevp = __libdw_dieabbrev (die, NULL);
+  if (unlikely (abbrevp == DWARF_END_ABBREV))
+    {
+    invalid_dwarf:
+      __libdw_seterrno (DWARF_E_INVALID_DWARF);
+      return 0;
+    }
 
-  return addr != NULL && code == search_name;
+  Dwarf *dbg = die->cu->dbg;
+
+  /* Search the name attribute.  */
+  unsigned char *const endp
+    = ((unsigned char *) dbg->sectiondata[IDX_debug_abbrev]->d_buf
+       + dbg->sectiondata[IDX_debug_abbrev]->d_size);
+
+  const unsigned char *attrp = abbrevp->attrp;
+  while (1)
+    {
+      /* Are we still in bounds?  This test needs to be refined.  */
+      if (unlikely (attrp + 1 >= endp))
+	goto invalid_dwarf;
+
+      /* Get attribute name and form.
+
+	 XXX We don't check whether this reads beyond the end of the
+	 section.  */
+      unsigned int attr_name;
+      get_uleb128 (attr_name, attrp);
+      unsigned int attr_form;
+      get_uleb128 (attr_form, attrp);
+
+      /* We can stop if we found the attribute with value zero.  */
+      if (attr_name == 0 || attr_form == 0)
+	return 0;
+
+      if (attr_name == search_name)
+	return 1;
+    }
 }
 INTDEF (dwarf_hasattr)