libdw: New get_uleb128_unchecked to use with already checked Dwarf_Abbrev.

When creating a Dwarf_Abbrev in dwarf_getabbrev (__libdw_getabbrev) we
already check it is fully readable from the .debug_abbrev section. So
whenever we reread it later using the attrp pointer we don't have to
check it again. Introduce get_uleb128_unchecked to use for ulebs we
know are safe to read directly.

Signed-off-by: Mark Wielaard <mark@klomp.org>

1 files changed, 5 insertions, 14 deletions

diff --git a/libdw/dwarf_child.c b/libdw/dwarf_child.c
index cc95fb3f..248338eb 100644
--- a/libdw/dwarf_child.c
+++ b/libdw/dwarf_child.c
@@ -1,5 +1,5 @@
 /* Return child of current DIE.
-   Copyright (C) 2003-2011, 2014 Red Hat, Inc.
+   Copyright (C) 2003-2011, 2014, 2017 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <drepper@redhat.com>, 2003.
 
@@ -43,36 +43,27 @@ internal_function
 __libdw_find_attr (Dwarf_Die *die, unsigned int search_name,
 		   unsigned int *codep, unsigned int *formp)
 {
-  Dwarf *dbg = die->cu->dbg;
   const unsigned char *readp;
 
   /* Find the abbreviation entry.  */
   Dwarf_Abbrev *abbrevp = __libdw_dieabbrev (die, &readp);
   if (unlikely (abbrevp == DWARF_END_ABBREV))
     {
-    invalid_dwarf:
       __libdw_seterrno (DWARF_E_INVALID_DWARF);
       return NULL;
     }
 
-  /* Search the name attribute.  */
-  unsigned char *const endp
-    = ((unsigned char *) dbg->sectiondata[IDX_debug_abbrev]->d_buf
-       + dbg->sectiondata[IDX_debug_abbrev]->d_size);
-
+  /* Search the name attribute.  Attribute has been checked when
+     Dwarf_Abbrev was created, we can read unchecked.  */
   const unsigned char *attrp = abbrevp->attrp;
   while (1)
     {
       /* Get attribute name and form.  */
-      if (unlikely (attrp >= endp))
-	goto invalid_dwarf;
       unsigned int attr_name;
-      get_uleb128 (attr_name, attrp, endp);
+      get_uleb128_unchecked (attr_name, attrp);
 
-      if (unlikely (attrp >= endp))
-	goto invalid_dwarf;
       unsigned int attr_form;
-      get_uleb128 (attr_form, attrp, endp);
+      get_uleb128_unchecked (attr_form, attrp);
 
       /* We can stop if we found the attribute with value zero.  */
       if (attr_name == 0 && attr_form == 0)