[Valgrind-developers] valgrind: r6327 - branches/VALGRIND_3_2_BRANCH/docs/xml

[<sv...@va...>]

Author: njn
Date: 2006-10-20 23:23:54 +0100 (Fri, 20 Oct 2006)
New Revision: 6327

Log:
Add an FAQ.

MERGED FROM TRUNK

Modified:
   branches/VALGRIND_3_2_BRANCH/docs/xml/FAQ.xml


Modified: branches/VALGRIND_3_2_BRANCH/docs/xml/FAQ.xml
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--- branches/VALGRIND_3_2_BRANCH/docs/xml/FAQ.xml	2006-10-20 22:16:57 UTC=
 (rev 6326)
+++ branches/VALGRIND_3_2_BRANCH/docs/xml/FAQ.xml	2006-10-20 22:23:54 UTC=
 (rev 6327)
@@ -517,6 +517,36 @@
   </answer>
 </qandaentry>
=20
+<qandaentry id=3D"faq.undeferrors">
+  <question id=3D"q-undeferrors">
+    <para>Memcheck's uninitialised value errors are hard to track down,
+    because they are often reported some time after they are caused.  Co=
uld=20
+    Memcheck record a trail of operations to better link the cause to th=
e
+    effect?  Or maybe just eagerly report any copies of uninitialised
+    memory values?</para>
+  </question>
+  <answer id=3D"a-undeferrors">
+    <para>We'd love to improve these errors, but we don't know how to do=
 it
+    without huge performance penalties.</para>
+
+    <para>You can use the client request
+    <computeroutput>VALGRIND_CHECK_VALUE_IS_DEFINED</computeroutput> to =
help
+    track these errors down -- work backwards from the point where the
+    uninitialised error occurs, checking suspect values until you find t=
he
+    cause.  This requires editing, compiling and re-running your program
+    multiple times, which is a pain, but still easier than debugging the
+    problem without Memcheck's help.</para>
+
+    <para>As for eager reporting of copies of uninitialised memory value=
s,
+    this has been suggested multiple times.  Unfortunately, almost all
+    programs legitimately copy uninitialise memory values around (becaus=
e
+    compilers pad structs to preserve alignment) and eager checking lead=
s to
+    hundreds of false positives.  Therefore Memcheck does not support ea=
ger
+    checking at this time.</para>
+  </answer>
+</qandaentry>
+
+
 </qandadiv>
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=20