Better document the limitation of gdbsrv for registers and flags values

During investigations of 303963, Josef found that flags are not always
up to date and that --vex-guest-max-insns=1 ensures flags values
are (more?) correct.

=> enhance the paragraph in the gdbserver limitations to reference
this option and give an idea of the performance impact of the other
options helping to increase the precision of registers and flags.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@12778

diff --git a/docs/xml/manual-core-adv.xml b/docs/xml/manual-core-adv.xml
index fe00ac1901e3484067ace2bc5401881b91e2ad2c..73179b568c9e083b70d92e77c65bccc224310d7a 100644 (file)
--- a/docs/xml/manual-core-adv.xml
+++ b/docs/xml/manual-core-adv.xml
@@ -784,12 +784,24 @@ are however some limitations and peculiarities:</para>
    </listitem>
 
    <listitem>
-     <para>Registers values.</para>
-     <para>When Valgrind gdbserver stops on an error, registers values
-     might not be always up to date due to the optimisations done by
-     the Valgrind core. The
-     option <option>--vex-iropt-precise-memory-exns=yes</option>
-     ensures precise registers values by disabling some optimisations.
+     <para>Processor registers and flags values.</para>
+     <para>When Valgrind gdbserver stops on an error, on a breakpoint
+     or when single stepping, registers and flags values might not be always
+     up to date due to the optimisations done by the Valgrind core.
+     Disabling some optimisations using the following options will increase
+     the precision of registers and flags values.
+     An idea of the performance impact for memcheck is given for each option.
+       <itemizedlist>
+         <listitem>
+           <option>--vex-iropt-precise-memory-exns=yes</option> (10% performance impact).
+         </listitem>
+         <listitem>
+           <option>--vex-guest-max-insns=1</option> (200% performance impact).
+         </listitem>
+         <listitem>
+           <option>--vgdb=full</option> (250% performance impact).
+         </listitem>
+       </itemizedlist>
      </para>
    </listitem>