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-rw-r--r--docs/devel/tcg-plugins.rst17
1 files changed, 16 insertions, 1 deletions
diff --git a/docs/devel/tcg-plugins.rst b/docs/devel/tcg-plugins.rst
index 81dcd43a61..fa7421279f 100644
--- a/docs/devel/tcg-plugins.rst
+++ b/docs/devel/tcg-plugins.rst
@@ -497,6 +497,22 @@ arguments if required::
   $ qemu-system-arm $(QEMU_ARGS) \
     -plugin ./contrib/plugins/libexeclog.so,ifilter=st1w,afilter=0x40001808 -d plugin
 
+This plugin can also dump registers when they change value. Specify the name of the
+registers with multiple ``reg`` options. You can also use glob style matching if you wish::
+
+  $ qemu-system-arm $(QEMU_ARGS) \
+    -plugin ./contrib/plugins/libexeclog.so,reg=\*_el2,reg=sp -d plugin
+
+Be aware that each additional register to check will slow down
+execution quite considerably. You can optimise the number of register
+checks done by using the rdisas option. This will only instrument
+instructions that mention the registers in question in disassembly.
+This is not foolproof as some instructions implicitly change
+instructions. You can use the ifilter to catch these cases:
+
+  $ qemu-system-arm $(QEMU_ARGS) \
+    -plugin ./contrib/plugins/libexeclog.so,ifilter=msr,ifilter=blr,reg=x30,reg=\*_el1,rdisas=on
+
 - contrib/plugins/cache.c
 
 Cache modelling plugin that measures the performance of a given L1 cache
@@ -583,4 +599,3 @@ The following API is generated from the inline documentation in
 include the full kernel-doc annotations.
 
 .. kernel-doc:: include/qemu/qemu-plugin.h
-