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-rw-r--r--Documentation/trace/kprobetrace.rst9
1 files changed, 7 insertions, 2 deletions
diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
index 235ce2ab131a..a3ac7c9ac242 100644
--- a/Documentation/trace/kprobetrace.rst
+++ b/Documentation/trace/kprobetrace.rst
@@ -55,7 +55,8 @@ Synopsis of kprobe_events
NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
(u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types
- (x8/x16/x32/x64), "string" and bitfield are supported.
+ (x8/x16/x32/x64), "string", "ustring" and bitfield
+ are supported.
(\*1) only for the probe on function entry (offs == 0).
(\*2) only for return probe.
@@ -77,7 +78,11 @@ apply it to registers/stack-entries etc. (for example, '$stack1:x8[8]' is
wrong, but '+8($stack):x8[8]' is OK.)
String type is a special type, which fetches a "null-terminated" string from
kernel space. This means it will fail and store NULL if the string container
-has been paged out.
+has been paged out. "ustring" type is an alternative of string for user-space.
+Note that kprobe-event provides string/ustring types, but doesn't change it
+automatically. So user has to decide if the targe string in kernel or in user
+space carefully. On some arch, if you choose wrong one, it always fails to
+record string data.
The string array type is a bit different from other types. For other base
types, <base-type>[1] is equal to <base-type> (e.g. +0(%di):x32[1] is same
as +0(%di):x32.) But string[1] is not equal to string. The string type itself