perf probe: Add ustring support for perf probe command

Kernel commit 88903c464321 ("tracing/probe: Add ustring type for user-space string") adds support for user-space strings when type ustring is specified.

Here is an example using command line setup of the kprobe.

Function to probe:
struct filename *
getname_flags(const char __user *filename, int flags, int *empty)

Setup:

  # cd /sys/kernel/debug/tracing/
  # echo 'p:tmr1 getname_flags +0(%r2):ustring' > kprobe_events
  # cat events/kprobes/tmr1/format | fgrep print
  print fmt: "(%lx) arg1=\"%s\"", REC->__probe_ip, REC->arg1
  # echo 1 > events/kprobes/tmr1/enable
  # touch /tmp/111
  # echo 0 > events/kprobes/tmr1/enable
  # cat trace|fgrep /tmp/111
  touch-5846  [005] d..2 255520.717960: tmr1:\
	  (getname_flags+0x0/0x400) arg1="/tmp/111"

Doing the same with the perf tool fails. First using string succeeds:

 # perf probe "vfs_getname=getname_flags:72 pathname=filename:string"
 Added new event:
   probe:vfs_getname (on getname_flags:72 with pathname=filename:string)
   ....
 # perf probe -d probe:vfs_getname
 Removed event: probe:vfs_getname

Using ustring fails (output before):

 # perf probe "vfs_getname=getname_flags:72 pathname=filename:ustring"
 Failed to write event: Invalid argument
   Error: Failed to add events.
 #

Fix this by added type 'ustring' in function convert_variable_type().

Using ustring succeeds (output after):

 # ./perf probe "vfs_getname=getname_flags:72 pathname=filename:ustring"
 Added new event:
   probe:vfs_getname (on getname_flags:72 with pathname=filename:ustring)

You can now use it in all perf tools, such as:

perf record -e probe:vfs_getname -aR sleep 1

#

Note: This issue also exists on x86, it is not s390 specific.

---
 tools/perf/util/probe-finder.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index c470c49a804f..1c817add6ca4 100644
@@ -303,7 +303,8 @@ static int convert_variable_type(Dwarf_Die *vr_die,
 	char prefix;
 
 	/* TODO: check all types */
-	if (cast && strcmp(cast, "string") != 0 && strcmp(cast, "x") != 0 &&
+	if (cast && strcmp(cast, "string") != 0 && strcmp(cast, "ustring") &&
+	    strcmp(cast, "x") != 0 &&
 	    strcmp(cast, "s") != 0 && strcmp(cast, "u") != 0) {
 		/* Non string type is OK */
 		/* and respect signedness/hexadecimal cast */

2.21.0

This test places a kprobe to function getname_flags() in the kernel which has the following prototype:

struct filename *
getname_flags(const char __user *filename, int flags, int *empty)

Variable filename points to a filename located in user space memory. Looking at
commit 88903c464321c ("tracing/probe: Add ustring type for user-space string") the kprobe should indicate that user space memory is accessed.

So I suggest the following patch to specify user space memory access where 'string' is replaced by 'ustring'.

---
 tools/perf/tests/shell/lib/probe_vfs_getname.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 7cb99b433888..7ecf117651dd 100644
@@ -13,8 +13,8 @@ add_probe_vfs_getname() {
 	local verbose=$1
 	if [ $had_vfs_getname -eq 1 ] ; then
 		line=$(perf probe -L getname_flags 2>&1 | egrep 'result.*=.*filename;' | sed -r 's/[[:space:]]+([[:digit:]]+)[[:space:]]+result->uptr.*/\1/')
-		perf probe -q       "vfs_getname=getname_flags:${line} pathname=result->name:string" || \
-		perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:string"
+		perf probe -q       "vfs_getname=getname_flags:${line} pathname=result->uptr:ustring" || \
+		perf probe $verbose "vfs_getname=getname_flags:${line} pathname=filename:ustring"
 	fi
 }
 

2.21.0