My environment is 2.6.22-rc7 kernel, systemtap-20070707 snapshot and elfutils-0.128.

context.exp testcase of systemtap-20070707 snapshot fails with below message.
==============================
Running
/home/systemtap/tmp/stap_testing_200707091005/src/testsuite/systemtap.context/context.exp
...
ERROR: tcl error sourcing
/home/systemtap/tmp/stap_testing_200707091005/src/testsuite/systemtap.context/context.exp.
ERROR: echo: write error: Invalid argument
    while executing
"exec echo 0 > /proc/stap_test_cmd"
    invoked from within
"expect -nobrace -timeout 240 {Systemtap probe: begin
} {
        pass "backtrace of begin probe"
        exec echo 0 > /proc/stap_test_cmd
        exp_continue
    } -re ..."
    invoked from within
"expect {
    -timeout 240
    "Systemtap probe: begin\r\n" {
        pass "backtrace of begin probe"
        exec echo 0 > /proc/stap_test_cmd
        exp_continue
    }
 ..."
    (file "backtrace.tcl" line 6)
    invoked from within
"source $test.tcl"
    ("foreach" body line 2)
    invoked from within
"foreach test $testlist {
    source $test.tcl
}"
    (file
"/home/systemtap/tmp/stap_testing_200707091005/src/testsuite/systemtap.context/context.exp"
line 74)
    invoked from within
"source
/home/systemtap/tmp/stap_testing_200707091005/src/testsuite/systemtap.context/context.exp"
    ("uplevel" body line 1)
    invoked from within
"uplevel #0 source
/home/systemtap/tmp/stap_testing_200707091005/src/testsuite/systemtap.context/context.exp"
    invoked from within
"catch "uplevel #0 source $test_file_name""
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