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Subject[PATCH 4.9 32/54] perf top: Fix stdio interface input handling with glibc 2.28+
From: Tommi Rantala <>

commit 29b4f5f188571c112713c35cc87eefb46efee612 upstream.

Since glibc 2.28 when running 'perf top --stdio', input handling no
longer works, but hitting any key always just prints the "Mapped keys"
help text.

To fix it, call clearerr() in the display_thread() loop to clear any EOF
sticky errors, as instructed in the glibc NEWS file

* All stdio functions now treat end-of-file as a sticky condition. If you
read from a file until EOF, and then the file is enlarged by another
process, you must call clearerr or another function with the same effect
(e.g. fseek, rewind) before you can read the additional data. This
corrects a longstanding C99 conformance bug. It is most likely to affect
programs that use stdio to read interactive input from a terminal.
(Bug #1190.)

Signed-off-by: Tommi Rantala <>
Tested-by: Arnaldo Carvalho de Melo <>
Cc: Alexander Shishkin <>
Cc: Jiri Olsa <>
Cc: Mark Rutland <>
Cc: Namhyung Kim <>
Cc: Peter Zijlstra <>
Signed-off-by: Arnaldo Carvalho de Melo <>
Signed-off-by: Greg Kroah-Hartman <>

tools/perf/builtin-top.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -633,7 +633,9 @@ repeat:
delay_msecs = top->delay_secs * MSEC_PER_SEC;
/* trash return*/
- getc(stdin);
+ clearerr(stdin);
+ if (poll(&stdin_poll, 1, 0) > 0)
+ getc(stdin);

while (!done) {

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