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trace: forbid use of %m in trace event format strings

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The '%m' format instructs glibc's printf()/syslog() implementation to
insert the contents of strerror(errno). Since this is a glibc extension
it should generally be avoided in QEMU due to need for portability to a
variety of platforms.

Even though vfio is Linux-only code that could otherwise use "%m", it
must still be avoided in trace-events files because several of the
backends do not use the format string and so this error information is
invisible to them.

The errno string value should be given as an explicit trace argument
instead, making it accessible to all backends. This also allows it to
work correctly with future patches that use the format string with
systemtap's simple printf code.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20190123120016.4538-4-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Daniel P. Berrangé 2019-01-23 12:00:15 +00:00 • committed by Stefan Hajnoczi
parent 7760636309
commit 772f1b3721
3 changed files with 6 additions and 2 deletions
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4
scripts/tracetool/__init__.py
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@ -274,6 +274,10 @@ class Event(object):
props = groups["props"].split()
fmt = groups["fmt"]
fmt_trans = groups["fmt_trans"]
if fmt.find("%m") != -1 or fmt_trans.find("%m") != -1:
raise ValueError("Event format '%m' is forbidden, pass the error "
"as an explicit trace argument")
if len(fmt_trans) > 0:
fmt = [fmt_trans, fmt]
args = Arguments.build(groups["args"])