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authorSteven Rostedt (Google) <rostedt@goodmis.org>2022-03-18 15:34:32 -0400
committerSteven Rostedt (Google) <rostedt@goodmis.org>2022-03-20 10:25:13 -0400
commit795301d3c28996219d555023ac6863401b6076bc (patch)
tree130aa75d2d6a55239b6da06dccf2d0b721c6d60a /include/trace
parent089331d47325d3f55016ed3d1f79ffd2754fb19e (diff)
downloadlinux-795301d3c28996219d555023ac6863401b6076bc.tar.bz2
tracing: Have type enum modifications copy the strings
When an enum is used in the visible parts of a trace event that is exported to user space, the user space applications like perf and trace-cmd do not have a way to know what the value of the enum is. To solve this, at boot up (or module load) the printk formats are modified to replace the enum with their numeric value in the string output. Array fields of the event are defined by [<nr-elements>] in the type portion of the format file so that the user space parsers can correctly parse the array into the appropriate size chunks. But in some trace events, an enum is used in defining the size of the array, which once again breaks the parsing of user space tooling. This was solved the same way as the print formats were, but it modified the type strings of the trace event. This caused crashes in some architectures because, as supposed to the print string, is a const string value. This was not detected on x86, as it appears that const strings are still writable (at least in boot up), but other architectures this is not the case, and writing to a const string will cause a kernel fault. To fix this, use kstrdup() to copy the type before modifying it. If the trace event is for the core kernel there's no need to free it because the string will be in use for the life of the machine being on line. For modules, create a link list to store all the strings being allocated for modules and when the module is removed, free them. Link: https://lore.kernel.org/all/yt9dr1706b4i.fsf@linux.ibm.com/ Link: https://lkml.kernel.org/r/20220318153432.3984b871@gandalf.local.home Tested-by: Marc Zyngier <maz@kernel.org> Tested-by: Sven Schnelle <svens@linux.ibm.com> Reported-by: Sven Schnelle <svens@linux.ibm.com> Fixes: b3bc8547d3be ("tracing: Have TRACE_DEFINE_ENUM affect trace event types as well") Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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