tracing: Silence GCC 9 array bounds warning (0c97bf86) · Commits · 戴 / test

Starting with GCC 9, -Warray-bounds detects cases when memset is called starting on a member of a struct but the size to be cleared ends up writing over further members. Such a call happens in the trace code to clear, at once, all members after and including `seq` on struct trace_iterator: In function 'memset', inlined from 'ftrace_dump' at kernel/trace/trace.c:8914:3: ./include/linux/string.h:344:9: warning: '__builtin_memset' offset [8505, 8560] from the object at 'iter' is out of the bounds of referenced subobject 'seq' with type 'struct trace_seq' at offset 4368 [-Warray-bounds] 344 | return __builtin_memset(p, c, size); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ In order to avoid GCC complaining about it, we compute the address ourselves by adding the offsetof distance instead of referring directly to the member. Since there are two places doing this clear (trace.c and trace_kdb.c), take the chance to move the workaround into a single place in the internal header. Link: http://lkml.kernel.org/r/20190523124535.GA12931@gmail.com Signed-off-by:

Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> [ Removed unnecessary parenthesis around "iter" ] Signed-off-by:

Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace.c

+1 −5

Original line number	Diff line number	Diff line
		@@ -8910,12 +8910,8 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode)

		cnt++;

		/* reset all but tr, trace, and overruns */
		memset(&iter.seq, 0,
		sizeof(struct trace_iterator) -
		offsetof(struct trace_iterator, seq));
		trace_iterator_reset(&iter);
		iter.iter_flags \|= TRACE_FILE_LAT_FMT;
		iter.pos = -1;

		if (trace_find_next_entry_inc(&iter) != NULL) {
		int ret;

kernel/trace/trace.h

+18 −0

Original line number	Diff line number	Diff line
		@@ -1966,4 +1966,22 @@ static inline void tracer_hardirqs_off(unsigned long a0, unsigned long a1) { }

		extern struct trace_iterator *tracepoint_print_iter;

		/*
		* Reset the state of the trace_iterator so that it can read consumed data.
		* Normally, the trace_iterator is used for reading the data when it is not
		* consumed, and must retain state.
		*/
		static __always_inline void trace_iterator_reset(struct trace_iterator *iter)
		{
		const size_t offset = offsetof(struct trace_iterator, seq);

		/*
		* Keep gcc from complaining about overwriting more than just one
		* member in the structure.
		*/
		memset((char *)iter + offset, 0, sizeof(struct trace_iterator) - offset);

		iter->pos = -1;
		}

		#endif /* _LINUX_KERNEL_TRACE_H */

kernel/trace/trace_kdb.c

+1 −5

Original line number	Diff line number	Diff line
		@@ -37,12 +37,8 @@ static void ftrace_dump_buf(int skip_entries, long cpu_file)
		if (skip_entries)
		kdb_printf("(skipping %d entries)\n", skip_entries);

		/* reset all but tr, trace, and overruns */
		memset(&iter.seq, 0,
		sizeof(struct trace_iterator) -
		offsetof(struct trace_iterator, seq));
		trace_iterator_reset(&iter);
		iter.iter_flags \|= TRACE_FILE_LAT_FMT;
		iter.pos = -1;

		if (cpu_file == RING_BUFFER_ALL_CPUS) {
		for_each_tracing_cpu(cpu) {

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