RE: [GIT PULL] tracing: Updates for 5.2

[David Laight]

> This code:
> 
>                 /* reset all but tr, trace, and overruns */
>                 memset(&iter.seq, 0,
>                        sizeof(struct trace_iterator) -
>                        offsetof(struct trace_iterator, seq));
> 
> not only has a completely misleading comment (it resets a lot more
> than the comment states), but modern gcc looks at that code and says
> "oh, you're passing it a pointer to 'iter.seq', but then clearing a
> lot more than a 'trace_seq'":
> 
>   In function âmemsetâ,
>       inlined from âftrace_dumpâ at kernel/trace/trace.c:8914:3:
>  /include/linux/string.h:344:9: warning: â__builtin_memsetâ offset
> [8505, 8560] from the object at âiterâ is out of the bounds of
> referenced subobject âseqâ with type âstruct trace_seqâ at offset 4368
> [-Warray-bounds]
>     344 |  return __builtin_memset(p, c, size);
>         |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> It's a somewhat annoying warning because the code itself is
> technically correct, but at the same time, I think the gcc warning is
> reasonable. You *are* passing it a 'struct trace_seq' pointer, and
> then you're clearing a whole lot more than that.
> 
> One option is to just rewrite it something like
> 
>         const unsigned int offset = offsetof(struct trace_iterator, seq);
>         memset(offset+(void *)&iter, 0, sizeof(iter) - offset);

I'd do (const char *)&iter + offset ...

A quick fix is (probably) just:
	memset((void *)(long)&iter.seq, ...

	David

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