From: Linus Torvalds <firstname.lastname@example.org> To: Steven Rostedt <email@example.com> Cc: LKML <firstname.lastname@example.org>, Ingo Molnar <email@example.com>, Andrew Morton <firstname.lastname@example.org> Subject: Re: [GIT PULL] tracing: Updates for 5.2 Date: Wed, 15 May 2019 16:29:50 -0700 [thread overview] Message-ID: <CAHk-=wihYB8w__YQjgYjYZsVniu5CtkTcFycmCGdqVg8GUje7g@mail.gmail.com> (raw) In-Reply-To: <email@example.com> On Wed, May 15, 2019 at 10:36 AM Steven Rostedt <firstname.lastname@example.org> wrote: > > The major changes in this tracing update includes: This is not directly related to this pull request, but newer versions of gcc hate your trace_iterator clearing trick. 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 ‘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); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~ 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); which should compile cleanly - because now you're doing the memset on a part of the much bigger 'iter' structure, not on one member (and overflowing that one member). Another option might be to separate the zeroed part of the structure into a sub-structure of its own, and then just use memset(&iter.sub, 0, sizeof(iter.sub)); but then you'd obviously have to change all the uses of the sub-fields.. Linus
next prev parent reply other threads:[~2019-05-15 23:32 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-05-15 17:36 Steven Rostedt 2019-05-15 23:29 ` Linus Torvalds [this message] 2019-05-15 23:31 ` Linus Torvalds 2019-05-16 0:27 ` Steven Rostedt 2019-05-16 1:21 ` Linus Torvalds 2019-05-16 9:08 ` David Laight 2019-05-15 23:50 ` pr-tracker-bot
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