Messages in this thread | | | Subject | Re: Warning from ring buffer code (Was: Re: linux-next: tip tree build warning) | From | Steven Rostedt <> | Date | Mon, 14 Sep 2009 14:17:18 -0400 |
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On Mon, 2009-09-14 at 10:09 -0700, Christopher Li wrote: > On Mon, Sep 14, 2009 at 8:16 AM, Steven Rostedt <srostedt@redhat.com> wrote: > > static void func(int size_me) { > > char array[size_me]; > > > > memcpy(array, "hello", size); > > }; > > > > and sparse failed on it as well. Note, you need to have something call > > func, or sparse will ignore it. > > Gcc allows variable size. Sparse expects the size of an array is constant. > For the kernel using variable array size is consider bad. Because the kernel > has very limited stack size. (8K if I remember correctly). Using dynamic array > is very easy to overflow the stack without realizing it. > > It deserves a warning. I agree the warning message can use a better description > though.
Good point!
I've added Frederic to the Cc list, since he wrote the code.
Frederic, how big can one of those events get. The ring buffer (and TRACE_EVENT) allow up to almost a page size, which is very hefty for the stack. This code needs to either be rewritten or we need to set a limit to the size of a profile entry.
We could add:
if (__entry_size > 256) return;
Thoughts?
-- Steve
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