Messages in this thread |  | | Date | Sat, 21 Dec 2019 18:47:41 -0500 | From | Joel Fernandes <> | Subject | Re: [PATCH] tracing: Fix printing ptrs in preempt/irq enable/disable events |
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On Wed, Dec 04, 2019 at 09:21:15AM -0500, Steven Rostedt wrote: > > Joel, > > Any comments on this patch?
Steve, it looks like this issue happens with trace-cmd not knowing what _stext is. If I do cat trace_pipe , then I don't see the issue as _stext is looked up correctly but the reporter of the bug is using trace-cmd. Is there a way to solve this within trace-cmd? Not knowing much about trace-cmd internals, I will have to defer to you on this though..
Other than this, I need to make the offset to _stext as s32 instead of u32 type so that the problem of the symbol location being before _stext does not cause overflow.
Lastly, I am not super convinced that we need to store the full pointer just to handle a case where the offset of the symbol might be more than +-2G from _stext. Once we see such issue, then we can handle it. But right now the size of the trace buffer is utilized better by just storing the offset IMHO.
thanks,
- Joel
> > -- Steve > > On Wed, 27 Nov 2019 16:44:28 +0100 > Antonio Borneo <antonio.borneo@st.com> wrote: > > > This tracing event class is the only instance in kernel that logs > > in the trace buffer the instruction pointer as offset to _stext, > > instead of logging the full pointer. > > This looks like a nice optimization for 64 bits platforms, where a > > 32 bit offset can take less space than a full 64 bits pointer. But > > the symbol _stext is incorrectly resolved as zero in the expansion > > of TP_printk(), which then prints only the hex offset instead of > > the name of the caller function. Plus, on arm arch the kernel > > modules are loaded at address lower than _stext, causing the u32 > > offset arithmetics to overflow and wrap at 32 bits. > > I did not identified a 64 bit arch where the modules are loaded at > > offset from _stext that exceed u32 range, but I also did not > > identified any constraint to feel safe with a u32 offset. > > > > Log directly the instruction pointer instead of the offset to > > _stext. > > > > Signed-off-by: Antonio Borneo <antonio.borneo@st.com> > > Fixes: d59158162e03 ("tracing: Add support for preempt and irq enable/disable events") > > --- > > include/trace/events/preemptirq.h | 12 ++++++------ > > 1 file changed, 6 insertions(+), 6 deletions(-) > > > > diff --git a/include/trace/events/preemptirq.h b/include/trace/events/preemptirq.h > > index 95fba0471e5b..d548a6aafa18 100644 > > --- a/include/trace/events/preemptirq.h > > +++ b/include/trace/events/preemptirq.h > > @@ -18,18 +18,18 @@ DECLARE_EVENT_CLASS(preemptirq_template, > > TP_ARGS(ip, parent_ip), > > > > TP_STRUCT__entry( > > - __field(u32, caller_offs) > > - __field(u32, parent_offs) > > + __field(unsigned long, caller_ip) > > + __field(unsigned long, parent_ip) > > ), > > > > TP_fast_assign( > > - __entry->caller_offs = (u32)(ip - (unsigned long)_stext); > > - __entry->parent_offs = (u32)(parent_ip - (unsigned long)_stext); > > + __entry->caller_ip = ip; > > + __entry->parent_ip = parent_ip; > > ), > > > > TP_printk("caller=%pS parent=%pS", > > - (void *)((unsigned long)(_stext) + __entry->caller_offs), > > - (void *)((unsigned long)(_stext) + __entry->parent_offs)) > > + (void *)__entry->caller_ip, > > + (void *)__entry->parent_ip) > > ); > > > > #ifdef CONFIG_TRACE_IRQFLAGS >
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