Re: [Xen-devel] Xen GCC coverage ARM64 testing - Unexpected Trap: Data Abort

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, May 03, 2019 at 02:35:08PM +0100, Julien Grall wrote:
> Hi Wei,
> 
> On 5/3/19 12:08 PM, Wei Liu wrote:
> > On Thu, May 02, 2019 at 09:43:17PM +0100, Julien Grall wrote:
> > > (+ Wei)
> > > 
> > > On 5/2/19 5:55 PM, Viktor Mitin wrote:
> > > > Hi Julien,
> > > 
> > > Hi,
> > > 
> > > > Please find trace log below:
> > > > 
> > > > root@h3ulcb:~# xencov reset
> > > > (XEN) Data Abort Trap. Syndrome=0x7
> > > > (XEN) Walking Hypervisor VA 0x361700 on CPU3 via TTBR 0x0000000078266000
> > > So this is a data abort when trying to access VA 0x361700 (it is part of 
> > > Xen
> > > itself). I misread the Arm Arm before, while ISV is 0 DFSC will still
> > > provide a correct value. So here we have a "Translation fault, level 3".
> > > 
> > > Which makes sense because ...
> > > 
> > > 
> > > > (XEN) 0TH[0x0] = 0x0000000078265f7f
> > > > (XEN) 1ST[0x0] = 0x0000000078262f7f
> > > > (XEN) 2ND[0x1] = 0x004000007825ff7f
> > > > (XEN) 3RD[0x161] = 0x00600000781e1f7e
> > > 
> > > the 3rd entry is not valid. I managed to reduce the error and it looks 
> > > like
> > > gcov is trying to access a counter in the section init.data.
> > > 
> > > As all the .init.* sections are stripped after boot, it means that 
> > > anything
> > > in .init.data cannot be accessed anymore.
> > > 
> > > Wei, how do you deal with counters in init.data on x86?
> > 
> > The build system explicitly compile any .init binary without gcov
> > option. So maybe some file was not correctly added?
> 
> Thank you for the pointer. The problem is coming from libfdt. The entire
> library is moved to .init using:
> 
>  $(OBJCOPY) $(foreach s,$(SECTIONS),--rename-section .$(s)=.init.$(s)) $< $@
> 
> So we need to tell the top Makefile to filter out libfdt. The patch below
> should do the job:
> 
> diff --git a/xen/common/libfdt/Makefile b/xen/common/libfdt/Makefile
> index d81f54b6b8..c075bbf546 100644
> --- a/xen/common/libfdt/Makefile
> +++ b/xen/common/libfdt/Makefile
> @@ -3,6 +3,7 @@ include Makefile.libfdt
>  SECTIONS := text data $(SPECIAL_DATA_SECTIONS)
> 
>  obj-y += libfdt.o
> +nocov-y += libfdt.o
> 
>  CFLAGS += -I$(BASEDIR)/include/xen/libfdt/
> 
> While looking at the code, I noticed libelf is also built with coverage but
> in .init section. So I would expect the same error on x86, did you try
> "xencov reset" on x86?

I did. It worked. Though at this point I'm not sure why it worked. :-/

Wei.

> 
> Cheers,
> 
> -- 
> Julien Grall

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