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

[Julien Grall <julien.grall@xxxxxxx>]

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?
Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel