Re: [Qemu-devel] subpage_write() and duplicated memory_region_ops_write tracepoints

[Hollis Blanchard]

On 12/09/2015 01:12 PM, Paolo Bonzini wrote:
> On 09/12/2015 21:54, Hollis Blanchard wrote:
> > #0  trace_memory_region_ops_write (mr=0x185b620, addr=16, absaddr=738205712, 
> > value=136, size=4)
> >      at 
> > /scratch1/hblancha/install/customq/qemu-2.4.0/src/trace/generated-tracers.h:7374
> > #1  0x000000000045eb8a in memory_region_write_with_attrs_accessor 
> > (mr=0x185b620, addr=16,
> >      value=0x45203338, size=4, shift=0, mask=4294967295, attrs=...)
> >      at /scratch1/hblancha/install/customq/qemu-2.4.0/src/memory.c:513
> > #2  0x000000000045ed08 in access_with_adjusted_size (addr=16, value=0x45203338, 
> > size=4,
> >      access_size_min=1, access_size_max=4, access=0x45eb15 
> > <memory_region_write_with_attrs_accessor>,
> >      mr=0x185b620, attrs=...) at 
> > /scratch1/hblancha/install/customq/qemu-2.4.0/src/memory.c:556
> > #3  0x0000000000461ed7 in memory_region_dispatch_write (mr=0x185b620, addr=16, 
> > data=136, size=4,
> >      attrs=...) at 
> > /scratch1/hblancha/install/customq/qemu-2.4.0/src/memory.c:1214
> > #4  0x0000000000411bbf in address_space_rw (as=0x11f3440, addr=738205712, 
> > attrs=...,
> >      buf=0x45203490 "\210", len=4, is_write=true)
> >      at /scratch1/hblancha/install/customq/qemu-2.4.0/src/exec.c:2497
> > #5  0x0000000000411ea9 in address_space_write (as=0x11f3440, addr=738205712, 
> > attrs=...,
> >      buf=0x45203490 "\210", len=4) at 
> > /scratch1/hblancha/install/customq/qemu-2.4.0/src/exec.c:2579
> > #6  0x0000000000410d89 in subpage_write (opaque=0x19148f0, addr=16, value=136, 
> > len=4, attrs=...)
> >      at /scratch1/hblancha/install/customq/qemu-2.4.0/src/exec.c:2139
> > #7  0x000000000045ebb2 in memory_region_write_with_attrs_accessor 
> > (mr=0x19148f0, addr=16,
> >      value=0x452035a8, size=4, shift=0, mask=4294967295, attrs=...)
> >      at /scratch1/hblancha/install/customq/qemu-2.4.0/src/memory.c:516
> > #8  0x000000000045ed08 in access_with_adjusted_size (addr=16, value=0x452035a8, 
> > size=4,
> >      access_size_min=1, access_size_max=8, access=0x45eb15 
> > <memory_region_write_with_attrs_accessor>,
> >      mr=0x19148f0, attrs=...) at 
> > /scratch1/hblancha/install/customq/qemu-2.4.0/src/memory.c:556
> > #9  0x0000000000461ed7 in memory_region_dispatch_write (mr=0x19148f0, addr=16, 
> > data=136, size=4,
> >      attrs=...) at 
> > /scratch1/hblancha/install/customq/qemu-2.4.0/src/memory.c:1214
> > #10 0x000000000046c61c in io_writel (env=0x2aabace89268, 
> > iotlbentry=0x2aabace99808, val=136,
> >      addr=18446743523953745936, retaddr=1107508028)
> >      at /scratch1/hblancha/install/customq/qemu-2.4.0/src/softmmu_template.h:470
> > #11 0x000000000046c3cb in helper_le_stl_mmu (env=0x2aabace89268, 
> > addr=18446743523953745936, val=136,
> >      oi=33, retaddr=1107508028)
> >      at /scratch1/hblancha/install/customq/qemu-2.4.0/src/softmmu_template.h:510
> > #12 0x0000000042033b3e in code_gen_buffer ()
> >
> >
> > The first tracepoint in each pair is an artifact, and should be omitted.
> > Any suggestions? We could special case "if (mr->ops->write !=
> > subpage_write) { emit tracepoint }", but that's a bit of a hack... :-)
> You can add an argument to the tracepoint for mr->subpage.  I would keep
> the duplicate however.

Not sure I understand. Do you mean something like this?
-trace_memory_region_ops_write(mr, addr, tmp, size);
+trace_memory_region_ops_write(mr, addr, mr->ops->write == 
subpage_write, tmp, size);

Maybe this isn't the right tracepoint to begin with. I'm trying to trace 
guest MMIO activity; is there a better place to intercept that?

Hollis Blanchard
Mentor Graphics Emulation Division