Re: [Qemu-devel] Monitoring memory access

[malc <av1474@comtv.ru>]

On Fri, 9 Jul 2010, Jun Koi wrote:

> On Fri, Jul 9, 2010 at 7:41 PM, malc <av1474@comtv.ru> wrote:
> > On Fri, 9 Jul 2010, Jun Koi wrote:
> >
> >> Hi,
> >>
> >> I want to monitor memory reading access in Qemu. According to function
> >> tcg/i386/tcg-target.c::tcg_out_qemu_ld(), all the memory access must
> >> call qemu_ld_helpers[] functions, which in turn calls __ldX_mmu
> >> functions.
> >>
> >> These __ldX_mmu() functions are declared in softmmu_template.c, with
> >> macro glue(glue(__ld, SUFFIX), MMUSUFFIX).
> >>
> >> To monitor memory reading access, I simply put my monitored code at
> >> the top of the above macro. But apparently I still miss something,
> >> because I dont see the memory access I am looking for.
> >>
> >> Any hint where I am wrong? Perhaps some memory access do not call the
> >> qemu_ld_helpers[] functions?
> >
> > Haven't we been through this already?
> > http://www.mail-archive.com/qemu-devel@nongnu.org/msg29788.html
> >
> 
> Yes, we did, but sorry I am still stuck there.
> 
> You said that once TLB is setup properly, future memory access would
> do directly, without going thru helpers any more. Is that correct?

Once TLB is filled helpers will be bypassed yes.

> 
> But what I see in tcg_out_qemu_ld() is that the below function is always 
> called:
> 
> ....
>     tcg_out_calli(s, (tcg_target_long)qemu_ld_helpers[s_bits]);
> ....

Even if you are looking only on, say, tcg/i386/tcg-target.c you should
notice that the function does a lot more than just ld_helpers call -
testing tlb and jumping around...

> And since qemu_ld_helpers[] points to __ldX_mmu, so that means below
> macro is always executed:
> 
> glue(glue(__ld, SUFFIX), MMUSUFFIX).
>
> I simply put my monitored code inside this macro.
> 
> Could you give me some hints where I am wrong?
> 

I have honestly nothing more to add, just look closer.

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