Re: [PATCH v3 3/7 UPDATE] perf tools: Add option for the path of buildid dsos under symfs

[Hekuang]

å 2016/5/18 9:51, David Ahern åé:
> On 5/17/16 7:47 PM, Hekuang wrote:
> > å 2016/5/16 10:50, David Ahern åé:
> > > On 5/15/16 7:30 PM, Hekuang wrote:
> > > > In previous patch, I use 'perf buildid-cache -a' to add vdso
> > > > binary into the HOST buildid dir.
> > >
> > > So 'perf buildid-cache' needs the symfs option?
> > With this patch 'PATCH v3 3/7 UPDATE', the tree of symfs dir is
> > like this:
> >
> > âââ debug($(dso-prefix))
> > â   âââ .build-id
> > â   â   âââ 3a
> > â   â   â   âââ e5ba6d4e532ad529e43ccf1ce1ddf8a64a4fdd ->
> > ../../[kernel.kallsyms]/3ae5ba6d4e532ad529e43ccf1ce1ddf8a64a4fdd
> > â   â   âââ 84
> > â   â       âââ dbd75729adba57cc42f5544b25de571c0c8731 ->
> > ../../[vdso32]/84dbd75729adba57cc42f5544b25de571c0c8731
> > â   âââ [kernel.kallsyms]
> > â   â   âââ 3ae5ba6d4e532ad529e43ccf1ce1ddf8a64a4fdd
> > â   âââ [vdso]
> > â   â   âââ 84dbd75729adba57cc42f5544b25de571c0c8731
> > â   âââ [vdso32]
> > â       âââ 84dbd75729adba57cc42f5544b25de571c0c8731
> > âââ lib
> > â   âââ ld-2.22.so
> > â   âââ libc-2.22.so
> > âââ tmp
> > â   âââ hello
> > âââ xxx
> >
> > So all binaries we need are included in the symfs dir. I think
> > this is consistent with your idea explained in previous mails.
> >
> > With this symfs, we do not need buildid dir anymore and what's
> > your idea on 'perf buildid-cache' needs symfs option? after all,
> > that only effects on buildid dir.
>
> I don't understand why dso-prefix option is needed? Why make me type 
> yet more options to the analysis command? Why can't the directory be 
> located under the symfs tree in a known location and populated the 
> same way it is without symfs?
Because the default buidid folder path is $HOME/.debug/.buildid,
and this $HOME is on the target machine, not the same as $HOME
on the host. Without that option, we need to copy $HOME/.debug/.buildid
to the 'known location in symfs', that's also an extra work.