Re: [PATCH v2 5/9] perf tools: Add methods to test dso is 64-bit or 32-bit

[Hekuang]

å 2016/5/10 19:59, Adrian Hunter åé:
> On 10/05/16 14:38, Hekuang wrote:
> > å 2016/5/10 18:34, Adrian Hunter åé:
> > > On 10/05/16 12:49, Hekuang wrote:
> > > > hi
> > > >
> > > > å 2016/5/10 16:08, Adrian Hunter åé:
> > > > > On 10/05/16 10:40, He Kuang wrote:
> > > > > > 32-bit programs can be run on 64-bit machines, so we should choose
> > > > > > unwind methods according to 'thread->map' instead of the host
> > > > > > architecture.
> > > > > >
> > > > > > This patch adds methods to test whether a dso is 64-bit or 32-bit by
> > > > > > the class info in elf.
> > > > > What about using dso->is_64_bit set by dso__load_sym() ?
> > > > I've noticed this variable, but it's value is not as its name said:
> > > >
> > > > util/dso.c: 1067    dso->is_64_bit = (sizeof(void *) == 8);
> > > That is just initialization i.e. before we know what it is we assume it is
> > > the same as the host.
> > >
> > > > This is only related to the host architecture.
> > > >
> > > > A closer one is 'is_64_bit' in 'struct symsrc', but the value is assigned
> > > > after dso
> > > > loaded. So I think we should provide individual methods to get that value.
> > > Are you saying you don't load dsos?  Or that is_64_bit is set incorrectly?
> > Yes, I know it's the inital value, but the correct value is
> > assigned in function dso__load_sym(), and have a look at the call
> > stack(gdb):
> >
> > #0  dso__load_sym
> > #1  in dso__load
> > #2  in map__load
> > #3  in map__find_symbol
> > #4  in thread__find_addr_location
> > #5  in entry
> > #6  in get_entries
> > #7  in _Ux86__unwind__get_entries
> > #8  in thread__resolve_callchain
> >
> > I think we should choose the right unwind method before
> > dso__load_sym(). i.e. line#7, which is called before dso__load_sym().
> >
> > I'm not very familiar with this, what's your opinion?
> Have you considered calling map__load() instead of dso_is_64_bit()

IMO, map__load() is heavy than dso_is_64_bit() test, because the
dso tested by unwind_get_arch(thread, map) may or may not be
referenced in the unwind process. For example, a thread can
have a large map but that map never appeared in the callcains
in perf.data.

Or in other words, should we load all symbols for that elf flag or
add a new method targeted for that purpose only.

Thanks.
>