Messages in this thread | | | Subject | Re: [PATCH v2 5/9] perf tools: Add methods to test dso is 64-bit or 32-bit | From | Hekuang <> | Date | Tue, 10 May 2016 20:29:09 +0800 |
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在 2016/5/10 19:59, Adrian Hunter 写道: > On 10/05/16 14:38, Hekuang wrote: >> >> 在 2016/5/10 18:34, Adrian Hunter 写道: >>> On 10/05/16 12:49, Hekuang wrote: >>>> hi >>>> >>>> 在 2016/5/10 16:08, Adrian Hunter 写道: >>>>> 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. > > >
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