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

[Hekuang <hekuang@huawei.com>]

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?

Thanks.
>> Thanks.
>>
>>>> Signed-off-by: He Kuang <hekuang@huawei.com>
>>>> ---
>>>>    tools/perf/util/symbol-elf.c | 16 +++++++++++++++
>>>>    tools/perf/util/symbol.c     | 49
>>>> ++++++++++++++++++++++++++++++++++++++++++++
>>>>    tools/perf/util/symbol.h     |  2 ++
>>>>    3 files changed, 67 insertions(+)
>>>>
>>>> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
>>>> index 3f9d679..9f290b9 100644
>>>> --- a/tools/perf/util/symbol-elf.c
>>>> +++ b/tools/perf/util/symbol-elf.c
>>>> @@ -636,6 +636,22 @@ bool __weak elf__needs_adjust_symbols(GElf_Ehdr ehdr)
>>>>        return ehdr.e_type == ET_EXEC || ehdr.e_type == ET_REL;
>>>>    }
>>>>    +int elf_is_64_bit(char *name)
>>>> +{
>>>> +    Elf *elf;
>>>> +    int fd;
>>>> +
>>>> +    fd = open(name, O_RDONLY);
>>>> +    if (fd < 0)
>>>> +        return -1;
>>>> +
>>>> +    elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
>>>> +    if (elf == NULL)
>>>> +        return -1;
>>>> +
>>>> +    return (gelf_getclass(elf) == ELFCLASS64);
>>>> +}
>>>> +
>>>>    int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
>>>>             enum dso_binary_type type)
>>>>    {
>>>> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
>>>> index 4630751..592bf8c 100644
>>>> --- a/tools/perf/util/symbol.c
>>>> +++ b/tools/perf/util/symbol.c
>>>> @@ -1395,6 +1395,55 @@ static bool dso__is_compatible_symtab_type(struct
>>>> dso *dso, bool kmod,
>>>>        }
>>>>    }
>>>>    +int dso_is_64_bit(struct dso *dso, struct map *map)
>>>> +{
>>>> +    char *name;
>>>> +    u_int i;
>>>> +    bool kmod;
>>>> +    char *root_dir = (char *) "";
>>>> +    struct machine *machine;
>>>> +
>>>> +    if (map->groups && map->groups->machine)
>>>> +        machine = map->groups->machine;
>>>> +    else
>>>> +        machine = NULL;
>>>> +
>>>> +    if (machine)
>>>> +        root_dir = machine->root_dir;
>>>> +
>>>> +    name = malloc(PATH_MAX);
>>>> +    if (!name)
>>>> +        return -1;
>>>> +
>>>> +    kmod = dso->symtab_type == DSO_BINARY_TYPE__SYSTEM_PATH_KMODULE ||
>>>> +        dso->symtab_type == DSO_BINARY_TYPE__SYSTEM_PATH_KMODULE_COMP ||
>>>> +        dso->symtab_type == DSO_BINARY_TYPE__GUEST_KMODULE ||
>>>> +        dso->symtab_type == DSO_BINARY_TYPE__GUEST_KMODULE_COMP;
>>>> +
>>>> +    /*
>>>> +     * Iterate over candidate debug images.
>>>> +     * Keep track of "interesting" ones (those which have a symtab, dynsym,
>>>> +     * and/or opd section) for processing.
>>>> +     */
>>>> +    for (i = 0; i < DSO_BINARY_TYPE__SYMTAB_CNT; i++) {
>>>> +        enum dso_binary_type symtab_type = binary_type_symtab[i];
>>>> +
>>>> +        if (!dso__is_compatible_symtab_type(dso, kmod, symtab_type))
>>>> +            continue;
>>>> +
>>>> +        if (dso__read_binary_type_filename(dso, symtab_type,
>>>> +                           root_dir, name, PATH_MAX))
>>>> +            continue;
>>>> +
>>>> +        if (!is_regular_file(name))
>>>> +            continue;
>>>> +
>>>> +        return elf_is_64_bit(name);
>>>> +    }
>>>> +
>>>> +    return -1;
>>>> +}
>>>> +
>>>>    int dso__load(struct dso *dso, struct map *map, symbol_filter_t filter)
>>>>    {
>>>>        char *name;
>>>> diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
>>>> index 4e6910e..d33fbf4 100644
>>>> --- a/tools/perf/util/symbol.h
>>>> +++ b/tools/perf/util/symbol.h
>>>> @@ -308,6 +308,8 @@ int setup_list(struct strlist **list, const char
>>>> *list_str,
>>>>               const char *list_name);
>>>>    int setup_intlist(struct intlist **list, const char *list_str,
>>>>              const char *list_name);
>>>> +int elf_is_64_bit(char *name);
>>>> +int dso_is_64_bit(struct dso *dso, struct map *map);
>>>>      #ifdef HAVE_LIBELF_SUPPORT
>>>>    bool elf__needs_adjust_symbols(GElf_Ehdr ehdr);
>>>>
>>
>>
>