Re: [PATCH 3/3] perf: parse the .debug_frame section in case.eh_frame is not present

[Jean Pihet]

Hi Jiri,

On 5 September 2013 18:30, Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> On Wed, Sep 04, 2013 at 08:04:14PM +0200, Jean Pihet wrote:
>> On ARM the debug info is not present in the .eh_frame sections but
>> instead in .debug_frame.
>> Use libunwind to load and parse the debug info.
>
> hum, cannot make final link:
>
> $ make LIBUNWIND_DIR=/opt/libunwind/
>     CHK -fstack-protector-all
>     CHK -Wstack-protector
>     CHK -Wvolatile-register-var
>     CHK -D_FORTIFY_SOURCE=2
>     CHK bionic
>     CHK libelf
>     CHK libdw
>     CHK -DLIBELF_MMAP
>     CHK -DLIBELF_MMAP
>     CHK libunwind
>     CHK libaudit
>
> ...
>
> make[1]: `liblk.a' is up to date.
>     SUBDIR /home/jolsa/linux-perf/tools/lib/traceevent/
>     LINK perf
> libperf.a(unwind.o): In function `find_proc_info':
> /home/jolsa/linux-perf/tools/perf/util/unwind.c:339: undefined reference to `_Ux86_64_dwarf_find_debug_frame'
> collect2: ld returned 1 exit status
> make: *** [perf] Error 1
>
>
> I'm using the latest code from git://git.sv.gnu.org/libunwind.git
>
> Looks like dwarf_find_debug_frame is not exported, although
> it looks like it is based on what I see in libunwind sources ;-)
>
> What did I miss?
libunwind needs to be configured with --enable-debug-frame for the
debug_frame code to be included in the lib.
On ARM the flag is always set while it isn't on x86. Here is the
culprit below (lines from libunwind configure).

Should that be changed in configure along with the changes in tools/perf?


{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether to load
.debug_frame  sections" >&5
$as_echo_n "checking whether to load .debug_frame sections... " >&6; }
# Check whether --enable-debug_frame was given.
if test "${enable_debug_frame+set}" = set; then :
  enableval=$enable_debug_frame;
else

case "${target_arch}" in
  (arm) enable_debug_frame=yes;;
  (*)   enable_debug_frame=no;;
esac
fi

if test x$enable_debug_frame = xyes; then
$as_echo "#define CONFIG_DEBUG_FRAME /**/" >>confdefs.h
fi


Regards,
Jean

>
> Also few typo comments below..
>
> thanks,
> jirka
>
>>
>> Signed-off-by: Jean Pihet <jean.pihet@xxxxxxxxxx>
>> ---
>>  tools/perf/util/unwind.c | 70 +++++++++++++++++++++++++++++++++++++-----------
>>  1 file changed, 54 insertions(+), 16 deletions(-)
>>
>> diff --git a/tools/perf/util/unwind.c b/tools/perf/util/unwind.c
>> index 958723b..5353b32 100644
>> --- a/tools/perf/util/unwind.c
>> +++ b/tools/perf/util/unwind.c
>> @@ -39,6 +39,14 @@ UNW_OBJ(dwarf_search_unwind_table) (unw_addr_space_t as,
>>
>>  #define dwarf_search_unwind_table UNW_OBJ(dwarf_search_unwind_table)
>>
>> +extern int
>> +UNW_OBJ(dwarf_find_debug_frame) (int found, unw_dyn_info_t *di_debug,
>> +                                                              unw_word_t ip, unw_word_t segbase,
>> +                                                              const char *obj_name, unw_word_t start,
>> +                                                              unw_word_t end);
>> +
>> +#define dwarf_find_debug_frame UNW_OBJ(dwarf_find_debug_frame)
>> +
>>  #define DW_EH_PE_FORMAT_MASK 0x0f    /* format of the encoded value */
>>  #define DW_EH_PE_APPL_MASK   0x70    /* how the value is to be applied */
>>
>> @@ -245,8 +253,9 @@ static int unwind_spec_ehframe(struct dso *dso, struct machine *machine,
>>       return 0;
>>  }
>>
>> -static int read_unwind_spec(struct dso *dso, struct machine *machine,
>> -                         u64 *table_data, u64 *segbase, u64 *fde_count)
>> +static int read_unwind_spec_eh_frame(struct dso *dso, struct machine *machine,
>> +                                  u64 *table_data, u64 *segbase,
>> +                                  u64 *fde_count)
>>  {
>>       int ret = -EINVAL, fd;
>>       u64 offset;
>> @@ -255,6 +264,7 @@ static int read_unwind_spec(struct dso *dso, struct machine *machine,
>>       if (fd < 0)
>>               return -EINVAL;
>>
>> +     /* Check the .eh_frame section for unwinding info */
>>       offset = elf_section_offset(fd, ".eh_frame_hdr");
>>       close(fd);
>>
>> @@ -263,10 +273,27 @@ static int read_unwind_spec(struct dso *dso, struct machine *machine,
>>                                         table_data, segbase,
>>                                         fde_count);
>>
>> -     /* TODO .debug_frame check if eh_frame_hdr fails */
>>       return ret;
>>  }
>>
>> +static int read_unwind_spec_debug_frame(struct dso *dso,
>> +                                                                             struct machine *machine, u64 *offset)
>> +{
>
> some strange formatting issue ^^^ ;-)
>
>
>> +     int fd = dso__data_fd(dso, machine);
>> +
>> +     if (fd < 0)
>> +             return -EINVAL;
>> +
>> +     /* Check the .debug_frame section for unwinding info */
>> +     *offset = elf_section_offset(fd, ".debug_frame");
>> +     close(fd);
>> +
>> +     if (*offset)
>> +             return 0;
>> +
>> +     return -EINVAL;
>> +}
>> +
>>  static struct map *find_map(unw_word_t ip, struct unwind_info *ui)
>>  {
>>       struct addr_location al;
>> @@ -291,20 +318,31 @@ find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
>>
>>       pr_debug("unwind: find_proc_info dso %s\n", map->dso->name);
>>
>> -     if (read_unwind_spec(map->dso, ui->machine,
>> -                          &table_data, &segbase, &fde_count))
>> -             return -EINVAL;
>> +     /* Check the .eh_frame section for unwinding info */
>> +     if (!read_unwind_spec_eh_frame(map->dso, ui->machine,
>> +                                                                &table_data, &segbase, &fde_count)) {
>
> ditto ^^^
>
>> +             memset(&di, 0, sizeof(di));
>> +             di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
>> +             di.start_ip = map->start;
>> +             di.end_ip   = map->end;
>> +             di.u.rti.segbase    = map->start + segbase;
>> +             di.u.rti.table_data = map->start + table_data;
>> +             di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
>> +                                                       / sizeof(unw_word_t);
>> +         return dwarf_search_unwind_table(as, ip, &di, pi,
>> +                                                                              need_unwind_info, arg);
>
> ditto ^^^
>
>> +     }
>> +
>> +     /* Check the .debug_frame section for unwinding info */
>> +     if (!read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
>> +             memset(&di, 0, sizeof(di));
>> +             dwarf_find_debug_frame(0, &di, ip, 0, map->dso->name,
>> +                                                        map->start, map->end);
>> +             return dwarf_search_unwind_table(as, ip, &di, pi,
>> +                                                                              need_unwind_info, arg);
>
> ditto ^^^
>
>> +     }
>>
>> -     memset(&di, 0, sizeof(di));
>> -     di.format   = UNW_INFO_FORMAT_REMOTE_TABLE;
>> -     di.start_ip = map->start;
>> -     di.end_ip   = map->end;
>> -     di.u.rti.segbase    = map->start + segbase;
>> -     di.u.rti.table_data = map->start + table_data;
>> -     di.u.rti.table_len  = fde_count * sizeof(struct table_entry)
>> -                           / sizeof(unw_word_t);
>> -     return dwarf_search_unwind_table(as, ip, &di, pi,
>> -                                      need_unwind_info, arg);
>> +     return -EINVAL;
>>  }
>>
>>  static int access_fpreg(unw_addr_space_t __maybe_unused as,
>> --
>> 1.7.11.7
>>
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