Re: [PATCH] perf: fix dwarf unwind using libunwind.

Wang Nan
2015-01-13T08:37:52Z

On 2015/1/13 15:10, Jiri Olsa wrote:
> On Tue, Jan 13, 2015 at 10:54:37AM +0800, Wang Nan wrote:
>
> SNIP
>
>>
>> +static int elf_is_exec(int fd, const char *name)
>> +{
>> + Elf *elf;
>> + GElf_Ehdr ehdr;
>> + int retval = 0;
>> +
>> + elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
>> + if (elf == NULL)
>> + return 0;
>> + if (gelf_getehdr(elf, &ehdr) == NULL)
>> + goto out;
>> +
>> + retval = (ehdr.e_type == ET_EXEC);
>> +
>> +out:
>> + elf_end(elf);
>> + pr_debug("unwind: elf_is_exec(%s): %d\n", name, retval);
>> + return retval;
>> +
>> +}
>
> yuou need to add stub for 'NO_LIBUNWIND_DEBUG_FRAME=1', otherwise:
>
> CC util/dwarf-aux.o
> CC util/unwind-libunwind.o
> util/unwind-libunwind.c:188:12: error: ‘elf_is_exec’ defined but not used [-Werror=unused-function]
> static int elf_is_exec(int fd, const char *name)
> ^
> cc1: all warnings being treated as errors
> make[1]: *** [util/unwind-libunwind.o] Error 1
> make[1]: *** Waiting for unfinished jobs....
> make: *** [all] Error 2
>
> jirka
>

Thanks. I haven't test NO_LIBUNWIND_DEBUG_FRAME=1 case.

I found that it is possible to utilize map->dso->adjust_symbols for this propose so
we don't need to introduce another function to check ehdr.e_type. However
map->dso->adjust_symbols checks not only ET_EXEC but also ET_REL. What do you think?

I'd like to check it and post another patch.

>> +
>> struct table_entry {
>> u32 start_ip_offset;
>> u32 fde_offset;
>> @@ -322,8 +343,12 @@ find_proc_info(unw_addr_space_t as, unw_word_t ip, unw_proc_info_t *pi,
>> #ifndef NO_LIBUNWIND_DEBUG_FRAME
>> /* Check the .debug_frame section for unwinding info */
>> if (!read_unwind_spec_debug_frame(map->dso, ui->machine, &segbase)) {
>> + int fd = dso__data_fd(map->dso, ui->machine);
>> + int is_exec = elf_is_exec(fd, map->dso->name);
>> + unw_word_t base = is_exec ? 0 : map->start;
>> +
>> memset(&di, 0, sizeof(di));
>> - if (dwarf_find_debug_frame(0, &di, ip, 0, map->dso->name,
>> + if (dwarf_find_debug_frame(0, &di, ip, base, map->dso->name,
>> map->start, map->end))
>> return dwarf_search_unwind_table(as, ip, &di, pi,
>> need_unwind_info, arg);
>> --
>> 1.8.4
>>