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

Jiri Olsa
2015-01-13T07:11:21Z

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

> +
> 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
>