perf symbols: Function descriptor symbol lookup

Currently symbol resolution does not work for 64-bit programs on architectures
that use function descriptors such as ppc64.

The problem is that a symbol doesn't point to a text address, it points to a
data area that contains (amongst other things) a pointer to the text address.

We look for a section called ".opd" which is the function descriptor area. To
create the full symbol table, when we see a symbol in the function descriptor
section we load the first pointer and use that as the text address.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <1276523793-15422-1-git-send-email-ebmunson@us.ibm.com>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Eric B Munson <ebmunson@us.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index b63e571..971d0a0 100644 (file)
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -933,6 +933,25 @@ static bool elf_sec__is_a(GElf_Shdr *self, Elf_Data *secstrs, enum map_type type
        }
 }
 
+static size_t elf_addr_to_index(Elf *elf, GElf_Addr addr)
+{
+       Elf_Scn *sec = NULL;
+       GElf_Shdr shdr;
+       size_t cnt = 1;
+
+       while ((sec = elf_nextscn(elf, sec)) != NULL) {
+               gelf_getshdr(sec, &shdr);
+
+               if ((addr >= shdr.sh_addr) &&
+                   (addr < (shdr.sh_addr + shdr.sh_size)))
+                       return cnt;
+
+               ++cnt;
+       }
+
+       return -1;
+}
+
 static int dso__load_sym(struct dso *self, struct map *map, const char *name,
                         int fd, symbol_filter_t filter, int kmodule)
 {
@@ -944,12 +963,13 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
        int err = -1;
        uint32_t idx;
        GElf_Ehdr ehdr;
-       GElf_Shdr shdr;
-       Elf_Data *syms;
+       GElf_Shdr shdr, opdshdr;
+       Elf_Data *syms, *opddata = NULL;
        GElf_Sym sym;
-       Elf_Scn *sec, *sec_strndx;
+       Elf_Scn *sec, *sec_strndx, *opdsec;
        Elf *elf;
        int nr = 0;
+       size_t opdidx = 0;
 
        elf = elf_begin(fd, PERF_ELF_C_READ_MMAP, NULL);
        if (elf == NULL) {
@@ -969,6 +989,10 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
                        goto out_elf_end;
        }
 
+       opdsec = elf_section_by_name(elf, &ehdr, &opdshdr, ".opd", &opdidx);
+       if (opdsec)
+               opddata = elf_rawdata(opdsec, NULL);
+
        syms = elf_getdata(sec, NULL);
        if (syms == NULL)
                goto out_elf_end;
@@ -1013,6 +1037,13 @@ static int dso__load_sym(struct dso *self, struct map *map, const char *name,
                if (!is_label && !elf_sym__is_a(&sym, map->type))
                        continue;
 
+               if (opdsec && sym.st_shndx == opdidx) {
+                       u32 offset = sym.st_value - opdshdr.sh_addr;
+                       u64 *opd = opddata->d_buf + offset;
+                       sym.st_value = *opd;
+                       sym.st_shndx = elf_addr_to_index(elf, sym.st_value);
+               }
+
                sec = elf_getscn(elf, sym.st_shndx);
                if (!sec)
                        goto out_elf_end;