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>

1 files changed, 34 insertions, 3 deletions

diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index b63e5713849f..971d0a05d6b4 100644
--- 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;