perf_counter tools: PLT info is stripped in -debuginfo packages
authorArnaldo Carvalho de Melo <acme@redhat.com>
Sat, 11 Jul 2009 15:18:36 +0000 (12:18 -0300)
committerIngo Molnar <mingo@elte.hu>
Sat, 11 Jul 2009 17:20:26 +0000 (19:20 +0200)
So we need to get the richer .symtab from the debuginfo
packages but the PLT info from the original DSO where we have
just the leaner .dynsym symtab.

Example:

| [acme@doppio pahole]$ perf report --sort comm,dso,symbol > before
| [acme@doppio pahole]$ perf report --sort comm,dso,symbol > after
| [acme@doppio pahole]$ diff -U1 before after
| --- before 2009-07-11 11:04:22.688595741 -0300
| +++ after 2009-07-11 11:04:33.380595676 -0300
| @@ -80,3 +80,2 @@
|       0.07%  pahole ./build/pahole              [.] pahole_stealer
| -     0.06%  pahole /usr/lib64/libdw-0.141.so   [.] 0x00000000007140
|       0.06%  pahole /usr/lib64/libdw-0.141.so   [.] __libdw_getabbrev
| @@ -91,2 +90,3 @@
|       0.06%  pahole [kernel]                    [k] free_hot_cold_page
| +     0.06%  pahole /usr/lib64/libdw-0.141.so   [.] tfind@plt
|       0.05%  pahole ./build/libdwarves.so.1.0.0 [.] ftype__add_parameter
| @@ -242,2 +242,3 @@
|       0.01%  pahole [kernel]                    [k] account_group_user_time
| +     0.01%  pahole /usr/lib64/libdw-0.141.so   [.] strlen@plt
|       0.01%  pahole ./build/pahole              [.] strcmp@plt
| [acme@doppio pahole]$

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <1247325517-12272-4-git-send-email-acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
tools/perf/util/symbol.c

index 8efe7e41109a7dcd3cd5fc876c29ab50af1b8fec..f40266b4845d2b7a65e04ec2d4b64cd9153dc2e7 100644 (file)
@@ -374,36 +374,61 @@ static Elf_Scn *elf_section_by_name(Elf *elf, GElf_Ehdr *ep,
             idx < nr_entries; \
             ++idx, pos = gelf_getrela(reldata, idx, &pos_mem))
 
-static int dso__synthesize_plt_symbols(struct  dso *self, Elf *elf,
-                                      GElf_Ehdr *ehdr, Elf_Scn *scn_dynsym,
-                                      GElf_Shdr *shdr_dynsym,
-                                      size_t dynsym_idx, int verbose)
+/*
+ * We need to check if we have a .dynsym, so that we can handle the
+ * .plt, synthesizing its symbols, that aren't on the symtabs (be it
+ * .dynsym or .symtab).
+ * And always look at the original dso, not at debuginfo packages, that
+ * have the PLT data stripped out (shdr_rel_plt.sh_type == SHT_NOBITS).
+ */
+static int dso__synthesize_plt_symbols(struct  dso *self, int verbose)
 {
        uint32_t nr_rel_entries, idx;
        GElf_Sym sym;
        u64 plt_offset;
        GElf_Shdr shdr_plt;
        struct symbol *f;
-       GElf_Shdr shdr_rel_plt;
+       GElf_Shdr shdr_rel_plt, shdr_dynsym;
        Elf_Data *reldata, *syms, *symstrs;
-       Elf_Scn *scn_plt_rel, *scn_symstrs;
+       Elf_Scn *scn_plt_rel, *scn_symstrs, *scn_dynsym;
+       size_t dynsym_idx;
+       GElf_Ehdr ehdr;
        char sympltname[1024];
-       int nr = 0, symidx;
+       Elf *elf;
+       int nr = 0, symidx, fd, err = 0;
+
+       fd = open(self->name, O_RDONLY);
+       if (fd < 0)
+               goto out;
+
+       elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
+       if (elf == NULL)
+               goto out_close;
+
+       if (gelf_getehdr(elf, &ehdr) == NULL)
+               goto out_elf_end;
+
+       scn_dynsym = elf_section_by_name(elf, &ehdr, &shdr_dynsym,
+                                        ".dynsym", &dynsym_idx);
+       if (scn_dynsym == NULL)
+               goto out_elf_end;
 
-       scn_plt_rel = elf_section_by_name(elf, ehdr, &shdr_rel_plt,
+       scn_plt_rel = elf_section_by_name(elf, &ehdr, &shdr_rel_plt,
                                          ".rela.plt", NULL);
        if (scn_plt_rel == NULL) {
-               scn_plt_rel = elf_section_by_name(elf, ehdr, &shdr_rel_plt,
+               scn_plt_rel = elf_section_by_name(elf, &ehdr, &shdr_rel_plt,
                                                  ".rel.plt", NULL);
                if (scn_plt_rel == NULL)
-                       return 0;
+                       goto out_elf_end;
        }
 
+       err = -1;
+
        if (shdr_rel_plt.sh_link != dynsym_idx)
-               return 0;
+               goto out_elf_end;
 
-       if (elf_section_by_name(elf, ehdr, &shdr_plt, ".plt", NULL) == NULL)
-               return 0;
+       if (elf_section_by_name(elf, &ehdr, &shdr_plt, ".plt", NULL) == NULL)
+               goto out_elf_end;
 
        /*
         * Fetch the relocation section to find the indexes to the GOT
@@ -411,19 +436,19 @@ static int dso__synthesize_plt_symbols(struct  dso *self, Elf *elf,
         */
        reldata = elf_getdata(scn_plt_rel, NULL);
        if (reldata == NULL)
-               return -1;
+               goto out_elf_end;
 
        syms = elf_getdata(scn_dynsym, NULL);
        if (syms == NULL)
-               return -1;
+               goto out_elf_end;
 
-       scn_symstrs = elf_getscn(elf, shdr_dynsym->sh_link);
+       scn_symstrs = elf_getscn(elf, shdr_dynsym.sh_link);
        if (scn_symstrs == NULL)
-               return -1;
+               goto out_elf_end;
 
        symstrs = elf_getdata(scn_symstrs, NULL);
        if (symstrs == NULL)
-               return -1;
+               goto out_elf_end;
 
        nr_rel_entries = shdr_rel_plt.sh_size / shdr_rel_plt.sh_entsize;
        plt_offset = shdr_plt.sh_offset;
@@ -442,7 +467,7 @@ static int dso__synthesize_plt_symbols(struct  dso *self, Elf *elf,
                        f = symbol__new(plt_offset, shdr_plt.sh_entsize,
                                        sympltname, self->sym_priv_size, 0, verbose);
                        if (!f)
-                               return -1;
+                               goto out_elf_end;
 
                        dso__insert_symbol(self, f);
                        ++nr;
@@ -460,19 +485,25 @@ static int dso__synthesize_plt_symbols(struct  dso *self, Elf *elf,
                        f = symbol__new(plt_offset, shdr_plt.sh_entsize,
                                        sympltname, self->sym_priv_size, 0, verbose);
                        if (!f)
-                               return -1;
+                               goto out_elf_end;
 
                        dso__insert_symbol(self, f);
                        ++nr;
                }
-       } else {
-               /*
-                * TODO: There are still one more shdr_rel_plt.sh_type
-                * I have to investigate, but probably should be ignored.
-                */
        }
 
-       return nr;
+       err = 0;
+out_elf_end:
+       elf_end(elf);
+out_close:
+       close(fd);
+
+       if (err == 0)
+               return nr;
+out:
+       fprintf(stderr, "%s: problems reading %s PLT info.\n",
+               __func__, self->name);
+       return 0;
 }
 
 static int dso__load_sym(struct dso *self, int fd, const char *name,
@@ -486,9 +517,8 @@ static int dso__load_sym(struct dso *self, int fd, const char *name,
        GElf_Shdr shdr;
        Elf_Data *syms;
        GElf_Sym sym;
-       Elf_Scn *sec, *sec_dynsym, *sec_strndx;
+       Elf_Scn *sec, *sec_strndx;
        Elf *elf;
-       size_t dynsym_idx;
        int nr = 0;
 
        elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
@@ -505,32 +535,11 @@ static int dso__load_sym(struct dso *self, int fd, const char *name,
                goto out_elf_end;
        }
 
-       /*
-        * We need to check if we have a .dynsym, so that we can handle the
-        * .plt, synthesizing its symbols, that aren't on the symtabs (be it
-        * .dynsym or .symtab)
-        */
-       sec_dynsym = elf_section_by_name(elf, &ehdr, &shdr,
-                                        ".dynsym", &dynsym_idx);
-       if (sec_dynsym != NULL) {
-               nr = dso__synthesize_plt_symbols(self, elf, &ehdr,
-                                                sec_dynsym, &shdr,
-                                                dynsym_idx, verbose);
-               if (nr < 0)
-                       goto out_elf_end;
-       }
-
-       /*
-        * But if we have a full .symtab (that is a superset of .dynsym) we
-        * should add the symbols not in the .dynsyn
-        */
        sec = elf_section_by_name(elf, &ehdr, &shdr, ".symtab", NULL);
        if (sec == NULL) {
-               if (sec_dynsym == NULL)
+               sec = elf_section_by_name(elf, &ehdr, &shdr, ".dynsym", NULL);
+               if (sec == NULL)
                        goto out_elf_end;
-
-               sec = sec_dynsym;
-               gelf_getshdr(sec, &shdr);
        }
 
        syms = elf_getdata(sec, NULL);
@@ -669,6 +678,11 @@ more:
        if (!ret)
                goto more;
 
+       if (ret > 0) {
+               int nr_plt = dso__synthesize_plt_symbols(self, verbose);
+               if (nr_plt > 0)
+                       ret += nr_plt;
+       }
 out:
        free(name);
        return ret;