readelf: display dynamic symtab without section headersusers/dichen/readelf-28873

This commit adds a new option "-D/--use-dynamic" to support printing the
dynamic symbol table from the PT_DYNAMIC segment. By using the
PT_DYNAMIC segment, eu-readelf can go through the contents of dynamic
section entries and the values of each tag. From that, we can get the
address and size of the dynamic symbol table, the address of the string
table, etc.

By using the new option "-D/--use-dynamic", eu-readelf can list the
symbols without section headers.

Example:
  $ ./src/readelf -Ds a.out
      0: 0000000000000000      0 NOTYPE  LOCAL  DEFAULT    UNDEF
      1: 0000000000000000      0 FUNC    GLOBAL DEFAULT    UNDEF __libc_start_main@GLIBC_2.34 (2)
      2: 0000000000000000      0 NOTYPE  WEAK   DEFAULT    UNDEF __gmon_start__

https://sourceware.org/bugzilla/show_bug.cgi?id=28873

Signed-off-by: Di Chen <dichen@redhat.com>

1 files changed, 283 insertions, 6 deletions

diff --git a/src/readelf.c b/src/readelf.c
index 451f8400..9e1e9b73 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -307,7 +307,8 @@ static void handle_relocs_rel (Ebl *ebl, GElf_Ehdr *ehdr, Elf_Scn *scn,
 static void handle_relocs_rela (Ebl *ebl, GElf_Ehdr *ehdr, Elf_Scn *scn,
 				GElf_Shdr *shdr);
 static bool print_symtab (Ebl *ebl, int type);
-static void handle_symtab (Ebl *ebl, Elf_Scn *scn, GElf_Shdr *shdr);
+static bool handle_symtab (Ebl *ebl, Elf_Scn *scn, GElf_Shdr *shdr);
+static bool handle_dynamic_symtab (Ebl *ebl);
 static void print_verinfo (Ebl *ebl);
 static void handle_verneed (Ebl *ebl, Elf_Scn *scn, GElf_Shdr *shdr);
 static void handle_verdef (Ebl *ebl, Elf_Scn *scn, GElf_Shdr *shdr);
@@ -327,7 +328,9 @@ enum dyn_idx
 {
   i_strsz,
   i_verneed,
+  i_verneednum,
   i_verdef,
+  i_verdefnum,
   i_versym,
   i_symtab,
   i_strtab,
@@ -1042,7 +1045,7 @@ process_elf_file (Dwfl_Module *dwflmod, int fd)
     symtab_printed |= print_symtab (ebl, SHT_DYNSYM);
   if (print_version_info)
     print_verinfo (ebl);
-  if (print_symbol_table)
+  if (print_symbol_table && !use_dynamic_segment)
     symtab_printed |= print_symtab (ebl, SHT_SYMTAB);
 
   if ((print_symbol_table || print_dynsym_table)
@@ -2442,6 +2445,12 @@ handle_relocs_rela (Ebl *ebl, GElf_Ehdr *ehdr, Elf_Scn *scn, GElf_Shdr *shdr)
 static bool
 print_symtab (Ebl *ebl, int type)
 {
+  /* Use the dynamic section info to display symbol tables.  */
+  if (use_dynamic_segment && type == SHT_DYNSYM)
+  {
+	return handle_dynamic_symtab(ebl);
+  }
+
   /* Find the symbol table(s).  For this we have to search through the
      section table.  */
   Elf_Scn *scn = NULL;
@@ -2480,16 +2489,275 @@ print_symtab (Ebl *ebl, int type)
 			    _("cannot get section [%zd] header: %s"),
 			    elf_ndxscn (scn), elf_errmsg (-1));
 	    }
-	  handle_symtab (ebl, scn, shdr);
-	  symtab_printed = true;
+	  symtab_printed = handle_symtab (ebl, scn, shdr);
 	}
     }
 
   return symtab_printed;
 }
 
+static bool
+handle_dynamic_symtab (Ebl *ebl)
+{
+  GElf_Phdr *phdr = NULL;
+  /* phnum is a static variable which already fetched in function process_elf_file.  */
+  for (size_t i = 0; i < phnum; ++i) {
+    GElf_Phdr phdr_mem;
+    phdr = gelf_getphdr(ebl->elf, i, &phdr_mem);
+    if (phdr->p_type == PT_DYNAMIC) {
+      break;
+    }
+  }
+  if (phdr == NULL)
+	return false;
 
-static void
+  GElf_Addr addrs[i_max] = {0,};
+  GElf_Off offs[i_max] = {0,};
+  get_dynscn_addrs(ebl->elf, phdr, addrs);
+  find_offsets(ebl->elf, 0, i_max, addrs, offs);
+
+  size_t syments;
+
+  GElf_Ehdr ehdr_mem;
+  GElf_Ehdr *ehdr = gelf_getehdr(ebl->elf, &ehdr_mem);
+
+  if (offs[i_hash] != 0) {
+    /* In the original format, .hash says the size of .dynsym.  */
+
+    size_t entsz = SH_ENTSIZE_HASH(ehdr);
+    Elf_Data *data =
+        elf_getdata_rawchunk(ebl->elf, offs[i_hash] + entsz, entsz,
+                             (entsz == 4 ? ELF_T_WORD : ELF_T_XWORD));
+    if (data != NULL)
+      syments = (entsz == 4 ? *(const GElf_Word *)data->d_buf
+                            : *(const GElf_Xword *)data->d_buf);
+  }
+  if (offs[i_gnu_hash] != 0 && syments == 0) {
+    /* In the new format, we can derive it with some work.  */
+
+    const struct {
+      Elf32_Word nbuckets;
+      Elf32_Word symndx;
+      Elf32_Word maskwords;
+      Elf32_Word shift2;
+    } * header;
+
+    Elf_Data *data = elf_getdata_rawchunk(ebl->elf, offs[i_gnu_hash],
+                                          sizeof *header, ELF_T_WORD);
+    if (data != NULL) {
+      header = data->d_buf;
+      Elf32_Word nbuckets = header->nbuckets;
+      Elf32_Word symndx = header->symndx;
+      GElf_Off buckets_at = (offs[i_gnu_hash] + sizeof *header +
+                             (gelf_getclass(ebl->elf) * sizeof(Elf32_Word) *
+                              header->maskwords));
+
+      // elf_getdata_rawchunk takes a size_t, make sure it
+      // doesn't overflow.
+  #if SIZE_MAX <= UINT32_MAX
+      if (nbuckets > SIZE_MAX / sizeof(Elf32_Word))
+        data = NULL;
+      else
+  #endif
+        data = elf_getdata_rawchunk(ebl->elf, buckets_at,
+                                    nbuckets * sizeof(Elf32_Word), ELF_T_WORD);
+      if (data != NULL && symndx < nbuckets) {
+        const Elf32_Word *const buckets = data->d_buf;
+        Elf32_Word maxndx = symndx;
+        for (Elf32_Word bucket = 0; bucket < nbuckets; ++bucket)
+          if (buckets[bucket] > maxndx)
+            maxndx = buckets[bucket];
+
+        GElf_Off hasharr_at = (buckets_at + nbuckets * sizeof(Elf32_Word));
+        hasharr_at += (maxndx - symndx) * sizeof(Elf32_Word);
+        do {
+          data = elf_getdata_rawchunk(ebl->elf, hasharr_at,
+                                      sizeof(Elf32_Word), ELF_T_WORD);
+          if (data != NULL && (*(const Elf32_Word *)data->d_buf & 1u)) {
+            syments = maxndx + 1;
+            break;
+          }
+          ++maxndx;
+          hasharr_at += sizeof(Elf32_Word);
+        } while (data != NULL);
+      }
+    }
+  }
+  if (offs[i_strtab] > offs[i_symtab] && syments == 0)
+    syments = ((offs[i_strtab] - offs[i_symtab]) /
+      gelf_fsize(ebl->elf, ELF_T_SYM, 1, EV_CURRENT));
+
+  if (syments <= 0 || offs[i_strtab] == 0 || offs[i_symtab] == 0) {
+    error_exit(0, _("Dynamic symbol information is not available for displaying symbols."));
+  }
+
+  /* All the data chunk initializaion.  */
+  Elf_Data *symdata = NULL;
+  Elf_Data *symstrdata = NULL;
+  Elf_Data *versym_data = NULL;
+  Elf_Data *verdef_data = NULL;
+  Elf_Data *verneed_data = NULL;
+
+  symdata = elf_getdata_rawchunk(
+      ebl->elf, offs[i_symtab],
+      gelf_fsize(ebl->elf, ELF_T_SYM, syments, EV_CURRENT), ELF_T_SYM);
+  symstrdata = elf_getdata_rawchunk(ebl->elf, offs[i_strtab], addrs[i_strsz],
+                                    ELF_T_BYTE);
+  versym_data = elf_getdata_rawchunk(ebl->elf, offs[i_versym],
+                                     syments * sizeof(Elf64_Half), ELF_T_HALF);
+
+  /* Get the verneed_data without vernaux.  */
+  verneed_data = elf_getdata_rawchunk(
+      ebl->elf, offs[i_verneed], addrs[i_verneednum] * sizeof(Elf64_Verneed),
+      ELF_T_VNEED);
+  size_t vernauxnum = 0;
+  size_t vn_next_offset = 0;
+
+  for (size_t i = 0; i < addrs[i_verneednum]; i++) {
+    GElf_Verneed *verneed =
+        (GElf_Verneed *)(verneed_data->d_buf + vn_next_offset);
+    vernauxnum += verneed->vn_cnt;
+    vn_next_offset += verneed->vn_next;
+  }
+
+  /* Update the verneed_data to include the vernaux.  */
+  verneed_data = elf_getdata_rawchunk(
+      ebl->elf, offs[i_verneed],
+      (addrs[i_verneednum] + vernauxnum) * sizeof(GElf_Verneed), ELF_T_VNEED);
+
+  /* Get the verdef_data without verdaux.  */
+  verdef_data = elf_getdata_rawchunk(ebl->elf, offs[i_verdef],
+                                     addrs[i_verdefnum] * sizeof(Elf64_Verdef),
+                                     ELF_T_VDEF);
+  size_t verdauxnum = 0;
+  size_t vd_next_offset = 0;
+
+  for (size_t i = 0; i < addrs[i_verdefnum]; i++) {
+    GElf_Verdef *verdef = (GElf_Verdef *)(verdef_data->d_buf + vd_next_offset);
+    verdauxnum += verdef->vd_cnt;
+    vd_next_offset += verdef->vd_next;
+  }
+
+  /* Update the verdef_data to include the verdaux.  */
+  verdef_data = elf_getdata_rawchunk(
+      ebl->elf, offs[i_verdef],
+      (addrs[i_verdefnum] + verdauxnum) * sizeof(GElf_Verdef), ELF_T_VDEF);
+
+  for (size_t i = 0; i < syments; i++) {
+    /* Get the symbol table entry.  */
+    GElf_Sym sym_mem;
+    GElf_Sym *sym;
+    sym = gelf_getsym(symdata, i, &sym_mem);
+
+    char bindbuf[64];
+    char typebuf[64];
+    char scnbuf[64];
+    int class = gelf_getclass(ebl->elf);
+    Elf32_Word xndx;
+    xndx = sym->st_shndx;
+
+    printf(_("\
+%5ld: %0*" PRIx64 " %6" PRId64 " %-7s %-6s %-9s %6s %s"),
+           i, class == ELFCLASS32 ? 8 : 16, sym->st_value, sym->st_size,
+           ebl_symbol_type_name(ebl, GELF_ST_TYPE(sym->st_info), typebuf,
+                                sizeof(typebuf)),
+           ebl_symbol_binding_name(ebl, GELF_ST_BIND(sym->st_info), bindbuf,
+                                   sizeof(bindbuf)),
+           get_visibility_type(GELF_ST_VISIBILITY(sym->st_other)),
+           ebl_section_name(ebl, sym->st_shndx, xndx, scnbuf, sizeof(scnbuf),
+                            NULL, shnum),
+           ((char *)symstrdata->d_buf) + sym->st_name);
+
+    if (versym_data != NULL) {
+      /* Get the version information.  */
+      GElf_Versym versym_mem;
+      GElf_Versym *versym = gelf_getversym(versym_data, i, &versym_mem);
+
+      if (versym != NULL && ((*versym & 0x8000) != 0 || *versym > 1)) {
+        GElf_Vernaux vernaux_mem;
+        GElf_Vernaux *vernaux = NULL;
+        size_t vn_offset = 0;
+        GElf_Verneed verneed_mem;
+        GElf_Verneed *verneed = (GElf_Verneed *)verneed_data->d_buf;
+
+        while (verneed != NULL) {
+          size_t vna_offset = vn_offset;
+
+          vernaux = gelf_getvernaux(verneed_data, vna_offset += verneed->vn_aux,
+                                    &vernaux_mem);
+          while (vernaux != NULL && vernaux->vna_other != *versym &&
+                 vernaux->vna_next != 0 &&
+                 (verneed_data->d_size - vna_offset >= vernaux->vna_next)) {
+            /* Update the offset.  */
+            vna_offset += vernaux->vna_next;
+
+            vernaux =
+                (vernaux->vna_next == 0
+                     ? NULL
+                     : gelf_getvernaux(verneed_data, vna_offset, &vernaux_mem));
+          }
+
+          /* Check whether we found the version.  */
+          if (vernaux != NULL && vernaux->vna_other == *versym)
+            /* Found it.  */
+            break;
+
+          if (verneed_data->d_size - vn_offset < verneed->vn_next)
+            break;
+
+          vn_offset += verneed->vn_next;
+          verneed =
+              (verneed->vn_next == 0
+                   ? NULL
+                   : gelf_getverneed(verneed_data, vn_offset, &verneed_mem));
+        }
+
+        if (vernaux != NULL && vernaux->vna_other == *versym) {
+          printf("@%s (%u)", (char *)symstrdata->d_buf + vernaux->vna_name,
+                 (unsigned int)vernaux->vna_other);
+        }
+
+        if (addrs[i_verdefnum] && *versym != 0x8001) {
+          /* We must test both.  */
+          size_t vd_offset = 0;
+
+          GElf_Verdef verdef_mem;
+          GElf_Verdef *verdef = gelf_getverdef(verdef_data, 0, &verdef_mem);
+          while (verdef != NULL) {
+            if (verdef->vd_ndx == (*versym & 0x7fff))
+              /* Found the definition.  */
+              break;
+
+            if (verdef_data->d_size - vd_offset < verdef->vd_next)
+              break;
+
+            vd_offset += verdef->vd_next;
+            verdef =
+                (verdef->vd_next == 0
+                     ? NULL
+                     : gelf_getverdef(verdef_data, vd_offset, &verdef_mem));
+          }
+
+          if (verdef != NULL) {
+            GElf_Verdaux verdaux_mem;
+            GElf_Verdaux *verdaux = gelf_getverdaux(
+                verdef_data, vd_offset + verdef->vd_aux, &verdaux_mem);
+
+            if (verdaux != NULL)
+              printf((*versym & 0x8000) ? "@%s" : "@@%s",
+                     (char *)symstrdata->d_buf + verdaux->vda_name);
+          }
+        }
+      }
+    }
+    putchar_unlocked('\n');
+  }
+  return true;
+}
+
+
+
+static bool
 handle_symtab (Ebl *ebl, Elf_Scn *scn, GElf_Shdr *shdr)
 {
   Elf_Data *versym_data = NULL;
@@ -2503,7 +2771,7 @@ handle_symtab (Ebl *ebl, Elf_Scn *scn, GElf_Shdr *shdr)
   /* Get the data of the section.  */
   Elf_Data *data = elf_getdata (scn, NULL);
   if (data == NULL)
-    return;
+    return false;
 
   /* Find out whether we have other sections we might need.  */
   Elf_Scn *runscn = NULL;
@@ -2730,6 +2998,7 @@ handle_symtab (Ebl *ebl, Elf_Scn *scn, GElf_Shdr *shdr)
 
       putchar_unlocked ('\n');
     }
+    return true;
 }
 
 
@@ -4955,10 +5224,18 @@ get_dynscn_addrs(Elf *elf, GElf_Phdr *phdr, GElf_Addr addrs[i_max])
       addrs[i_verdef] = dyn->d_un.d_ptr;
       break;
 
+    case DT_VERDEFNUM:
+      addrs[i_verdefnum] = dyn->d_un.d_val;
+      break;
+
     case DT_VERNEED:
       addrs[i_verneed] = dyn->d_un.d_ptr;
       break;
 
+    case DT_VERNEEDNUM:
+      addrs[i_verneednum] = dyn->d_un.d_val;
+      break;
+
     case DT_STRSZ:
       addrs[i_strsz] = dyn->d_un.d_val;
       break;