libdwfl: find_dynsym don't assume dynamic linker has adjusted DYNAMIC entries.

commit 037505 "Fix resolving ELF symbols for live PIDs with deleted files"
changed find_dynsym to assume the PT_DYNAMIC entries had been adjusted by
the dynamic linker. That is often a correct assumption when the ELF image
comes from remote memory. But we cannot rely on that. In the case of the
vdso image the DYNAMIC segment has not been adjusted for example.

There is no good way to determine whether the DYNAMIC segment has or
hasn't been adjusted already to the load address by the dynamic linker.
So we just try twice. Once without and if the fails again with assuming
adjustments being applied.

Includes a new vdsosyms testcase that fails on i686 before and succeeds
after the fix.

Signed-off-by: Mark Wielaard <mjw@redhat.com>

1 files changed, 115 insertions, 104 deletions

diff --git a/libdwfl/dwfl_module_getdwarf.c b/libdwfl/dwfl_module_getdwarf.c
index e705f57e..adb94b4c 100644
--- a/libdwfl/dwfl_module_getdwarf.c
+++ b/libdwfl/dwfl_module_getdwarf.c
@@ -718,114 +718,125 @@ find_dynsym (Dwfl_Module *mod)
 	      break;
 	    }
 
-	  /* Translate pointers into file offsets.  */
-	  GElf_Off offs[i_max] = { 0, };
-	  find_offsets (mod->main.elf, mod->main_bias, phnum, i_max, addrs,
-			offs);
-
-	  /* Figure out the size of the symbol table.  */
-	  if (offs[i_hash] != 0)
-	    {
-	      /* In the original format, .hash says the size of .dynsym.  */
-
-	      size_t entsz = SH_ENTSIZE_HASH (ehdr);
-	      data = elf_getdata_rawchunk (mod->main.elf,
-					   offs[i_hash] + entsz, entsz,
-					   entsz == 4 ? ELF_T_WORD
-					   : ELF_T_XWORD);
-	      if (data != NULL)
-		mod->syments = (entsz == 4
-				? *(const GElf_Word *) data->d_buf
-				: *(const GElf_Xword *) data->d_buf);
-	    }
-	  if (offs[i_gnu_hash] != 0 && mod->syments == 0)
-	    {
-	      /* In the new format, we can derive it with some work.  */
+	  /* Translate pointers into file offsets.  ADJUST is either zero
+	     in case the dynamic segment wasn't adjusted or mod->main_bias.  */
+	  void translate_offs (GElf_Addr adjust)
+	  {
+	    GElf_Off offs[i_max] = { 0, };
+	    find_offsets (mod->main.elf, adjust, phnum, i_max, addrs, offs);
 
-	      const struct
+	    /* Figure out the size of the symbol table.  */
+	    if (offs[i_hash] != 0)
 	      {
-		Elf32_Word nbuckets;
-		Elf32_Word symndx;
-		Elf32_Word maskwords;
-		Elf32_Word shift2;
-	      } *header;
-
-	      data = elf_getdata_rawchunk (mod->main.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 (mod->main.elf)
-					    * sizeof (Elf32_Word)
-					    * header->maskwords));
-
-		  data = elf_getdata_rawchunk (mod->main.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 (mod->main.elf,
-						       hasharr_at,
-						       sizeof (Elf32_Word),
-						       ELF_T_WORD);
-			  if (data != NULL
-			      && (*(const Elf32_Word *) data->d_buf & 1u))
-			    {
-			      mod->syments = maxndx + 1;
-			      break;
-			    }
-			  ++maxndx;
-			  hasharr_at += sizeof (Elf32_Word);
-			} while (data != NULL);
-		    }
-		}
-	    }
-	  if (offs[i_strtab] > offs[i_symtab] && mod->syments == 0)
-	    mod->syments = ((offs[i_strtab] - offs[i_symtab])
-			    / gelf_fsize (mod->main.elf,
-					  ELF_T_SYM, 1, EV_CURRENT));
+		/* In the original format, .hash says the size of .dynsym.  */
+
+		size_t entsz = SH_ENTSIZE_HASH (ehdr);
+		data = elf_getdata_rawchunk (mod->main.elf,
+					     offs[i_hash] + entsz, entsz,
+					     entsz == 4 ? ELF_T_WORD
+					     : ELF_T_XWORD);
+		if (data != NULL)
+		  mod->syments = (entsz == 4
+				  ? *(const GElf_Word *) data->d_buf
+				  : *(const GElf_Xword *) data->d_buf);
+	      }
+	    if (offs[i_gnu_hash] != 0 && mod->syments == 0)
+	      {
+		/* In the new format, we can derive it with some work.  */
 
-	  if (mod->syments > 0)
-	    {
-	      mod->symdata = elf_getdata_rawchunk (mod->main.elf,
-						   offs[i_symtab],
-						   gelf_fsize (mod->main.elf,
-							       ELF_T_SYM,
-							       mod->syments,
-							       EV_CURRENT),
-						   ELF_T_SYM);
-	      if (mod->symdata != NULL)
-		{
-		  mod->symstrdata = elf_getdata_rawchunk (mod->main.elf,
-							  offs[i_strtab],
-							  strsz,
-							  ELF_T_BYTE);
-		  if (mod->symstrdata == NULL)
-		    mod->symdata = NULL;
-		}
-	      if (mod->symdata == NULL)
-		mod->symerr = DWFL_E (LIBELF, elf_errno ());
-	      else
+		const struct
 		{
-		  mod->symfile = &mod->main;
-		  mod->symerr = DWFL_E_NOERROR;
-		}
-	      return;
-	    }
+		  Elf32_Word nbuckets;
+		  Elf32_Word symndx;
+		  Elf32_Word maskwords;
+		  Elf32_Word shift2;
+		} *header;
+
+		data = elf_getdata_rawchunk (mod->main.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 (mod->main.elf)
+					      * sizeof (Elf32_Word)
+					      * header->maskwords));
+
+		    data = elf_getdata_rawchunk (mod->main.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 (mod->main.elf,
+							 hasharr_at,
+							 sizeof (Elf32_Word),
+							 ELF_T_WORD);
+			    if (data != NULL
+				&& (*(const Elf32_Word *) data->d_buf & 1u))
+			      {
+				mod->syments = maxndx + 1;
+				break;
+			      }
+			    ++maxndx;
+			    hasharr_at += sizeof (Elf32_Word);
+			  } while (data != NULL);
+		      }
+		  }
+	      }
+	    if (offs[i_strtab] > offs[i_symtab] && mod->syments == 0)
+	      mod->syments = ((offs[i_strtab] - offs[i_symtab])
+			      / gelf_fsize (mod->main.elf,
+					    ELF_T_SYM, 1, EV_CURRENT));
+
+	    if (mod->syments > 0)
+	      {
+		mod->symdata = elf_getdata_rawchunk (mod->main.elf,
+						     offs[i_symtab],
+						     gelf_fsize (mod->main.elf,
+								 ELF_T_SYM,
+								 mod->syments,
+								 EV_CURRENT),
+						     ELF_T_SYM);
+		if (mod->symdata != NULL)
+		  {
+		    mod->symstrdata = elf_getdata_rawchunk (mod->main.elf,
+							    offs[i_strtab],
+							    strsz,
+							    ELF_T_BYTE);
+		    if (mod->symstrdata == NULL)
+		      mod->symdata = NULL;
+		  }
+		if (mod->symdata == NULL)
+		  mod->symerr = DWFL_E (LIBELF, elf_errno ());
+		else
+		  {
+		    mod->symfile = &mod->main;
+		    mod->symerr = DWFL_E_NOERROR;
+		  }
+	      }
+	  }
+
+	  /* First try unadjusted, like ELF files from disk, vdso.
+	     Then try for already adjusted dynamic section, like ELF
+	     from remote memory.  */
+	  translate_offs (0);
+	  if (mod->symfile == NULL)
+	    translate_offs (mod->main_bias);
+
+	  return;
 	}
     }
 }