strip, unstrip: Handle SHT_GROUP correctly.

The usage of annobin in Fedora showed a couple of bugs when using
eu-strip and eu-unstrip on ET_REL files that contain multiple group
sections.

When stripping we should not remove the SHF_GROUP flag from sections
even if the group section itself might be removed. Either the section
itself gets removed, and so the flag doesn't matter. Or it gets moved
together with the group section into the debug file, and then it still
needs to have the flag set. Also we would "renumber" the section group
flag field (which isn't a section index, and so shouldn't be changed).

Often the group sections have the exact same name (".group"), flags
(none) and sometimes the same sizes. Which makes matching them hard.
Extract the group signature and compare those when comparing two
group sections.

Signed-off-by: Mark Wielaard <[email protected]>

3 files changed, 76 insertions, 8 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 7b59ed60..d151e0d9 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,15 @@
+2018-10-12  Mark Wielaard  <[email protected]>
+
+	* strip.c (handle_elf): Don't remove SHF_GROUP flag from sections.
+	Skip group section flag when renumbering section indexes.
+	* unstrip.c (struct section): Add sig field.
+	(compare_unalloc_sections): Take and use sig1 and sig2 as arguments.
+	(compare_sections): Pass signatures to compare_unalloc_sections.
+	(get_group_sig): New function.
+	(find_alloc_sections_prelink): Set signature.
+	(copy_elided_sections): Likewise and pass them on.
+	(find_unalloc_section): Take and pass signatures.
+
 2018-10-02  Andreas Schwab  <[email protected]>
 
 	* strip.c (handle_elf): Handle ADD/SUB relocation.
diff --git a/src/strip.c b/src/strip.c
index 1f7b3cab..fdebc5e2 100644
--- a/src/strip.c
+++ b/src/strip.c
@@ -792,9 +792,13 @@ handle_elf (int fd, Elf *elf, const char *prefix, const char *fname,
 
 	  if (shdr_info[shdr_info[cnt].group_idx].idx == 0)
 	    {
-	      /* The section group section will be removed.  */
+	      /* The section group section might be removed.
+		 Don't remove the SHF_GROUP flag.  The section is
+		 either also removed, in which case the flag doesn't matter.
+		 Or it moves with the group into the debug file, then
+		 it will be reconnected with the new group and should
+		 still have the flag set.  */
 	      shdr_info[cnt].group_idx = 0;
-	      shdr_info[cnt].shdr.sh_flags &= ~SHF_GROUP;
 	    }
 	}
 
@@ -1368,7 +1372,9 @@ handle_elf (int fd, Elf *elf, const char *prefix, const char *fname,
 			&& shdr_info[cnt].data->d_buf != NULL);
 
 	    Elf32_Word *grpref = (Elf32_Word *) shdr_info[cnt].data->d_buf;
-	    for (size_t inner = 0;
+	    /* First word is the section group flag.
+	       Followed by section indexes, that need to be renumbered.  */
+	    for (size_t inner = 1;
 		 inner < shdr_info[cnt].data->d_size / sizeof (Elf32_Word);
 		 ++inner)
 	      if (grpref[inner] < shnum)
diff --git a/src/unstrip.c b/src/unstrip.c
index e6f09478..03a03462 100644
--- a/src/unstrip.c
+++ b/src/unstrip.c
@@ -696,6 +696,7 @@ struct section
 {
   Elf_Scn *scn;
   const char *name;
+  const char *sig;
   Elf_Scn *outscn;
   Dwelf_Strent *strent;
   GElf_Shdr shdr;
@@ -720,7 +721,8 @@ compare_alloc_sections (const struct section *s1, const struct section *s2,
 
 static int
 compare_unalloc_sections (const GElf_Shdr *shdr1, const GElf_Shdr *shdr2,
-			  const char *name1, const char *name2)
+			  const char *name1, const char *name2,
+			  const char *sig1, const char *sig2)
 {
   /* Sort by sh_flags as an arbitrary ordering.  */
   if (shdr1->sh_flags < shdr2->sh_flags)
@@ -734,6 +736,10 @@ compare_unalloc_sections (const GElf_Shdr *shdr1, const GElf_Shdr *shdr2,
   if (shdr1->sh_size > shdr2->sh_size)
     return 1;
 
+  /* Are they both SHT_GROUP sections? Then compare signatures.  */
+  if (sig1 != NULL && sig2 != NULL)
+    return strcmp (sig1, sig2);
+
   /* Sort by name as last resort.  */
   return strcmp (name1, name2);
 }
@@ -751,7 +757,8 @@ compare_sections (const void *a, const void *b, bool rel)
   return ((s1->shdr.sh_flags & SHF_ALLOC)
 	  ? compare_alloc_sections (s1, s2, rel)
 	  : compare_unalloc_sections (&s1->shdr, &s2->shdr,
-				      s1->name, s2->name));
+				      s1->name, s2->name,
+				      s1->sig, s2->sig));
 }
 
 static int
@@ -986,6 +993,44 @@ get_section_name (size_t ndx, const GElf_Shdr *shdr, const Elf_Data *shstrtab)
   return shstrtab->d_buf + shdr->sh_name;
 }
 
+/* Returns the signature of a group section, or NULL if the given
+   section isn't a group.  */
+static const char *
+get_group_sig (Elf *elf, GElf_Shdr *shdr)
+{
+  if (shdr->sh_type != SHT_GROUP)
+    return NULL;
+
+  Elf_Scn *symscn = elf_getscn (elf, shdr->sh_link);
+  if (symscn == NULL)
+    error (EXIT_FAILURE, 0, _("bad sh_link for group section: %s"),
+	   elf_errmsg (-1));
+
+  GElf_Shdr symshdr_mem;
+  GElf_Shdr *symshdr = gelf_getshdr (symscn, &symshdr_mem);
+  if (symshdr == NULL)
+    error (EXIT_FAILURE, 0, _("couldn't get shdr for group section: %s"),
+	   elf_errmsg (-1));
+
+  Elf_Data *symdata = elf_getdata (symscn, NULL);
+  if (symdata == NULL)
+    error (EXIT_FAILURE, 0, _("bad data for group symbol section: %s"),
+	   elf_errmsg (-1));
+
+  GElf_Sym sym_mem;
+  GElf_Sym *sym = gelf_getsym (symdata, shdr->sh_info, &sym_mem);
+  if (sym == NULL)
+    error (EXIT_FAILURE, 0, _("couldn't get symbol for group section: %s"),
+	   elf_errmsg (-1));
+
+  const char *sig = elf_strptr (elf, symshdr->sh_link, sym->st_name);
+  if (sig == NULL)
+    error (EXIT_FAILURE, 0, _("bad symbol name for group section: %s"),
+	   elf_errmsg (-1));
+
+  return sig;
+}
+
 /* Fix things up when prelink has moved some allocated sections around
    and the debuginfo file's section headers no longer match up.
    This fills in SECTIONS[0..NALLOC-1].outscn or exits.
@@ -1111,6 +1156,7 @@ find_alloc_sections_prelink (Elf *debug, Elf_Data *debug_shstrtab,
 	      sec->scn = elf_getscn (main, i + 1); /* Really just for ndx.  */
 	      sec->outscn = NULL;
 	      sec->strent = NULL;
+	      sec->sig = get_group_sig (main, &sec->shdr);
 	      ++undo_nalloc;
 	    }
 	}
@@ -1336,6 +1382,7 @@ more sections in stripped file than debug file -- arguments reversed?"));
       sections[i].scn = scn;
       sections[i].outscn = NULL;
       sections[i].strent = NULL;
+      sections[i].sig = get_group_sig (stripped, shdr);
     }
 
   const struct section *stripped_symtab = NULL;
@@ -1354,7 +1401,8 @@ more sections in stripped file than debug file -- arguments reversed?"));
 
   /* Locate a matching unallocated section in SECTIONS.  */
   inline struct section *find_unalloc_section (const GElf_Shdr *shdr,
-					       const char *name)
+					       const char *name,
+					       const char *sig)
     {
       size_t l = nalloc, u = stripped_shnum - 1;
       while (l < u)
@@ -1362,7 +1410,8 @@ more sections in stripped file than debug file -- arguments reversed?"));
 	  size_t i = (l + u) / 2;
 	  struct section *sec = &sections[i];
 	  int cmp = compare_unalloc_sections (shdr, &sec->shdr,
-					      name, sec->name);
+					      name, sec->name,
+					      sig, sec->sig);
 	  if (cmp < 0)
 	    u = i;
 	  else if (cmp > 0)
@@ -1435,7 +1484,8 @@ more sections in stripped file than debug file -- arguments reversed?"));
       else
 	{
 	  /* Look for the section that matches.  */
-	  sec = find_unalloc_section (shdr, name);
+	  sec = find_unalloc_section (shdr, name,
+				      get_group_sig (unstripped, shdr));
 	  if (sec == NULL)
 	    {
 	      /* An additional unallocated section is fine if not SHT_NOBITS.