[PATCH] elf: Properly compute offsets of desc and next note

["H.J. Lu" <hjl dot tools at gmail dot com>]

According to gABI, in a note entry, the note name field, not note name
size, is padded for the note descriptor.  And the note descriptor field,
not note descriptor size, is padded for the next note entry.  Also notes
are aligned to 4 bytes in 32-bit objects and 8 bytes in 64-bit objects.
Since on Linux, .note.ABI-tag and .note.gnu.build-id notes are always
aligned to 4 bytes, we need to use alignment of note section or note
segment, instead of assuming alignment based on ELF file class.

Tested on i686 and x86-64.

Any comments or objections?

H.J.
---
bfd/

	PR binutils/22444
	* elf.c (elf_read_notes): Add an argument for note aligment.
	(elf_parse_notes): Likewise.
	(_bfd_elf_make_section_from_shdr): Pass section aligment to
	elf_parse_notes.
	(bfd_section_from_phdr): Pass segment aligment to elf_read_notes.
	(elf_parse_notes): Add an argument for note aligment.  Use
	ELF_NOTE_DESC_OFFSET to get the offset of the note descriptor.
	Use ELF_NOTE_NEXT_OFFSET to get the offset of the next note
	entry.
	(elf_read_notes): Add an argument for note aligment and pass it
	to elf_parse_notes.

binutils/

	PR binutils/22444
	* readelf.c (process_notes_at): Use ELF_NOTE_DESC_OFFSET to get
	the offset of the note descriptor.  Use ELF_NOTE_NEXT_OFFSET to
	get the offset of the next note entry.

include/

	PR binutils/22444
	* elf/external.h (ELF_ALIGN_UP): New.
	(ELF_NOTE_DESC_OFFSET): Likewise.
	(ELF_NOTE_NEXT_OFFSET): Likewise.
---
 bfd/elf.c              | 24 ++++++++++++++----------
 binutils/readelf.c     |  8 ++++++--
 include/elf/external.h | 16 ++++++++++++++++
 3 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/bfd/elf.c b/bfd/elf.c
index 694e43540f..54fa57c4db 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -52,9 +52,10 @@ static int elf_sort_sections (const void *, const void *);
 static bfd_boolean assign_file_positions_except_relocs (bfd *, struct bfd_link_info *);
 static bfd_boolean prep_headers (bfd *);
 static bfd_boolean swap_out_syms (bfd *, struct elf_strtab_hash **, int) ;
-static bfd_boolean elf_read_notes (bfd *, file_ptr, bfd_size_type) ;
+static bfd_boolean elf_read_notes (bfd *, file_ptr, bfd_size_type,
+				   size_t align) ;
 static bfd_boolean elf_parse_notes (bfd *abfd, char *buf, size_t size,
-				    file_ptr offset);
+				    file_ptr offset, size_t align);
 
 /* Swap version information in and out.  The version information is
    currently size independent.  If that ever changes, this code will
@@ -1089,7 +1090,8 @@ _bfd_elf_make_section_from_shdr (bfd *abfd,
       if (!bfd_malloc_and_get_section (abfd, newsect, &contents))
 	return FALSE;
 
-      elf_parse_notes (abfd, (char *) contents, hdr->sh_size, hdr->sh_offset);
+      elf_parse_notes (abfd, (char *) contents, hdr->sh_size,
+		       hdr->sh_offset, hdr->sh_addralign);
       free (contents);
     }
 
@@ -2990,7 +2992,8 @@ bfd_section_from_phdr (bfd *abfd, Elf_Internal_Phdr *hdr, int hdr_index)
     case PT_NOTE:
       if (! _bfd_elf_make_section_from_phdr (abfd, hdr, hdr_index, "note"))
 	return FALSE;
-      if (! elf_read_notes (abfd, hdr->p_offset, hdr->p_filesz))
+      if (! elf_read_notes (abfd, hdr->p_offset, hdr->p_filesz,
+			    hdr->p_align))
 	return FALSE;
       return TRUE;
 
@@ -10952,14 +10955,14 @@ elfcore_write_register_note (bfd *abfd,
 }
 
 static bfd_boolean
-elf_parse_notes (bfd *abfd, char *buf, size_t size, file_ptr offset)
+elf_parse_notes (bfd *abfd, char *buf, size_t size, file_ptr offset,
+		 size_t align)
 {
   char *p;
 
   p = buf;
   while (p < buf + size)
     {
-      /* FIXME: bad alignment assumption.  */
       Elf_External_Note *xnp = (Elf_External_Note *) p;
       Elf_Internal_Note in;
 
@@ -10974,7 +10977,7 @@ elf_parse_notes (bfd *abfd, char *buf, size_t size, file_ptr offset)
 	return FALSE;
 
       in.descsz = H_GET_32 (abfd, xnp->descsz);
-      in.descdata = in.namedata + BFD_ALIGN (in.namesz, 4);
+      in.descdata = p + ELF_NOTE_DESC_OFFSET (in.namesz, align);
       in.descpos = offset + (in.descdata - buf);
       if (in.descsz != 0
 	  && (in.descdata >= buf + size
@@ -11036,14 +11039,15 @@ elf_parse_notes (bfd *abfd, char *buf, size_t size, file_ptr offset)
 	  break;
 	}
 
-      p = in.descdata + BFD_ALIGN (in.descsz, 4);
+      p += ELF_NOTE_NEXT_OFFSET (in.namesz, in.descsz, align);
     }
 
   return TRUE;
 }
 
 static bfd_boolean
-elf_read_notes (bfd *abfd, file_ptr offset, bfd_size_type size)
+elf_read_notes (bfd *abfd, file_ptr offset, bfd_size_type size,
+		size_t align)
 {
   char *buf;
 
@@ -11062,7 +11066,7 @@ elf_read_notes (bfd *abfd, file_ptr offset, bfd_size_type size)
   buf[size] = 0;
 
   if (bfd_bread (buf, size, abfd) != size
-      || !elf_parse_notes (abfd, buf, size, offset))
+      || !elf_parse_notes (abfd, buf, size, offset, align))
     {
       free (buf);
       return FALSE;
diff --git a/binutils/readelf.c b/binutils/readelf.c
index b7f1e091e0..3eb43920e1 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -17805,9 +17805,13 @@ process_notes_at (Filedata *           filedata,
 	  inote.namesz   = BYTE_GET (external->namesz);
 	  inote.namedata = external->name;
 	  inote.descsz   = BYTE_GET (external->descsz);
-	  inote.descdata = inote.namedata + align_power (inote.namesz, 2);
+	  inote.descdata = ((char *) external
+			    + ELF_NOTE_DESC_OFFSET (inote.namesz,
+						    section->sh_addralign));
 	  inote.descpos  = offset + (inote.descdata - (char *) pnotes);
-	  next = inote.descdata + align_power (inote.descsz, 2);
+	  next = ((char *) external
+		  + ELF_NOTE_NEXT_OFFSET (inote.namesz, inote.descsz,
+					  section->sh_addralign));
 	}
       else
 	{
diff --git a/include/elf/external.h b/include/elf/external.h
index d65bae0b21..eb0a53a9a9 100644
--- a/include/elf/external.h
+++ b/include/elf/external.h
@@ -183,6 +183,22 @@ typedef struct {
   char		name[1];		/* Start of the name+desc data */
 } Elf_External_Note;
 
+/* Align an address upward to a boundary, expressed as a number of bytes.
+   E.g. align to an 8-byte boundary with argument of 8.  */
+#define ELF_ALIGN_UP(addr, boundary) \
+  (((bfd_vma) (addr) + ((boundary) - 1)) & ~ (bfd_vma) ((boundary) -1))
+
+/* Compute the offset of the note descriptor from size of note entry's
+   owner string and note alignment.  */
+#define ELF_NOTE_DESC_OFFSET(namesz, align) \
+  ELF_ALIGN_UP (offsetof (Elf_External_Note, name) + (namesz), (align))
+
+/* Compute the offset of the next note entry from size of note entry's
+   owner string, size of the note descriptor and note alignment.  */
+#define ELF_NOTE_NEXT_OFFSET(namesz, descsz, align) \
+  ELF_ALIGN_UP (ELF_NOTE_DESC_OFFSET ((namesz), (align)) + (descsz), \
+		(align))
+
 /* Relocation Entries */
 typedef struct {
   unsigned char r_offset[4];	/* Location at which to apply the action */
-- 
2.13.6