Handle GNU Build Attribute ELF Notes.

GNU Build Attribute ELF Notes are generated by the GCC annobin plugin
and described at https://fedoraproject.org/wiki/Toolchain/Watermark

Unfortunately the constants aren't yet described in the standard glibc
elf.h so they have been added to the elfutils specific elf-knowledge.h.

The notes abuse the name owner field to encode some data not in the
description. This makes it a bit hard to parse. We have to match the
note owner name prefix (to "GA") to be sure the type is valid. We also
cannot rely on the owner name being a valid C string since the attribute
name and value can contain zero (terminators). So pass around namesz
to the ebl note parsing functions.

eu-elflint will recognize and eu-readelf -n will now show the notes:

Note section [27] '.gnu.build.attributes' of 56080 bytes at offset 0x114564:
  Owner          Data size  Type
  GA                    16  GNU Build Attribute OPEN
    Address Range: 0x2f30f - 0x2f30f
    VERSION: "3p8"
  GA                     0  GNU Build Attribute OPEN
    TOOL: "gcc 8.2.1 20180801"
  GA                     0  GNU Build Attribute OPEN
    "GOW": 45
  GA                     0  GNU Build Attribute OPEN
    STACK_PROT: 0
  GA                     0  GNU Build Attribute OPEN
    "stack_clash": TRUE
  GA                     0  GNU Build Attribute OPEN
    "cf_protection": 0
  GA                     0  GNU Build Attribute OPEN
    "GLIBCXX_ASSERTIONS": TRUE
  GA                     0  GNU Build Attribute OPEN
    "FORTIFY": 0
  GA                     0  GNU Build Attribute OPEN
    PIC: 3
  GA                     0  GNU Build Attribute OPEN
    SHORT_ENUM: FALSE
  GA                     0  GNU Build Attribute OPEN
    ABI: c001100000012
  GA                     0  GNU Build Attribute OPEN
    "stack_realign": FALSE

A new test was added to run-readelf -n for the existing annobin file.

Signed-off-by: Mark Wielaard <mark@klomp.org>

3 files changed, 35 insertions, 2 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 0ed86bbf..f014de8f 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,11 @@
+2018-11-12  Mark Wielaard  <mark@klomp.org>
+
+	* elflint.c (check_note_data): Recognize NT_GNU_BUILD_ATTRIBUTE_OPEN
+	and NT_GNU_BUILD_ATTRIBUTE_OPEN.
+	* readelf.c (handle_notes_data): Handle
+	ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX. Pass nhdr.n_namesz to
+	ebl_object_note.
+
 2018-11-11  Mark Wielaard  <mark@klomp.org>
 
 	* readelf.c (handle_notes_data): Pass n_descsz to
diff --git a/src/elflint.c b/src/elflint.c
index dff74eee..184ca125 100644
--- a/src/elflint.c
+++ b/src/elflint.c
@@ -4344,6 +4344,19 @@ section [%2d] '%s': unknown core file note type %" PRIu32
 	      }
 	      goto unknown_note;
 
+	  case NT_GNU_BUILD_ATTRIBUTE_OPEN:
+	  case NT_GNU_BUILD_ATTRIBUTE_FUNC:
+	    /* GNU Build Attributes store most data in the owner
+	       name, which must start with the
+	       ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX "GA".  */
+	    if (nhdr.n_namesz >= sizeof ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX
+		&& strncmp (data->d_buf + name_offset,
+			    ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX,
+			    strlen (ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX)) == 0)
+	      break;
+	    else
+	      goto unknown_note;
+
 	  case 0:
 	    /* Linux vDSOs use a type 0 note for the kernel version word.  */
 	    if (nhdr.n_namesz == sizeof "Linux"
diff --git a/src/readelf.c b/src/readelf.c
index 659e34fb..3a73710f 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -12193,10 +12193,21 @@ handle_notes_data (Ebl *ebl, const GElf_Ehdr *ehdr,
       const char *name = nhdr.n_namesz == 0 ? "" : data->d_buf + name_offset;
       const char *desc = data->d_buf + desc_offset;
 
+      /* GNU Build Attributes are weird, they store most of their data
+	 into the owner name field.  Extract just the owner name
+	 prefix here, then use the rest later as data.  */
+      bool is_gnu_build_attr
+	= strncmp (name, ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX,
+		   strlen (ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX)) == 0;
+      const char *print_name = (is_gnu_build_attr
+				? ELF_NOTE_GNU_BUILD_ATTRIBUTE_PREFIX : name);
+      size_t print_namesz = (is_gnu_build_attr
+			     ? strlen (print_name) : nhdr.n_namesz);
+
       char buf[100];
       char buf2[100];
       printf (gettext ("  %-13.*s  %9" PRId32 "  %s\n"),
-	      (int) nhdr.n_namesz, name, nhdr.n_descsz,
+	      (int) print_namesz, print_name, nhdr.n_descsz,
 	      ehdr->e_type == ET_CORE
 	      ? ebl_core_note_type_name (ebl, nhdr.n_type,
 					 buf, sizeof (buf))
@@ -12237,7 +12248,8 @@ handle_notes_data (Ebl *ebl, const GElf_Ehdr *ehdr,
 		handle_core_note (ebl, &nhdr, name, desc);
 	    }
 	  else
-	    ebl_object_note (ebl, name, nhdr.n_type, nhdr.n_descsz, desc);
+	    ebl_object_note (ebl, nhdr.n_namesz, name, nhdr.n_type,
+			     nhdr.n_descsz, desc);
 	}
     }