libelf: If xlate can only convert the ELF note header, just do that.

When we started parsing new style ELF_T_NHDR8 notes we added extra
checks on alignment and padding. When those failed we would stop
converting and just return the rest of the ELF Note unconverted.
In the case were we just had enough data for just the ELF Note header
and the destionation and source weren't the same we would then
accidentially throw away the Note header conversion we just did.

Fix that by indicating we did correctly convert just the header.

Adds testcase that compares parsing ELF notes with gelf_getnote
and parsing the raw data by hand using elf32_xlatetom using just
the Note header and ignoring the (raw) note data.

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

1 files changed, 157 insertions, 0 deletions

diff --git a/tests/xlate_notes.c b/tests/xlate_notes.c
new file mode 100644
index 00000000..90a4ae27
--- /dev/null
+++ b/tests/xlate_notes.c
@@ -0,0 +1,157 @@
+/* Test program for extracting ELF Note headers and getting whole notes.
+   Copyright (C) 2019 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include ELFUTILS_HEADER(elf)
+#include <gelf.h>
+
+int
+main (int argc, char *argv[])
+{
+  if (argc != 2)
+    {
+      printf ("No ELF file given as argument\n");
+      exit (1);
+    }
+
+  const char *fname = argv[1];
+
+  // Initialize libelf.
+  elf_version (EV_CURRENT);
+
+  /* Read the ELF from disk now.  */
+  int fd = open (fname, O_RDONLY);
+  if (fd == -1)
+    {
+      printf ("cannot open '%s': %s\n", fname, strerror (errno));
+      exit (1);
+    }
+
+  Elf *elf = elf_begin (fd, ELF_C_READ, NULL);
+  if (elf == NULL)
+    {
+      printf ("cannot create ELF descriptor: %s\n", elf_errmsg (-1));
+      exit (1);
+    }
+
+  GElf_Ehdr ehdr;
+  if (gelf_getehdr (elf, &ehdr) == NULL)
+    {
+      printf ("cannot get Ehdr: %s\n", elf_errmsg (-1));
+      exit (1);
+    }
+
+  /* Search for all SHT_NOTE sections.  */
+  Elf_Scn *scn = NULL;
+  while ((scn = elf_nextscn (elf, scn)) != NULL)
+    {
+      /* Get the header.  */
+      GElf_Shdr shdr;
+      if (gelf_getshdr (scn, &shdr) == NULL)
+	{
+	  printf ("couldn't get shdr: %s\n", elf_errmsg (-1));
+	  exit (1);
+	}
+
+      if (shdr.sh_type == SHT_NOTE)
+	{
+	  printf ("Notes in section %zd:\n", elf_ndxscn (scn));
+
+	  Elf_Data *raw = elf_rawdata (scn, NULL);
+	  if (raw == NULL)
+	    {
+	      printf ("couldn't get raw data: %s\n", elf_errmsg (-1));
+	      exit (1);
+	    }
+
+	  Elf_Data *data = elf_getdata (scn, NULL);
+	  if (data == NULL)
+	    {
+	      printf ("couldn't get data: %s\n", elf_errmsg (-1));
+	      exit (1);
+	    }
+
+	  size_t off = 0;
+	  size_t next;
+	  GElf_Nhdr nhdr;
+	  size_t n_off;
+	  size_t d_off;
+	  while ((next = gelf_getnote (data, off, &nhdr, &n_off, &d_off)) > 0)
+	    {
+	      /* Now just get the note header "raw" (don't
+		 copy/translate the note data). This only handles
+		 traditional GNU ELF Notes, so we still use the next
+		 from gelf_getnote (padding is different for new style
+		 ELF_T_NHDR8 notes).  */
+	      Elf32_Nhdr nh;
+	      Elf_Data src =
+                {
+                  .d_version = EV_CURRENT, .d_type = ELF_T_NHDR,
+		  .d_size = sizeof nh
+                };
+	      Elf_Data dst = src;
+	      src.d_buf = raw->d_buf + off;
+	      dst.d_buf = &nh;
+
+	      if (elf32_xlatetom (&dst, &src, ehdr.e_ident[EI_DATA]) == NULL)
+		{
+		  printf ("couldn't xlate note: %s\n", elf_errmsg (-1));
+		  exit (1);
+		}
+
+	      printf ("type: %" PRId32 ",%" PRId32
+		      ", namesz: %" PRId32 ",%" PRId32
+		      ", descsz: %" PRId32 ",%" PRId32 "\n",
+		      nhdr.n_type, nh.n_type,
+		      nhdr.n_namesz, nh.n_namesz,
+		      nhdr.n_descsz, nh.n_descsz);
+
+	      if (nhdr.n_type != nh.n_type
+		  || nhdr.n_namesz != nh.n_namesz
+		  || nhdr.n_descsz != nh.n_descsz)
+		{
+		  printf ("Nhdrs not equal!\n");
+		  exit (1);
+		}
+
+	      off = next;
+	    }
+	}
+
+    }
+
+  if (elf_end (elf) != 0)
+    {
+      printf ("failure in elf_end: %s\n", elf_errmsg (-1));
+      exit (1);
+    }
+
+  close (fd);
+
+  return 0;
+}