libdwelf: Add dwelf_elf_gnu_build_id.

Move internal function __libdwfl_find_build_id to libdwelf and use it to
add a public dwelf_elf_gnu_build_id function to extract the NT_GNU_BUILD_ID
from an ELF file using either the shdrs or phdrs. Adjust internal callers
and add a testcase.

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

16 files changed, 333 insertions, 126 deletions

diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index 3152239f..94ef03ca 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,7 @@
+2014-04-30  Mark Wielaard  <mjw@redhat.com>
+
+	* libdw.map (ELFUTILS_0.159): Add dwelf_elf_gnu_build_id.
+
 2014-04-15  Florian Weimer  <fweimer@redhat.com>
 
 	* dwarf_begin_elf.c (__check_build_id, try_debugaltlink)
diff --git a/libdw/libdw.map b/libdw/libdw.map
index 35299808..899e13e1 100644
--- a/libdw/libdw.map
+++ b/libdw/libdw.map
@@ -299,4 +299,5 @@ ELFUTILS_0.159 {
     dwarf_setalt;
     dwelf_dwarf_gnu_debugaltlink;
     dwelf_elf_gnu_debuglink;
+    dwelf_elf_gnu_build_id;
 } ELFUTILS_0.158;
diff --git a/libdwelf/ChangeLog b/libdwelf/ChangeLog
index aa291320..9f95ea81 100644
--- a/libdwelf/ChangeLog
+++ b/libdwelf/ChangeLog
@@ -1,3 +1,12 @@
+2014-04-30  Mark Wielaard  <mjw@redhat.com>
+
+	* Makefile.am (AM_CPPFLAGS): Add libdwfl and libebl include dirs.
+	(libdwelf_a_SOURCES): Add dwelf_elf_gnu_build_id.c
+	* dwelf_elf_gnu_build_id.c: New file. Moved libdwfl function
+	__libdwfl_find_elf_build_id here.
+	* libdwelf.h (dwelf_elf_gnu_build_id): Declare new function.
+	* libdwelfP.h (dwelf_elf_gnu_build_id): Add internal declaration.
+
 2014-04-24  Florian Weimer  <fweimer@redhat.com>
 
 	* dwelf_dwarf_gnu_debugaltlink.c: New file.
diff --git a/libdwelf/Makefile.am b/libdwelf/Makefile.am
index 1ca3a5cd..cd4b7ddf 100644
--- a/libdwelf/Makefile.am
+++ b/libdwelf/Makefile.am
@@ -30,7 +30,8 @@
 ## not, see <http://www.gnu.org/licenses/>.
 ##
 include $(top_srcdir)/config/eu.am
-AM_CPPFLAGS += -I$(srcdir)/../libelf -I$(srcdir)/../libdw
+AM_CPPFLAGS += -I$(srcdir)/../libelf -I$(srcdir)/../libdw \
+	       -I$(srcdir)/../libdwfl -I$(srcdir)/../libebl
 VERSION = 1
 
 noinst_LIBRARIES = libdwelf.a libdwelf_pic.a
@@ -38,7 +39,8 @@ noinst_LIBRARIES = libdwelf.a libdwelf_pic.a
 pkginclude_HEADERS = libdwelf.h
 noinst_HEADERS = libdwelfP.h
 
-libdwelf_a_SOURCES = dwelf_elf_gnu_debuglink.c dwelf_dwarf_gnu_debugaltlink.c
+libdwelf_a_SOURCES = dwelf_elf_gnu_debuglink.c dwelf_dwarf_gnu_debugaltlink.c \
+	dwelf_elf_gnu_build_id.c
 
 libdwelf = $(libdw)
 
diff --git a/libdwelf/dwelf_elf_gnu_build_id.c b/libdwelf/dwelf_elf_gnu_build_id.c
new file mode 100644
index 00000000..1ed501d9
--- /dev/null
+++ b/libdwelf/dwelf_elf_gnu_build_id.c
@@ -0,0 +1,147 @@
+/* Returns the build id if found in a NT_GNU_BUILD_ID note.
+   Copyright (C) 2014 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 either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   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 copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "libdwelfP.h"
+#include "libdwflP.h"
+
+#define NO_VADDR	((GElf_Addr) -1l)
+
+/* Defined here for reuse. The dwelf interface doesn't care about the
+   address of the note, but libdwfl does.  */
+static int
+find_elf_build_id (Dwfl_Module *mod, int e_type, Elf *elf,
+		   const void **build_id_bits, GElf_Addr *build_id_elfaddr,
+		   int *build_id_len)
+{
+  int check_notes (Elf_Data *data, GElf_Addr data_elfaddr)
+  {
+    size_t pos = 0;
+    GElf_Nhdr nhdr;
+    size_t name_pos;
+    size_t desc_pos;
+    while ((pos = gelf_getnote (data, pos, &nhdr, &name_pos, &desc_pos)) > 0)
+      if (nhdr.n_type == NT_GNU_BUILD_ID
+	  && nhdr.n_namesz == sizeof "GNU" && !memcmp (data->d_buf + name_pos,
+						       "GNU", sizeof "GNU"))
+	{
+	  *build_id_bits = data->d_buf + desc_pos;
+	  *build_id_elfaddr = (data_elfaddr == NO_VADDR
+			       ? 0 : data_elfaddr + desc_pos);
+	  *build_id_len = nhdr.n_descsz;
+	  return 1;
+	}
+    return 0;
+  }
+
+  size_t shstrndx = SHN_UNDEF;
+  int result = 0;
+
+  Elf_Scn *scn = elf_nextscn (elf, NULL);
+
+  if (scn == NULL)
+    {
+      /* No sections, have to look for phdrs.  */
+      size_t phnum;
+      if (unlikely (elf_getphdrnum (elf, &phnum) != 0))
+	{
+	  if (mod != NULL)
+	    __libdwfl_seterrno (DWFL_E_LIBELF);
+	  return -1;
+	}
+      for (size_t i = 0; result == 0 && i < phnum; ++i)
+	{
+	  GElf_Phdr phdr_mem;
+	  GElf_Phdr *phdr = gelf_getphdr (elf, i, &phdr_mem);
+	  if (likely (phdr != NULL) && phdr->p_type == PT_NOTE)
+	    result = check_notes (elf_getdata_rawchunk (elf,
+							phdr->p_offset,
+							phdr->p_filesz,
+							ELF_T_NHDR),
+				  phdr->p_vaddr);
+	}
+    }
+  else
+    do
+      {
+	GElf_Shdr shdr_mem;
+	GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
+	if (likely (shdr != NULL) && shdr->sh_type == SHT_NOTE)
+	  {
+	    /* Determine the right sh_addr in this module.  */
+	    GElf_Addr vaddr = 0;
+	    if (!(shdr->sh_flags & SHF_ALLOC))
+	      vaddr = NO_VADDR;
+	    else if (mod == NULL || e_type != ET_REL)
+	      vaddr = shdr->sh_addr;
+	    else if (__libdwfl_relocate_value (mod, elf, &shstrndx,
+					       elf_ndxscn (scn), &vaddr))
+	      vaddr = NO_VADDR;
+	    result = check_notes (elf_getdata (scn, NULL), vaddr);
+	  }
+      }
+    while (result == 0 && (scn = elf_nextscn (elf, scn)) != NULL);
+
+  return result;
+}
+
+int
+internal_function
+__libdwfl_find_elf_build_id (Dwfl_Module *mod, Elf *elf,
+			     const void **build_id_bits,
+			     GElf_Addr *build_id_elfaddr, int *build_id_len)
+{
+  GElf_Ehdr ehdr_mem, *ehdr = gelf_getehdr (elf, &ehdr_mem);
+  if (unlikely (ehdr == NULL))
+    {
+      __libdwfl_seterrno (DWFL_E_LIBELF);
+      return -1;
+    }
+  // MOD->E_TYPE is zero here.
+  assert (ehdr->e_type != ET_REL || mod != NULL);
+
+  return find_elf_build_id (mod, ehdr->e_type, elf,
+			    build_id_bits, build_id_elfaddr, build_id_len);
+}
+
+ssize_t
+dwelf_elf_gnu_build_id (Elf *elf, const void **build_idp)
+{
+  GElf_Addr build_id_elfaddr;
+  int build_id_len;
+  int result = find_elf_build_id (NULL, ET_NONE, elf, build_idp,
+				  &build_id_elfaddr, &build_id_len);
+  if (result > 0)
+    return build_id_len;
+
+  return result;
+}
+INTDEF(dwelf_elf_gnu_build_id)
diff --git a/libdwelf/libdwelf.h b/libdwelf/libdwelf.h
index 6f1dbd3a..e16dc0f3 100644
--- a/libdwelf/libdwelf.h
+++ b/libdwelf/libdwelf.h
@@ -57,6 +57,14 @@ extern ssize_t dwelf_dwarf_gnu_debugaltlink (Dwarf *dwarf,
 					     const char **namep,
 					     const void **build_idp);
 
+/* Returns the build ID as found in a NT_GNU_BUILD_ID note from either
+   a SHT_NOTE section or from a PT_NOTE segment if the ELF file
+   doesn't contain any section headers.  On success a pointer to the
+   build ID is written to *BUILDID_P, and the positive length of the
+   build ID is returned.  Returns 0 if the ELF lacks a NT_GNU_BUILD_ID
+   note.  Returns -1 in case of malformed data or other errors.  */
+extern ssize_t dwelf_elf_gnu_build_id (Elf *elf, const void **build_idp);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/libdwelf/libdwelfP.h b/libdwelf/libdwelfP.h
index c00a834c..d83c759a 100644
--- a/libdwelf/libdwelfP.h
+++ b/libdwelf/libdwelfP.h
@@ -37,5 +37,6 @@
 /* Avoid PLT entries.  */
 INTDECL (dwelf_elf_gnu_debuglink)
 INTDECL (dwelf_dwarf_gnu_debugaltlink)
+INTDECL (dwelf_elf_gnu_build_id)
 
 #endif	/* libdwelfP.h */
diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index 62ea412c..7e4234db 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,13 @@
+2014-04-30  Mark Wielaard  <mjw@redhat.com>
+
+	* dwfl_module_build_id.c (__libdwfl_find_elf_build_id): Moved to
+	dwelf_elf_gnu_build_id.c.
+	(__libdwfl_find_build_id): Add assert to make sure mod is never NULL.
+	* dwfl_segment_report_module.c (dwfl_segment_report_module): Call
+	dwelf_elf_gnu_build_id directly instead of __libdwfl_find_build_id.
+	* dwfl_module_getdwarf.c (__check_build_id): Implement using
+	dwelf_elf_gnu_build_id.
+
 2014-04-15  Florian Weimer  <fweimer@redhat.com>
 
 	* dwfl_module_getdwarf.c (__check_build_id): Moved from libdw.
diff --git a/libdwfl/dwfl_module_build_id.c b/libdwfl/dwfl_module_build_id.c
index cae007b4..350bbf83 100644
--- a/libdwfl/dwfl_module_build_id.c
+++ b/libdwfl/dwfl_module_build_id.c
@@ -1,5 +1,5 @@
 /* Return build ID information for a module.
-   Copyright (C) 2007-2010 Red Hat, Inc.
+   Copyright (C) 2007-2010, 2014 Red Hat, Inc.
    This file is part of elfutils.
 
    This file is free software; you can redistribute it and/or modify
@@ -52,93 +52,6 @@ found_build_id (Dwfl_Module *mod, bool set,
   return len;
 }
 
-#define NO_VADDR	((GElf_Addr) -1l)
-
-int
-internal_function
-__libdwfl_find_elf_build_id (Dwfl_Module *mod, Elf *elf,
-			     const void **build_id_bits,
-			     GElf_Addr *build_id_elfaddr, int *build_id_len)
-{
-  GElf_Ehdr ehdr_mem, *ehdr = gelf_getehdr (elf, &ehdr_mem);
-  if (unlikely (ehdr == NULL))
-    {
-      __libdwfl_seterrno (DWFL_E_LIBELF);
-      return -1;
-    }
-  // MOD->E_TYPE is zero here.
-  assert (ehdr->e_type != ET_REL || mod != NULL);
-
-  int check_notes (Elf_Data *data, GElf_Addr data_elfaddr)
-  {
-    size_t pos = 0;
-    GElf_Nhdr nhdr;
-    size_t name_pos;
-    size_t desc_pos;
-    while ((pos = gelf_getnote (data, pos, &nhdr, &name_pos, &desc_pos)) > 0)
-      if (nhdr.n_type == NT_GNU_BUILD_ID
-	  && nhdr.n_namesz == sizeof "GNU" && !memcmp (data->d_buf + name_pos,
-						       "GNU", sizeof "GNU"))
-	{
-	  *build_id_bits = data->d_buf + desc_pos;
-	  *build_id_elfaddr = (data_elfaddr == NO_VADDR
-			       ? 0 : data_elfaddr + desc_pos);
-	  *build_id_len = nhdr.n_descsz;
-	  return 1;
-	}
-    return 0;
-  }
-
-  size_t shstrndx = SHN_UNDEF;
-  int result = 0;
-
-  Elf_Scn *scn = elf_nextscn (elf, NULL);
-
-  if (scn == NULL)
-    {
-      /* No sections, have to look for phdrs.  */
-      size_t phnum;
-      if (unlikely (elf_getphdrnum (elf, &phnum) != 0))
-	{
-	  __libdwfl_seterrno (DWFL_E_LIBELF);
-	  return -1;
-	}
-      for (size_t i = 0; result == 0 && i < phnum; ++i)
-	{
-	  GElf_Phdr phdr_mem;
-	  GElf_Phdr *phdr = gelf_getphdr (elf, i, &phdr_mem);
-	  if (likely (phdr != NULL) && phdr->p_type == PT_NOTE)
-	    result = check_notes (elf_getdata_rawchunk (elf,
-							phdr->p_offset,
-							phdr->p_filesz,
-							ELF_T_NHDR),
-				  phdr->p_vaddr);
-	}
-    }
-  else
-    do
-      {
-	GElf_Shdr shdr_mem;
-	GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
-	if (likely (shdr != NULL) && shdr->sh_type == SHT_NOTE)
-	  {
-	    /* Determine the right sh_addr in this module.  */
-	    GElf_Addr vaddr = 0;
-	    if (!(shdr->sh_flags & SHF_ALLOC))
-	      vaddr = NO_VADDR;
-	    else if (mod == NULL || ehdr->e_type != ET_REL)
-	      vaddr = shdr->sh_addr;
-	    else if (__libdwfl_relocate_value (mod, elf, &shstrndx,
-					       elf_ndxscn (scn), &vaddr))
-	      vaddr = NO_VADDR;
-	    result = check_notes (elf_getdata (scn, NULL), vaddr);
-	  }
-      }
-    while (result == 0 && (scn = elf_nextscn (elf, scn)) != NULL);
-
-  return result;
-}
-
 int
 internal_function
 __libdwfl_find_build_id (Dwfl_Module *mod, bool set, Elf *elf)
@@ -147,6 +60,9 @@ __libdwfl_find_build_id (Dwfl_Module *mod, bool set, Elf *elf)
   GElf_Addr build_id_elfaddr;
   int build_id_len;
 
+  /* For mod == NULL use dwelf_elf_gnu_build_id directly.  */
+  assert (mod != NULL);
+
   int result = __libdwfl_find_elf_build_id (mod, elf, &build_id_bits,
 					    &build_id_elfaddr, &build_id_len);
   if (result <= 0)
diff --git a/libdwfl/dwfl_module_getdwarf.c b/libdwfl/dwfl_module_getdwarf.c
index 6163ddbe..e8087bfb 100644
--- a/libdwfl/dwfl_module_getdwarf.c
+++ b/libdwfl/dwfl_module_getdwarf.c
@@ -42,34 +42,13 @@ __check_build_id (Dwarf *dw, const uint8_t *build_id, const size_t id_len)
     return -1;
 
   Elf *elf = dw->elf;
-  Elf_Scn *scn = elf_nextscn (elf, NULL);
-  if (scn == NULL)
+  const void *elf_build_id;
+  ssize_t elf_id_len = INTUSE(dwelf_elf_gnu_build_id) (elf, &elf_build_id);
+  if (elf_id_len < 0)
     return -1;
 
-  do
-    {
-      GElf_Shdr shdr_mem;
-      GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
-      if (likely (shdr != NULL) && shdr->sh_type == SHT_NOTE)
-	{
-	  size_t pos = 0;
-	  GElf_Nhdr nhdr;
-	  size_t name_pos;
-	  size_t desc_pos;
-	  Elf_Data *data = elf_getdata (scn, NULL);
-	  while ((pos = gelf_getnote (data, pos, &nhdr, &name_pos,
-				      &desc_pos)) > 0)
-	    if (nhdr.n_type == NT_GNU_BUILD_ID
-	        && nhdr.n_namesz == sizeof "GNU"
-		&& ! memcmp (data->d_buf + name_pos, "GNU", sizeof "GNU"))
-	      return (nhdr.n_descsz == id_len
-		      && ! memcmp (data->d_buf + desc_pos,
-				   build_id, id_len)) ? 0 : 1;
-        }
-      }
-    while ((scn = elf_nextscn (elf, scn)) != NULL);
-
-  return -1;
+  return (id_len == (size_t) elf_id_len
+	  && memcmp (build_id, elf_build_id, id_len) == 0) ? 0 : 1;
 }
 
 /* Try to open an debug alt link by name, checking build_id.
diff --git a/libdwfl/dwfl_segment_report_module.c b/libdwfl/dwfl_segment_report_module.c
index fd967e9a..dfecb517 100644
--- a/libdwfl/dwfl_segment_report_module.c
+++ b/libdwfl/dwfl_segment_report_module.c
@@ -494,13 +494,12 @@ dwfl_segment_report_module (Dwfl *dwfl, int ndx, const char *name,
 		&& module->disk_file_has_build_id && build_id_len > 0)
 	      {
 		const void *elf_build_id;
-		GElf_Addr elf_build_id_elfaddr;
-		int elf_build_id_len;
+		ssize_t elf_build_id_len;
 
-		if (__libdwfl_find_elf_build_id (NULL, module->elf,
-						 &elf_build_id,
-						 &elf_build_id_elfaddr,
-						 &elf_build_id_len) > 0)
+		/* If there is a build id in the elf file, check it.  */
+		elf_build_id_len = INTUSE(dwelf_elf_gnu_build_id) (module->elf,
+								&elf_build_id);
+		if (elf_build_id_len > 0)
 		  {
 		    if (build_id_len != (size_t) elf_build_id_len
 			|| memcmp (build_id, elf_build_id, build_id_len) != 0)
diff --git a/tests/ChangeLog b/tests/ChangeLog
index 1c30778d..ff396d50 100644
--- a/tests/ChangeLog
+++ b/tests/ChangeLog
@@ -1,3 +1,11 @@
+2014-04-30  Mark Wielaard  <mjw@redhat.com>
+
+	* buildid.c, buildid.sh, testfile42_noshdrs.bz2: New files.
+	* Makefile.am (check_PROGRAMS): Add buildid.
+	(TESTS): Add run-buildid.sh.
+	(EXTRA_DISTS): Add run-buildid.sh and testfile42_noshdrs.bz2.
+	(buildid_LDADD): New variable.
+
 2014-04-24  Florian Weimer  <fweimer@redhat.com>
 
 	* allfcts.c (setup_alt): New function.
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 33803fca..dd110a52 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -49,7 +49,9 @@ check_PROGRAMS = arextract arsymtest newfile saridx scnnames sectiondump \
 		  alldts md5-sha1-test typeiter typeiter2 low_high_pc \
 		  test-elf_cntl_gelf_getshdr dwflsyms dwfllines \
 		  dwfl-report-elf-align varlocs backtrace backtrace-child \
-		  backtrace-data backtrace-dwarf debuglink debugaltlink
+		  backtrace-data backtrace-dwarf debuglink debugaltlink \
+		  buildid
+
 asm_TESTS = asm-tst1 asm-tst2 asm-tst3 asm-tst4 asm-tst5 \
 	    asm-tst6 asm-tst7 asm-tst8 asm-tst9
 
@@ -86,7 +88,7 @@ TESTS = run-arextract.sh run-arsymtest.sh newfile test-nlist \
 	run-readelf-macro.sh run-readelf-loc.sh \
 	run-readelf-aranges.sh run-readelf-line.sh \
 	run-native-test.sh run-bug1-test.sh \
-	run-debuglink.sh run-debugaltlink.sh \
+	run-debuglink.sh run-debugaltlink.sh run-buildid.sh \
 	dwfl-bug-addr-overflow run-addrname-test.sh \
 	dwfl-bug-fd-leak dwfl-bug-report \
 	run-dwfl-bug-offline-rel.sh run-dwfl-addr-sect.sh \
@@ -176,14 +178,15 @@ EXTRA_DIST = run-arextract.sh run-arsymtest.sh \
 	     run-readelf-test1.sh run-readelf-test2.sh run-readelf-test3.sh \
 	     run-readelf-test4.sh run-readelf-twofiles.sh \
 	     run-bug1-test.sh testfile28.bz2 testfile28.rdwr.bz2 \
-	     run-debuglink.sh run-debugaltlink.sh \
+	     run-debuglink.sh run-debugaltlink.sh run-buildid.sh \
 	     testfile29.bz2 testfile29.rdwr.bz2 \
 	     testfile30.bz2 testfile31.bz2 testfile32.bz2 testfile33.bz2 \
 	     testfile34.bz2 testfile35.bz2 testfile35.debug.bz2 \
 	     testfile36.bz2 testfile36.debug.bz2 \
 	     testfile37.bz2 testfile37.debug.bz2 \
 	     testfile38.bz2 testfile39.bz2 testfile40.bz2 testfile40.debug.bz2 \
-	     testfile41.bz2 testfile42.bz2 testfile43.bz2 \
+	     testfile41.bz2 testfile42.bz2 testfile42_noshdrs.bz2 \
+	     testfile43.bz2 \
 	     testfile44.S.bz2 testfile44.expect.bz2 run-disasm-x86.sh \
 	     testfile45.S.bz2 testfile45.expect.bz2 run-disasm-x86-64.sh \
 	     testfile46.bz2 testfile47.bz2 testfile48.bz2 testfile48.debug.bz2 \
@@ -406,6 +409,7 @@ backtrace_dwarf_CFLAGS = -Wno-unused-parameter
 backtrace_dwarf_LDADD = $(libdw) $(libelf)
 debuglink_LDADD = $(libdw) $(libelf)
 debugaltlink_LDADD = $(libdw) $(libelf)
+buildid_LDADD = $(libdw) $(libelf)
 
 if GCOV
 check: check-am coverage
diff --git a/tests/buildid.c b/tests/buildid.c
new file mode 100644
index 00000000..87c18773
--- /dev/null
+++ b/tests/buildid.c
@@ -0,0 +1,81 @@
+/* Test program for dwelf_elf_gnu_build_id, print build ID.
+   Copyright (C) 2014 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/>.  */
+
+#include <config.h>
+#include <assert.h>
+#include <inttypes.h>
+#include <err.h>
+#include <errno.h>
+#include ELFUTILS_HEADER(elf)
+#include ELFUTILS_HEADER(dwelf)
+#include <stdio.h>
+#include <error.h>
+#include <string.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+int
+main (int argc, char *argv[])
+{
+  if (argc < 2)
+    error (EXIT_FAILURE, 0, "No input file given");
+
+  elf_version (EV_CURRENT);
+
+  for (int i = 1; i < argc; i++)
+    {
+      const char *file = argv[i];
+      int fd = open (file, O_RDONLY);
+      if (fd < 0)
+	error (EXIT_FAILURE, errno, "couldn't open file '%s'", file);
+
+      Elf *elf = elf_begin (fd, ELF_C_READ, NULL);
+      if (elf == NULL)
+	{
+	  printf("%s: elf_begin failed: %s\n", file, elf_errmsg (-1));
+	  close (fd);
+	  continue;
+	}
+
+      const void *build_id;
+      ssize_t len = dwelf_elf_gnu_build_id (elf, &build_id);
+      switch (len)
+	{
+	case 0:
+	  printf ("%s: <no NT_GNU_BUILD_ID note>\n", file);
+	  break;
+	case -1:
+	  errx (1, "dwelf_elf_gnu_build_id (%s): %s",
+		file, elf_errmsg (-1));
+	default:
+	  printf ("%s: build ID: ", file);
+	  const unsigned char *p = build_id;
+	  const unsigned char *end = p + len;
+	  while (p < end)
+	      printf("%02x", (unsigned)*p++);
+	  putchar('\n');
+	}
+
+      elf_end (elf);
+      close (fd);
+    }
+
+  return 0;
+}
diff --git a/tests/run-buildid.sh b/tests/run-buildid.sh
new file mode 100755
index 00000000..31cec24d
--- /dev/null
+++ b/tests/run-buildid.sh
@@ -0,0 +1,38 @@
+#! /bin/sh
+# Copyright (C) 2014 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/>.
+
+. $srcdir/test-subr.sh
+
+# Just some random testfiles, four with, one without build-id,
+# and one without shdrs forcing reading the notes through phdrs.
+# eu-strip --strip-sections -g --output=testfile42_noshdrs testfile42
+# See also run-debugaltlink.sh.
+testfiles testfile42 testfile_multi.dwz testfile-dwzstr.multi \
+    test-offset-loop.alt testfile14 testfile42_noshdrs
+
+testrun_compare  ${abs_builddir}/buildid testfile42 testfile42_noshdrs \
+    testfile_multi.dwz testfile-dwzstr.multi \
+    test-offset-loop.alt testfile14 <<\EOF
+testfile42: build ID: d826d96c4d097bdc5c254b1f7344a907e36b0439
+testfile42_noshdrs: build ID: d826d96c4d097bdc5c254b1f7344a907e36b0439
+testfile_multi.dwz: build ID: a0d6c06e0d912d74033b6fe2808753cae8f6f594
+testfile-dwzstr.multi: build ID: 6da22627dae55c1d62cf9122827c665e240a056b
+test-offset-loop.alt: build ID: 066bbf1a7bc5676f5015ee1966a088f23bdb83ae
+testfile14: <no NT_GNU_BUILD_ID note>
+EOF
+
+exit 0
diff --git a/tests/testfile42_noshdrs.bz2 b/tests/testfile42_noshdrs.bz2
new file mode 100644
index 00000000..e50f7500
--- /dev/null
+++ b/tests/testfile42_noshdrs.bz2