[patch 1/2] build id

[sami wagiaalla <swagiaal at redhat dot com>]

This patch comes from the Fedora rpm and supports the use of build id 
for locating and loading core file executables, and printing information 
about missing debug info files.

I will post the patch in this message and the next message will contain 
my modifications to the patch based on my understanding of it.

Review is greatly appreciated :)


gdb-6.6-buildid-locate.patch


diff --git a/gdb/corelow.c b/gdb/corelow.c
index e138ff2..9948809 100644
--- a/gdb/corelow.c
+++ b/gdb/corelow.c
@@ -47,6 +47,9 @@
 #include "filenames.h"
 #include "progspace.h"
 #include "objfiles.h"
+#include "auxv.h"
+#include "elf/common.h"
+#include "gdbcmd.h"
 
 
 #ifndef O_LARGEFILE
@@ -275,6 +278,52 @@ add_to_thread_list (bfd *abfd, asection *asect, void *reg_sect_arg)
     inferior_ptid = ptid;			 /* Yes, make it current */
 }
 
+static int build_id_core_loads = 1;
+
+static void
+build_id_locate_exec (int from_tty)
+{
+  CORE_ADDR at_entry;
+  struct build_id *build_id;
+  char *exec_filename, *debug_filename;
+  char *build_id_filename;
+  struct cleanup *back_to;
+
+  if (exec_bfd != NULL || symfile_objfile != NULL)
+    return;
+
+  if (target_auxv_search (&current_target, AT_ENTRY, &at_entry) <= 0)
+    return;
+
+  build_id = build_id_addr_get (at_entry);
+  if (build_id == NULL)
+    return;
+
+  /* SYMFILE_OBJFILE should refer to the main executable (not only to its
+     separate debug info file).  gcc44+ keeps .eh_frame only in the main
+     executable without its duplicate .debug_frame in the separate debug info
+     file - such .eh_frame would not be found if SYMFILE_OBJFILE would refer
+     directly to the separate debug info file.  */
+
+  exec_filename = build_id_to_filename (build_id, &build_id_filename, 0);
+  back_to = make_cleanup (xfree, build_id_filename);
+
+  if (exec_filename != NULL)
+    {
+      make_cleanup (xfree, exec_filename);
+      exec_file_attach (exec_filename, from_tty);
+      symbol_file_add_main (exec_filename, from_tty);
+      if (symfile_objfile != NULL)
+        symfile_objfile->flags |= OBJF_BUILD_ID_CORE_LOADED;
+    }
+  else
+    debug_print_missing (_("the main executable file"), build_id_filename);
+
+  do_cleanups (back_to);
+
+  /* No automatic SOLIB_ADD as the libraries would get read twice.  */
+}
+
 /* This routine opens and sets up the core file bfd.  */
 
 static void
@@ -372,6 +421,12 @@ core_open (char *filename, int from_tty)
   push_target (&core_ops);
   discard_cleanups (old_chain);
 
+  /* Find the build_id identifiers.  If it gets executed after
+     POST_CREATE_INFERIOR we would clash with asking to discard the already
+     loaded VDSO symbols.  */
+  if (build_id_core_loads != 0)
+    build_id_locate_exec (from_tty);
+
   /* Do this before acknowledging the inferior, so if
      post_create_inferior throws (can happen easilly if you're loading
      a core file with the wrong exec), we aren't left with threads
@@ -913,4 +968,11 @@ _initialize_corelow (void)
   init_core_ops ();
 
   add_target (&core_ops);
+
+  add_setshow_boolean_cmd ("build-id-core-loads", class_files,
+			   &build_id_core_loads, _("\
+Set whether CORE-FILE loads the build-id associated files automatically."), _("\
+Show whether CORE-FILE loads the build-id associated files automatically.."),
+			   NULL, NULL, NULL,
+			   &setlist, &showlist);
 }
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index ddc711b..cb19edd 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -15237,6 +15237,27 @@ information files.
 
 @end table
 
+You can also adjust the current verbosity of the @dfn{build id} locating.
+
+@table @code
+
+@kindex set build-id-verbose
+@item set build-id-verbose 0
+No additional messages are printed.
+
+@item set build-id-verbose 1
+Missing separate debug filenames are printed.
+
+@item set build-id-verbose 2
+Missing separate debug filenames are printed and also all the parsing of the
+binaries to find their @dfn{build id} content is printed.
+
+@kindex show build-id-verbose
+@item show build-id-verbose
+Show the current verbosity value for the @dfn{build id} content locating.
+
+@end table
+
 @cindex @code{.gnu_debuglink} sections
 @cindex debug link sections
 A debug link is a special section of the executable file named
diff --git a/gdb/elfread.c b/gdb/elfread.c
index 270f93f..903612b 100644
--- a/gdb/elfread.c
+++ b/gdb/elfread.c
@@ -37,6 +37,10 @@
 #include "complaints.h"
 #include "demangle.h"
 #include "psympriv.h"
+#include "libbfd.h"
+#include "gdbcore.h"
+#include "gdbcmd.h"
+#include "observer.h"
 
 extern void _initialize_elfread (void);
 
@@ -572,16 +576,65 @@ elf_symtab_read (struct objfile *objfile, int type,
     }
 }
 
+/* Locate NT_GNU_BUILD_ID and return its matching debug filename.
+   FIXME: NOTE decoding should be unified with the BFD core notes decoding.  */
+
+#define BUILD_ID_VERBOSE_NONE 0
+#define BUILD_ID_VERBOSE_FILENAMES 1
+#define BUILD_ID_VERBOSE_BINARY_PARSE 2
+static int build_id_verbose = BUILD_ID_VERBOSE_FILENAMES;
+static void
+show_build_id_verbose (struct ui_file *file, int from_tty,
+		       struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("Verbosity level of the build-id locator is %s.\n"),
+		    value);
+}
+
 struct build_id
   {
     size_t size;
     gdb_byte data[1];
   };
 
-/* Locate NT_GNU_BUILD_ID from ABFD and return its content.  */
+struct build_id *
+build_id_buf_get (bfd *templ, gdb_byte *buf, bfd_size_type size)
+{
+  bfd_byte *p;
+
+  p = buf;
+  while (p < buf + size)
+    {
+      /* FIXME: bad alignment assumption.  */
+      Elf_External_Note *xnp = (Elf_External_Note *) p;
+      size_t namesz = H_GET_32 (templ, xnp->namesz);
+      size_t descsz = H_GET_32 (templ, xnp->descsz);
+      bfd_byte *descdata = xnp->name + BFD_ALIGN (namesz, 4);
+
+      if (H_GET_32 (templ, xnp->type) == NT_GNU_BUILD_ID
+	  && namesz == sizeof "GNU"
+	  && memcmp (xnp->name, "GNU", sizeof "GNU") == 0)
+	{
+	  size_t size = descsz;
+	  gdb_byte *data = (void *) descdata;
+	  struct build_id *retval;
+
+	  retval = xmalloc (sizeof *retval - 1 + size);
+	  retval->size = size;
+	  memcpy (retval->data, data, size);
+
+	  return retval;
+	}
+      p = descdata + BFD_ALIGN (descsz, 4);
+    }
+  return NULL;
+}
+
+/* Separate debuginfo files have corrupted PHDR but SHDR is correct there.
+   Locate NT_GNU_BUILD_ID from ABFD and return its content.  */
 
 static struct build_id *
-build_id_bfd_get (bfd *abfd)
+build_id_bfd_shdr_get (bfd *abfd)
 {
   struct build_id *retval;
 
@@ -597,6 +650,348 @@ build_id_bfd_get (bfd *abfd)
   return retval;
 }
 
+/* Core files may have missing (corrupt) SHDR but PDHR is correct there.
+   bfd_elf_bfd_from_remote_memory () has too much overhead by
+   allocating/reading all the available ELF PT_LOADs.  */
+
+static struct build_id *
+build_id_phdr_get (bfd *templ, bfd_vma loadbase, unsigned e_phnum,
+		   Elf_Internal_Phdr *i_phdr)
+{
+  int i;
+  struct build_id *retval = NULL;
+
+  for (i = 0; i < e_phnum; i++)
+    if (i_phdr[i].p_type == PT_NOTE && i_phdr[i].p_filesz > 0)
+      {
+	Elf_Internal_Phdr *hdr = &i_phdr[i];
+	gdb_byte *buf;
+	int err;
+
+	buf = xmalloc (hdr->p_filesz);
+	err = target_read_memory (loadbase + i_phdr[i].p_vaddr, buf,
+				  hdr->p_filesz);
+	if (err == 0)
+	  retval = build_id_buf_get (templ, buf, hdr->p_filesz);
+	else
+	  retval = NULL;
+	xfree (buf);
+	if (retval != NULL)
+	  break;
+      }
+  return retval;
+}
+
+/* First we validate the file by reading in the ELF header and checking
+   the magic number.  */
+
+static inline bfd_boolean
+elf_file_p (Elf64_External_Ehdr *x_ehdrp64)
+{
+  gdb_assert (sizeof (Elf64_External_Ehdr) >= sizeof (Elf32_External_Ehdr));
+  gdb_assert (offsetof (Elf64_External_Ehdr, e_ident)
+	      == offsetof (Elf32_External_Ehdr, e_ident));
+  gdb_assert (sizeof (((Elf64_External_Ehdr *) 0)->e_ident)
+	      == sizeof (((Elf32_External_Ehdr *) 0)->e_ident));
+
+  return ((x_ehdrp64->e_ident[EI_MAG0] == ELFMAG0)
+	  && (x_ehdrp64->e_ident[EI_MAG1] == ELFMAG1)
+	  && (x_ehdrp64->e_ident[EI_MAG2] == ELFMAG2)
+	  && (x_ehdrp64->e_ident[EI_MAG3] == ELFMAG3));
+}
+
+/* Translate an ELF file header in external format into an ELF file header in
+   internal format.  */
+
+#define H_GET_WORD(bfd, ptr) (is64 ? H_GET_64 (bfd, (ptr))		\
+				   : H_GET_32 (bfd, (ptr)))
+#define H_GET_SIGNED_WORD(bfd, ptr) (is64 ? H_GET_S64 (bfd, (ptr))	\
+					  : H_GET_S32 (bfd, (ptr)))
+
+static void
+elf_swap_ehdr_in (bfd *abfd,
+		  const Elf64_External_Ehdr *src64,
+		  Elf_Internal_Ehdr *dst)
+{
+  int is64 = bfd_get_arch_size (abfd) == 64;
+#define SRC(field) (is64 ? src64->field \
+			 : ((const Elf32_External_Ehdr *) src64)->field)
+
+  int signed_vma = get_elf_backend_data (abfd)->sign_extend_vma;
+  memcpy (dst->e_ident, SRC (e_ident), EI_NIDENT);
+  dst->e_type = H_GET_16 (abfd, SRC (e_type));
+  dst->e_machine = H_GET_16 (abfd, SRC (e_machine));
+  dst->e_version = H_GET_32 (abfd, SRC (e_version));
+  if (signed_vma)
+    dst->e_entry = H_GET_SIGNED_WORD (abfd, SRC (e_entry));
+  else
+    dst->e_entry = H_GET_WORD (abfd, SRC (e_entry));
+  dst->e_phoff = H_GET_WORD (abfd, SRC (e_phoff));
+  dst->e_shoff = H_GET_WORD (abfd, SRC (e_shoff));
+  dst->e_flags = H_GET_32 (abfd, SRC (e_flags));
+  dst->e_ehsize = H_GET_16 (abfd, SRC (e_ehsize));
+  dst->e_phentsize = H_GET_16 (abfd, SRC (e_phentsize));
+  dst->e_phnum = H_GET_16 (abfd, SRC (e_phnum));
+  dst->e_shentsize = H_GET_16 (abfd, SRC (e_shentsize));
+  dst->e_shnum = H_GET_16 (abfd, SRC (e_shnum));
+  dst->e_shstrndx = H_GET_16 (abfd, SRC (e_shstrndx));
+
+#undef SRC
+}
+
+/* Translate an ELF program header table entry in external format into an
+   ELF program header table entry in internal format.  */
+
+void
+elf_swap_phdr_in (bfd *abfd,
+		  const Elf64_External_Phdr *src64,
+		  Elf_Internal_Phdr *dst)
+{
+  int is64 = bfd_get_arch_size (abfd) == 64;
+#define SRC(field) (is64 ? src64->field					\
+			 : ((const Elf32_External_Phdr *) src64)->field)
+
+  int signed_vma = get_elf_backend_data (abfd)->sign_extend_vma;
+
+  dst->p_type = H_GET_32 (abfd, SRC (p_type));
+  dst->p_flags = H_GET_32 (abfd, SRC (p_flags));
+  dst->p_offset = H_GET_WORD (abfd, SRC (p_offset));
+  if (signed_vma)
+    {
+      dst->p_vaddr = H_GET_SIGNED_WORD (abfd, SRC (p_vaddr));
+      dst->p_paddr = H_GET_SIGNED_WORD (abfd, SRC (p_paddr));
+    }
+  else
+    {
+      dst->p_vaddr = H_GET_WORD (abfd, SRC (p_vaddr));
+      dst->p_paddr = H_GET_WORD (abfd, SRC (p_paddr));
+    }
+  dst->p_filesz = H_GET_WORD (abfd, SRC (p_filesz));
+  dst->p_memsz = H_GET_WORD (abfd, SRC (p_memsz));
+  dst->p_align = H_GET_WORD (abfd, SRC (p_align));
+
+#undef SRC
+}
+
+#undef H_GET_SIGNED_WORD
+#undef H_GET_WORD
+
+static Elf_Internal_Phdr *
+elf_get_phdr (bfd *templ, bfd_vma ehdr_vma, unsigned *e_phnum_pointer,
+              bfd_vma *loadbase_pointer)
+{
+  /* sizeof (Elf64_External_Ehdr) >= sizeof (Elf32_External_Ehdr)  */
+  Elf64_External_Ehdr x_ehdr64;	/* Elf file header, external form */
+  Elf_Internal_Ehdr i_ehdr;	/* Elf file header, internal form */
+  bfd_size_type x_phdrs_size;
+  gdb_byte *x_phdrs_ptr;
+  Elf_Internal_Phdr *i_phdrs;
+  int err;
+  unsigned int i;
+  bfd_vma loadbase;
+  int loadbase_set;
+
+  gdb_assert (templ != NULL);
+  gdb_assert (sizeof (Elf64_External_Ehdr) >= sizeof (Elf32_External_Ehdr));
+
+  /* Read in the ELF header in external format.  */
+  err = target_read_memory (ehdr_vma, (bfd_byte *) &x_ehdr64, sizeof x_ehdr64);
+  if (err)
+    {
+      if (build_id_verbose >= BUILD_ID_VERBOSE_BINARY_PARSE)
+        warning (_("build-id: Error reading ELF header at address 0x%lx"),
+		 (unsigned long) ehdr_vma);
+      return NULL;
+    }
+
+  /* Now check to see if we have a valid ELF file, and one that BFD can
+     make use of.  The magic number must match, the address size ('class')
+     and byte-swapping must match our XVEC entry.  */
+
+  if (! elf_file_p (&x_ehdr64)
+      || x_ehdr64.e_ident[EI_VERSION] != EV_CURRENT
+      || !((bfd_get_arch_size (templ) == 64
+            && x_ehdr64.e_ident[EI_CLASS] == ELFCLASS64)
+           || (bfd_get_arch_size (templ) == 32
+	       && x_ehdr64.e_ident[EI_CLASS] == ELFCLASS32)))
+    {
+      if (build_id_verbose >= BUILD_ID_VERBOSE_BINARY_PARSE)
+        warning (_("build-id: Unrecognized ELF header at address 0x%lx"),
+		 (unsigned long) ehdr_vma);
+      return NULL;
+    }
+
+  /* Check that file's byte order matches xvec's */
+  switch (x_ehdr64.e_ident[EI_DATA])
+    {
+    case ELFDATA2MSB:		/* Big-endian */
+      if (! bfd_header_big_endian (templ))
+	{
+	  if (build_id_verbose >= BUILD_ID_VERBOSE_BINARY_PARSE)
+	    warning (_("build-id: Unrecognized "
+		       "big-endian ELF header at address 0x%lx"),
+		     (unsigned long) ehdr_vma);
+	  return NULL;
+	}
+      break;
+    case ELFDATA2LSB:		/* Little-endian */
+      if (! bfd_header_little_endian (templ))
+	{
+	  if (build_id_verbose >= BUILD_ID_VERBOSE_BINARY_PARSE)
+	    warning (_("build-id: Unrecognized "
+		       "little-endian ELF header at address 0x%lx"),
+		     (unsigned long) ehdr_vma);
+	  return NULL;
+	}
+      break;
+    case ELFDATANONE:		/* No data encoding specified */
+    default:			/* Unknown data encoding specified */
+      if (build_id_verbose >= BUILD_ID_VERBOSE_BINARY_PARSE)
+	warning (_("build-id: Unrecognized "
+		   "ELF header endianity at address 0x%lx"),
+		 (unsigned long) ehdr_vma);
+      return NULL;
+    }
+
+  elf_swap_ehdr_in (templ, &x_ehdr64, &i_ehdr);
+
+  /* The file header tells where to find the program headers.
+     These are what we use to actually choose what to read.  */
+
+  if (i_ehdr.e_phentsize != (bfd_get_arch_size (templ) == 64
+                             ? sizeof (Elf64_External_Phdr)
+			     : sizeof (Elf32_External_Phdr))
+      || i_ehdr.e_phnum == 0)
+    {
+      if (build_id_verbose >= BUILD_ID_VERBOSE_BINARY_PARSE)
+	warning (_("build-id: Invalid ELF program headers from the ELF header "
+		   "at address 0x%lx"), (unsigned long) ehdr_vma);
+      return NULL;
+    }
+
+  x_phdrs_size = (bfd_get_arch_size (templ) == 64 ? sizeof (Elf64_External_Phdr)
+						: sizeof (Elf32_External_Phdr));
+
+  i_phdrs = xmalloc (i_ehdr.e_phnum * (sizeof *i_phdrs + x_phdrs_size));
+  x_phdrs_ptr = (void *) &i_phdrs[i_ehdr.e_phnum];
+  err = target_read_memory (ehdr_vma + i_ehdr.e_phoff, (bfd_byte *) x_phdrs_ptr,
+			    i_ehdr.e_phnum * x_phdrs_size);
+  if (err)
+    {
+      free (i_phdrs);
+      if (build_id_verbose >= BUILD_ID_VERBOSE_BINARY_PARSE)
+        warning (_("build-id: Error reading "
+		   "ELF program headers at address 0x%lx"),
+		 (unsigned long) (ehdr_vma + i_ehdr.e_phoff));
+      return NULL;
+    }
+
+  loadbase = ehdr_vma;
+  loadbase_set = 0;
+  for (i = 0; i < i_ehdr.e_phnum; ++i)
+    {
+      elf_swap_phdr_in (templ, (Elf64_External_Phdr *)
+			       (x_phdrs_ptr + i * x_phdrs_size), &i_phdrs[i]);
+      /* IA-64 vDSO may have two mappings for one segment, where one mapping
+	 is executable only, and one is read only.  We must not use the
+	 executable one (PF_R is the first one, PF_X the second one).  */
+      if (i_phdrs[i].p_type == PT_LOAD && (i_phdrs[i].p_flags & PF_R))
+	{
+	  /* Only the first PT_LOAD segment indicates the file bias.
+	     Next segments may have P_VADDR arbitrarily higher.
+	     If the first segment has P_VADDR zero any next segment must not
+	     confuse us, the first one sets LOADBASE certainly enough.  */
+	  if (!loadbase_set && i_phdrs[i].p_offset == 0)
+	    {
+	      loadbase = ehdr_vma - i_phdrs[i].p_vaddr;
+	      loadbase_set = 1;
+	    }
+	}
+    }
+
+  if (build_id_verbose >= BUILD_ID_VERBOSE_BINARY_PARSE)
+    warning (_("build-id: Found ELF header at address 0x%lx, loadbase 0x%lx"),
+	     (unsigned long) ehdr_vma, (unsigned long) loadbase);
+
+  *e_phnum_pointer = i_ehdr.e_phnum;
+  *loadbase_pointer = loadbase;
+  return i_phdrs;
+}
+
+/* BUILD_ID_ADDR_GET gets ADDR located somewhere in the object.
+   Find the first section before ADDR containing an ELF header.
+   We rely on the fact the sections from multiple files do not mix.
+   FIXME: We should check ADDR is contained _inside_ the section with possibly
+   missing content (P_FILESZ < P_MEMSZ).  These omitted sections are currently
+   hidden by _BFD_ELF_MAKE_SECTION_FROM_PHDR.  */
+
+static CORE_ADDR build_id_addr;
+struct build_id_addr_sect
+  {
+    struct build_id_addr_sect *next;
+    asection *sect;
+  };
+static struct build_id_addr_sect *build_id_addr_sect;
+
+static void build_id_addr_candidate (bfd *abfd, asection *sect, void *obj)
+{
+  if (build_id_addr >= bfd_section_vma (abfd, sect))
+    {
+      struct build_id_addr_sect *candidate;
+
+      candidate = xmalloc (sizeof *candidate);
+      candidate->next = build_id_addr_sect;
+      build_id_addr_sect = candidate;
+      candidate->sect = sect;
+    }
+}
+
+struct build_id *
+build_id_addr_get (CORE_ADDR addr)
+{
+  struct build_id_addr_sect *candidate;
+  struct build_id *retval = NULL;
+  Elf_Internal_Phdr *i_phdr = NULL;
+  bfd_vma loadbase = 0;
+  unsigned e_phnum = 0;
+
+  if (core_bfd == NULL)
+    return NULL;
+
+  build_id_addr = addr;
+  gdb_assert (build_id_addr_sect == NULL);
+  bfd_map_over_sections (core_bfd, build_id_addr_candidate, NULL);
+
+  /* Sections are sorted in the high-to-low VMAs order.
+     Stop the search on the first ELF header we find.
+     Do not continue the search even if it does not contain NT_GNU_BUILD_ID.  */
+
+  for (candidate = build_id_addr_sect; candidate != NULL;
+       candidate = candidate->next)
+    {
+      i_phdr = elf_get_phdr (core_bfd,
+			     bfd_section_vma (core_bfd, candidate->sect),
+			     &e_phnum, &loadbase);
+      if (i_phdr != NULL)
+	break;
+    }
+
+  if (i_phdr != NULL)
+    {
+      retval = build_id_phdr_get (core_bfd, loadbase, e_phnum, i_phdr);
+      xfree (i_phdr);
+    }
+
+  while (build_id_addr_sect != NULL)
+    {
+      candidate = build_id_addr_sect;
+      build_id_addr_sect = candidate->next;
+      xfree (candidate);
+    }
+
+  return retval;
+}
+
 /* Return if FILENAME has NT_GNU_BUILD_ID matching the CHECK value.  */
 
 static int
@@ -611,7 +1006,7 @@ build_id_verify (const char *filename, struct build_id *check)
   if (abfd == NULL)
     return 0;
 
-  found = build_id_bfd_get (abfd);
+  found = build_id_bfd_shdr_get (abfd);
 
   if (found == NULL)
     warning (_("File \"%s\" has no build-id, file skipped"), filename);
@@ -628,14 +1023,16 @@ build_id_verify (const char *filename, struct build_id *check)
   return retval;
 }
 
-static char *
-build_id_to_debug_filename (struct build_id *build_id)
+char *
+build_id_to_filename (struct build_id *build_id, char **link_return,
+		      int add_debug_suffix)
 {
   char *link, *debugdir, *retval = NULL;
+  char *link_all = NULL;
 
   /* DEBUG_FILE_DIRECTORY/.build-id/ab/cdef */
-  link = alloca (strlen (debug_file_directory) + (sizeof "/.build-id/" - 1) + 1
-		 + 2 * build_id->size + (sizeof ".debug" - 1) + 1);
+  link = xmalloc (strlen (debug_file_directory) + (sizeof "/.build-id/" - 1) + 1
+		  + 2 * build_id->size + (sizeof ".debug" - 1) + 1);
 
   /* Keep backward compatibility so that DEBUG_FILE_DIRECTORY being "" will
      cause "/.build-id/..." lookups.  */
@@ -666,7 +1063,10 @@ build_id_to_debug_filename (struct build_id *build_id)
 	*s++ = '/';
       while (size-- > 0)
 	s += sprintf (s, "%02x", (unsigned) *data++);
-      strcpy (s, ".debug");
+      if (add_debug_suffix)
+	strcpy (s, ".debug");
+      else
+	*s = 0;
 
       /* lrealpath() is expensive even for the usually non-existent files.  */
       if (access (link, F_OK) == 0)
@@ -679,26 +1079,201 @@ build_id_to_debug_filename (struct build_id *build_id)
 	}
 
       if (retval != NULL)
-	break;
+	{
+	  /* LINK_ALL is not used below in this non-NULL RETVAL case.  */
+	  break;
+	}
+
+	if (link_all == NULL)
+	  link_all = xstrdup (link);
+	else
+	  {
+	    size_t len_orig = strlen (link_all);
+
+	    link_all = xrealloc (link_all, len_orig + 1 + strlen (link) + 1);
+
+	    /* Use whitespace instead of DIRNAME_SEPARATOR to be compatible with
+	       its possible use as an argument for installation command.  */
+	    link_all[len_orig] = ' ';
+
+	    strcpy (&link_all[len_orig + 1], link);
+	  }
 
       debugdir = debugdir_end;
     }
   while (*debugdir != 0);
 
+  if (link_return != NULL)
+    {
+      if (retval != NULL)
+       {
+         *link_return = link;
+         link = NULL;
+       }
+      else
+       {
+         *link_return = link_all;
+         link_all = NULL;
+       }
+    }
+  xfree (link);
+  xfree (link_all);
+
   return retval;
 }
 
+/* This MISSING_FILEPAIR_HASH tracker is used only for the duplicite messages
+     Try to install the hash file ...
+   avoidance.  */
+
+struct missing_filepair
+  {
+    char *binary;
+    char *debug;
+    char data[1];
+  };
+
+static struct htab *missing_filepair_hash;
+static struct obstack missing_filepair_obstack;
+
+static void *
+missing_filepair_xcalloc (size_t nmemb, size_t nmemb_size)
+{
+  void *retval;
+  size_t size = nmemb * nmemb_size;
+
+  retval = obstack_alloc (&missing_filepair_obstack, size);
+  memset (retval, 0, size);
+  return retval;
+}
+
+static hashval_t
+missing_filepair_hash_func (const struct missing_filepair *elem)
+{
+  hashval_t retval = 0;
+
+  retval ^= htab_hash_string (elem->binary);
+  if (elem->debug != NULL)
+    retval ^= htab_hash_string (elem->debug);
+
+  return retval;
+}
+
+static int
+missing_filepair_eq (const struct missing_filepair *elem1,
+		       const struct missing_filepair *elem2)
+{
+  return strcmp (elem1->binary, elem2->binary) == 0
+         && ((elem1->debug == NULL) == (elem2->debug == NULL))
+         && (elem1->debug == NULL || strcmp (elem1->debug, elem2->debug) == 0);
+}
+
+static void
+missing_filepair_change (void)
+{
+  if (missing_filepair_hash != NULL)
+    {
+      obstack_free (&missing_filepair_obstack, NULL);
+      /* All their memory came just from missing_filepair_OBSTACK.  */
+      missing_filepair_hash = NULL;
+    }
+}
+
+static void
+debug_print_executable_changed (void)
+{
+  missing_filepair_change ();
+}
+
+/* Notify user the file BINARY with (possibly NULL) associated separate debug
+   information file DEBUG is missing.  DEBUG may or may not be the build-id
+   file such as would be:
+     /usr/lib/debug/.build-id/dd/b1d2ce632721c47bb9e8679f369e2295ce71be.debug
+   */
+
+void
+debug_print_missing (const char *binary, const char *debug)
+{
+  size_t binary_len0 = strlen (binary) + 1;
+  size_t debug_len0 = debug ? strlen (debug) + 1 : 0;
+  struct missing_filepair missing_filepair_find;
+  struct missing_filepair *missing_filepair;
+  struct missing_filepair **slot;
+
+  if (build_id_verbose < BUILD_ID_VERBOSE_FILENAMES)
+    return;
+
+  if (missing_filepair_hash == NULL)
+    {
+      obstack_init (&missing_filepair_obstack);
+      missing_filepair_hash = htab_create_alloc (64,
+	(hashval_t (*) (const void *)) missing_filepair_hash_func,
+	(int (*) (const void *, const void *)) missing_filepair_eq, NULL,
+	missing_filepair_xcalloc, NULL);
+    }
+
+  /* Use MISSING_FILEPAIR_FIND first instead of calling obstack_alloc with
+     obstack_free in the case of a (rare) match.  The problem is ALLOC_F for
+     MISSING_FILEPAIR_HASH allocates from MISSING_FILEPAIR_OBSTACK maintenance
+     structures for MISSING_FILEPAIR_HASH.  Calling obstack_free would possibly
+     not to free only MISSING_FILEPAIR but also some such structures (allocated
+     during the htab_find_slot call).  */
+
+  missing_filepair_find.binary = (char *) binary;
+  missing_filepair_find.debug = (char *) debug;
+  slot = (struct missing_filepair **) htab_find_slot (missing_filepair_hash,
+						      &missing_filepair_find,
+						      INSERT);
+
+  /* While it may be still printed duplicitely with the missing debuginfo file
+   * it is due to once printing about the binary file build-id link and once
+   * about the .debug file build-id link as both the build-id symlinks are
+   * located in the debuginfo package.  */
+
+  if (*slot != NULL)
+    return;
+
+  missing_filepair = obstack_alloc (&missing_filepair_obstack,
+				      sizeof (*missing_filepair) - 1
+				      + binary_len0 + debug_len0);
+  missing_filepair->binary = missing_filepair->data;
+  memcpy (missing_filepair->binary, binary, binary_len0);
+  if (debug != NULL)
+    {
+      missing_filepair->debug = missing_filepair->binary + binary_len0;
+      memcpy (missing_filepair->debug, debug, debug_len0);
+    }
+  else
+    missing_filepair->debug = NULL;
+
+  *slot = missing_filepair;
+
+  /* We do not collect and flush these messages as each such message
+     already requires its own separate lines.  */
+
+  fprintf_unfiltered (gdb_stdlog,
+		      _("Missing separate debuginfo for %s\n"), binary);
+  if (debug != NULL)
+    fprintf_unfiltered (gdb_stdlog, _("Try to install the hash file %s\n"),
+			debug);
+}
+
 static char *
-find_separate_debug_file_by_buildid (struct objfile *objfile)
+find_separate_debug_file_by_buildid (struct objfile *objfile,
+				     char **build_id_filename_return)
 {
   struct build_id *build_id;
 
-  build_id = build_id_bfd_get (objfile->obfd);
+  if (build_id_filename_return)
+    *build_id_filename_return = NULL;
+
+  build_id = build_id_bfd_shdr_get (objfile->obfd);
   if (build_id != NULL)
     {
       char *build_id_name;
 
-      build_id_name = build_id_to_debug_filename (build_id);
+      build_id_name = build_id_to_filename (build_id, build_id_filename_return,
+					    1);
       xfree (build_id);
       /* Prevent looping on a stripped .debug file.  */
       if (build_id_name != NULL && strcmp (build_id_name, objfile->name) == 0)
@@ -708,7 +1283,7 @@ find_separate_debug_file_by_buildid (struct objfile *objfile)
 	  xfree (build_id_name);
 	}
       else if (build_id_name != NULL)
-        return build_id_name;
+	return build_id_name;
     }
   return NULL;
 }
@@ -881,9 +1456,10 @@ elf_symfile_read (struct objfile *objfile, int symfile_flags)
      `.gnu_debuglink' may no longer be present with `.note.gnu.build-id'.  */
   if (!objfile_has_partial_symbols (objfile))
     {
-      char *debugfile;
+      char *debugfile, *build_id_filename;
 
-      debugfile = find_separate_debug_file_by_buildid (objfile);
+      debugfile = find_separate_debug_file_by_buildid (objfile,
+						       &build_id_filename);
 
       if (debugfile == NULL)
 	debugfile = find_separate_debug_file_by_debuglink (objfile);
@@ -895,6 +1471,12 @@ elf_symfile_read (struct objfile *objfile, int symfile_flags)
 	  symbol_file_add_separate (abfd, symfile_flags, objfile);
 	  xfree (debugfile);
 	}
+      /* Check if any separate debug info has been extracted out.  */
+      else if (bfd_get_section_by_name (objfile->obfd, ".gnu_debuglink")
+	       != NULL)
+	debug_print_missing (objfile->name, build_id_filename);
+
+      xfree (build_id_filename);
     }
 }
 
@@ -1070,4 +1652,16 @@ void
 _initialize_elfread (void)
 {
   add_symtab_fns (&elf_sym_fns);
+
+  add_setshow_zinteger_cmd ("build-id-verbose", no_class, &build_id_verbose,
+			    _("\
+Set debugging level of the build-id locator."), _("\
+Show debugging level of the build-id locator."), _("\
+Level 1 (default) enables printing the missing debug filenames,\n\
+level 2 also prints the parsing of binaries to find the identificators."),
+			    NULL,
+			    show_build_id_verbose,
+			    &setlist, &showlist);
+
+  observer_attach_executable_changed (debug_print_executable_changed);
 }
diff --git a/gdb/objfiles.h b/gdb/objfiles.h
index 130ae26..f004ff1 100644
--- a/gdb/objfiles.h
+++ b/gdb/objfiles.h
@@ -432,6 +432,10 @@ struct objfile
 
 #define OBJF_USERLOADED	(1 << 3)	/* User loaded */
 
+/* This file was loaded according to the BUILD_ID_CORE_LOADS rules.  */
+
+#define OBJF_BUILD_ID_CORE_LOADED (1 << 12)
+
 /* The object file that contains the runtime common minimal symbols
    for SunOS4. Note that this objfile has no associated BFD.  */
 
diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index db21360..1f40d25 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -1179,9 +1179,49 @@ svr4_current_sos (void)
 		     safe_strerror (errcode));
 	  else
 	    {
-	      strncpy (new->so_name, buffer, SO_NAME_MAX_PATH_SIZE - 1);
-	      new->so_name[SO_NAME_MAX_PATH_SIZE - 1] = '\0';
-	      strcpy (new->so_original_name, new->so_name);
+	      struct build_id *build_id;
+
+	      strncpy (new->so_original_name, buffer, SO_NAME_MAX_PATH_SIZE - 1);
+	      new->so_original_name[SO_NAME_MAX_PATH_SIZE - 1] = '\0';
+	      /* May get overwritten below.  */
+	      strcpy (new->so_name, new->so_original_name);
+
+	      build_id = build_id_addr_get (LM_DYNAMIC_FROM_LINK_MAP (new));
+	      if (build_id != NULL)
+		{
+		  char *name, *build_id_filename;
+
+		  /* Missing the build-id matching separate debug info file
+		     would be handled while SO_NAME gets loaded.  */
+		  name = build_id_to_filename (build_id, &build_id_filename, 0);
+		  if (name != NULL)
+		    {
+		      strncpy (new->so_name, name, SO_NAME_MAX_PATH_SIZE - 1);
+		      new->so_name[SO_NAME_MAX_PATH_SIZE - 1] = '\0';
+		      xfree (name);
+		    }
+		  else
+		    {
+		      debug_print_missing (new->so_name, build_id_filename);
+
+		      /* In the case the main executable was found according to
+			 its build-id (from a core file) prevent loading
+			 a different build of a library with accidentally the
+			 same SO_NAME.
+
+			 It suppresses bogus backtraces (and prints "??" there
+			 instead) if the on-disk files no longer match the
+			 running program version.  */
+
+		      if (symfile_objfile != NULL
+			  && (symfile_objfile->flags
+			      & OBJF_BUILD_ID_CORE_LOADED) != 0)
+			new->so_name[0] = 0;
+		    }
+
+		  xfree (build_id_filename);
+		  xfree (build_id);
+		}
 	    }
 	  xfree (buffer);
 
diff --git a/gdb/symfile.h b/gdb/symfile.h
index c9f4e65..0df6883 100644
--- a/gdb/symfile.h
+++ b/gdb/symfile.h
@@ -546,6 +546,13 @@ void free_symfile_segment_data (struct symfile_segment_data *data);
 
 extern struct cleanup *increment_reading_symtab (void);
 
+/* build-id support.  */
+struct build_id;
+extern struct build_id *build_id_addr_get (CORE_ADDR addr);
+extern char *build_id_to_filename (struct build_id *build_id,
+				   char **link_return, int add_debug_suffix);
+extern void debug_print_missing (const char *binary, const char *debug);
+
 /* From dwarf2read.c */
 
 extern int dwarf2_has_info (struct objfile *);
diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index 63e68d3..6ff682a 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -1349,6 +1349,16 @@ proc default_gdb_start { } {
 	    warning "Couldn't set the width to 0."
 	}
     }
+    # Turn off the missing warnings as the testsuite does not expect it.
+    send_gdb "set build-id-verbose 0\n"
+    gdb_expect 10 {
+	-re "$gdb_prompt $" {
+	    verbose "Disabled the missing debug infos warnings." 2
+	}
+	timeout {
+	    warning "Could not disable the missing debug infos warnings.."
+	}
+    }
     return 0;
 }
 
diff --git a/gdb/testsuite/lib/mi-support.exp b/gdb/testsuite/lib/mi-support.exp
index 5de3183..2c046f7 100644
--- a/gdb/testsuite/lib/mi-support.exp
+++ b/gdb/testsuite/lib/mi-support.exp
@@ -221,6 +221,16 @@ proc default_mi_gdb_start { args } {
 	    }
     	}
     }
+    # Turn off the missing warnings as the testsuite does not expect it.
+    send_gdb "190-gdb-set build-id-verbose 0\n"
+    gdb_expect 10 {
+	-re ".*190-gdb-set build-id-verbose 0\r\n190\\\^done\r\n$mi_gdb_prompt$" {
+	    verbose "Disabled the missing debug infos warnings." 2
+	}
+	timeout {
+	    warning "Could not disable the missing debug infos warnings.."
+	}
+    }
 
     detect_async