gdb: Add soname to build-id mapping for core files

Since commit aa2d5a422 gdb has been able to read executable and shared
library build-ids within core files.

Expand this functionality so that each core file bfd maintains a map of
soname to build-id for each shared library referenced in the core file.

This feature may be used to verify that gdb has found the correct shared
libraries for core files and to facilitate downloading shared libaries via
debuginfod.

gdb/corelow.c

@@ -282,6 +282,17 @@ core_target::build_file_mappings ()
 
 	/* Set target_section fields.  */
 	m_core_file_mappings.emplace_back (start, end, sec);
+
+	/* If this is a bfd of a shared library, record its soname
+	   and build id.  */
+	if (build_id != nullptr)
+	  {
+	    gdb::unique_xmalloc_ptr<char> soname
+	      = gdb_bfd_read_elf_soname (bfd->filename);
+	    if (soname != nullptr)
+	      set_cbfd_soname_build_id (current_program_space->cbfd,
+					soname.get (), build_id);
+	  }
       });
 
   normalize_mem_ranges (&m_core_unavailable_mappings);

gdb/linux-tdep.c

@@ -44,6 +44,7 @@
 #include "solib-svr4.h"
 
 #include <ctype.h>
+#include <unordered_map>
 
 /* This enum represents the values that the user can choose when
    informing the Linux kernel about which memory mappings will be
@@ -1185,6 +1186,22 @@ linux_read_core_file_mappings
   if (f != descend)
     warning (_("malformed note - filename area is too big"));
 
+  const bfd_build_id *orig_build_id = cbfd->build_id;
+  std::unordered_map<ULONGEST, const bfd_build_id *> vma_map;
+
+  /* Search for solib build-ids in the core file.  Each time one is found,
+     map the start vma of the corresponding elf header to the build-id.  */
+  for (bfd_section *sec = cbfd->sections; sec != nullptr; sec = sec->next)
+    {
+      cbfd->build_id = nullptr;
+
+      if (sec->flags & SEC_LOAD
+	  && (get_elf_backend_data (cbfd)->elf_backend_core_find_build_id
+	       (cbfd, (bfd_vma) sec->filepos)))
+	vma_map[sec->vma] = cbfd->build_id;
+    }
+
+  cbfd->build_id = orig_build_id;
   pre_loop_cb (count);
 
   for (int i = 0; i < count; i++)
@@ -1198,8 +1215,13 @@ linux_read_core_file_mappings
       descdata += addr_size;
       char * filename = filenames;
       filenames += strlen ((char *) filenames) + 1;
+      const bfd_build_id *build_id = nullptr;
+      auto vma_map_it = vma_map.find (start);
 
-      loop_cb (i, start, end, file_ofs, filename, nullptr);
+      if (vma_map_it != vma_map.end ())
+	build_id = vma_map_it->second;
+
+      loop_cb (i, start, end, file_ofs, filename, build_id);
     }
 }
 

gdb/solib.c

@@ -23,6 +23,7 @@
 #include <fcntl.h>
 #include "symtab.h"
 #include "bfd.h"
+#include "build-id.h"
 #include "symfile.h"
 #include "objfiles.h"
 #include "gdbcore.h"
@@ -519,6 +520,55 @@ solib_bfd_open (const char *pathname)
   return abfd;
 }
 
+/* Mapping of a core file's shared library sonames to their respective
+   build-ids.  Added to the registries of core file bfds.  */
+
+typedef std::unordered_map<std::string, std::string> soname_build_id_map;
+
+/* Key used to associate a soname_build_id_map to a core file bfd.  */
+
+static const struct bfd_key<soname_build_id_map> cbfd_soname_build_id_data_key;
+
+/* See solib.h.  */
+
+void
+set_cbfd_soname_build_id (gdb_bfd_ref_ptr abfd,
+			  const char *soname,
+			  const bfd_build_id *build_id)
+{
+  gdb_assert (abfd.get () != nullptr);
+  gdb_assert (soname != nullptr);
+  gdb_assert (build_id != nullptr);
+
+  soname_build_id_map *mapptr = cbfd_soname_build_id_data_key.get (abfd.get ());
+
+  if (mapptr == nullptr)
+    mapptr = cbfd_soname_build_id_data_key.emplace (abfd.get ());
+
+  (*mapptr)[soname] = build_id_to_string (build_id);
+}
+
+/* See solib.h.  */
+
+gdb::unique_xmalloc_ptr<char>
+get_cbfd_soname_build_id (gdb_bfd_ref_ptr abfd, const char *soname)
+{
+  if (abfd.get () == nullptr || soname == nullptr)
+    return {};
+
+  soname_build_id_map *mapptr
+    = cbfd_soname_build_id_data_key.get (abfd.get ());
+
+  if (mapptr == nullptr)
+    return {};
+
+  auto it = mapptr->find (lbasename (soname));
+  if (it == mapptr->end ())
+    return {};
+
+  return make_unique_xstrdup (it->second.c_str ());
+}
+
 /* Given a pointer to one of the shared objects in our list of mapped
    objects, use the recorded name to open a bfd descriptor for the
    object, build a section table, relocate all the section addresses
@@ -1586,6 +1636,43 @@ gdb_bfd_scan_elf_dyntag (const int desired_dyntag, bfd *abfd, CORE_ADDR *ptr,
   return 0;
 }
 
+/* See solib.h.  */
+
+gdb::unique_xmalloc_ptr<char>
+gdb_bfd_read_elf_soname (const char *filename)
+{
+  gdb_bfd_ref_ptr abfd = gdb_bfd_open (filename, gnutarget);
+
+  if (abfd == nullptr)
+    return {};
+
+  /* Check that ABFD is an ET_DYN ELF file.  */
+  if (!bfd_check_format (abfd.get (), bfd_object)
+      || !(bfd_get_file_flags (abfd.get ()) & DYNAMIC))
+    return {};
+
+  CORE_ADDR idx;
+  if (!gdb_bfd_scan_elf_dyntag (DT_SONAME, abfd.get (), &idx, nullptr))
+    return {};
+
+  struct bfd_section *dynstr = bfd_get_section_by_name (abfd.get (), ".dynstr");
+  int sect_size = bfd_section_size (dynstr);
+  if (dynstr == nullptr || sect_size <= idx)
+    return {};
+
+  /* Read soname from the string table.  */
+  gdb::byte_vector dynstr_buf;
+  if (!gdb_bfd_get_full_section_contents (abfd.get (), dynstr, &dynstr_buf))
+    return {};
+
+  /* Ensure soname is null-terminated before returning a copy.  */
+  char *soname = (char *) dynstr_buf.data () + idx;
+  if (strnlen (soname, sect_size - idx) == sect_size - idx)
+    return {};
+
+  return make_unique_xstrdup (soname);
+}
+
 /* Lookup the value for a specific symbol from symbol table.  Look up symbol
    from ABFD.  MATCH_SYM is a callback function to determine whether to pick
    up a symbol.  DATA is the input of this callback function.  Return NULL

gdb/solib.h

@@ -118,6 +118,12 @@ extern CORE_ADDR gdb_bfd_lookup_symbol_from_symtab (bfd *abfd,
 extern int gdb_bfd_scan_elf_dyntag (const int desired_dyntag, bfd *abfd,
 				    CORE_ADDR *ptr, CORE_ADDR *ptr_addr);
 
+/* If FILENAME refers to an ELF shared object then attempt to return the
+   string referred to by its DT_SONAME tag.   */
+
+extern gdb::unique_xmalloc_ptr<char> gdb_bfd_read_elf_soname
+  (const char *filename);
+
 /* Enable or disable optional solib event breakpoints as appropriate.  */
 
 extern void update_solib_breakpoints (void);
@@ -126,4 +132,18 @@ extern void update_solib_breakpoints (void);
 
 extern void handle_solib_event (void);
 
+/* Associate SONAME with BUILD_ID in ABFD's registry so that it can be
+   retrieved with get_cbfd_soname_build_id.  */
+
+extern void set_cbfd_soname_build_id (gdb_bfd_ref_ptr abfd,
+				      const char *soname,
+				      const bfd_build_id *build_id);
+
+/* If SONAME had a build-id associated with it in ABFD's registry by a
+   previous call to set_cbfd_soname_build_id then return the build-id
+   as a NULL-terminated hex string.  */
+
+extern gdb::unique_xmalloc_ptr<char> get_cbfd_soname_build_id
+  (gdb_bfd_ref_ptr abfd, const char *soname);
+
 #endif /* SOLIB_H */