gdb: unify parts of the Linux and FreeBSD core dumping code

While reviewing the Linux and FreeBSD core dumping code within GDB for
another patch series, I noticed that the code that collects the
registers for each thread and writes these into ELF note format is
basically identical between Linux and FreeBSD.

This commit merges this code and moves it into a new file gcore-elf.c.

The function find_signalled_thread is moved from linux-tdep.c to
gcore.c despite not being shared.  A later commit will make use of
this function.

I did merge, and then revert a previous version of this patch (commit
82a1fd3a4935 for the original patch and 03642b7189bc for the revert).
The problem with the original patch is that it introduced a
unconditional dependency between GDB and some ELF specific functions
in the BFD library, e.g. elfcore_write_prstatus and
elfcore_write_register_note.  It was pointed out in this mailing list
post:

  https://sourceware.org/pipermail/gdb-patches/2021-February/175750.html

that this change was breaking any build of GDB for non-ELF targets.
To confirm this breakage, and to test this new version of GDB I
configured and built for the target x86_64-apple-darwin20.3.0.

Where the previous version of this patch placed all of the common code
into gcore.c, which is included in all builds of GDB, this new patch
only places non-ELF specific generic code (i.e. find_signalled_thread)
into gcore.c, the ELF specific code is put into the new gcore-elf.c
file, which is only included in GDB if BFD has ELF support.

The contents of gcore-elf.c are referenced unconditionally from
linux-tdep.c and fbsd-tdep.c, this is fine, we previously always
assumed that these two targets required ELF support, and we continue
to make that assumption after this patch; nothing has changed there.

With my previous version of this patch the darwin target mentioned
above failed to build, but with the new version, the target builds
fine.

There are a couple of minor changes to the FreeBSD target after this
commit, but I believe that these are changes for the better:

(1) For FreeBSD we always used to record the thread-id in the core
file by using ptid_t.lwp ().  In contrast the Linux code did this:

    /* For remote targets the LWP may not be available, so use the TID.  */
    long lwp = ptid.lwp ();
    if (lwp == 0)
      lwp = ptid.tid ();

Both target now do this:

    /* The LWP is often not available for bare metal target, in which case
       use the tid instead.  */
    if (ptid.lwp_p ())
      lwp = ptid.lwp ();
    else
      lwp = ptid.tid ();

Which is equivalent for Linux, but is a change for FreeBSD.  I think
that all this means is that in some cases where GDB might have
previously recorded a thread-id of 0 for each thread, we might now get
something more useful.

(2) When collecting the registers for Linux we collected into a zero
initialised buffer.  By contrast on FreeBSD the buffer is left
uninitialised.  In the new code the buffer is always zero initialised.
I suspect once the registers are copied into the buffer there's
probably no gaps left so this makes no difference, but if it does then
using zeros rather than random bits of GDB's memory is probably a good
thing.

Otherwise, there should be no other user visible changes after this
commit.

Tested this on x86-64/GNU-Linux and x86-64/FreeBSD-12.2 with no
regressions.

gdb/ChangeLog:

	* Makefile.in (SFILES): Add gcore-elf.c.
	(HFILES_NO_SRCDIR): Add gcore-elf.h
	* configure: Regenerate.
	* configure.ac: Add gcore-elf.o to CONFIG_OBS if we have ELF
	support.
	* fbsd-tdep.c: Add 'gcore-elf.h' include.
	(struct fbsd_collect_regset_section_cb_data): Delete.
	(fbsd_collect_regset_section_cb): Delete.
	(fbsd_collect_thread_registers): Delete.
	(struct fbsd_corefile_thread_data): Delete.
	(fbsd_corefile_thread): Delete.
	(fbsd_make_corefile_notes): Call
	gcore_elf_build_thread_register_notes instead of the now deleted
	FreeBSD code.
	* gcore-elf.c: New file, the content was moved here from
	linux-tdep.c, functions were renamed and given minor cleanup.
	* gcore-elf.h: New file.
	* gcore.c (gcore_find_signalled_thread): Moved here from
	linux-tdep.c and given a new name.  Minor cleanups.
	* gcore.h (gcore_find_signalled_thread): Declare.
	* linux-tdep.c: Add 'gcore.h' and 'gcore-elf.h' includes.
	(struct linux_collect_regset_section_cb_data): Delete.
	(linux_collect_regset_section_cb): Delete.
	(linux_collect_thread_registers): Delete.
	(linux_corefile_thread): Call
	gcore_elf_build_thread_register_notes.
	(find_signalled_thread): Delete.
	(linux_make_corefile_notes): Call gcore_find_signalled_thread.

10 files changed, 255 insertions, 264 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index cfdf530..6d2d390 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,34 @@
+2021-03-05  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* Makefile.in (SFILES): Add gcore-elf.c.
+	(HFILES_NO_SRCDIR): Add gcore-elf.h
+	* configure: Regenerate.
+	* configure.ac: Add gcore-elf.o to CONFIG_OBS if we have ELF
+	support.
+	* fbsd-tdep.c: Add 'gcore-elf.h' include.
+	(struct fbsd_collect_regset_section_cb_data): Delete.
+	(fbsd_collect_regset_section_cb): Delete.
+	(fbsd_collect_thread_registers): Delete.
+	(struct fbsd_corefile_thread_data): Delete.
+	(fbsd_corefile_thread): Delete.
+	(fbsd_make_corefile_notes): Call
+	gcore_elf_build_thread_register_notes instead of the now deleted
+	FreeBSD code.
+	* gcore-elf.c: New file, the content was moved here from
+	linux-tdep.c, functions were renamed and given minor cleanup.
+	* gcore-elf.h: New file.
+	* gcore.c (gcore_find_signalled_thread): Moved here from
+	linux-tdep.c and given a new name.  Minor cleanups.
+	* gcore.h (gcore_find_signalled_thread): Declare.
+	* linux-tdep.c: Add 'gcore.h' and 'gcore-elf.h' includes.
+	(struct linux_collect_regset_section_cb_data): Delete.
+	(linux_collect_regset_section_cb): Delete.
+	(linux_collect_thread_registers): Delete.
+	(linux_corefile_thread): Call
+	gcore_elf_build_thread_register_notes.
+	(find_signalled_thread): Delete.
+	(linux_make_corefile_notes): Call gcore_find_signalled_thread.
+
 2021-03-04  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	PR gdb/27147
diff --git a/gdb/Makefile.in b/gdb/Makefile.in
index ae89b85..cf5017e 100644
--- a/gdb/Makefile.in
+++ b/gdb/Makefile.in
@@ -1191,6 +1191,7 @@ SFILES = \
 	dtrace-probe.c \
 	elfread.c \
 	f-exp.y \
+	gcore-elf.c \
 	gdb.c \
 	go-exp.y \
 	m2-exp.y \
@@ -1292,6 +1293,7 @@ HFILES_NO_SRCDIR = \
 	frame-unwind.h \
 	frv-tdep.h \
 	ft32-tdep.h \
+	gcore-elf.h \
 	gcore.h \
 	gdb_bfd.h \
 	gdb_curses.h \
diff --git a/gdb/configure b/gdb/configure
index 51b4d19..4707fd0 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -17264,7 +17264,7 @@ $as_echo "$gdb_cv_var_elf" >&6; }
   LDFLAGS=$OLD_LDFLAGS
   LIBS=$OLD_LIBS
 if test "$gdb_cv_var_elf" = yes; then
-  CONFIG_OBS="$CONFIG_OBS elfread.o stap-probe.o dtrace-probe.o"
+  CONFIG_OBS="$CONFIG_OBS elfread.o stap-probe.o dtrace-probe.o gcore-elf.o"
 
 $as_echo "#define HAVE_ELF 1" >>confdefs.h
 
diff --git a/gdb/configure.ac b/gdb/configure.ac
index 618c591..db765af 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -1882,7 +1882,7 @@ WIN32LIBS="$WIN32LIBS $WIN32APILIBS"
 GDB_AC_CHECK_BFD([for ELF support in BFD], gdb_cv_var_elf,
                  [bfd_get_elf_phdr_upper_bound (NULL)], elf-bfd.h)
 if test "$gdb_cv_var_elf" = yes; then
-  CONFIG_OBS="$CONFIG_OBS elfread.o stap-probe.o dtrace-probe.o"
+  CONFIG_OBS="$CONFIG_OBS elfread.o stap-probe.o dtrace-probe.o gcore-elf.o"
   AC_DEFINE(HAVE_ELF, 1,
 	    [Define if ELF support should be included.])
   # -ldl is provided by bfd/Makfile.am (LIBDL) <PLUGINS>.
diff --git a/gdb/fbsd-tdep.c b/gdb/fbsd-tdep.c
index cc51e92..dc4278c 100644
--- a/gdb/fbsd-tdep.c
+++ b/gdb/fbsd-tdep.c
@@ -32,6 +32,7 @@
 
 #include "elf-bfd.h"
 #include "fbsd-tdep.h"
+#include "gcore-elf.h"
 
 /* This enum is derived from FreeBSD's <sys/signal.h>.  */
 
@@ -583,129 +584,6 @@ find_signalled_thread (struct thread_info *info, void *data)
   return 0;
 }
 
-/* Structure for passing information from
-   fbsd_collect_thread_registers via an iterator to
-   fbsd_collect_regset_section_cb. */
-
-struct fbsd_collect_regset_section_cb_data
-{
-  fbsd_collect_regset_section_cb_data (const struct regcache *regcache,
-				       bfd *obfd,
-				       gdb::unique_xmalloc_ptr<char> &note_data,
-				       int *note_size,
-				       unsigned long lwp,
-				       gdb_signal stop_signal)
-    : regcache (regcache),
-      obfd (obfd),
-      note_data (note_data),
-      note_size (note_size),
-      lwp (lwp),
-      stop_signal (stop_signal)
-  {}
-
-  const struct regcache *regcache;
-  bfd *obfd;
-  gdb::unique_xmalloc_ptr<char> &note_data;
-  int *note_size;
-  unsigned long lwp;
-  enum gdb_signal stop_signal;
-  bool abort_iteration = false;
-};
-
-static void
-fbsd_collect_regset_section_cb (const char *sect_name, int supply_size,
-				int collect_size, const struct regset *regset,
-				const char *human_name, void *cb_data)
-{
-  char *buf;
-  struct fbsd_collect_regset_section_cb_data *data
-    = (struct fbsd_collect_regset_section_cb_data *) cb_data;
-
-  if (data->abort_iteration)
-    return;
-
-  gdb_assert (regset->collect_regset);
-
-  buf = (char *) xmalloc (collect_size);
-  regset->collect_regset (regset, data->regcache, -1, buf, collect_size);
-
-  /* PRSTATUS still needs to be treated specially.  */
-  if (strcmp (sect_name, ".reg") == 0)
-    data->note_data.reset (elfcore_write_prstatus
-			     (data->obfd, data->note_data.release (),
-			      data->note_size, data->lwp,
-			      gdb_signal_to_host (data->stop_signal),
-			      buf));
-  else
-    data->note_data.reset (elfcore_write_register_note
-			     (data->obfd, data->note_data.release (),
-			      data->note_size, sect_name, buf,
-			      collect_size));
-  xfree (buf);
-
-  if (data->note_data == NULL)
-    data->abort_iteration = true;
-}
-
-/* Records the thread's register state for the corefile note
-   section.  */
-
-static void
-fbsd_collect_thread_registers (const struct regcache *regcache,
-			       ptid_t ptid, bfd *obfd,
-			       gdb::unique_xmalloc_ptr<char> &note_data,
-			       int *note_size,
-			       enum gdb_signal stop_signal)
-{
-  fbsd_collect_regset_section_cb_data data (regcache, obfd, note_data,
-					    note_size, ptid.lwp (),
-					    stop_signal);
-
-  gdbarch_iterate_over_regset_sections (regcache->arch (),
-					fbsd_collect_regset_section_cb,
-					&data, regcache);
-}
-
-struct fbsd_corefile_thread_data
-{
-  fbsd_corefile_thread_data (struct gdbarch *gdbarch,
-			     bfd *obfd,
-			     gdb::unique_xmalloc_ptr<char> &note_data,
-			     int *note_size,
-			     gdb_signal stop_signal)
-    : gdbarch (gdbarch),
-      obfd (obfd),
-      note_data (note_data),
-      note_size (note_size),
-      stop_signal (stop_signal)
-  {}
-
-  struct gdbarch *gdbarch;
-  bfd *obfd;
-  gdb::unique_xmalloc_ptr<char> &note_data;
-  int *note_size;
-  enum gdb_signal stop_signal;
-};
-
-/* Records the thread's register state for the corefile note
-   section.  */
-
-static void
-fbsd_corefile_thread (struct thread_info *info,
-		      struct fbsd_corefile_thread_data *args)
-{
-  struct regcache *regcache;
-
-  regcache = get_thread_arch_regcache (info->inf->process_target (),
-				       info->ptid, args->gdbarch);
-
-  target_fetch_registers (regcache, -1);
-
-  fbsd_collect_thread_registers (regcache, info->ptid, args->obfd,
-				 args->note_data, args->note_size,
-				 args->stop_signal);
-}
-
 /* Return a byte_vector containing the contents of a core dump note
    for the target object of type OBJECT.  If STRUCTSIZE is non-zero,
    the data is prefixed with a 32-bit integer size to match the format
@@ -782,16 +660,16 @@ fbsd_make_corefile_notes (struct gdbarch *gdbarch, bfd *obfd, int *note_size)
 	signalled_thr = curr_thr;
     }
 
-  fbsd_corefile_thread_data thread_args (gdbarch, obfd, note_data, note_size,
-					 signalled_thr->suspend.stop_signal);
-
-  fbsd_corefile_thread (signalled_thr, &thread_args);
+  enum gdb_signal stop_signal = signalled_thr->suspend.stop_signal;
+  gcore_elf_build_thread_register_notes (gdbarch, signalled_thr, stop_signal,
+					 obfd, &note_data, note_size);
   for (thread_info *thr : current_inferior ()->non_exited_threads ())
     {
       if (thr == signalled_thr)
 	continue;
 
-      fbsd_corefile_thread (thr, &thread_args);
+      gcore_elf_build_thread_register_notes (gdbarch, thr, stop_signal,
+					     obfd, &note_data, note_size);
     }
 
   /* Auxiliary vector.  */
diff --git a/gdb/gcore-elf.c b/gdb/gcore-elf.c
new file mode 100644
index 0000000..b0fb808
--- /dev/null
+++ b/gdb/gcore-elf.c
@@ -0,0 +1,136 @@
+/* Copyright (C) 2021 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program 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.
+
+   This program 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 "defs.h"
+#include "gcore-elf.h"
+#include "elf-bfd.h"
+#include "target.h"
+#include "regcache.h"
+#include "gdbarch.h"
+#include "gdbthread.h"
+#include "inferior.h"
+#include "regset.h"
+
+/* Structure for passing information from GCORE_COLLECT_THREAD_REGISTERS
+   via an iterator to GCORE_COLLECT_REGSET_SECTION_CB. */
+
+struct gcore_elf_collect_regset_section_cb_data
+{
+  gcore_elf_collect_regset_section_cb_data
+	(struct gdbarch *gdbarch, const struct regcache *regcache,
+	 bfd *obfd, ptid_t ptid, gdb_signal stop_signal,
+	 gdb::unique_xmalloc_ptr<char> *note_data, int *note_size)
+    : gdbarch (gdbarch), regcache (regcache), obfd (obfd),
+      note_data (note_data), note_size (note_size),
+      stop_signal (stop_signal)
+  {
+    /* The LWP is often not available for bare metal target, in which case
+       use the tid instead.  */
+    if (ptid.lwp_p ())
+      lwp = ptid.lwp ();
+    else
+      lwp = ptid.tid ();
+  }
+
+  struct gdbarch *gdbarch;
+  const struct regcache *regcache;
+  bfd *obfd;
+  gdb::unique_xmalloc_ptr<char> *note_data;
+  int *note_size;
+  unsigned long lwp;
+  enum gdb_signal stop_signal;
+  bool abort_iteration = false;
+};
+
+/* Callback for ITERATE_OVER_REGSET_SECTIONS that records a single
+   regset in the core file note section.  */
+
+static void
+gcore_elf_collect_regset_section_cb (const char *sect_name,
+				     int supply_size, int collect_size,
+				     const struct regset *regset,
+				     const char *human_name, void *cb_data)
+{
+  struct gcore_elf_collect_regset_section_cb_data *data
+    = (struct gcore_elf_collect_regset_section_cb_data *) cb_data;
+  bool variable_size_section = (regset != nullptr
+				&& regset->flags & REGSET_VARIABLE_SIZE);
+
+  gdb_assert (variable_size_section || supply_size == collect_size);
+
+  if (data->abort_iteration)
+    return;
+
+  gdb_assert (regset != nullptr && regset->collect_regset != nullptr);
+
+  /* This is intentionally zero-initialized by using std::vector, so
+     that any padding bytes in the core file will show as 0.  */
+  std::vector<gdb_byte> buf (collect_size);
+
+  regset->collect_regset (regset, data->regcache, -1, buf.data (),
+			  collect_size);
+
+  /* PRSTATUS still needs to be treated specially.  */
+  if (strcmp (sect_name, ".reg") == 0)
+    data->note_data->reset (elfcore_write_prstatus
+			    (data->obfd, data->note_data->release (),
+			     data->note_size, data->lwp,
+			     gdb_signal_to_host (data->stop_signal),
+			     buf.data ()));
+  else
+    data->note_data->reset (elfcore_write_register_note
+			    (data->obfd, data->note_data->release (),
+			     data->note_size, sect_name, buf.data (),
+			     collect_size));
+
+  if (*data->note_data == nullptr)
+    data->abort_iteration = true;
+}
+
+/* Records the register state of thread PTID out of REGCACHE into the note
+   buffer represented by *NOTE_DATA and NOTE_SIZE.  OBFD is the bfd into
+   which the core file is being created, and STOP_SIGNAL is the signal that
+   cause thread PTID to stop.  */
+
+static void
+gcore_elf_collect_thread_registers
+	(const struct regcache *regcache, ptid_t ptid, bfd *obfd,
+	 gdb::unique_xmalloc_ptr<char> *note_data, int *note_size,
+	 enum gdb_signal stop_signal)
+{
+  struct gdbarch *gdbarch = regcache->arch ();
+  gcore_elf_collect_regset_section_cb_data data (gdbarch, regcache, obfd,
+						 ptid, stop_signal,
+						 note_data, note_size);
+  gdbarch_iterate_over_regset_sections
+    (gdbarch, gcore_elf_collect_regset_section_cb, &data, regcache);
+}
+
+/* See gcore-elf.h.  */
+
+void
+gcore_elf_build_thread_register_notes
+  (struct gdbarch *gdbarch, struct thread_info *info, gdb_signal stop_signal,
+   bfd *obfd, gdb::unique_xmalloc_ptr<char> *note_data, int *note_size)
+{
+  struct regcache *regcache
+    = get_thread_arch_regcache (info->inf->process_target (),
+				info->ptid, gdbarch);
+  target_fetch_registers (regcache, -1);
+  gcore_elf_collect_thread_registers (regcache, info->ptid, obfd,
+				      note_data, note_size, stop_signal);
+}
diff --git a/gdb/gcore-elf.h b/gdb/gcore-elf.h
new file mode 100644
index 0000000..d667686
--- /dev/null
+++ b/gdb/gcore-elf.h
@@ -0,0 +1,39 @@
+/* Copyright (C) 2021 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program 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.
+
+   This program 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/>.  */
+
+/* This file contains generic functions for writing ELF based core files.  */
+
+#if !defined (GCORE_ELF_H)
+#define GCORE_ELF_H 1
+
+#include "gdb_bfd.h"
+#include "gdbsupport/gdb_signals.h"
+#include "gcore.h"
+
+struct gdbarch;
+struct thread_info;
+
+/* Add content to *NOTE_DATA (and update *NOTE_SIZE) to describe the
+   registers of thread INFO.  Report the thread as having stopped with
+   STOP_SIGNAL.  The core file is being written to OBFD, and GDBARCH is the
+   architecture for which the core file is being generated.  */
+
+extern void gcore_elf_build_thread_register_notes
+  (struct gdbarch *gdbarch, struct thread_info *info, gdb_signal stop_signal,
+   bfd *obfd, gdb::unique_xmalloc_ptr<char> *note_data, int *note_size);
+
+#endif /* GCORE_ELF_H */
diff --git a/gdb/gcore.c b/gdb/gcore.c
index 73ac6b0..3b90253 100644
--- a/gdb/gcore.c
+++ b/gdb/gcore.c
@@ -579,6 +579,27 @@ gcore_memory_sections (bfd *obfd)
   return 1;
 }
 
+/* See gcore.h.  */
+
+thread_info *
+gcore_find_signalled_thread ()
+{
+  thread_info *curr_thr = inferior_thread ();
+  if (curr_thr->state != THREAD_EXITED
+      && curr_thr->suspend.stop_signal != GDB_SIGNAL_0)
+    return curr_thr;
+
+  for (thread_info *thr : current_inferior ()->non_exited_threads ())
+    if (thr->suspend.stop_signal != GDB_SIGNAL_0)
+      return thr;
+
+  /* Default to the current thread, unless it has exited.  */
+  if (curr_thr->state != THREAD_EXITED)
+    return curr_thr;
+
+  return nullptr;
+}
+
 void _initialize_gcore ();
 void
 _initialize_gcore ()
diff --git a/gdb/gcore.h b/gdb/gcore.h
index af37ff3..7e8e316 100644
--- a/gdb/gcore.h
+++ b/gdb/gcore.h
@@ -22,10 +22,19 @@
 
 #include "gdb_bfd.h"
 
+struct thread_info;
+
 extern gdb_bfd_ref_ptr create_gcore_bfd (const char *filename);
 extern void write_gcore_file (bfd *obfd);
 extern int objfile_find_memory_regions (struct target_ops *self,
 					find_memory_region_ftype func,
 					void *obfd);
 
+/* Find the signalled thread.  In case there's more than one signalled
+   thread, prefer the current thread, if it is signalled.  If no thread was
+   signalled, default to the current thread, unless it has exited, in which
+   case return NULL.  */
+
+extern thread_info *gcore_find_signalled_thread ();
+
 #endif /* GCORE_H */
diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
index e9f8e1b..5bfd82d 100644
--- a/gdb/linux-tdep.c
+++ b/gdb/linux-tdep.c
@@ -39,6 +39,8 @@
 #include "gdb_regex.h"
 #include "gdbsupport/enum-flags.h"
 #include "gdbsupport/gdb_optional.h"
+#include "gcore.h"
+#include "gcore-elf.h"
 
 #include <ctype.h>
 
@@ -1597,104 +1599,6 @@ linux_make_mappings_corefile_notes (struct gdbarch *gdbarch, bfd *obfd,
     }
 }
 
-/* Structure for passing information from
-   linux_collect_thread_registers via an iterator to
-   linux_collect_regset_section_cb. */
-
-struct linux_collect_regset_section_cb_data
-{
-  linux_collect_regset_section_cb_data (struct gdbarch *gdbarch,
-					const struct regcache *regcache,
-					bfd *obfd,
-					gdb::unique_xmalloc_ptr<char> &note_data,
-					int *note_size,
-					unsigned long lwp,
-					gdb_signal stop_signal)
-    : gdbarch (gdbarch), regcache (regcache), obfd (obfd),
-      note_data (note_data), note_size (note_size), lwp (lwp),
-      stop_signal (stop_signal)
-  {}
-
-  struct gdbarch *gdbarch;
-  const struct regcache *regcache;
-  bfd *obfd;
-  gdb::unique_xmalloc_ptr<char> &note_data;
-  int *note_size;
-  unsigned long lwp;
-  enum gdb_signal stop_signal;
-  bool abort_iteration = false;
-};
-
-/* Callback for iterate_over_regset_sections that records a single
-   regset in the corefile note section.  */
-
-static void
-linux_collect_regset_section_cb (const char *sect_name, int supply_size,
-				 int collect_size, const struct regset *regset,
-				 const char *human_name, void *cb_data)
-{
-  struct linux_collect_regset_section_cb_data *data
-    = (struct linux_collect_regset_section_cb_data *) cb_data;
-  bool variable_size_section = (regset != NULL
-				&& regset->flags & REGSET_VARIABLE_SIZE);
-
-  if (!variable_size_section)
-    gdb_assert (supply_size == collect_size);
-
-  if (data->abort_iteration)
-    return;
-
-  gdb_assert (regset && regset->collect_regset);
-
-  /* This is intentionally zero-initialized by using std::vector, so
-     that any padding bytes in the core file will show as 0.  */
-  std::vector<gdb_byte> buf (collect_size);
-
-  regset->collect_regset (regset, data->regcache, -1, buf.data (),
-			  collect_size);
-
-  /* PRSTATUS still needs to be treated specially.  */
-  if (strcmp (sect_name, ".reg") == 0)
-    data->note_data.reset (elfcore_write_prstatus
-			     (data->obfd, data->note_data.release (),
-			      data->note_size, data->lwp,
-			      gdb_signal_to_host (data->stop_signal),
-			      buf.data ()));
-  else
-    data->note_data.reset (elfcore_write_register_note
-			   (data->obfd, data->note_data.release (),
-			    data->note_size, sect_name, buf.data (),
-			    collect_size));
-
-  if (data->note_data == NULL)
-    data->abort_iteration = true;
-}
-
-/* Records the thread's register state for the corefile note
-   section.  */
-
-static void
-linux_collect_thread_registers (const struct regcache *regcache,
-				ptid_t ptid, bfd *obfd,
-				gdb::unique_xmalloc_ptr<char> &note_data,
-				int *note_size,
-				enum gdb_signal stop_signal)
-{
-  struct gdbarch *gdbarch = regcache->arch ();
-
-  /* For remote targets the LWP may not be available, so use the TID.  */
-  long lwp = ptid.lwp ();
-  if (lwp == 0)
-    lwp = ptid.tid ();
-
-  linux_collect_regset_section_cb_data data (gdbarch, regcache, obfd, note_data,
-					     note_size, lwp, stop_signal);
-
-  gdbarch_iterate_over_regset_sections (gdbarch,
-					linux_collect_regset_section_cb,
-					&data, regcache);
-}
-
 /* Fetch the siginfo data for the specified thread, if it exists.  If
    there is no data, or we could not read it, return an empty
    buffer.  */
@@ -1746,22 +1650,17 @@ static void
 linux_corefile_thread (struct thread_info *info,
 		       struct linux_corefile_thread_data *args)
 {
-  struct regcache *regcache;
-
-  regcache = get_thread_arch_regcache (info->inf->process_target (),
-				       info->ptid, args->gdbarch);
-
-  target_fetch_registers (regcache, -1);
-  gdb::byte_vector siginfo_data = linux_get_siginfo_data (info, args->gdbarch);
-
-  linux_collect_thread_registers (regcache, info->ptid, args->obfd,
-				  args->note_data, args->note_size,
-				  args->stop_signal);
+  gcore_elf_build_thread_register_notes (args->gdbarch, info,
+					 args->stop_signal,
+					 args->obfd, &args->note_data,
+					 args->note_size);
 
   /* Don't return anything if we got no register information above,
      such a core file is useless.  */
   if (args->note_data != NULL)
     {
+      gdb::byte_vector siginfo_data
+	= linux_get_siginfo_data (info, args->gdbarch);
       if (!siginfo_data.empty ())
 	args->note_data.reset (elfcore_write_note (args->obfd,
 						   args->note_data.release (),
@@ -1960,30 +1859,6 @@ linux_fill_prpsinfo (struct elf_internal_linux_prpsinfo *p)
   return 1;
 }
 
-/* Find the signalled thread.  In case there's more than one signalled
-   thread, prefer the current thread, if it is signalled.  If no
-   thread was signalled, default to the current thread, unless it has
-   exited, in which case return NULL.  */
-
-static thread_info *
-find_signalled_thread ()
-{
-  thread_info *curr_thr = inferior_thread ();
-  if (curr_thr->state != THREAD_EXITED
-      && curr_thr->suspend.stop_signal != GDB_SIGNAL_0)
-    return curr_thr;
-
-  for (thread_info *thr : current_inferior ()->non_exited_threads ())
-    if (thr->suspend.stop_signal != GDB_SIGNAL_0)
-      return thr;
-
-  /* Default to the current thread, unless it has exited.  */
-  if (curr_thr->state != THREAD_EXITED)
-    return curr_thr;
-
-  return nullptr;
-}
-
 /* Build the note section for a corefile, and return it in a malloc
    buffer.  */
 
@@ -2021,7 +1896,7 @@ linux_make_corefile_notes (struct gdbarch *gdbarch, bfd *obfd, int *note_size)
   /* Like the kernel, prefer dumping the signalled thread first.
      "First thread" is what tools use to infer the signalled
      thread.  */
-  thread_info *signalled_thr = find_signalled_thread ();
+  thread_info *signalled_thr = gcore_find_signalled_thread ();
   gdb_signal stop_signal;
   if (signalled_thr != nullptr)
     stop_signal = signalled_thr->suspend.stop_signal;