gdb/gcore.c

/* Generate a core file for the inferior process.

   Copyright (C) 2001-2022 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 "elf-bfd.h"
#include "infcall.h"
#include "inferior.h"
#include "gdbcore.h"
#include "objfiles.h"
#include "solib.h"
#include "symfile.h"
#include "arch-utils.h"
#include "completer.h"
#include "gcore.h"
#include "cli/cli-decode.h"
#include <fcntl.h>
#include "regcache.h"
#include "regset.h"
#include "gdb_bfd.h"
#include "readline/tilde.h"
#include <algorithm>
#include "gdbsupport/gdb_unlinker.h"
#include "gdbsupport/byte-vector.h"
#include "gdbsupport/scope-exit.h"

/* The largest amount of memory to read from the target at once.  We
   must throttle it to limit the amount of memory used by GDB during
   generate-core-file for programs with large resident data.  */
#define MAX_COPY_BYTES (1024 * 1024)

static const char *default_gcore_target (void);
static enum bfd_architecture default_gcore_arch (void);
static int gcore_memory_sections (bfd *);

/* create_gcore_bfd -- helper for gcore_command (exported).
   Open a new bfd core file for output, and return the handle.  */

gdb_bfd_ref_ptr
create_gcore_bfd (const char *filename)
{
  gdb_bfd_ref_ptr obfd (gdb_bfd_openw (filename, default_gcore_target ()));

  if (obfd == NULL)
    error (_("Failed to open '%s' for output."), filename);
  bfd_set_format (obfd.get (), bfd_core);
  bfd_set_arch_mach (obfd.get (), default_gcore_arch (), 0);
  return obfd;
}

/* write_gcore_file_1 -- do the actual work of write_gcore_file.  */

static void
write_gcore_file_1 (bfd *obfd)
{
  gdb::unique_xmalloc_ptr<char> note_data;
  int note_size = 0;
  asection *note_sec = NULL;

  /* An external target method must build the notes section.  */
  /* FIXME: uweigand/2011-10-06: All architectures that support core file
     generation should be converted to gdbarch_make_corefile_notes; at that
     point, the target vector method can be removed.  */
  if (!gdbarch_make_corefile_notes_p (target_gdbarch ()))
    note_data = target_make_corefile_notes (obfd, &note_size);
  else
    note_data = gdbarch_make_corefile_notes (target_gdbarch (), obfd,
					     &note_size);

  if (note_data == NULL || note_size == 0)
    error (_("Target does not support core file generation."));

  /* Create the note section.  */
  note_sec = bfd_make_section_anyway_with_flags (obfd, "note0",
						 SEC_HAS_CONTENTS
						 | SEC_READONLY
						 | SEC_ALLOC);
  if (note_sec == NULL)
    error (_("Failed to create 'note' section for corefile: %s"),
	   bfd_errmsg (bfd_get_error ()));

  bfd_set_section_vma (note_sec, 0);
  bfd_set_section_alignment (note_sec, 0);
  bfd_set_section_size (note_sec, note_size);

  /* Now create the memory/load sections.  */
  if (gcore_memory_sections (obfd) == 0)
    error (_("gcore: failed to get corefile memory sections from target."));

  /* Write out the contents of the note section.  */
  if (!bfd_set_section_contents (obfd, note_sec, note_data.get (), 0,
				 note_size))
    warning (_("writing note section (%s)"), bfd_errmsg (bfd_get_error ()));
}

/* write_gcore_file -- helper for gcore_command (exported).
   Compose and write the corefile data to the core file.  */

void
write_gcore_file (bfd *obfd)
{
  target_prepare_to_generate_core ();
  SCOPE_EXIT { target_done_generating_core (); };
  write_gcore_file_1 (obfd);
}

/* gcore_command -- implements the 'gcore' command.
   Generate a core file from the inferior process.  */

static void
gcore_command (const char *args, int from_tty)
{
  gdb::unique_xmalloc_ptr<char> corefilename;

  /* No use generating a corefile without a target process.  */
  if (!target_has_execution ())
    noprocess ();

  if (args && *args)
    corefilename.reset (tilde_expand (args));
  else
    {
      /* Default corefile name is "core.PID".  */
      corefilename = xstrprintf ("core.%d", inferior_ptid.pid ());
    }

  if (info_verbose)
    gdb_printf ("Opening corefile '%s' for output.\n",
		corefilename.get ());

  if (target_supports_dumpcore ())
    target_dumpcore (corefilename.get ());
  else
    {
      /* Open the output file.  */
      gdb_bfd_ref_ptr obfd (create_gcore_bfd (corefilename.get ()));

      /* Arrange to unlink the file on failure.  */
      gdb::unlinker unlink_file (corefilename.get ());

      /* Call worker function.  */
      write_gcore_file (obfd.get ());

      /* Succeeded.  */
      unlink_file.keep ();
    }

  gdb_printf ("Saved corefile %s\n", corefilename.get ());
}

static enum bfd_architecture
default_gcore_arch (void)
{
  const struct bfd_arch_info *bfdarch = gdbarch_bfd_arch_info (target_gdbarch ());

  if (bfdarch != NULL)
    return bfdarch->arch;
  if (current_program_space->exec_bfd () == NULL)
    error (_("Can't find bfd architecture for corefile (need execfile)."));

  return bfd_get_arch (current_program_space->exec_bfd ());
}

static const char *
default_gcore_target (void)
{
  /* The gdbarch may define a target to use for core files.  */
  if (gdbarch_gcore_bfd_target_p (target_gdbarch ()))
    return gdbarch_gcore_bfd_target (target_gdbarch ());

  /* Otherwise, try to fall back to the exec target.  This will probably
     not work for non-ELF targets.  */
  if (current_program_space->exec_bfd () == NULL)
    return NULL;
  else
    return bfd_get_target (current_program_space->exec_bfd ());
}

/* Derive a reasonable stack segment by unwinding the target stack,
   and store its limits in *BOTTOM and *TOP.  Return non-zero if
   successful.  */

static int
derive_stack_segment (bfd_vma *bottom, bfd_vma *top)
{
  struct frame_info *fi, *tmp_fi;

  gdb_assert (bottom);
  gdb_assert (top);

  /* Can't succeed without stack and registers.  */
  if (!target_has_stack () || !target_has_registers ())
    return 0;

  /* Can't succeed without current frame.  */
  fi = get_current_frame ();
  if (fi == NULL)
    return 0;

  /* Save frame pointer of TOS frame.  */
  *top = get_frame_base (fi);
  /* If current stack pointer is more "inner", use that instead.  */
  if (gdbarch_inner_than (get_frame_arch (fi), get_frame_sp (fi), *top))
    *top = get_frame_sp (fi);

  /* Find prev-most frame.  */
  while ((tmp_fi = get_prev_frame (fi)) != NULL)
    fi = tmp_fi;

  /* Save frame pointer of prev-most frame.  */
  *bottom = get_frame_base (fi);

  /* Now canonicalize their order, so that BOTTOM is a lower address
     (as opposed to a lower stack frame).  */
  if (*bottom > *top)
    {
      bfd_vma tmp_vma;

      tmp_vma = *top;
      *top = *bottom;
      *bottom = tmp_vma;
    }

  return 1;
}

/* call_target_sbrk --
   helper function for derive_heap_segment.  */

static bfd_vma
call_target_sbrk (int sbrk_arg)
{
  struct objfile *sbrk_objf;
  struct gdbarch *gdbarch;
  bfd_vma top_of_heap;
  struct value *target_sbrk_arg;
  struct value *sbrk_fn, *ret;
  bfd_vma tmp;

  if (lookup_minimal_symbol ("sbrk", NULL, NULL).minsym != NULL)
    {
      sbrk_fn = find_function_in_inferior ("sbrk", &sbrk_objf);
      if (sbrk_fn == NULL)
	return (bfd_vma) 0;
    }
  else if (lookup_minimal_symbol ("_sbrk", NULL, NULL).minsym != NULL)
    {
      sbrk_fn = find_function_in_inferior ("_sbrk", &sbrk_objf);
      if (sbrk_fn == NULL)
	return (bfd_vma) 0;
    }
  else
    return (bfd_vma) 0;

  gdbarch = sbrk_objf->arch ();
  target_sbrk_arg = value_from_longest (builtin_type (gdbarch)->builtin_int, 
					sbrk_arg);
  gdb_assert (target_sbrk_arg);
  ret = call_function_by_hand (sbrk_fn, NULL, target_sbrk_arg);
  if (ret == NULL)
    return (bfd_vma) 0;

  tmp = value_as_long (ret);
  if ((LONGEST) tmp <= 0 || (LONGEST) tmp == 0xffffffff)
    return (bfd_vma) 0;

  top_of_heap = tmp;
  return top_of_heap;
}

/* Derive a reasonable heap segment for ABFD by looking at sbrk and
   the static data sections.  Store its limits in *BOTTOM and *TOP.
   Return non-zero if successful.  */

static int
derive_heap_segment (bfd *abfd, bfd_vma *bottom, bfd_vma *top)
{
  bfd_vma top_of_data_memory = 0;
  bfd_vma top_of_heap = 0;
  bfd_size_type sec_size;
  bfd_vma sec_vaddr;
  asection *sec;

  gdb_assert (bottom);
  gdb_assert (top);

  /* This function depends on being able to call a function in the
     inferior.  */
  if (!target_has_execution ())
    return 0;

  /* The following code assumes that the link map is arranged as
     follows (low to high addresses):

     ---------------------------------
     | text sections                 |
     ---------------------------------
     | data sections (including bss) |
     ---------------------------------
     | heap                          |
     --------------------------------- */

  for (sec = abfd->sections; sec; sec = sec->next)
    {
      if (bfd_section_flags (sec) & SEC_DATA
	  || strcmp (".bss", bfd_section_name (sec)) == 0)
	{
	  sec_vaddr = bfd_section_vma (sec);
	  sec_size = bfd_section_size (sec);
	  if (sec_vaddr + sec_size > top_of_data_memory)
	    top_of_data_memory = sec_vaddr + sec_size;
	}
    }

  top_of_heap = call_target_sbrk (0);
  if (top_of_heap == (bfd_vma) 0)
    return 0;

  /* Return results.  */
  if (top_of_heap > top_of_data_memory)
    {
      *bottom = top_of_data_memory;
      *top = top_of_heap;
      return 1;
    }

  /* No additional heap space needs to be saved.  */
  return 0;
}

static void
make_output_phdrs (bfd *obfd, asection *osec)
{
  int p_flags = 0;
  int p_type = 0;

  /* Memory tag segments have already been handled by the architecture, as
     those contain arch-specific information.  If we have one of those, just
     return.  */
  if (startswith (bfd_section_name (osec), "memtag"))
    return;

  /* FIXME: these constants may only be applicable for ELF.  */
  if (startswith (bfd_section_name (osec), "load"))
    p_type = PT_LOAD;
  else if (startswith (bfd_section_name (osec), "note"))
    p_type = PT_NOTE;
  else
    p_type = PT_NULL;

  p_flags |= PF_R;	/* Segment is readable.  */
  if (!(bfd_section_flags (osec) & SEC_READONLY))
    p_flags |= PF_W;	/* Segment is writable.  */
  if (bfd_section_flags (osec) & SEC_CODE)
    p_flags |= PF_X;	/* Segment is executable.  */

  bfd_record_phdr (obfd, p_type, 1, p_flags, 0, 0, 0, 0, 1, &osec);
}

/* find_memory_region_ftype implementation.  DATA is 'bfd *' for the core file
   GDB is creating.  */

static int
gcore_create_callback (CORE_ADDR vaddr, unsigned long size, int read,
		       int write, int exec, int modified, bool memory_tagged,
		       void *data)
{
  bfd *obfd = (bfd *) data;
  asection *osec;
  flagword flags = SEC_ALLOC | SEC_HAS_CONTENTS | SEC_LOAD;

  /* If the memory segment has no permissions set, ignore it, otherwise
     when we later try to access it for read/write, we'll get an error
     or jam the kernel.  */
  if (read == 0 && write == 0 && exec == 0 && modified == 0)
    {
      if (info_verbose)
	{
	  gdb_printf ("Ignore segment, %s bytes at %s\n",
		      plongest (size), paddress (target_gdbarch (), vaddr));
	}

      return 0;
    }

  if (write == 0 && modified == 0 && !solib_keep_data_in_core (vaddr, size))
    {
      /* See if this region of memory lies inside a known file on disk.
	 If so, we can avoid copying its contents by clearing SEC_LOAD.  */
      struct obj_section *objsec;

      for (objfile *objfile : current_program_space->objfiles ())
	ALL_OBJFILE_OSECTIONS (objfile, objsec)
	  {
	    bfd *abfd = objfile->obfd.get ();
	    asection *asec = objsec->the_bfd_section;
	    bfd_vma align = (bfd_vma) 1 << bfd_section_alignment (asec);
	    bfd_vma start = objsec->addr () & -align;
	    bfd_vma end = (objsec->endaddr () + align - 1) & -align;

	    /* Match if either the entire memory region lies inside the
	       section (i.e. a mapping covering some pages of a large
	       segment) or the entire section lies inside the memory region
	       (i.e. a mapping covering multiple small sections).

	       This BFD was synthesized from reading target memory,
	       we don't want to omit that.  */
	    if (objfile->separate_debug_objfile_backlink == NULL
		&& ((vaddr >= start && vaddr + size <= end)
		    || (start >= vaddr && end <= vaddr + size))
		&& !(bfd_get_file_flags (abfd) & BFD_IN_MEMORY))
	      {
		flags &= ~(SEC_LOAD | SEC_HAS_CONTENTS);
		goto keep;	/* Break out of two nested for loops.  */
	      }
	  }

    keep:;
    }

  if (write == 0)
    flags |= SEC_READONLY;

  if (exec)
    flags |= SEC_CODE;
  else
    flags |= SEC_DATA;

  osec = bfd_make_section_anyway_with_flags (obfd, "load", flags);
  if (osec == NULL)
    {
      warning (_("Couldn't make gcore segment: %s"),
	       bfd_errmsg (bfd_get_error ()));
      return 1;
    }

  if (info_verbose)
    {
      gdb_printf ("Save segment, %s bytes at %s\n",
		  plongest (size), paddress (target_gdbarch (), vaddr));
    }

  bfd_set_section_size (osec, size);
  bfd_set_section_vma (osec, vaddr);
  bfd_set_section_lma (osec, 0);
  return 0;
}

/* gdbarch_find_memory_region callback for creating a memory tag section.
   DATA is 'bfd *' for the core file GDB is creating.  */

static int
gcore_create_memtag_section_callback (CORE_ADDR vaddr, unsigned long size,
				      int read, int write, int exec,
				      int modified, bool memory_tagged,
				      void *data)
{
  /* Are there memory tags in this particular memory map entry?  */
  if (!memory_tagged)
    return 0;

  bfd *obfd = (bfd *) data;

  /* Ask the architecture to create a memory tag section for this particular
     memory map entry.  It will be populated with contents later, as we can't
     start writing the contents before we have all the sections sorted out.  */
  asection *memtag_section
    = gdbarch_create_memtag_section (target_gdbarch (), obfd, vaddr, size);

  if (memtag_section == nullptr)
    {
      warning (_("Couldn't make gcore memory tag segment: %s"),
	       bfd_errmsg (bfd_get_error ()));
      return 1;
    }

  if (info_verbose)
    {
      gdb_printf (gdb_stdout, "Saved memory tag segment, %s bytes "
			      "at %s\n",
		  plongest (bfd_section_size (memtag_section)),
		  paddress (target_gdbarch (), vaddr));
    }

  return 0;
}

int
objfile_find_memory_regions (struct target_ops *self,
			     find_memory_region_ftype func, void *obfd)
{
  /* Use objfile data to create memory sections.  */
  struct obj_section *objsec;
  bfd_vma temp_bottom, temp_top;

  /* Call callback function for each objfile section.  */
  for (objfile *objfile : current_program_space->objfiles ())
    ALL_OBJFILE_OSECTIONS (objfile, objsec)
      {
	asection *isec = objsec->the_bfd_section;
	flagword flags = bfd_section_flags (isec);

	/* Separate debug info files are irrelevant for gcore.  */
	if (objfile->separate_debug_objfile_backlink != NULL)
	  continue;

	if ((flags & SEC_ALLOC) || (flags & SEC_LOAD))
	  {
	    int size = bfd_section_size (isec);
	    int ret;

	    ret = (*func) (objsec->addr (), size,
			   1, /* All sections will be readable.  */
			   (flags & SEC_READONLY) == 0, /* Writable.  */
			   (flags & SEC_CODE) != 0, /* Executable.  */
			   1, /* MODIFIED is unknown, pass it as true.  */
			   false, /* No memory tags in the object file.  */
			   obfd);
	    if (ret != 0)
	      return ret;
	  }
      }

  /* Make a stack segment.  */
  if (derive_stack_segment (&temp_bottom, &temp_top))
    (*func) (temp_bottom, temp_top - temp_bottom,
	     1, /* Stack section will be readable.  */
	     1, /* Stack section will be writable.  */
	     0, /* Stack section will not be executable.  */
	     1, /* Stack section will be modified.  */
	     false, /* No memory tags in the object file.  */
	     obfd);

  /* Make a heap segment.  */
  if (derive_heap_segment (current_program_space->exec_bfd (), &temp_bottom,
			   &temp_top))
    (*func) (temp_bottom, temp_top - temp_bottom,
	     1, /* Heap section will be readable.  */
	     1, /* Heap section will be writable.  */
	     0, /* Heap section will not be executable.  */
	     1, /* Heap section will be modified.  */
	     false, /* No memory tags in the object file.  */
	     obfd);

  return 0;
}

static void
gcore_copy_callback (bfd *obfd, asection *osec)
{
  bfd_size_type size, total_size = bfd_section_size (osec);
  file_ptr offset = 0;

  /* Read-only sections are marked; we don't have to copy their contents.  */
  if ((bfd_section_flags (osec) & SEC_LOAD) == 0)
    return;

  /* Only interested in "load" sections.  */
  if (!startswith (bfd_section_name (osec), "load"))
    return;

  size = std::min (total_size, (bfd_size_type) MAX_COPY_BYTES);
  gdb::byte_vector memhunk (size);

  while (total_size > 0)
    {
      if (size > total_size)
	size = total_size;

      if (target_read_memory (bfd_section_vma (osec) + offset,
			      memhunk.data (), size) != 0)
	{
	  warning (_("Memory read failed for corefile "
		     "section, %s bytes at %s."),
		   plongest (size),
		   paddress (target_gdbarch (), bfd_section_vma (osec)));
	  break;
	}
      if (!bfd_set_section_contents (obfd, osec, memhunk.data (),
				     offset, size))
	{
	  warning (_("Failed to write corefile contents (%s)."),
		   bfd_errmsg (bfd_get_error ()));
	  break;
	}

      total_size -= size;
      offset += size;
    }
}

/* Callback to copy contents to a particular memory tag section.  */

static void
gcore_copy_memtag_section_callback (bfd *obfd, asection *osec)
{
  /* We are only interested in "memtag" sections.  */
  if (!startswith (bfd_section_name (osec), "memtag"))
    return;

  /* Fill the section with memory tag contents.  */
  if (!gdbarch_fill_memtag_section (target_gdbarch (), osec))
    error (_("Failed to fill memory tag section for core file."));
}

static int
gcore_memory_sections (bfd *obfd)
{
  /* Try gdbarch method first, then fall back to target method.  */
  if (!gdbarch_find_memory_regions_p (target_gdbarch ())
      || gdbarch_find_memory_regions (target_gdbarch (),
				      gcore_create_callback, obfd) != 0)
    {
      if (target_find_memory_regions (gcore_create_callback, obfd) != 0)
	return 0;			/* FIXME: error return/msg?  */
    }

  /* Take care of dumping memory tags, if there are any.  */
  if (!gdbarch_find_memory_regions_p (target_gdbarch ())
      || gdbarch_find_memory_regions (target_gdbarch (),
				      gcore_create_memtag_section_callback,
				      obfd) != 0)
    {
      if (target_find_memory_regions (gcore_create_memtag_section_callback,
				      obfd) != 0)
	return 0;
    }

  /* Record phdrs for section-to-segment mapping.  */
  for (asection *sect : gdb_bfd_sections (obfd))
    make_output_phdrs (obfd, sect);

  /* Copy memory region and memory tag contents.  */
  for (asection *sect : gdb_bfd_sections (obfd))
    {
      gcore_copy_callback (obfd, sect);
      gcore_copy_memtag_section_callback (obfd, sect);
    }

  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->stop_signal () != GDB_SIGNAL_0)
    return curr_thr;

  for (thread_info *thr : current_inferior ()->non_exited_threads ())
    if (thr->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 ()
{
  cmd_list_element *generate_core_file_cmd
    = add_com ("generate-core-file", class_files, gcore_command, _("\
Save a core file with the current state of the debugged process.\n\
Usage: generate-core-file [FILENAME]\n\
Argument is optional filename.  Default filename is 'core.PROCESS_ID'."));

  add_com_alias ("gcore", generate_core_file_cmd, class_files, 1);
}