gdb/gcore.c

/* Generate a core file for the inferior process.

   Copyright (C) 2001-2021 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 "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.reset (xstrprintf ("core.%d", inferior_ptid.pid ()));
    }

  if (info_verbose)
    fprintf_filtered (gdb_stdout,
		      "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 ();
    }

  fprintf_filtered (gdb_stdout, "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;

  /* 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, 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)
	{
	  fprintf_filtered (gdb_stdout, "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;
	    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)
    {
      fprintf_filtered (gdb_stdout, "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;
}

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.  */
			   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.  */
	     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.  */
	     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;
    }
}

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?  */
    }

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

  /* Copy memory region contents.  */
  for (asection *sect : gdb_bfd_sections (obfd))
    gcore_copy_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);
}