libctf: ELF file opening via BFD

These functions let you open an ELF file with a customarily-named CTF
section in it, automatically opening the CTF file or archive and
associating the symbol and string tables in the ELF file with the CTF
container, so that you can look up the types of symbols in the ELF file
via ctf_lookup_by_symbol(), and so that strings can be shared between
the ELF file and CTF container, to save space.

It uses BFD machinery to do so.  This has now been lightly tested and
seems to work.  In particular, if you already have a bfd you can pass
it in to ctf_bfdopen(), and if you want a bfd made for you you can
call ctf_open() or ctf_fdopen(), optionally specifying a target (or
try once without a target and then again with one if you get
ECTF_BFD_AMBIGUOUS back).

We use a forward declaration for the struct bfd in ctf-api.h, so that
ctf-api.h users are not required to pull in <bfd.h>.  (This is mostly
for the sake of readelf.)

libctf/
	* ctf-open-bfd.c: New file.
	* ctf-open.c (ctf_close): New.
	* ctf-impl.h: Include bfd.h.
	(ctf_file): New members ctf_data_mmapped, ctf_data_mmapped_len.
	(ctf_archive_internal): New members ctfi_abfd, ctfi_data,
	ctfi_bfd_close.
	(ctf_bfdopen_ctfsect): New declaration.
	(_CTF_SECTION): likewise.

include/
	* ctf-api.h (struct bfd): New forward.
	(ctf_fdopen): New.
	(ctf_bfdopen): Likewise.
	(ctf_open): Likewise.
	(ctf_arc_open): Likewise.

4 files changed, 376 insertions, 0 deletions

diff --git a/libctf/ChangeLog b/libctf/ChangeLog
index aa3fb3b..23a8b89 100644
--- a/libctf/ChangeLog
+++ b/libctf/ChangeLog
@@ -1,5 +1,16 @@
 2019-05-28  Nick Alcock  <nick.alcock@oracle.com>
 
+	* ctf-open-bfd.c: New file.
+	* ctf-open.c (ctf_close): New.
+	* ctf-impl.h: Include bfd.h.
+	(ctf_file): New members ctf_data_mmapped, ctf_data_mmapped_len.
+	(ctf_archive_internal): New members ctfi_abfd, ctfi_data,
+	ctfi_bfd_close.
+	(ctf_bfdopen_ctfsect): New declaration.
+	(_CTF_SECTION): likewise.
+
+2019-05-28  Nick Alcock  <nick.alcock@oracle.com>
+
 	* ctf-archive.c: New.
 	* ctf-impl.h (ctf_archive_internal): New type.
 	(ctf_arc_open_internal): New declaration.
diff --git a/libctf/ctf-impl.h b/libctf/ctf-impl.h
index 898be8c..8522a03 100644
--- a/libctf/ctf-impl.h
+++ b/libctf/ctf-impl.h
@@ -31,6 +31,7 @@
 #include <limits.h>
 #include <ctype.h>
 #include <elf.h>
+#include <bfd.h>
 
 #ifdef	__cplusplus
 extern "C"
@@ -188,6 +189,8 @@ struct ctf_file
   ctf_sect_t ctf_data;		    /* CTF data from object file.  */
   ctf_sect_t ctf_symtab;	    /* Symbol table from object file.  */
   ctf_sect_t ctf_strtab;	    /* String table from object file.  */
+  void *ctf_data_mmapped;	    /* CTF data we mmapped, to free later.  */
+  size_t ctf_data_mmapped_len;	    /* Length of CTF data we mmapped.  */
   ctf_hash_t *ctf_structs;	    /* Hash table of struct types.  */
   ctf_hash_t *ctf_unions;	    /* Hash table of union types.  */
   ctf_hash_t *ctf_enums;	    /* Hash table of enum types.  */
@@ -240,6 +243,8 @@ struct ctf_archive_internal
   ctf_sect_t ctfi_symsect;
   ctf_sect_t ctfi_strsect;
   void *ctfi_data;
+  bfd *ctfi_abfd;		    /* Optional source of section data.  */
+  void (*ctfi_bfd_close) (struct ctf_archive_internal *);
 };
 
 /* Return x rounded up to an alignment boundary.
@@ -358,6 +363,7 @@ extern Elf64_Sym *ctf_sym_to_elf64 (const Elf32_Sym *src, Elf64_Sym *dst);
 
 /* Variables, all underscore-prepended. */
 
+extern const char _CTF_SECTION[];	/* name of CTF ELF section */
 extern const char _CTF_NULLSTR[];	/* empty string */
 
 extern int _libctf_debug;	/* debugging messages enabled */
diff --git a/libctf/ctf-open-bfd.c b/libctf/ctf-open-bfd.c
new file mode 100644
index 0000000..d6d442e
--- /dev/null
+++ b/libctf/ctf-open-bfd.c
@@ -0,0 +1,351 @@
+/* Opening CTF files with BFD.
+   Copyright (C) 2019 Free Software Foundation, Inc.
+
+   This file is part of libctf.
+
+   libctf 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, 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; see the file COPYING.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <ctf-impl.h>
+#include <stddef.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <string.h>
+#include <fcntl.h>
+#include <elf.h>
+#include <bfd.h>
+
+#include "elf-bfd.h"
+
+/* Make a new struct ctf_archive_internal wrapper for a ctf_archive or a
+   ctf_file.  Closes ARC and/or FP on error.  Arrange to free the SYMSECT and
+   STRSECT interior on close.  */
+
+static struct ctf_archive_internal *
+ctf_new_archive_internal (int is_archive, struct ctf_archive *arc,
+			  ctf_file_t *fp, const ctf_sect_t *symsect,
+			  const ctf_sect_t *strsect,
+			  int *errp)
+{
+  struct ctf_archive_internal *arci;
+
+  if ((arci = calloc (1, sizeof (struct ctf_archive_internal))) == NULL)
+    {
+      if (is_archive)
+	ctf_arc_close_internal (arc);
+      else
+	ctf_file_close (fp);
+      return (ctf_set_open_errno (errp, errno));
+    }
+  arci->ctfi_is_archive = is_archive;
+  if (is_archive)
+    arci->ctfi_archive = arc;
+  else
+    arci->ctfi_file = fp;
+  if (symsect)
+     memcpy (&arci->ctfi_symsect, symsect, sizeof (struct ctf_sect));
+  if (strsect)
+     memcpy (&arci->ctfi_strsect, strsect, sizeof (struct ctf_sect));
+
+  return arci;
+}
+
+/* Free the BFD bits of a CTF file on ctf_file_close().  */
+
+static void
+ctf_bfdclose (struct ctf_archive_internal *arci)
+{
+  if (arci->ctfi_abfd != NULL)
+    if (!bfd_close_all_done (arci->ctfi_abfd))
+      ctf_dprintf ("Cannot close BFD: %s\n", bfd_errmsg (bfd_get_error()));
+}
+
+/* Open a CTF file given the specified BFD.  */
+
+ctf_archive_t *
+ctf_bfdopen (struct bfd *abfd, int *errp)
+{
+  ctf_archive_t *arc;
+  asection *ctf_asect;
+  bfd_byte *contents;
+  ctf_sect_t ctfsect;
+
+  libctf_init_debug();
+
+  if ((ctf_asect = bfd_get_section_by_name (abfd, _CTF_SECTION)) == NULL)
+    {
+      return (ctf_set_open_errno (errp, ECTF_NOCTFDATA));
+    }
+
+  if (!bfd_malloc_and_get_section (abfd, ctf_asect, &contents))
+    {
+      ctf_dprintf ("ctf_bfdopen(): cannot malloc CTF section: %s\n",
+		   bfd_errmsg (bfd_get_error()));
+      return (ctf_set_open_errno (errp, ECTF_FMT));
+    }
+
+  ctfsect.cts_name = _CTF_SECTION;
+  ctfsect.cts_type = SHT_PROGBITS;
+  ctfsect.cts_flags = 0;
+  ctfsect.cts_entsize = 1;
+  ctfsect.cts_offset = 0;
+  ctfsect.cts_size = bfd_section_size (abfd, ctf_asect);
+  ctfsect.cts_data = contents;
+
+  if ((arc = ctf_bfdopen_ctfsect (abfd, &ctfsect, errp)) != NULL)
+    {
+      arc->ctfi_data = (void *) ctfsect.cts_data;
+      return arc;
+    }
+
+  free (contents);
+  return NULL;				/* errno is set for us.  */
+}
+
+/* Open a CTF file given the specified BFD and CTF section (which may contain a
+   CTF archive or a file).  Takes ownership of the ctfsect, and frees it
+   later.  */
+
+ctf_archive_t *
+ctf_bfdopen_ctfsect (struct bfd *abfd, const ctf_sect_t *ctfsect, int *errp)
+{
+  struct ctf_archive *arc = NULL;
+  ctf_archive_t *arci;
+  ctf_file_t *fp = NULL;
+  ctf_sect_t *symsectp = NULL;
+  ctf_sect_t *strsectp = NULL;
+  const char *bfderrstr = NULL;
+  int is_archive;
+
+  asection *sym_asect;
+  ctf_sect_t symsect, strsect;
+  /* TODO: handle SYMTAB_SHNDX.  */
+
+  if ((sym_asect = bfd_section_from_elf_index (abfd,
+					       elf_onesymtab (abfd))) != NULL)
+    {
+      Elf_Internal_Shdr *symhdr = &elf_symtab_hdr (abfd);
+      asection *str_asect = NULL;
+      bfd_byte *contents;
+
+      if (symhdr->sh_link != SHN_UNDEF &&
+	  symhdr->sh_link <= elf_numsections (abfd))
+	str_asect = bfd_section_from_elf_index (abfd, symhdr->sh_link);
+
+      Elf_Internal_Shdr *strhdr = elf_elfsections (abfd)[symhdr->sh_link];
+
+      if (sym_asect && str_asect)
+	{
+	  if (!bfd_malloc_and_get_section (abfd, str_asect, &contents))
+	    {
+	      bfderrstr = "Cannot malloc string table";
+	      free (contents);
+	      goto err;
+	    }
+	  strsect.cts_data = contents;
+	  strsect.cts_name = (char *) strsect.cts_data + strhdr->sh_name;
+	  strsect.cts_type = strhdr->sh_type;
+	  strsect.cts_flags = strhdr->sh_flags;
+	  strsect.cts_entsize = strhdr->sh_size;
+	  strsect.cts_offset = strhdr->sh_offset;
+	  strsectp = &strsect;
+
+	  if (!bfd_malloc_and_get_section (abfd, sym_asect, &contents))
+	    {
+	      bfderrstr = "Cannot malloc symbol table";
+	      free (contents);
+	      goto err_free_str;
+	    }
+
+	  symsect.cts_name = (char *) strsect.cts_data + symhdr->sh_name;
+	  symsect.cts_type = symhdr->sh_type;
+	  symsect.cts_flags = symhdr->sh_flags;
+	  symsect.cts_entsize = symhdr->sh_size;
+	  symsect.cts_data = contents;
+	  symsect.cts_offset = symhdr->sh_offset;
+	  symsectp = &symsect;
+	}
+    }
+
+  if (ctfsect->cts_size > sizeof (uint64_t) &&
+      ((*(uint64_t *) ctfsect->cts_data) == CTFA_MAGIC))
+    {
+      is_archive = 1;
+      if ((arc = ctf_arc_bufopen ((void *) ctfsect->cts_data,
+				  ctfsect->cts_size, errp)) == NULL)
+	goto err_free_sym;
+    }
+  else
+    {
+      is_archive = 0;
+      if ((fp = ctf_bufopen (ctfsect, symsectp, strsectp, errp)) == NULL)
+	{
+	  ctf_dprintf ("ctf_internal_open(): cannot open CTF: %s\n",
+		       ctf_errmsg (*errp));
+	  goto err_free_sym;
+	}
+    }
+  arci = ctf_new_archive_internal (is_archive, arc, fp, symsectp, strsectp,
+				   errp);
+
+  if (arci)
+    return arci;
+ err_free_sym:
+  free ((void *) symsect.cts_data);
+err_free_str:
+  free ((void *) strsect.cts_data);
+err: _libctf_unused_;
+  if (bfderrstr)
+    {
+      ctf_dprintf ("ctf_bfdopen(): %s: %s\n", bfderrstr,
+		   bfd_errmsg (bfd_get_error()));
+      ctf_set_open_errno (errp, ECTF_FMT);
+    }
+  return NULL;
+}
+
+/* Open the specified file descriptor and return a pointer to a CTF archive that
+   contains one or more CTF containers.  The file can be an ELF file, a raw CTF
+   file, or a CTF archive.  The caller is responsible for closing the file
+   descriptor when it is no longer needed.  If this is an ELF file, TARGET, if
+   non-NULL, should be the name of a suitable BFD target.  */
+
+ctf_archive_t *
+ctf_fdopen (int fd, const char *filename, const char *target, int *errp)
+{
+  ctf_archive_t *arci;
+  bfd *abfd;
+  int nfd;
+
+  struct stat st;
+  ssize_t nbytes;
+
+  ctf_preamble_t ctfhdr;
+  uint64_t arc_magic;
+
+  memset (&ctfhdr, 0, sizeof (ctfhdr));
+
+  libctf_init_debug();
+
+  if (fstat (fd, &st) == -1)
+    return (ctf_set_open_errno (errp, errno));
+
+  if ((nbytes = ctf_pread (fd, &ctfhdr, sizeof (ctfhdr), 0)) <= 0)
+    return (ctf_set_open_errno (errp, nbytes < 0 ? errno : ECTF_FMT));
+
+  /* If we have read enough bytes to form a CTF header and the magic
+     string matches, attempt to interpret the file as raw CTF.  */
+
+  if ((size_t) nbytes >= sizeof (ctf_preamble_t) &&
+      ctfhdr.ctp_magic == CTF_MAGIC)
+    {
+      ctf_file_t *fp = NULL;
+      void *data;
+
+      if (ctfhdr.ctp_version > CTF_VERSION)
+	return (ctf_set_open_errno (errp, ECTF_CTFVERS));
+
+      if ((data = ctf_mmap (st.st_size, 0, fd)) == NULL)
+	return (ctf_set_open_errno (errp, errno));
+
+      if ((fp = ctf_simple_open (data, (size_t) st.st_size, NULL, 0, 0,
+				 NULL, 0, errp)) == NULL)
+	ctf_munmap (data, (size_t) st.st_size);
+      fp->ctf_data_mmapped = data;
+      fp->ctf_data_mmapped_len = (size_t) st.st_size;
+
+      return ctf_new_archive_internal (0, NULL, fp, NULL, NULL, errp);
+    }
+
+  if ((nbytes = ctf_pread (fd, &arc_magic, sizeof (arc_magic), 0)) <= 0)
+    return (ctf_set_open_errno (errp, nbytes < 0 ? errno : ECTF_FMT));
+
+  if ((size_t) nbytes >= sizeof (uint64_t) && arc_magic == CTFA_MAGIC)
+    {
+      struct ctf_archive *arc;
+
+      if ((arc = ctf_arc_open_internal (filename, errp)) == NULL)
+	return NULL;			/* errno is set for us.  */
+
+      return ctf_new_archive_internal (1, arc, NULL, NULL, NULL, errp);
+    }
+
+  /* Attempt to open the file with BFD.  We must dup the fd first, since bfd
+     takes ownership of the passed fd.  */
+
+  if ((nfd = dup (fd)) < 0)
+      return (ctf_set_open_errno (errp, errno));
+
+  if ((abfd = bfd_fdopenr (filename, target, nfd)) == NULL)
+    {
+      ctf_dprintf ("Cannot open BFD from %s: %s\n",
+		   filename ? filename : "(unknown file)",
+		   bfd_errmsg (bfd_get_error()));
+      return (ctf_set_open_errno (errp, ECTF_FMT));
+    }
+
+  if (!bfd_check_format (abfd, bfd_object))
+    {
+      ctf_dprintf ("BFD format problem in %s: %s\n",
+		   filename ? filename : "(unknown file)",
+		   bfd_errmsg (bfd_get_error()));
+      if (bfd_get_error() == bfd_error_file_ambiguously_recognized)
+	return (ctf_set_open_errno (errp, ECTF_BFD_AMBIGUOUS));
+      else
+	return (ctf_set_open_errno (errp, ECTF_FMT));
+    }
+
+  if ((arci = ctf_bfdopen (abfd, errp)) == NULL)
+    {
+      if (!bfd_close_all_done (abfd))
+	ctf_dprintf ("Cannot close BFD: %s\n", bfd_errmsg (bfd_get_error()));
+      return NULL;			/* errno is set for us.  */
+    }
+  arci->ctfi_bfd_close = ctf_bfdclose;
+  arci->ctfi_abfd = abfd;
+
+  return arci;
+}
+
+/* Open the specified file and return a pointer to a CTF container.  The file
+   can be either an ELF file or raw CTF file.  This is just a convenient
+   wrapper around ctf_fdopen() for callers.  */
+
+ctf_archive_t *
+ctf_open (const char *filename, const char *target, int *errp)
+{
+  ctf_archive_t *arc;
+  int fd;
+
+  if ((fd = open (filename, O_RDONLY)) == -1)
+    {
+      if (errp != NULL)
+	*errp = errno;
+      return NULL;
+    }
+
+  arc = ctf_fdopen (fd, filename, target, errp);
+  (void) close (fd);
+  return arc;
+}
+
+/* Public entry point: open a CTF archive, or CTF file.  Returns the archive, or
+   NULL and an error in *err.  Despite the fact that this uses CTF archives, it
+   must be in this file to avoid dragging in BFD into non-BFD-using programs.  */
+ctf_archive_t *
+ctf_arc_open (const char *filename, int *errp)
+{
+  return ctf_open (filename, NULL, errp);
+}
diff --git a/libctf/ctf-open.c b/libctf/ctf-open.c
index 8c6294a..5230d09 100644
--- a/libctf/ctf-open.c
+++ b/libctf/ctf-open.c
@@ -1572,6 +1572,14 @@ ctf_file_close (ctf_file_t *fp)
   ctf_free (fp);
 }
 
+/* The converse of ctf_open().  ctf_open() disguises whatever it opens as an
+   archive, so closing one is just like closing an archive.  */
+void
+ctf_close (ctf_archive_t *arc)
+{
+  ctf_arc_close (arc);
+}
+
 /* Get the CTF archive from which this ctf_file_t is derived.  */
 ctf_archive_t *
 ctf_get_arc (const ctf_file_t *fp)