libctf: add the ctf_link machinery

This is the start of work on the core of the linking mechanism for CTF
sections.  This commit handles the type and string sections.

The linker calls these functions in sequence:

ctf_link_add_ctf: to add each CTF section in the input in turn to a
  newly-created ctf_file_t (which will appear in the output, and which
  itself will become the shared parent that contains types that all
  TUs have in common (in all link modes) and all types that do not
  have conflicting definitions between types (by default).  Input files
  that are themselves products of ld -r are supported, though this is
  not heavily tested yet.

ctf_link: called once all input files are added to merge the types in
  all the input containers into the output container, eliminating
  duplicates.

ctf_link_add_strtab: called once the ELF string table is finalized and
  all its offsets are known, this calls a callback provided by the
  linker which returns the string content and offset of every string in
  the ELF strtab in turn: all these strings which appear in the input
  CTF strtab are eliminated from it in favour of the ELF strtab:
  equally, any strings that only appear in the input strtab will
  reappear in the internal CTF strtab of the output.

ctf_link_shuffle_syms (not yet implemented): called once the ELF symtab
  is finalized, this calls a callback provided by the linker which
  returns information on every symbol in turn as a ctf_link_sym_t.  This
  is then used to shuffle the function info and data object sections in
  the CTF section into symbol table order, eliminating the index
  sections which map those sections to symbol names before that point.
  Currently just returns ECTF_NOTYET.

ctf_link_write: Returns a buffer containing either a serialized
  ctf_file_t (if there are no types with conflicting definitions in the
  object files in the link) or a ctf_archive_t containing a large
  ctf_file_t (the common types) and a bunch of small ones named after
  individual CUs in which conflicting types are found (containing the
  conflicting types, and all types that reference them).  A threshold
  size above which compression takes place is passed as one parameter.
  (Currently, only gzip compression is supported, but I hope to add lzma
  as well.)

Lifetime rules for this are simple: don't close the input CTF files
until you've called ctf_link for the last time.  We do not assume
that symbols or strings passed in by the callback outlast the
call to ctf_link_add_strtab or ctf_link_shuffle_syms.

Right now, the duplicate elimination mechanism is the one already
present as part of the ctf_add_type function, and is not particularly
good: it misses numerous actual duplicates, and the conflicting-types
detection hardly ever reports that types conflict, even when they do
(one of them just tends to get silently dropped): it is also very slow.
This will all be fixed in the next few weeks, but the fix hardly touches
any of this code, and the linker does work without it, just not as
well as it otherwise might.  (And when no CTF section is present,
there is no effect on performance, of course.  So only people using
a trunk GCC with not-yet-committed patches will even notice.  By the
time it gets upstream, things should be better.)

v3: Fix error handling.
v4: check for strdup failure.
v5: fix tabdamage.

include/
	* ctf-api.h (struct ctf_link_sym): New, a symbol in flight to the
	libctf linking machinery.
	(CTF_LINK_SHARE_UNCONFLICTED): New.
	(CTF_LINK_SHARE_DUPLICATED): New.
	(ECTF_LINKADDEDLATE): New, replacing ECTF_UNUSED.
	(ECTF_NOTYET): New, a 'not yet implemented' message.
	(ctf_link_add_ctf): New, add an input file's CTF to the link.
	(ctf_link): New, merge the type and string sections.
	(ctf_link_strtab_string_f): New, callback for feeding strtab info.
	(ctf_link_iter_symbol_f): New, callback for feeding symtab info.
	(ctf_link_add_strtab): New, tell the CTF linker about the ELF
	strtab's strings.
	(ctf_link_shuffle_syms): New, ask the CTF linker to shuffle its
	symbols into symtab order.
	(ctf_link_write): New, ask the CTF linker to write the CTF out.

libctf/
	* ctf-link.c: New file, linking of the string and type sections.
	* Makefile.am (libctf_a_SOURCES): Add it.
	* Makefile.in: Regenerate.

	* ctf-impl.h (ctf_file_t): New fields ctf_link_inputs,
	ctf_link_outputs.
	* ctf-create.c (ctf_update): Update accordingly.
	* ctf-open.c (ctf_file_close): Likewise.
	* ctf-error.c (_ctf_errlist): Updated with new errors.

10 files changed, 619 insertions, 16 deletions

diff --git a/include/ChangeLog b/include/ChangeLog
index ddc5667..6980ec2 100644
--- a/include/ChangeLog
+++ b/include/ChangeLog
@@ -1,5 +1,23 @@
 2019-07-13  Nick Alcock  <nick.alcock@oracle.com>
 
+	* ctf-api.h (struct ctf_link_sym): New, a symbol in flight to the
+	libctf linking machinery.
+	(CTF_LINK_SHARE_UNCONFLICTED): New.
+	(CTF_LINK_SHARE_DUPLICATED): New.
+	(ECTF_LINKADDEDLATE): New, replacing ECTF_UNUSED.
+	(ECTF_NOTYET): New, a 'not yet implemented' message.
+	(ctf_link_add_ctf): New, add an input file's CTF to the link.
+	(ctf_link): New, merge the type and string sections.
+	(ctf_link_strtab_string_f): New, callback for feeding strtab info.
+	(ctf_link_iter_symbol_f): New, callback for feeding symtab info.
+	(ctf_link_add_strtab): New, tell the CTF linker about the ELF
+	strtab's strings.
+	(ctf_link_shuffle_syms): New, ask the CTF linker to shuffle its
+	symbols into symtab order.
+	(ctf_link_write): New, ask the CTF linker to write the CTF out.
+
+2019-07-13  Nick Alcock  <nick.alcock@oracle.com>
+
 	* ctf-api.h (ctf_arc_write_fd): New.
 	(ctf_write_mem): Likewise.
 	(ctf_gzwrite): Spacing fix.
diff --git a/include/ctf-api.h b/include/ctf-api.h
index 2bee08b..e4c6f9f 100644
--- a/include/ctf-api.h
+++ b/include/ctf-api.h
@@ -65,6 +65,28 @@ typedef struct ctf_sect
   size_t cts_entsize;		  /* Size of each section entry (symtab only).  */
 } ctf_sect_t;
 
+/* A minimal symbol extracted from a linker's internal symbol table
+   representation.  */
+
+typedef struct ctf_link_sym
+{
+  /* The st_name will not be accessed outside the call to
+     ctf_link_shuffle_syms().  */
+
+  const char *st_name;
+  uint32_t st_shndx;
+  uint32_t st_type;
+  uint32_t st_value;
+} ctf_link_sym_t;
+
+/* Indication of how to share types when linking.  */
+
+/* Share all types thare are not in conflict.  The default.  */
+#define CTF_LINK_SHARE_UNCONFLICTED 0x0
+
+/* Share only types that are used by multiple inputs.  Not implemented yet.  */
+#define CTF_LINK_SHARE_DUPLICATED 0x1
+
 /* Symbolic names for CTF sections.  */
 
 typedef enum ctf_sect_names
@@ -145,7 +167,7 @@ enum
    ECTF_NOSYMTAB,		/* Symbol table data is not available.  */
    ECTF_NOPARENT,		/* Parent CTF container is not available.  */
    ECTF_DMODEL,			/* Data model mismatch.  */
-   ECTF_UNUSED,			/* Unused error.  */
+   ECTF_LINKADDEDLATE,		/* File added to link too late.  */
    ECTF_ZALLOC,			/* Failed to allocate (de)compression buffer.  */
    ECTF_DECOMPRESS,		/* Failed to decompress CTF data.  */
    ECTF_STRTAB,			/* String table for this string is missing.  */
@@ -180,7 +202,8 @@ enum
    ECTF_ARNNAME,		/* Name not found in CTF archive.  */
    ECTF_SLICEOVERFLOW,		/* Overflow of type bitness or offset in slice.  */
    ECTF_DUMPSECTUNKNOWN,	/* Unknown section number in dump.  */
-   ECTF_DUMPSECTCHANGED		/* Section changed in middle of dump.  */
+   ECTF_DUMPSECTCHANGED,	/* Section changed in middle of dump.  */
+   ECTF_NOTYET			/* Feature not yet implemented.  */
   };
 
 /* The CTF data model is inferred to be the caller's data model or the data
@@ -385,6 +408,18 @@ extern int ctf_gzwrite (ctf_file_t *fp, gzFile fd);
 extern int ctf_compress_write (ctf_file_t * fp, int fd);
 extern unsigned char *ctf_write_mem (ctf_file_t *, size_t *, size_t threshold);
 
+extern int ctf_link_add_ctf (ctf_file_t *, ctf_archive_t *, const char *);
+extern int ctf_link (ctf_file_t *, int share_mode);
+typedef const char *ctf_link_strtab_string_f (uint32_t *offset, void *arg);
+extern int ctf_link_add_strtab (ctf_file_t *, ctf_link_strtab_string_f *,
+				void *);
+typedef ctf_link_sym_t *ctf_link_iter_symbol_f (ctf_link_sym_t *dest,
+						void *arg);
+extern int ctf_link_shuffle_syms (ctf_file_t *, ctf_link_iter_symbol_f *,
+				  void *);
+extern unsigned char *ctf_link_write (ctf_file_t *, size_t *size,
+				      size_t threshold);
+
 extern void ctf_setdebug (int debug);
 extern int ctf_getdebug (void);
 
diff --git a/libctf/ChangeLog b/libctf/ChangeLog
index c23e5ae..959a038 100644
--- a/libctf/ChangeLog
+++ b/libctf/ChangeLog
@@ -1,5 +1,17 @@
 2019-07-13  Nick Alcock  <nick.alcock@oracle.com>
 
+	* ctf-link.c: New file, linking of the string and type sections.
+	* Makefile.am (libctf_a_SOURCES): Add it.
+	* Makefile.in: Regenerate.
+
+	* ctf-impl.h (ctf_file_t): New fields ctf_link_inputs,
+	ctf_link_outputs.
+	* ctf-create.c (ctf_update): Update accordingly.
+	* ctf-open.c (ctf_file_close): Likewise.
+	* ctf-error.c (_ctf_errlist): Updated with new errors.
+
+2019-07-13  Nick Alcock  <nick.alcock@oracle.com>
+
 	* ctf-dump.c (ctf_dump_funcs): Check the right error value.
 
 2019-07-13  Nick Alcock  <nick.alcock@oracle.com>
diff --git a/libctf/Makefile.am b/libctf/Makefile.am
index 43fc78a..a0a27b4 100644
--- a/libctf/Makefile.am
+++ b/libctf/Makefile.am
@@ -33,8 +33,8 @@ AM_CFLAGS = -std=gnu99 @ac_libctf_warn_cflags@ @warn@ @c_warn@ @WARN_PEDANTIC@ @
 noinst_LIBRARIES = libctf.a
 
 libctf_a_SOURCES = ctf-archive.c ctf-dump.c ctf-create.c ctf-decl.c ctf-error.c \
-		   ctf-hash.c ctf-labels.c ctf-lookup.c ctf-open.c ctf-open-bfd.c \
-		   ctf-string.c ctf-subr.c ctf-types.c ctf-util.c
+		   ctf-hash.c ctf-labels.c ctf-link.c ctf-lookup.c ctf-open.c \
+		   ctf-open-bfd.c ctf-string.c ctf-subr.c ctf-types.c ctf-util.c
 if NEED_CTF_QSORT_R
 libctf_a_SOURCES += ctf-qsort_r.c
 endif
diff --git a/libctf/Makefile.in b/libctf/Makefile.in
index c898eb4..1d2efb9 100644
--- a/libctf/Makefile.in
+++ b/libctf/Makefile.in
@@ -131,16 +131,16 @@ am__v_AR_1 =
 libctf_a_AR = $(AR) $(ARFLAGS)
 libctf_a_LIBADD =
 am__libctf_a_SOURCES_DIST = ctf-archive.c ctf-dump.c ctf-create.c \
-	ctf-decl.c ctf-error.c ctf-hash.c ctf-labels.c ctf-lookup.c \
-	ctf-open.c ctf-open-bfd.c ctf-string.c ctf-subr.c ctf-types.c \
-	ctf-util.c ctf-qsort_r.c
+	ctf-decl.c ctf-error.c ctf-hash.c ctf-labels.c ctf-link.c \
+	ctf-lookup.c ctf-open.c ctf-open-bfd.c ctf-string.c ctf-subr.c \
+	ctf-types.c ctf-util.c ctf-qsort_r.c
 @NEED_CTF_QSORT_R_TRUE@am__objects_1 = ctf-qsort_r.$(OBJEXT)
 am_libctf_a_OBJECTS = ctf-archive.$(OBJEXT) ctf-dump.$(OBJEXT) \
 	ctf-create.$(OBJEXT) ctf-decl.$(OBJEXT) ctf-error.$(OBJEXT) \
-	ctf-hash.$(OBJEXT) ctf-labels.$(OBJEXT) ctf-lookup.$(OBJEXT) \
-	ctf-open.$(OBJEXT) ctf-open-bfd.$(OBJEXT) ctf-string.$(OBJEXT) \
-	ctf-subr.$(OBJEXT) ctf-types.$(OBJEXT) ctf-util.$(OBJEXT) \
-	$(am__objects_1)
+	ctf-hash.$(OBJEXT) ctf-labels.$(OBJEXT) ctf-link.$(OBJEXT) \
+	ctf-lookup.$(OBJEXT) ctf-open.$(OBJEXT) ctf-open-bfd.$(OBJEXT) \
+	ctf-string.$(OBJEXT) ctf-subr.$(OBJEXT) ctf-types.$(OBJEXT) \
+	ctf-util.$(OBJEXT) $(am__objects_1)
 libctf_a_OBJECTS = $(am_libctf_a_OBJECTS)
 AM_V_P = $(am__v_P_@AM_V@)
 am__v_P_ = $(am__v_P_@AM_DEFAULT_V@)
@@ -331,9 +331,9 @@ AM_CPPFLAGS = -D_GNU_SOURCE -I$(top_srcdir) -I$(top_srcdir)/../include -I$(top_s
 AM_CFLAGS = -std=gnu99 @ac_libctf_warn_cflags@ @warn@ @c_warn@ @WARN_PEDANTIC@ @WERROR@ $(ZLIBINC)
 noinst_LIBRARIES = libctf.a
 libctf_a_SOURCES = ctf-archive.c ctf-dump.c ctf-create.c ctf-decl.c \
-	ctf-error.c ctf-hash.c ctf-labels.c ctf-lookup.c ctf-open.c \
-	ctf-open-bfd.c ctf-string.c ctf-subr.c ctf-types.c ctf-util.c \
-	$(am__append_1)
+	ctf-error.c ctf-hash.c ctf-labels.c ctf-link.c ctf-lookup.c \
+	ctf-open.c ctf-open-bfd.c ctf-string.c ctf-subr.c ctf-types.c \
+	ctf-util.c $(am__append_1)
 all: config.h
 	$(MAKE) $(AM_MAKEFLAGS) all-am
 
@@ -409,6 +409,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/ctf-error.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/ctf-hash.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/ctf-labels.Po@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/ctf-link.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/ctf-lookup.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/ctf-open-bfd.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/ctf-open.Po@am__quote@
diff --git a/libctf/ctf-create.c b/libctf/ctf-create.c
index d75de91..fc37d6a 100644
--- a/libctf/ctf-create.c
+++ b/libctf/ctf-create.c
@@ -470,6 +470,8 @@ ctf_update (ctf_file_t *fp)
   nfp->ctf_dtoldid = fp->ctf_dtnextid - 1;
   nfp->ctf_snapshots = fp->ctf_snapshots + 1;
   nfp->ctf_specific = fp->ctf_specific;
+  nfp->ctf_link_inputs = fp->ctf_link_inputs;
+  nfp->ctf_link_outputs = fp->ctf_link_outputs;
   nfp->ctf_syn_ext_strtab = fp->ctf_syn_ext_strtab;
 
   nfp->ctf_snapshot_lu = fp->ctf_snapshots;
@@ -480,6 +482,8 @@ ctf_update (ctf_file_t *fp)
   nfp->ctf_str_atoms = fp->ctf_str_atoms;
   fp->ctf_str_atoms = NULL;
   memset (&fp->ctf_dtdefs, 0, sizeof (ctf_list_t));
+  fp->ctf_link_inputs = NULL;
+  fp->ctf_link_outputs = NULL;
   fp->ctf_syn_ext_strtab = NULL;
 
   fp->ctf_dvhash = NULL;
diff --git a/libctf/ctf-error.c b/libctf/ctf-error.c
index 660a30a..7f6a4ce 100644
--- a/libctf/ctf-error.c
+++ b/libctf/ctf-error.c
@@ -33,7 +33,7 @@ static const char *const _ctf_errlist[] = {
   "Symbol table information is not available",	     /* ECTF_NOSYMTAB */
   "Type information is in parent and unavailable",   /* ECTF_NOPARENT */
   "Cannot import types with different data model",   /* ECTF_DMODEL */
-  "Unused error",				     /* ECTF_UNUSED */
+  "File added to link too late",		     /* ECTF_LINKADDEDLATE */
   "Failed to allocate (de)compression buffer",	     /* ECTF_ZALLOC */
   "Failed to decompress CTF data",		     /* ECTF_DECOMPRESS */
   "External string table is not available",	     /* ECTF_STRTAB */
@@ -68,7 +68,8 @@ static const char *const _ctf_errlist[] = {
   "Name not found in CTF archive",		     /* ECTF_ARNNAME */
   "Overflow of type bitness or offset in slice",     /* ECTF_SLICEOVERFLOW */
   "Unknown section number in dump",		     /* ECTF_DUMPSECTUNKNOWN */
-  "Section changed in middle of dump"		     /* ECTF_DUMPSECTCHANGED */
+  "Section changed in middle of dump",		     /* ECTF_DUMPSECTCHANGED */
+  "Feature not yet implemented"			     /* ECTF_NOTYET */
 };
 
 static const int _ctf_nerr = sizeof (_ctf_errlist) / sizeof (_ctf_errlist[0]);
diff --git a/libctf/ctf-impl.h b/libctf/ctf-impl.h
index 03c48cf..9fb58f5 100644
--- a/libctf/ctf-impl.h
+++ b/libctf/ctf-impl.h
@@ -267,6 +267,8 @@ struct ctf_file
   unsigned long ctf_snapshots;	  /* ctf_snapshot() plus ctf_update() count.  */
   unsigned long ctf_snapshot_lu;  /* ctf_snapshot() call count at last update.  */
   ctf_archive_t *ctf_archive;	  /* Archive this ctf_file_t came from.  */
+  ctf_dynhash_t *ctf_link_inputs; /* Inputs to this link.  */
+  ctf_dynhash_t *ctf_link_outputs; /* Additional outputs from this link.  */
   char *ctf_tmp_typeslice;	  /* Storage for slicing up type names.  */
   size_t ctf_tmp_typeslicelen;	  /* Size of the typeslice.  */
   void *ctf_specific;		  /* Data for ctf_get/setspecific().  */
diff --git a/libctf/ctf-link.c b/libctf/ctf-link.c
new file mode 100644
index 0000000..8f18a49
--- /dev/null
+++ b/libctf/ctf-link.c
@@ -0,0 +1,528 @@
+/* CTF linking.
+   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 <string.h>
+
+/* Linker machinery.
+
+   CTF linking consists of adding CTF archives full of content to be merged into
+   this one to the current file (which must be writable) by calling
+   ctf_link_add_ctf().  Once this is done, a call to ctf_link() will merge the
+   type tables together, generating new CTF files as needed, with this one as a
+   parent, to contain types from the inputs which conflict.
+   ctf_link_add_strtab() takes a callback which provides string/offset pairs to
+   be added to the external symbol table and deduplicated from all CTF string
+   tables in the output link; ctf_link_shuffle_syms() takes a callback which
+   provides symtab entries in ascending order, and shuffles the function and
+   data sections to match; and ctf_link_write() emits a CTF file (if there are
+   no conflicts requiring per-compilation-unit sub-CTF files) or CTF archives
+   (otherwise) and returns it, suitable for addition in the .ctf section of the
+   output.  */
+
+/* Add a file to a link.  */
+
+static void ctf_arc_close_thunk (void *arc)
+{
+  ctf_arc_close ((ctf_archive_t *) arc);
+}
+
+static void ctf_file_close_thunk (void *file)
+{
+  ctf_file_close ((ctf_file_t *) file);
+}
+
+int
+ctf_link_add_ctf (ctf_file_t *fp, ctf_archive_t *ctf, const char *name)
+{
+  char *dupname = NULL;
+
+  if (fp->ctf_link_outputs)
+    return (ctf_set_errno (fp, ECTF_LINKADDEDLATE));
+  if (fp->ctf_link_inputs == NULL)
+    fp->ctf_link_inputs = ctf_dynhash_create (ctf_hash_string,
+					      ctf_hash_eq_string, free,
+					      ctf_arc_close_thunk);
+
+  if (fp->ctf_link_inputs == NULL)
+    goto oom;
+
+  if ((dupname = strdup (name)) == NULL)
+    goto oom;
+
+  if (ctf_dynhash_insert (fp->ctf_link_inputs, dupname, ctf) < 0)
+    goto oom;
+
+  return 0;
+ oom:
+  free (fp->ctf_link_inputs);
+  fp->ctf_link_inputs = NULL;
+  free (dupname);
+  return (ctf_set_errno (fp, ENOMEM));
+}
+
+typedef struct ctf_link_in_member_cb_arg
+{
+  ctf_file_t *out_fp;
+  const char *file_name;
+  ctf_file_t *in_fp;
+  ctf_file_t *main_input_fp;
+  const char *cu_name;
+  char *arcname;
+  int done_main_member;
+  int share_mode;
+  int in_input_cu_file;
+} ctf_link_in_member_cb_arg_t;
+
+/* Link one type into the link.  We rely on ctf_add_type() to detect
+   duplicates.  This is not terribly reliable yet (unnmamed types will be
+   mindlessly duplicated), but will improve shortly.  */
+
+static int
+ctf_link_one_type (ctf_id_t type, int isroot _libctf_unused_, void *arg_)
+{
+  ctf_link_in_member_cb_arg_t *arg = (ctf_link_in_member_cb_arg_t *) arg_;
+  ctf_file_t *per_cu_out_fp;
+  int err;
+
+  if (arg->share_mode != CTF_LINK_SHARE_UNCONFLICTED)
+    {
+      ctf_dprintf ("Share-duplicated mode not yet implemented.\n");
+      return ctf_set_errno (arg->out_fp, ECTF_NOTYET);
+    }
+
+  /* Simply call ctf_add_type: if it reports a conflict and we're adding to the
+     main CTF file, add to the per-CU archive member instead, creating it if
+     necessary.  If we got this type from a per-CU archive member, add it
+     straight back to the corresponding member in the output.  */
+
+  if (!arg->in_input_cu_file)
+    {
+      if (ctf_add_type (arg->out_fp, arg->in_fp, type) != CTF_ERR)
+	return 0;
+
+      err = ctf_errno (arg->out_fp);
+      if (err != ECTF_CONFLICT)
+	{
+	  ctf_dprintf ("Cannot link type %lx from archive member %s, input file %s "
+		       "into output link: %s\n", type, arg->arcname, arg->file_name,
+		       ctf_errmsg (err));
+	  return -1;
+	}
+      ctf_set_errno (arg->out_fp, 0);
+    }
+
+  if ((per_cu_out_fp = ctf_dynhash_lookup (arg->out_fp->ctf_link_outputs,
+					   arg->arcname)) == NULL)
+    {
+      int err;
+
+      if ((per_cu_out_fp = ctf_create (&err)) == NULL)
+	{
+	  ctf_dprintf ("Cannot create per-CU CTF archive for member %s: %s\n",
+		       arg->arcname, ctf_errmsg (err));
+	  ctf_set_errno (arg->out_fp, err);
+	  return -1;
+	}
+
+      if (ctf_dynhash_insert (arg->out_fp->ctf_link_outputs, arg->arcname,
+			      per_cu_out_fp) < 0)
+	{
+	  ctf_set_errno (arg->out_fp, ENOMEM);
+	  return -1;
+	}
+
+      ctf_import (per_cu_out_fp, arg->out_fp);
+      ctf_cuname_set (per_cu_out_fp, arg->cu_name);
+    }
+
+  if (ctf_add_type (per_cu_out_fp, arg->in_fp, type) != CTF_ERR)
+    return 0;
+
+  err = ctf_errno (per_cu_out_fp);
+  if (err == ECTF_CONFLICT)
+      /* Conflicts are possible at this stage only if a non-ld user has combined
+	 multiple TUs into a single output dictionary.  Even in this case we do not
+	 want to stop the link or propagate the error.  */
+      ctf_set_errno (arg->out_fp, 0);
+
+  return 0;					/* As above: do not lose types.  */
+}
+
+/* Merge every type and variable in this archive member into the link, so we can
+   relink things that have already had ld run on them.  We use the archive
+   member name, sans any leading '.ctf.', as the CU name for ambiguous types if
+   there is one and it's not the default: otherwise, we use the name of the
+   input file.  */
+static int
+ctf_link_one_input_archive_member (ctf_file_t *in_fp, const char *name, void *arg_)
+{
+  ctf_link_in_member_cb_arg_t *arg = (ctf_link_in_member_cb_arg_t *) arg_;
+  int err = 0;
+
+  if (strcmp (name, _CTF_SECTION) == 0)
+    {
+      /* This file is the default member of this archive, and has already been
+	 explicitly processed.
+
+	 In the default sharing mode of CTF_LINK_SHARE_UNCONFLICTED, it does no
+	 harm to rescan an existing shared repo again: all the types will just
+	 end up in the same place.  But in CTF_LINK_SHARE_DUPLICATED mode, this
+	 causes the system to erroneously conclude that all types are duplicated
+	 and should be shared, even if they are not.  */
+
+      if (arg->done_main_member)
+	return 0;
+      arg->arcname = strdup (".ctf.");
+      if (arg->arcname)
+	{
+	  char *new_name;
+
+	  new_name = ctf_str_append (arg->arcname, arg->file_name);
+	  if (new_name)
+	    arg->arcname = new_name;
+	  else
+	    free (arg->arcname);
+	}
+    }
+  else
+    {
+      arg->arcname = strdup (name);
+
+      /* Get ambiguous types from our parent.  */
+      ctf_import (in_fp, arg->main_input_fp);
+      arg->in_input_cu_file = 1;
+    }
+
+  if (!arg->arcname)
+    return ctf_set_errno (in_fp, ENOMEM);
+
+  arg->cu_name = name;
+  if (strncmp (arg->cu_name, ".ctf.", strlen (".ctf.")) == 0)
+    arg->cu_name += strlen (".ctf.");
+  arg->in_fp = in_fp;
+
+  err = ctf_type_iter_all (in_fp, ctf_link_one_type, arg);
+
+  arg->in_input_cu_file = 0;
+  free (arg->arcname);
+
+  if (err < 0)
+      return -1;				/* Errno is set for us.  */
+
+  return 0;
+}
+
+/* Link one input file's types into the output file.  */
+static void
+ctf_link_one_input_archive (void *key, void *value, void *arg_)
+{
+  const char *file_name = (const char *) key;
+  ctf_archive_t *arc = (ctf_archive_t *) value;
+  ctf_link_in_member_cb_arg_t *arg = (ctf_link_in_member_cb_arg_t *) arg_;
+  int err;
+
+  arg->file_name = file_name;
+  arg->done_main_member = 0;
+  if ((arg->main_input_fp = ctf_arc_open_by_name (arc, NULL, &err)) == NULL)
+    if (err != ECTF_ARNNAME)
+      {
+	ctf_dprintf ("Cannot open main archive member in input file %s in the "
+		     "link: skipping: %s.\n", arg->file_name,
+		     ctf_errmsg (err));
+	return;
+      }
+
+  if (ctf_link_one_input_archive_member (arg->main_input_fp,
+					 _CTF_SECTION, arg) < 0)
+    {
+      ctf_file_close (arg->main_input_fp);
+      return;
+    }
+  arg->done_main_member = 1;
+  if (ctf_archive_iter (arc, ctf_link_one_input_archive_member, arg) < 0)
+    ctf_dprintf ("Cannot traverse archive in input file %s: link "
+		 "cannot continue: %s.\n", arg->file_name,
+		 ctf_errmsg (ctf_errno (arg->out_fp)));
+  else
+    {
+      /* The only error indication to the caller is the errno: so ensure that it
+	 is zero if there was no actual error from the caller.  */
+      ctf_set_errno (arg->out_fp, 0);
+    }
+  ctf_file_close (arg->main_input_fp);
+}
+
+/* Merge types and variable sections in all files added to the link
+   together.  */
+int
+ctf_link (ctf_file_t *fp, int share_mode)
+{
+  ctf_link_in_member_cb_arg_t arg;
+
+  memset (&arg, 0, sizeof (struct ctf_link_in_member_cb_arg));
+  arg.out_fp = fp;
+  arg.share_mode = share_mode;
+
+  if (fp->ctf_link_inputs == NULL)
+    return 0;					/* Nothing to do. */
+
+  if (fp->ctf_link_outputs == NULL)
+    fp->ctf_link_outputs = ctf_dynhash_create (ctf_hash_string,
+					       ctf_hash_eq_string, free,
+					       ctf_file_close_thunk);
+
+  if (fp->ctf_link_outputs == NULL)
+    return ctf_set_errno (fp, ENOMEM);
+
+  ctf_dynhash_iter (fp->ctf_link_inputs, ctf_link_one_input_archive,
+		    &arg);
+
+  if (ctf_errno (fp) != 0)
+    return -1;
+  return 0;
+}
+
+typedef struct ctf_link_out_string_cb_arg
+{
+  const char *str;
+  uint32_t offset;
+  int err;
+} ctf_link_out_string_cb_arg_t;
+
+/* Intern a string in the string table of an output per-CU CTF file.  */
+static void
+ctf_link_intern_extern_string (void *key _libctf_unused_, void *value,
+			       void *arg_)
+{
+  ctf_file_t *fp = (ctf_file_t *) value;
+  ctf_link_out_string_cb_arg_t *arg = (ctf_link_out_string_cb_arg_t *) arg_;
+
+  fp->ctf_flags |= LCTF_DIRTY;
+  if (ctf_str_add_external (fp, arg->str, arg->offset) == NULL)
+    arg->err = ENOMEM;
+}
+
+/* Repeatedly call ADD_STRING to acquire strings from the external string table,
+   adding them to the atoms table for this CU and all subsidiary CUs.
+
+   If ctf_link() is also called, it must be called first if you want the new CTF
+   files ctf_link() can create to get their strings dedupped against the ELF
+   strtab properly.  */
+int
+ctf_link_add_strtab (ctf_file_t *fp, ctf_link_strtab_string_f *add_string,
+		     void *arg)
+{
+  const char *str;
+  uint32_t offset;
+  int err = 0;
+
+  while ((str = add_string (&offset, arg)) != NULL)
+    {
+      ctf_link_out_string_cb_arg_t iter_arg = { str, offset, 0 };
+
+      fp->ctf_flags |= LCTF_DIRTY;
+      if (ctf_str_add_external (fp, str, offset) == NULL)
+	err = ENOMEM;
+
+      ctf_dynhash_iter (fp->ctf_link_outputs, ctf_link_intern_extern_string,
+			&iter_arg);
+      if (iter_arg.err)
+	err = iter_arg.err;
+    }
+
+  return -err;
+}
+
+/* Not yet implemented.  */
+int
+ctf_link_shuffle_syms (ctf_file_t *fp _libctf_unused_,
+		       ctf_link_iter_symbol_f *add_sym _libctf_unused_,
+		       void *arg _libctf_unused_)
+{
+  return 0;
+}
+
+typedef struct ctf_name_list_accum_cb_arg
+{
+  char **names;
+  ctf_file_t *fp;
+  ctf_file_t **files;
+  size_t i;
+} ctf_name_list_accum_cb_arg_t;
+
+/* Accumulate the names and a count of the names in the link output hash,
+   and run ctf_update() on them to generate them.  */
+static void
+ctf_accumulate_archive_names (void *key, void *value, void *arg_)
+{
+  const char *name = (const char *) key;
+  ctf_file_t *fp = (ctf_file_t *) value;
+  char **names;
+  ctf_file_t **files;
+  ctf_name_list_accum_cb_arg_t *arg = (ctf_name_list_accum_cb_arg_t *) arg_;
+  int err;
+
+  if ((err = ctf_update (fp)) < 0)
+    {
+      ctf_set_errno (arg->fp, ctf_errno (fp));
+      return;
+    }
+
+  if ((names = realloc (arg->names, sizeof (char *) * ++(arg->i))) == NULL)
+    {
+      (arg->i)--;
+      ctf_set_errno (arg->fp, ENOMEM);
+      return;
+    }
+
+  if ((files = realloc (arg->files, sizeof (ctf_file_t *) * arg->i)) == NULL)
+    {
+      (arg->i)--;
+      ctf_set_errno (arg->fp, ENOMEM);
+      return;
+    }
+  arg->names = names;
+  arg->names[(arg->i) - 1] = (char *) name;
+  arg->files = files;
+  arg->files[(arg->i) - 1] = fp;
+}
+
+/* Write out a CTF archive (if there are per-CU CTF files) or a CTF file
+   (otherwise) into a new dynamically-allocated string, and return it.
+   Members with sizes above THRESHOLD are compressed.  */
+unsigned char *
+ctf_link_write (ctf_file_t *fp, size_t *size, size_t threshold)
+{
+  ctf_name_list_accum_cb_arg_t arg;
+  char **names;
+  ctf_file_t **files;
+  FILE *f = NULL;
+  int err;
+  long fsize;
+  const char *errloc;
+  unsigned char *buf = NULL;
+
+  memset (&arg, 0, sizeof (ctf_name_list_accum_cb_arg_t));
+  arg.fp = fp;
+
+  if (ctf_update (fp) < 0)
+    {
+      errloc = "CTF file construction";
+      goto err;
+    }
+
+  if (fp->ctf_link_outputs)
+    {
+      ctf_dynhash_iter (fp->ctf_link_outputs, ctf_accumulate_archive_names, &arg);
+      if (ctf_errno (fp) < 0)
+	{
+	  errloc = "hash creation";
+	  goto err;
+	}
+    }
+
+  /* No extra outputs? Just write a simple ctf_file_t.  */
+  if (arg.i == 0)
+    return ctf_write_mem (fp, size, threshold);
+
+  /* Writing an archive.  Stick ourselves (the shared repository, parent of all
+     other archives) on the front of it with the default name.  */
+  if ((names = realloc (arg.names, sizeof (char *) * (arg.i + 1))) == NULL)
+    {
+      errloc = "name reallocation";
+      goto err_no;
+    }
+  arg.names = names;
+  memmove (&(arg.names[1]), arg.names, sizeof (char *) * (arg.i));
+  arg.names[0] = (char *) _CTF_SECTION;
+
+  if ((files = realloc (arg.files,
+			sizeof (struct ctf_file *) * (arg.i + 1))) == NULL)
+    {
+      errloc = "ctf_file reallocation";
+      goto err_no;
+    }
+  arg.files = files;
+  memmove (&(arg.files[1]), arg.files, sizeof (ctf_file_t *) * (arg.i));
+  arg.files[0] = fp;
+
+  if ((f = tmpfile ()) == NULL)
+    {
+      errloc = "tempfile creation";
+      goto err_no;
+    }
+
+  if ((err = ctf_arc_write_fd (fileno (f), arg.files, arg.i + 1,
+			       (const char **) arg.names,
+			       threshold)) < 0)
+    {
+      errloc = "archive writing";
+      ctf_set_errno (fp, err);
+      goto err;
+    }
+
+  if (fseek (f, 0, SEEK_END) < 0)
+    {
+      errloc = "seeking to end";
+      goto err_no;
+    }
+
+  if ((fsize = ftell (f)) < 0)
+    {
+      errloc = "filesize determination";
+      goto err_no;
+    }
+
+  if (fseek (f, 0, SEEK_SET) < 0)
+    {
+      errloc = "filepos resetting";
+      goto err_no;
+    }
+
+  if ((buf = malloc (fsize)) == NULL)
+    {
+      errloc = "CTF archive buffer allocation";
+      goto err_no;
+    }
+
+  while (!feof (f) && fread (buf, fsize, 1, f) == 0)
+    if (ferror (f))
+      {
+	errloc = "reading archive from temporary file";
+	goto err_no;
+      }
+
+  *size = fsize;
+  free (arg.names);
+  free (arg.files);
+  return buf;
+
+ err_no:
+  ctf_set_errno (fp, errno);
+ err:
+  free (buf);
+  if (f)
+    fclose (f);
+  free (arg.names);
+  free (arg.files);
+  ctf_dprintf ("Cannot write archive in link: %s failure: %s\n", errloc,
+	       ctf_errmsg (ctf_errno (fp)));
+  return NULL;
+}
diff --git a/libctf/ctf-open.c b/libctf/ctf-open.c
index f4179cb..3bc102a 100644
--- a/libctf/ctf-open.c
+++ b/libctf/ctf-open.c
@@ -1625,6 +1625,8 @@ ctf_file_close (ctf_file_t *fp)
   ctf_free (fp->ctf_dynbase);
 
   ctf_dynhash_destroy (fp->ctf_syn_ext_strtab);
+  ctf_dynhash_destroy (fp->ctf_link_inputs);
+  ctf_dynhash_destroy (fp->ctf_link_outputs);
 
   ctf_free (fp->ctf_sxlate);
   ctf_free (fp->ctf_txlate);