Re: [PATCH v3 3/6] btf: refactor and simplify implementation

[Indu Bhagat <indu.bhagat@oracle.com>]

On 5/30/24 14:32, David Faust wrote:
> This patch heavily refactors btfout.cc to take advantage of the
> structural changes in the prior commits.
> 
> Now that inter-type references are internally stored as simply pointers,
> all the painful, brittle, confusing infrastructure that was used in the
> process of converting CTF type IDs to BTF type IDs can be thrown out.
> This greatly simplifies the entire process of converting from CTF to
> BTF, making the code cleaner, easier to read, and easier to maintain.
> 
> In addition, we no longer need to worry about destructive changes in
> internal data structures used commonly by CTF and BTF, which allows
> deleting several ancillary data structures previously used in btfout.cc.
> 
> This is nearly transparent, but a few improvements have also been made:
> 
>   1) BTF_KIND_FUNC records are now _always_ constructed at early_finish,
>      allowing us to construct records even for functions which are later
>      inlined by optimizations. DATASEC entries for functions are only
>      constructed at late_finish, to avoid incorrectly generating entries
>      for functions which get inlined.
> 

I find this aspect of the BTF specification "interesting": Neither 
BTF_KIND_VAR record, nor DATASEC entry must be emitted for optimized 
away variables.  But for functions, OTH,  BTF_KIND_FUNC (and 
BTF_KIND_FUNC_PROTO (albeit anon) ?) are expected for inlined functions, 
but no DATASEC.

Anayway, that aside, I have one comment below.  Other than that, this 
looks OK to me.

Thanks

>   2) BTF_KIND_VAR records and DATASEC entries for them are now always
>      constructed at (late) finish, which avoids cases where we could
>      incorrectly create records for variables which were completely
>      optimized away.  This fixes PR debug/113566 for non-LTO builds.
>      In LTO builds, BTF must be emitted at early_finish, so some VAR
>      records may be emitted for variables which are later optimized away.
> 
>   3) Some additional assembler comments have been added with more
>      information for debugging.
> 
> gcc/
> 	* btfout.cc (struct btf_datasec_entry): New.
> 	(struct btf_datasec): Add `id' member.  Change `entries' to use
> 	new struct btf_datasec_entry.
> 	(func_map): New hash_map.
> 	(max_translated_id): New.
> 	(btf_var_ids, btf_id_map, holes, voids, num_vars_added)
> 	(num_types_added, num_types_created): Delete.
> 	(btf_absolute_var_id, btf_relative_var_id, btf_absolute_func_id)
> 	(btf_relative_func_id, btf_absolute_datasec_id, init_btf_id_map)
> 	(get_btf_id, set_btf_id, btf_emit_id_p): Delete.
> 	(btf_removed_type_p): Delete.
> 	(btf_dtd_kind, btf_emit_type_p): New helpers.
> 	(btf_fwd_to_enum_p, btf_calc_num_vbytes): Use them.
> 	(btf_collect_datasec): Delete.
> 	(btf_dtd_postprocess_cb, btf_dvd_emit_preprocess_cb)
> 	(btf_dtd_emit_preprocess_cb, btf_emit_preprocess): Delete.
> 	(btf_dmd_representable_bitfield_p): Adapt to type reference changes
> 	and delete now-unused ctfc argument.
> 	(btf_asm_datasec_type_ref): Delete.
> 	(btf_asm_type_ref): Adapt to type reference changes, simplify.
> 	(btf_asm_type): Likewise. Mark struct/union types with bitfield
> 	members.
> 	(btf_asm_array): Adapt to data structure changes.
> 	(btf_asm_varent): Likewise.
> 	(btf_asm_sou_member): Likewise. Ensure non-bitfield members are
> 	correctly re-encoded if struct or union contains any bitfield.
> 	(btf_asm_func_arg, btf_asm_func_type, btf_asm_datasec_entry)
> 	(btf_asm_datasec_type): Adapt to data structure changes.
> 	(output_btf_header): Adapt to other changes, simplify type
> 	length calculation, add info to assembler comments.
> 	(output_btf_vars): Adapt to other changes.
> 	(output_btf_strs): Fix overlong lines.
> 	(output_asm_btf_sou_fields, output_asm_btf_enum_list)
> 	(output_asm_btf_func_args_list, output_asm_btf_vlen_bytes)
> 	(output_asm_btf_type, output_btf_types, output_btf_func_types)
> 	(output_btf_datasec_types): Adapt to other changes.
> 	(btf_init_postprocess): Delete.
> 	(btf_output): Change to only perform output.
> 	(btf_early_add_const_void, btf_early_add_func_records): New.
> 	(btf_early_finish): Use them here. New.
> 	(btf_datasec_push_entry): Adapt to data structure changes.
> 	(btf_datasec_add_func, btf_datasec_add_var): New.
> 	(btf_late_add_func_datasec_entries): New.
> 	(btf_emit_variable_p): New helper.
> 	(btf_late_add_vars): Use it here. New.
> 	(btf_type_list_cb, btf_late_collect_translated_types): New.
> 	(btf_late_assign_func_ids, btf_late_assign_var_ids)
> 	(btf_late_assign_datasec_ids): New.
> 	(btf_finish): Remove unused argument. Call new btf_late*
> 	functions and btf_output.
> 	(btf_finalize): Adapt to data structure changes.
> 	* ctfc.h (struct ctf_dtdef): Convert existing boolean flags to
> 	BOOL_BITFIELD and reorder.
> 	(struct ctf_dvdef): Add dvd_id member.
> 	(btf_finish): Remove argument from prototype.
> 	(get_btf_id): Delete prototype.
> 	(funcs_traverse_callback, traverse_btf_func_types): Add an
> 	explanatory comment.
> 	* dwarf2ctf.cc (ctf_debug_finish): Remove unused argument.
> 	* dwarf2ctf.h: Analogous change.
> 	* dwarf2out.cc: Likewise.
> ---
>   gcc/btfout.cc    | 1254 +++++++++++++++++++---------------------------
>   gcc/ctfc.h       |   17 +-
>   gcc/dwarf2ctf.cc |    6 +-
>   gcc/dwarf2ctf.h  |    2 +-
>   gcc/dwarf2out.cc |    2 +-
>   5 files changed, 539 insertions(+), 742 deletions(-)
> 
> diff --git a/gcc/btfout.cc b/gcc/btfout.cc
> index 40e8d8c5c01b..32fda14f704b 100644
> --- a/gcc/btfout.cc
> +++ b/gcc/btfout.cc
> @@ -63,53 +63,44 @@ static char btf_info_section_label[MAX_BTF_LABEL_BYTES];
>   
>   #define BTF_INVALID_TYPEID 0xFFFFFFFF
>   
> -/* Mapping of CTF variables to the IDs they will be assigned when they are
> -   converted to BTF_KIND_VAR type records. Strictly accounts for the index
> -   from the start of the variable type entries, does not include the number
> -   of types emitted prior to the variable records.  */
> -static GTY (()) hash_map <ctf_dvdef_ref, unsigned> *btf_var_ids;
> -
> -/* Mapping of type IDs from original CTF ID to BTF ID. Types do not map
> -   1-to-1 from CTF to BTF. To avoid polluting the CTF container when updating
> -   type references-by-ID, we use this map instead.  */
> -static ctf_id_t * btf_id_map = NULL;
> -
> -/* Information for creating the BTF_KIND_DATASEC records.  */
> +/* Internal representation of an entry in a BTF_KIND_DATASEC record.  */
> +struct btf_datasec_entry
> +{
> +  union {
> +    ctf_dvdef_ref dvd; /* Reference to the underlying variable represented.  */
> +    ctf_dtdef_ref dtd; /* Reference to the underlying type represented.  */
> +  };
> +  bool is_var;	       /* True iff this entry represents a variable.  */
> +  uint32_t size;       /* Size of variable or function, in bytes.
> +			  For functions, always zero at compile time.  */
> +};
> +
> +/* Internal representation of a BTF_KIND_DATASEC record.  */
>   typedef struct btf_datasec
>   {
> -  const char *name;                    /* Section name, e.g. ".bss".  */
> -  uint32_t name_offset;                /* Offset to name in string table.  */
> -  vec<struct btf_var_secinfo> entries; /* Variable entries in this section.  */
> +  ctf_id_t id;				 /* BTF type ID of this record.  */
> +  const char *name;			 /* Section name, e.g. ".bss".  */
> +  uint32_t name_offset;			 /* Offset to name in string table.  */
> +  vec<struct btf_datasec_entry> entries; /* Entries in this section.  */
>   } btf_datasec_t;
>   
>   /* One BTF_KIND_DATASEC record is created for each output data section which
>      will hold at least one variable.  */
>   static vec<btf_datasec_t> datasecs;
>   
> -/* Holes occur for types which are present in the CTF container, but are either
> -   non-representable or redundant in BTF.  */
> -static vec<ctf_id_t> holes;
> -
> -/* CTF definition(s) of void. Only one definition of void should be generated.
> -   We should not encounter more than one definition of void, but use a vector
> -   to be safe.  */
> -static vec<ctf_id_t> voids;
> -
>   /* Functions in BTF have two separate type records - one for the prototype
>      (BTF_KIND_FUNC_PROTO), as well as a BTF_KIND_FUNC. CTF_K_FUNCTION types
>      map closely to BTF_KIND_FUNC_PROTO, but the BTF_KIND_FUNC records must be
>      created. This vector holds them.  */
>   static GTY (()) vec<ctf_dtdef_ref, va_gc> *funcs;
>   
> -/* The number of BTF variables added to the TU CTF container.  */
> -static unsigned int num_vars_added = 0;
> -
> -/* The number of BTF types added to the TU CTF container.  */
> -static unsigned int num_types_added = 0;
> +/* Maps BTF_KIND_FUNC_PROTO to the BTF_KIND_FUNC record for it.  Used when
> +   creating DATASEC entries.  */
> +static GTY (()) hash_map<ctf_dtdef_ref, ctf_dtdef_ref> *func_map;
>   
> -/* The number of types synthesized for BTF that do not correspond to
> -   CTF types.  */
> -static unsigned int num_types_created = 0;
> +/* Highest BTF ID assigned to any regular type translated from CTF.
> +   Does not include BTF_KIND_{VAR,FUNC,DATASEC} types.  */
> +static ctf_id_t max_translated_id = 0;
>   
>   /* Name strings for BTF kinds.
>      Note: the indices here must match the type defines in btf.h.  */
> @@ -155,6 +146,16 @@ get_btf_kind (uint32_t ctf_kind)
>     return BTF_KIND_UNKN;
>   }
>   
> +/* Convenience wrapper around get_btf_kind for the common case.  */
> +
> +static uint32_t
> +btf_dtd_kind (ctf_dtdef_ref dtd)
> +{
> +  if (!dtd)
> +    return BTF_KIND_UNKN;
> +  return get_btf_kind (CTF_V2_INFO_KIND (dtd->dtd_data.ctti_info));
> +}
> +
>   /* Some BTF types, like BTF_KIND_FUNC_PROTO, are anonymous.  The machinery
>      in btfout to emit BTF, may reset dtd_data->ctti_name, but does not update
>      the name in the ctf_dtdef_ref type object (deliberate choice).  This
> @@ -168,101 +169,20 @@ get_btf_type_name (ctf_dtdef_ref dtd)
>     return (dtd->dtd_data.ctti_name) ? dtd->dtd_name : anon;
>   }
>   
> -/* Helper routines to map between 'relative' and 'absolute' IDs.
> -
> -   In BTF all records (including variables) are output in one long list, and all
> -   inter-type references are via index into that list.  But internally since we
> -   a) translate from CTF, which separates variable records from regular types
> -   and b) create some additional types after the fact, things like VAR and FUNC
> -   records are stored in separate vectors with their own indices.  These
> -   functions map between the 'relative' IDs (i.e.  indices in their respective
> -   containers) and 'absolute' IDs (i.e.  indices in the final contiguous
> -   output list), which goes in order:
> -     all normal type records translated from CTF
> -     all BTF_KIND_VAR records
> -     all BTF_KIND_FUNC records (synthesized split function records)
> -     all BTF_KIND_DATASEC records (synthesized)
> -
> -   The extra '+ 1's below are to account for the implicit "void" record, which
> -   has index 0 but isn't actually contained in the type list.  */
> -
> -/* Return the final BTF ID of the variable at relative index REL.  */
> -
> -static ctf_id_t
> -btf_absolute_var_id (ctf_id_t rel)
> -{
> -  return rel + (num_types_added + 1);
> -}
> -
> -/* Return the relative index of the variable with final BTF ID ABS.  */
> -
> -static ctf_id_t
> -btf_relative_var_id (ctf_id_t abs)
> -{
> -  return abs - (num_types_added + 1);
> -}
> -
> -/* Return the final BTF ID of the func record at relative index REL.  */
> -
> -static ctf_id_t
> -btf_absolute_func_id (ctf_id_t rel)
> -{
> -  return rel + (num_types_added + 1) + num_vars_added;
> -}
> -
> -/* Return the relative index of the func record with final BTF ID ABS.  */
> -
> -static ctf_id_t
> -btf_relative_func_id (ctf_id_t abs)
> -{
> -  return abs - ((num_types_added + 1) + num_vars_added);
> -}
> -
> -/* Return the final BTF ID of the datasec record at relative index REL.  */
> -
> -static ctf_id_t
> -btf_absolute_datasec_id (ctf_id_t rel)
> -{
> -  return rel + (num_types_added + 1) + num_vars_added + funcs->length ();
> -}
> -
> -
> -/* Allocate the btf_id_map, and initialize elements to BTF_INVALID_TYPEID.  */
> -
> -static void
> -init_btf_id_map (size_t len)
> +static bool
> +btf_emit_type_p (ctf_dtdef_ref dtd)
>   {
> -  btf_id_map = XNEWVEC (ctf_id_t, len);
> +  uint32_t kind = btf_dtd_kind (dtd);
>   
> -  btf_id_map[0] = BTF_VOID_TYPEID;
> -  for (size_t i = 1; i < len; i++)
> -    btf_id_map[i] = BTF_INVALID_TYPEID;
> -}
> +  if (kind == BTF_KIND_UNKN)
> +    /* This type is not representable in BTF.  */
> +    return false;
>   
> -/* Return the BTF type ID of CTF type ID KEY, or BTF_INVALID_TYPEID if the CTF
> -   type with ID KEY does not map to a BTF type.  */
> +  if (kind == BTF_KIND_INT && dtd->dtd_data.ctti_size == 0)
> +    /* This is a (redundant) definition of void.  */
> +    return false;
>   
> -ctf_id_t
> -get_btf_id (ctf_id_t key)
> -{
> -  return btf_id_map[key];
> -}
> -
> -/* Set the CTF type ID KEY to map to BTF type ID VAL.  */
> -
> -static inline void
> -set_btf_id (ctf_id_t key, ctf_id_t val)
> -{
> -  btf_id_map[key] = val;
> -}
> -
> -/* Return TRUE iff the given CTF type ID maps to a BTF type which will
> -   be emitted.  */
> -static inline bool
> -btf_emit_id_p (ctf_id_t id)
> -{
> -  return ((btf_id_map[id] != BTF_VOID_TYPEID)
> -	  && (btf_id_map[id] <= BTF_MAX_TYPE));
> +  return true;
>   }
>   
>   /* Return true if DTD is a forward-declared enum.  The BTF representation
> @@ -271,9 +191,8 @@ btf_emit_id_p (ctf_id_t id)
>   static bool
>   btf_fwd_to_enum_p (ctf_dtdef_ref dtd)
>   {
> -  uint32_t btf_kind = get_btf_kind (CTF_V2_INFO_KIND (dtd->dtd_data.ctti_info));
> -
> -  return (btf_kind == BTF_KIND_FWD && dtd->dtd_data.ctti_type == CTF_K_ENUM);
> +  uint32_t kind = btf_dtd_kind (dtd);
> +  return (kind == BTF_KIND_FWD && dtd->dtd_data.ctti_type == CTF_K_ENUM);
>   }
>   
>   /* Each BTF type can be followed additional, variable-length information
> @@ -285,7 +204,7 @@ btf_calc_num_vbytes (ctf_dtdef_ref dtd)
>   {
>     uint64_t vlen_bytes = 0;
>   
> -  uint32_t kind = get_btf_kind (CTF_V2_INFO_KIND (dtd->dtd_data.ctti_info));
> +  uint32_t kind = btf_dtd_kind (dtd);
>     uint32_t vlen = CTF_V2_INFO_VLEN (dtd->dtd_data.ctti_info);
>   
>     switch (kind)
> @@ -355,41 +274,6 @@ init_btf_sections (void)
>   			       BTF_INFO_SECTION_LABEL, btf_label_num++);
>   }
>   
> -/* Push a BTF datasec variable entry INFO into the datasec named SECNAME,
> -   creating the datasec if it does not already exist.  */
> -
> -static void
> -btf_datasec_push_entry (ctf_container_ref ctfc, const char *secname,
> -			struct btf_var_secinfo info)
> -{
> -  if (secname == NULL)
> -    return;
> -
> -  for (size_t i = 0; i < datasecs.length (); i++)
> -    if (strcmp (datasecs[i].name, secname) == 0)
> -      {
> -	datasecs[i].entries.safe_push (info);
> -	return;
> -      }
> -
> -  /* If we don't already have a datasec record for secname, make one.  */
> -
> -  uint32_t str_off;
> -  ctf_add_string (ctfc, secname, &str_off, CTF_AUX_STRTAB);
> -  if (strcmp (secname, ""))
> -    ctfc->ctfc_aux_strlen += strlen (secname) + 1;
> -
> -  btf_datasec_t ds;
> -  ds.name = secname;
> -  ds.name_offset = str_off;
> -
> -  ds.entries.create (0);
> -  ds.entries.safe_push (info);
> -
> -  datasecs.safe_push (ds);
> -}
> -
> -
>   /* Return the section name, as of interest to btf_collect_datasec, for the
>      given symtab node.  Note that this deliberately returns NULL for objects
>      which do not go in a section btf_collect_datasec cares about.  */
> @@ -418,301 +302,15 @@ get_section_name (symtab_node *node)
>     return section_name;
>   }
>   
> -/* Construct all BTF_KIND_DATASEC records for CTFC. One such record is created
> -   for each non-empty data-containing section in the output. Each record is
> -   followed by a variable number of entries describing the variables stored
> -   in that section.  */
> -
> -static void
> -btf_collect_datasec (ctf_container_ref ctfc)
> -{
> -  cgraph_node *func;
> -  FOR_EACH_FUNCTION (func)
> -    {
> -      dw_die_ref die = lookup_decl_die (func->decl);
> -      if (die == NULL)
> -	continue;
> -
> -      ctf_dtdef_ref dtd = ctf_dtd_lookup (ctfc, die);
> -      if (dtd == NULL)
> -	continue;
> -
> -      if (DECL_EXTERNAL (func->decl)
> -	  && (lookup_attribute ("kernel_helper",
> -				DECL_ATTRIBUTES (func->decl))) != NULL_TREE)
> -	continue;
> -
> -      /* Functions actually get two types: a BTF_KIND_FUNC_PROTO, and
> -	 also a BTF_KIND_FUNC.  But the CTF container only allocates one
> -	 type per function, which matches closely with BTF_KIND_FUNC_PROTO.
> -	 For each such function, also allocate a BTF_KIND_FUNC entry.
> -	 These will be output later.  */
> -      ctf_dtdef_ref func_dtd = ggc_cleared_alloc<ctf_dtdef_t> ();
> -      func_dtd->dtd_data = dtd->dtd_data;
> -      func_dtd->dtd_data.ctti_type = dtd->dtd_type;
> -      func_dtd->linkage = dtd->linkage;
> -      func_dtd->dtd_name = dtd->dtd_name;
> -      /* +1 for the sentinel type not in the types map.  */
> -      func_dtd->dtd_type = num_types_added + num_types_created + 1;
> -
> -      /* Only the BTF_KIND_FUNC type actually references the name. The
> -	 BTF_KIND_FUNC_PROTO is always anonymous.  */
> -      dtd->dtd_data.ctti_name = 0;
> -
> -      vec_safe_push (funcs, func_dtd);
> -      num_types_created++;
> -
> -      /* Mark any 'extern' funcs and add DATASEC entries for them.  */
> -      if (DECL_EXTERNAL (func->decl))
> -	{
> -	  func_dtd->linkage = BTF_FUNC_EXTERN;
> -
> -	  const char *section_name = get_section_name (func);
> -	  /* Note: get_section_name () returns NULL for functions in text
> -	     section.  This is intentional, since we do not want to generate
> -	     DATASEC entries for them.  */
> -	  if (section_name == NULL)
> -	    continue;
> -
> -	  struct btf_var_secinfo info;
> -
> -	  info.type = func_dtd->dtd_type;
> -
> -	  /* Both zero at compile time.  */
> -	  info.size = 0;
> -	  info.offset = 0;
> -
> -	  btf_datasec_push_entry (ctfc, section_name, info);
> -	}
> -    }
> -
> -  varpool_node *node;
> -  FOR_EACH_VARIABLE (node)
> -    {
> -      dw_die_ref die = lookup_decl_die (node->decl);
> -      if (die == NULL)
> -	continue;
> -
> -      ctf_dvdef_ref dvd = ctf_dvd_lookup (ctfc, die);
> -      if (dvd == NULL)
> -	continue;
> -
> -      /* Mark extern variables.  */
> -      if (DECL_EXTERNAL (node->decl))
> -	{
> -	  dvd->dvd_visibility = BTF_VAR_GLOBAL_EXTERN;
> -
> -	  /* PR112849: avoid assuming a section for extern decls without
> -	     an explicit section, which would result in incorrectly
> -	     emitting a BTF_KIND_DATASEC entry for them.  */
> -	  if (node->get_section () == NULL)
> -	    continue;
> -	}
> -
> -      const char *section_name = get_section_name (node);
> -      if (section_name == NULL)
> -	continue;
> -
> -      struct btf_var_secinfo info;
> -
> -      info.type = 0;
> -      unsigned int *var_id = btf_var_ids->get (dvd);
> -      if (var_id)
> -	info.type = btf_absolute_var_id (*var_id);
> -      else
> -	continue;
> -
> -      info.size = 0;
> -      tree size = DECL_SIZE_UNIT (node->decl);
> -      if (tree_fits_uhwi_p (size))
> -	info.size = tree_to_uhwi (size);
> -      else if (VOID_TYPE_P (TREE_TYPE (node->decl)))
> -	info.size = 1;
> -
> -      /* Offset is left as 0 at compile time, to be filled in by loaders such
> -	 as libbpf.  */
> -      info.offset = 0;
> -
> -      btf_datasec_push_entry (ctfc, section_name, info);
> -    }
> -
> -  num_types_created += datasecs.length ();
> -}
> -
> -/* Return true if the type ID is that of a type which will not be emitted (for
> -   example, if it is not representable in BTF).  */
> -
> -static bool
> -btf_removed_type_p (ctf_id_t id)
> -{
> -  return holes.contains (id);
> -}
> -
> -/* Adjust the given type ID to account for holes and duplicate definitions of
> -   void.  */
> -
> -static ctf_id_t
> -btf_adjust_type_id (ctf_id_t id)
> -{
> -  size_t n;
> -  ctf_id_t i = 0;
> -
> -  /* Do not adjust invalid type markers.  */
> -  if (id == BTF_INVALID_TYPEID)
> -    return id;
> -
> -  for (n = 0; n < voids.length (); n++)
> -    if (id == voids[n])
> -      return BTF_VOID_TYPEID;
> -
> -  for (n = 0; n < holes.length (); n++)
> -    {
> -      if (holes[n] < id)
> -	i++;
> -      else if (holes[n] == id)
> -	return BTF_VOID_TYPEID;
> -    }
> -
> -  return id - i;
> -}
> -
> -/* Postprocessing callback routine for types.  */
> -
> -int
> -btf_dtd_postprocess_cb (ctf_dtdef_ref *slot, ctf_container_ref arg_ctfc)
> -{
> -  ctf_dtdef_ref ctftype = (ctf_dtdef_ref) * slot;
> -
> -  size_t index = ctftype->dtd_type;
> -  gcc_assert (index <= arg_ctfc->ctfc_types->elements ());
> -
> -  uint32_t ctf_kind, btf_kind;
> -
> -  ctf_kind = CTF_V2_INFO_KIND (ctftype->dtd_data.ctti_info);
> -  btf_kind = get_btf_kind (ctf_kind);
> -
> -  if (btf_kind == BTF_KIND_UNKN)
> -    /* This type is not representable in BTF. Create a hole.  */
> -    holes.safe_push (ctftype->dtd_type);
> -
> -  else if (btf_kind == BTF_KIND_INT && ctftype->dtd_data.ctti_size == 0)
> -    {
> -      /* This is a (redundant) definition of void.  */
> -      voids.safe_push (ctftype->dtd_type);
> -      holes.safe_push (ctftype->dtd_type);
> -    }
> -
> -  arg_ctfc->ctfc_types_list[index] = ctftype;
> -
> -  return 1;
> -}
> -
> -/* Preprocessing callback routine for variables.  */
> -
> -int
> -btf_dvd_emit_preprocess_cb (ctf_dvdef_ref *slot, ctf_container_ref arg_ctfc)
> -{
> -  ctf_dvdef_ref var = (ctf_dvdef_ref) * slot;
> -
> -  /* If this is an extern variable declaration with a defining declaration
> -     later, skip it so that only the defining declaration is emitted.
> -     This is the same case, fix and reasoning as in CTF; see PR105089.  */
> -  if (ctf_dvd_ignore_lookup (arg_ctfc, var->dvd_key))
> -    return 1;
> -
> -  /* Do not add variables which refer to unsupported types.  */
> -  if (!voids.contains (var->dvd_type->dtd_type)
> -      && btf_removed_type_p (var->dvd_type->dtd_type))
> -    return 1;
> -
> -  arg_ctfc->ctfc_vars_list[num_vars_added] = var;
> -  btf_var_ids->put (var, num_vars_added);
> -
> -  num_vars_added++;
> -  num_types_created++;
> -
> -  return 1;
> -}
> -
> -/* Preprocessing callback routine for types.  */
> -
> -static void
> -btf_dtd_emit_preprocess_cb (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
> -{
> -  if (!btf_emit_id_p (dtd->dtd_type))
> -    return;
> -
> -  ctfc->ctfc_num_vlen_bytes += btf_calc_num_vbytes (dtd);
> -}
> -
> -/* Preprocess the CTF information to prepare for BTF output.  BTF is almost a
> -   subset of CTF, with many small differences in encoding, and lacking support
> -   for some types (notably floating point formats).
> -
> -   During the preprocessing pass:
> -   - Ascertain that the sorted list of types has been prepared.  For the BTF
> -     generation process, this is taken care of by the btf_init_postprocess ().
> -
> -   - BTF_KIND_FUNC and BTF_KIND_DATASEC records are constructed. These types do
> -     not have analogues in CTF (the analogous type to CTF_K_FUNCTION is
> -     BTF_KIND_FUNC_PROTO), but can be relatively easily deduced from CTF
> -     information.
> -
> -   - Construct BTF_KIND_VAR records, representing variables.
> -
> -   - Calculate the total size in bytes of variable-length information following
> -     BTF type records. This is used for outputting the BTF header.
> -
> -   After preprocessing, all BTF information is ready to be output:
> -   - ctfc->ctfc_types_list holdstypes converted from CTF types. This does not
> -     include KIND_VAR, KIND_FUNC, nor KIND_DATASEC types. These types have been
> -     re-encoded to the appropriate representation in BTF.
> -   - ctfc->ctfc_vars_list holds all variables which should be output.
> -     Variables of unsupported types are not present in this list.
> -   - Vector 'funcs' holds all BTF_KIND_FUNC types, one to match each
> -     BTF_KIND_FUNC_PROTO.
> -   - Vector 'datasecs' holds all BTF_KIND_DATASEC types.  */
> -
> -static void
> -btf_emit_preprocess (ctf_container_ref ctfc)
> -{
> -  size_t num_ctf_types = ctfc->ctfc_types->elements ();
> -  size_t num_ctf_vars = ctfc->ctfc_vars->elements ();
> -  size_t i;
> -
> -  if (num_ctf_types)
> -    {
> -      gcc_assert (ctfc->ctfc_types_list);
> -      /* Preprocess the types.  */
> -      for (i = 1; i <= num_ctf_types; i++)
> -	btf_dtd_emit_preprocess_cb (ctfc, ctfc->ctfc_types_list[i]);
> -    }
> -
> -  btf_var_ids = hash_map<ctf_dvdef_ref, unsigned int>::create_ggc (100);
> -
> -  if (num_ctf_vars)
> -    {
> -      /* Allocate and construct the list of variables. While BTF variables are
> -	 not distinct from types (in that variables are simply types with
> -	 BTF_KIND_VAR), it is simpler to maintain a separate list of variables
> -	 and append them to the types list during output.  */
> -      ctfc->ctfc_vars_list = ggc_vec_alloc<ctf_dvdef_ref>(num_ctf_vars);
> -      ctfc->ctfc_vars->traverse<ctf_container_ref, btf_dvd_emit_preprocess_cb>
> -	(ctfc);
> -
> -      ctfc->ctfc_num_vlen_bytes += (num_vars_added * sizeof (struct btf_var));
> -    }
> -
> -  btf_collect_datasec (ctfc);
> -}
> -
>   /* Return true iff DMD is a member description of a bit-field which can be
>      validly represented in BTF.  */
>   
>   static bool
> -btf_dmd_representable_bitfield_p (ctf_container_ref ctfc, ctf_dmdef_t *dmd)
> +btf_dmd_representable_bitfield_p (ctf_dmdef_t *dmd)
>   {
> -  ctf_dtdef_ref ref_type = ctfc->ctfc_types_list[dmd->dmd_type->dtd_type];
> +  ctf_dtdef_ref ref_type = dmd->dmd_type;
> +  if (!ref_type)
> +    return false;
>   
>     if (CTF_V2_INFO_KIND (ref_type->dtd_data.ctti_info) == CTF_K_SLICE)
>       {
> @@ -734,76 +332,34 @@ btf_dmd_representable_bitfield_p (ctf_container_ref ctfc, ctf_dmdef_t *dmd)
>   /* Asm'out a reference to another BTF type.  */
>   
>   static void
> -btf_asm_type_ref (const char *prefix, ctf_container_ref ctfc, ctf_id_t ctf_id)
> +btf_asm_type_ref (const char *prefix, ctf_dtdef_ref dtd)
>   {
> -  ctf_id_t btf_id = get_btf_id (ctf_id);
> -  if (btf_id == BTF_VOID_TYPEID || btf_id == BTF_INVALID_TYPEID)
> -    {
> -      /* There is no explicit void type.
> -	 Also handle any invalid refs that made it this far, just in case.  */
> -      dw2_asm_output_data (4, btf_id, "%s: void", prefix);
> -    }
> +  if (!dtd || !btf_emit_type_p (dtd))
> +    dw2_asm_output_data (4, BTF_VOID_TYPEID, "%s: void", prefix);
>     else
>       {
> -      gcc_assert (btf_id <= num_types_added);
> -
> -      /* Ref to a standard type in the types list.  Note: take care that we
> -	 must index the type list by the original CTF id, not the BTF id.  */
> -      ctf_dtdef_ref ref_type = ctfc->ctfc_types_list[ctf_id];
> -      uint32_t ref_kind
> -	= get_btf_kind (CTF_V2_INFO_KIND (ref_type->dtd_data.ctti_info));
> -
> -      const char *kind_name = btf_fwd_to_enum_p (ref_type)
> -	? btf_kind_name (BTF_KIND_ENUM)
> -	: btf_kind_name (ref_kind);
> -
> -      dw2_asm_output_data (4, btf_id, "%s: (BTF_KIND_%s '%s')",
> -			   prefix, kind_name,
> -			   get_btf_type_name (ref_type));
> -    }
> -}
> -
> -/* Asm'out a reference to a BTF_KIND_VAR or BTF_KIND_FUNC type.  These type
> -   kinds are BTF-specific, and should only be referred to by entries in
> -   BTF_KIND_DATASEC records.  */
> -
> -static void
> -btf_asm_datasec_type_ref (const char *prefix, ctf_container_ref ctfc,
> -			  ctf_id_t btf_id)
> -{
> -  if (btf_id >= num_types_added + 1
> -      && btf_id < num_types_added + num_vars_added + 1)
> -    {
> -      /* Ref to a variable.  Should only appear in DATASEC entries.  */
> -      ctf_id_t var_id = btf_relative_var_id (btf_id);
> -      ctf_dvdef_ref dvd = ctfc->ctfc_vars_list[var_id];
> -      dw2_asm_output_data (4, btf_id, "%s: (BTF_KIND_VAR '%s')",
> -			   prefix, dvd->dvd_name);
> -
> -    }
> -  else if (btf_id >= num_types_added + num_vars_added + 1)
> -    {
> -      /* Ref to a FUNC record.  */
> -      size_t func_id = btf_relative_func_id (btf_id);
> -      ctf_dtdef_ref ref_type = (*funcs)[func_id];
> -      dw2_asm_output_data (4, btf_id, "%s: (BTF_KIND_FUNC '%s')",
> -			   prefix, get_btf_type_name (ref_type));
> +      uint32_t kind = btf_dtd_kind (dtd);
> +      if (btf_fwd_to_enum_p (dtd))
> +	kind = BTF_KIND_ENUM;
> +      else if (kind == BTF_KIND_FUNC_PROTO && dtd->dtd_type > max_translated_id)
> +	kind = BTF_KIND_FUNC;
> +
> +      dw2_asm_output_data (4, dtd->dtd_type, "%s: (BTF_KIND_%s '%s')",
> +			   prefix, btf_kind_name (kind),
> +			   get_btf_type_name (dtd));
>       }
> -  else
> -    /* The caller should not be calling this.  */
> -    gcc_unreachable ();
>   }
>   
>   /* Asm'out a BTF type. This routine is responsible for the bulk of the task
>      of converting CTF types to their BTF representation.  */
>   
>   static void
> -btf_asm_type (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
> +btf_asm_type (ctf_dtdef_ref dtd)
>   {
>     uint32_t btf_kind, btf_kflag, btf_vlen, btf_size;
>     uint32_t ctf_info = dtd->dtd_data.ctti_info;
>   
> -  btf_kind = get_btf_kind (CTF_V2_INFO_KIND (ctf_info));
> +  btf_kind = btf_dtd_kind (dtd);
>     btf_size = dtd->dtd_data.ctti_size;
>     btf_vlen = CTF_V2_INFO_VLEN (ctf_info);
>   
> @@ -822,17 +378,17 @@ btf_asm_type (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>   
>     if (btf_kind == BTF_KIND_STRUCT || btf_kind == BTF_KIND_UNION)
>       {
> -      /* If a struct/union has ANY bitfield members, set kflag=1.
> -	 Note that we must also change the encoding of every member to encode
> -	 both member bitfield size (stealing most-significant 8 bits) and bit
> -	 offset (LS 24 bits). This is done during preprocessing.  */
> +      /* If a struct/union has ANY bitfield members, set kflag=1.  */
>         ctf_dmdef_t *dmd;
>         for (dmd = dtd->dtd_u.dtu_members;
>   	   dmd != NULL; dmd = (ctf_dmdef_t *) ctf_dmd_list_next (dmd))
>   	{
>   	  /* Set kflag if this member is a representable bitfield.  */
> -	  if (btf_dmd_representable_bitfield_p (ctfc, dmd))
> -	    btf_kflag = 1;
> +	  if (btf_dmd_representable_bitfield_p (dmd))
> +	    {
> +	      btf_kflag = 1;
> +	      break;
> +	    }
>   	}
>       }
>   
> @@ -866,7 +422,7 @@ btf_asm_type (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>   		    : BTF_KF_ENUM_SIGNED;
>         if (dtd->dtd_data.ctti_size == 0x8)
>   	btf_kind = BTF_KIND_ENUM64;
> -   }
> +    }
>   
>     /* PR debug/112656.  BTF_KIND_FUNC_PROTO is always anonymous.  */
>     else if (btf_kind == BTF_KIND_FUNC_PROTO)
> @@ -874,7 +430,7 @@ btf_asm_type (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>   
>     dw2_asm_output_data (4, dtd->dtd_data.ctti_name,
>   		       "TYPE %" PRIu64 " BTF_KIND_%s '%s'",
> -		       get_btf_id (dtd->dtd_type), btf_kind_name (btf_kind),
> +		       dtd->dtd_type, btf_kind_name (btf_kind),
>   		       get_btf_type_name (dtd));
>     dw2_asm_output_data (4, BTF_TYPE_INFO (btf_kind, btf_kflag, btf_vlen),
>   		       "btt_info: kind=%u, kflag=%u, vlen=%u",
> @@ -900,30 +456,29 @@ btf_asm_type (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>         break;
>       }
>   
> -  ctf_id_t ref_id = dtd->dtd_data.ctti_type;
> -  btf_asm_type_ref ("btt_type", ctfc, ref_id);
> +  btf_asm_type_ref ("btt_type", dtd->ref_type);
>   }
>   
>   /* Asm'out the variable information following a BTF_KIND_ARRAY.  */
>   
>   static void
> -btf_asm_array (ctf_container_ref ctfc, ctf_arinfo_t arr)
> +btf_asm_array (ctf_arinfo_t arr)
>   {
> -  btf_asm_type_ref ("bta_elem_type", ctfc, arr.ctr_contents->dtd_type);
> -  btf_asm_type_ref ("bta_index_type", ctfc, arr.ctr_index->dtd_type);
> +  btf_asm_type_ref ("bta_elem_type", arr.ctr_contents);
> +  btf_asm_type_ref ("bta_index_type", arr.ctr_index);
>     dw2_asm_output_data (4, arr.ctr_nelems, "bta_nelems");
>   }
>   
>   /* Asm'out a BTF_KIND_VAR.  */
>   
>   static void
> -btf_asm_varent (ctf_container_ref ctfc, ctf_dvdef_ref var)
> +btf_asm_varent (ctf_dvdef_ref var)
>   {
> -  dw2_asm_output_data (4, var->dvd_name_offset, "TYPE %u BTF_KIND_VAR '%s'",
> -		       (*(btf_var_ids->get (var)) + num_types_added + 1),
> -		       var->dvd_name);
> +  dw2_asm_output_data (4, var->dvd_name_offset,
> +		       "TYPE %" PRIu64 " BTF_KIND_VAR '%s'",
> +		       var->dvd_id, var->dvd_name);
>     dw2_asm_output_data (4, BTF_TYPE_INFO (BTF_KIND_VAR, 0, 0), "btv_info");
> -  btf_asm_type_ref ("btv_type", ctfc, var->dvd_type->dtd_type);
> +  btf_asm_type_ref ("btv_type", var->dvd_type);
>     dw2_asm_output_data (4, var->dvd_visibility, "btv_linkage");
>   }
>   
> @@ -931,23 +486,22 @@ btf_asm_varent (ctf_container_ref ctfc, ctf_dvdef_ref var)
>      BTF_KIND_UNION.  */
>   
>   static void
> -btf_asm_sou_member (ctf_container_ref ctfc, ctf_dmdef_t * dmd, unsigned int idx)
> +btf_asm_sou_member (ctf_dmdef_t * dmd, unsigned int idx)
>   {
> -  ctf_dtdef_ref ref_type = ctfc->ctfc_types_list[dmd->dmd_type->dtd_type];
> -  ctf_id_t base_type = dmd->dmd_type->dtd_type;
> +  ctf_dtdef_ref base_type = dmd->dmd_type;
>     uint64_t sou_offset = dmd->dmd_offset;
>   
>     dw2_asm_output_data (4, dmd->dmd_name_offset,
>   		       "MEMBER '%s' idx=%u",
>   		       dmd->dmd_name, idx);
>   
> -  /* Re-encode bitfields to BTF representation.  */
> -  if (CTF_V2_INFO_KIND (ref_type->dtd_data.ctti_info) == CTF_K_SLICE)
> +  if (base_type
> +      && CTF_V2_INFO_KIND (base_type->dtd_data.ctti_info) == CTF_K_SLICE)
>       {
> -      if (btf_dmd_representable_bitfield_p (ctfc, dmd))
> +      if (btf_dmd_representable_bitfield_p (dmd))
>   	{
> -	  unsigned short word_offset = ref_type->dtd_u.dtu_slice.cts_offset;
> -	  unsigned short bits = ref_type->dtd_u.dtu_slice.cts_bits;
> +	  unsigned short word_offset = base_type->dtd_u.dtu_slice.cts_offset;
> +	  unsigned short bits = base_type->dtd_u.dtu_slice.cts_bits;
>   
>   	  /* Pack the bit offset and bitfield size together.  */
>   	  sou_offset += word_offset;
> @@ -955,17 +509,17 @@ btf_asm_sou_member (ctf_container_ref ctfc, ctf_dmdef_t * dmd, unsigned int idx)
>   	  sou_offset |= ((bits & 0xff) << 24);
>   
>   	  /* Refer to the base type of the slice.  */
> -	  base_type = ref_type->dtd_u.dtu_slice.cts_type->dtd_type;
> +	  base_type = base_type->dtd_u.dtu_slice.cts_type;
>   	}
>         else
>   	{
>   	  /* Bitfield cannot be represented in BTF.  Emit the member as having
>   	     'void' type.  */
> -	  base_type = BTF_VOID_TYPEID;
> +	  base_type = NULL;
>   	}
>       }
>   
> -  btf_asm_type_ref ("btm_type", ctfc, base_type);
> +  btf_asm_type_ref ("btm_type", base_type);
>     dw2_asm_output_data (4, sou_offset, "btm_offset");
>   }
>   
> @@ -988,86 +542,68 @@ btf_asm_enum_const (unsigned int size, ctf_dmdef_t * dmd, unsigned int idx)
>   /* Asm'out a function parameter description following a BTF_KIND_FUNC_PROTO.  */
>   
>   static void
> -btf_asm_func_arg (ctf_container_ref ctfc, ctf_func_arg_t * farg,
> -		  size_t stroffset)
> +btf_asm_func_arg (ctf_func_arg_t * farg, size_t stroffset)
>   {
>     /* If the function arg does not have a name, refer to the null string at
>        the start of the string table. This ensures correct encoding for varargs
>        '...' arguments.  */
>     if ((farg->farg_name != NULL) && strcmp (farg->farg_name, ""))
> -    dw2_asm_output_data (4, farg->farg_name_offset + stroffset, "farg_name");
> +    dw2_asm_output_data (4, farg->farg_name_offset + stroffset,
> +			 "farg_name '%s'", farg->farg_name);
>     else
> -    dw2_asm_output_data (4, 0, "farg_name");
> -
> -  ctf_id_t ref_id = BTF_VOID_TYPEID;
> -  if (farg->farg_type && !btf_removed_type_p (farg->farg_type->dtd_type))
> -    ref_id = farg->farg_type->dtd_type;
> +    dw2_asm_output_data (4, 0, "farg_name ''");
>   
> -  btf_asm_type_ref ("farg_type", ctfc, ref_id);
> +  btf_asm_type_ref ("farg_type", farg->farg_type);
>   }
>   
>   /* Asm'out a BTF_KIND_FUNC type.  */
>   
>   static void
> -btf_asm_func_type (ctf_container_ref ctfc, ctf_dtdef_ref dtd, ctf_id_t id)
> +btf_asm_func_type (ctf_dtdef_ref dtd)
>   {
> -  ctf_id_t ref_id = dtd->dtd_data.ctti_type;
>     dw2_asm_output_data (4, dtd->dtd_data.ctti_name,
>   		       "TYPE %" PRIu64 " BTF_KIND_FUNC '%s'",
> -		       btf_absolute_func_id (id), get_btf_type_name (dtd));
> +		       dtd->dtd_type, get_btf_type_name (dtd));
>     dw2_asm_output_data (4, BTF_TYPE_INFO (BTF_KIND_FUNC, 0, dtd->linkage),
>   		       "btt_info: kind=%u, kflag=%u, linkage=%u",
>   		       BTF_KIND_FUNC, 0, dtd->linkage);
> -  btf_asm_type_ref ("btt_type", ctfc, ref_id);
> +  btf_asm_type_ref ("btt_type", dtd->ref_type);
>   }
>   
> -/* Collect the name for the DATASEC reference required to be output as a
> -   symbol. */
> +/* Asm'out a variable entry following a BTF_KIND_DATASEC.  */
>   
> -static const char *
> -get_name_for_datasec_entry (ctf_container_ref ctfc, ctf_id_t ref_id)
> +static void
> +btf_asm_datasec_entry (struct btf_datasec_entry entry)
>   {
> -  if (ref_id >= num_types_added + 1
> -      && ref_id < num_types_added + num_vars_added + 1)
> +  const char *symbol_name = NULL;
> +  if (entry.is_var)
>       {
> -      /* Ref to a variable.  Should only appear in DATASEC entries.  */
> -      ctf_id_t var_id = btf_relative_var_id (ref_id);
> -      ctf_dvdef_ref dvd = ctfc->ctfc_vars_list[var_id];
> -      return dvd->dvd_name;
> +      symbol_name = entry.dvd->dvd_name;
> +      dw2_asm_output_data (4, entry.dvd->dvd_id,
> +			   "bts_type: (BTF_KIND_VAR '%s')", symbol_name);
>       }
> -  else if (ref_id >= num_types_added + num_vars_added + 1)
> +  else
>       {
> -      /* Ref to a FUNC record.  */
> -      size_t func_id = btf_relative_func_id (ref_id);
> -      ctf_dtdef_ref ref_type = (*funcs)[func_id];
> -      return get_btf_type_name (ref_type);
> +      symbol_name = entry.dtd->dtd_name;
> +      btf_asm_type_ref ("bts_type", entry.dtd);
>       }
> -  return NULL;
> -}
> -
> -/* Asm'out a variable entry following a BTF_KIND_DATASEC.  */
>   
> -static void
> -btf_asm_datasec_entry (ctf_container_ref ctfc, struct btf_var_secinfo info)
> -{
> -  const char *symbol_name = get_name_for_datasec_entry (ctfc, info.type);
> -  btf_asm_datasec_type_ref ("bts_type", ctfc, info.type);
>     if (!btf_with_core_debuginfo_p () || symbol_name == NULL)
> -    dw2_asm_output_data (4, info.offset, "bts_offset");
> +    dw2_asm_output_data (4, 0, "bts_offset");
>     else
>       dw2_asm_output_offset (4, symbol_name, NULL, "bts_offset");
> -  dw2_asm_output_data (4, info.size, "bts_size");
> +
> +  dw2_asm_output_data (4, entry.size, "bts_size");
>   }
>   
>   /* Asm'out a whole BTF_KIND_DATASEC, including its variable entries.  */
>   
>   static void
> -btf_asm_datasec_type (ctf_container_ref ctfc, btf_datasec_t ds, ctf_id_t id,
> -		      size_t stroffset)
> +btf_asm_datasec_type (btf_datasec_t ds)
>   {
> -  dw2_asm_output_data (4, ds.name_offset + stroffset,
> +  dw2_asm_output_data (4, ds.name_offset,
>   		       "TYPE %" PRIu64 " BTF_KIND_DATASEC '%s'",
> -		       btf_absolute_datasec_id (id), ds.name);
> +		       ds.id, ds.name);
>     dw2_asm_output_data (4, BTF_TYPE_INFO (BTF_KIND_DATASEC, 0,
>   					 ds.entries.length ()),
>   		       "btt_info: n_entries=%u", ds.entries.length ());
> @@ -1075,7 +611,7 @@ btf_asm_datasec_type (ctf_container_ref ctfc, btf_datasec_t ds, ctf_id_t id,
>        loaders such as libbpf.  */
>     dw2_asm_output_data (4, 0, "btt_size");
>     for (size_t i = 0; i < ds.entries.length (); i++)
> -    btf_asm_datasec_entry (ctfc, ds.entries[i]);
> +    btf_asm_datasec_entry (ds.entries[i]);
>   }
>   
>   /* Compute and output the header information for a .BTF section.  */
> @@ -1094,20 +630,11 @@ output_btf_header (ctf_container_ref ctfc)
>   
>      uint32_t type_off = 0, type_len = 0;
>      uint32_t str_off = 0, str_len = 0;
> -   uint32_t datasec_vlen_bytes = 0;
>   
>      if (!ctfc_is_empty_container (ctfc))
>        {
> -       for (size_t i = 0; i < datasecs.length (); i++)
> -	 {
> -	   datasec_vlen_bytes += ((datasecs[i].entries.length ())
> -				  * sizeof (struct btf_var_secinfo));
> -	 }
> -
>          /* Total length (bytes) of the types section.  */
> -       type_len = (num_types_added * sizeof (struct btf_type))
> -	 + (num_types_created * sizeof (struct btf_type))
> -	 + datasec_vlen_bytes
> +       type_len = ctfc->ctfc_num_types * sizeof (struct btf_type)
>   	 + ctfc->ctfc_num_vlen_bytes;
>   
>          str_off = type_off + type_len;
> @@ -1119,7 +646,9 @@ output_btf_header (ctf_container_ref ctfc)
>      /* Offset of type section.  */
>      dw2_asm_output_data (4, type_off, "type_off");
>      /* Length of type section in bytes.  */
> -   dw2_asm_output_data (4, type_len, "type_len");
> +   dw2_asm_output_data (4, type_len, "type_len: ntypes=%u, vlen=%u",
> +			(uint32_t) ctfc->ctfc_num_types,
> +			(uint32_t) ctfc->ctfc_num_vlen_bytes);
>       /* Offset of string section.  */
>      dw2_asm_output_data (4, str_off, "str_off");
>       /* Length of string section in bytes.  */
> @@ -1132,11 +661,11 @@ static void
>   output_btf_vars (ctf_container_ref ctfc)
>   {
>     size_t i;
> -  size_t num_ctf_vars = num_vars_added;
> +  size_t num_ctf_vars = ctfc->ctfc_vars_list_count;
>     if (num_ctf_vars)
>       {
>         for (i = 0; i < num_ctf_vars; i++)
> -	btf_asm_varent (ctfc, ctfc->ctfc_vars_list[i]);
> +	btf_asm_varent (ctfc->ctfc_vars_list[i]);
>       }
>   }
>   
> @@ -1151,7 +680,8 @@ output_btf_strs (ctf_container_ref ctfc)
>   
>     while (ctf_string)
>       {
> -      dw2_asm_output_nstring (ctf_string->cts_str, -1, "btf_string, str_pos = 0x%x", str_pos);
> +      dw2_asm_output_nstring (ctf_string->cts_str, -1,
> +			      "btf_string, str_pos = 0x%x", str_pos);
>         str_pos += strlen(ctf_string->cts_str) + 1;
>         ctf_string = ctf_string->cts_next;
>       }
> @@ -1159,7 +689,8 @@ output_btf_strs (ctf_container_ref ctfc)
>     ctf_string = ctfc->ctfc_aux_strtable.ctstab_head;
>     while (ctf_string)
>       {
> -      dw2_asm_output_nstring (ctf_string->cts_str, -1, "btf_aux_string, str_pos = 0x%x", str_pos);
> +      dw2_asm_output_nstring (ctf_string->cts_str, -1,
> +			      "btf_aux_string, str_pos = 0x%x", str_pos);
>         str_pos += strlen(ctf_string->cts_str) + 1;
>         ctf_string = ctf_string->cts_next;
>       }
> @@ -1169,7 +700,7 @@ output_btf_strs (ctf_container_ref ctfc)
>      BTF_KIND_UNION type.  */
>   
>   static void
> -output_asm_btf_sou_fields (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
> +output_asm_btf_sou_fields (ctf_dtdef_ref dtd)
>   {
>     ctf_dmdef_t * dmd;
>   
> @@ -1177,7 +708,7 @@ output_asm_btf_sou_fields (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>     for (dmd = dtd->dtd_u.dtu_members;
>          dmd != NULL; dmd = (ctf_dmdef_t *) ctf_dmd_list_next (dmd))
>       {
> -      btf_asm_sou_member (ctfc, dmd, idx);
> +      btf_asm_sou_member (dmd, idx);
>         idx++;
>       }
>   }
> @@ -1185,8 +716,7 @@ output_asm_btf_sou_fields (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>   /* Output all enumerator constants following a BTF_KIND_ENUM{,64}.  */
>   
>   static void
> -output_asm_btf_enum_list (ctf_container_ref ARG_UNUSED (ctfc),
> -			  ctf_dtdef_ref dtd)
> +output_asm_btf_enum_list (ctf_dtdef_ref dtd)
>   {
>     ctf_dmdef_t * dmd;
>   
> @@ -1209,7 +739,7 @@ output_asm_btf_func_args_list (ctf_container_ref ctfc,
>     ctf_func_arg_t * farg;
>     for (farg = dtd->dtd_u.dtu_argv;
>          farg != NULL; farg = (ctf_func_arg_t *) ctf_farg_list_next (farg))
> -    btf_asm_func_arg (ctfc, farg, farg_name_offset);
> +    btf_asm_func_arg (farg, farg_name_offset);
>   }
>   
>   /* Output the variable portion of a BTF type record. The information depends
> @@ -1220,7 +750,7 @@ output_asm_btf_vlen_bytes (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>   {
>     uint32_t btf_kind, encoding;
>   
> -  btf_kind = get_btf_kind (CTF_V2_INFO_KIND (dtd->dtd_data.ctti_info));
> +  btf_kind = btf_dtd_kind (dtd);
>   
>     if (btf_kind == BTF_KIND_UNKN)
>       return;
> @@ -1233,8 +763,7 @@ output_asm_btf_vlen_bytes (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>         if (dtd->dtd_data.ctti_size < 1)
>   	break;
>   
> -      /* In BTF the CHAR `encoding' seems to not be used, so clear it
> -         here.  */
> +      /* In BTF the CHAR `encoding' seems to not be used, so clear it here.  */
>         dtd->dtd_u.dtu_enc.cte_format &= ~BTF_INT_CHAR;
>   
>         encoding = BTF_INT_DATA (dtd->dtd_u.dtu_enc.cte_format,
> @@ -1245,16 +774,16 @@ output_asm_btf_vlen_bytes (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>         break;
>   
>       case BTF_KIND_ARRAY:
> -      btf_asm_array (ctfc, dtd->dtd_u.dtu_arr);
> +      btf_asm_array (dtd->dtd_u.dtu_arr);
>         break;
>   
>       case BTF_KIND_STRUCT:
>       case BTF_KIND_UNION:
> -      output_asm_btf_sou_fields (ctfc, dtd);
> +      output_asm_btf_sou_fields (dtd);
>         break;
>   
>       case BTF_KIND_ENUM:
> -      output_asm_btf_enum_list (ctfc, dtd);
> +      output_asm_btf_enum_list (dtd);
>         break;
>   
>       case BTF_KIND_FUNC_PROTO:
> @@ -1284,9 +813,9 @@ output_asm_btf_vlen_bytes (ctf_container_ref ctfc, ctf_dtdef_ref dtd)
>   static void
>   output_asm_btf_type (ctf_container_ref ctfc, ctf_dtdef_ref type)
>   {
> -  if (btf_emit_id_p (type->dtd_type))
> +  if (btf_emit_type_p (type))
>       {
> -      btf_asm_type (ctfc, type);
> +      btf_asm_type (type);
>         output_asm_btf_vlen_bytes (ctfc, type);
>       }
>   }
> @@ -1298,7 +827,9 @@ static void
>   output_btf_types (ctf_container_ref ctfc)
>   {
>     size_t i;
> -  size_t num_types = ctfc->ctfc_types->elements ();
> +  size_t num_types;
> +  num_types = ctfc->ctfc_types->elements ();
> +
>     if (num_types)
>       {
>         for (i = 1; i <= num_types; i++)
> @@ -1309,76 +840,45 @@ output_btf_types (ctf_container_ref ctfc)
>   /* Output all BTF_KIND_FUNC type records.  */
>   
>   static void
> -output_btf_func_types (ctf_container_ref ctfc)
> +output_btf_func_types (void)
>   {
>     ctf_dtdef_ref ref;
>     unsigned i;
>     FOR_EACH_VEC_ELT (*funcs, i, ref)
> -    btf_asm_func_type (ctfc, ref, i);
> +    btf_asm_func_type (ref);
>   }
>   
>   /* Output all BTF_KIND_DATASEC records.  */
>   
>   static void
> -output_btf_datasec_types (ctf_container_ref ctfc)
> +output_btf_datasec_types (void)
>   {
> -  size_t name_offset = ctfc_get_strtab_len (ctfc, CTF_STRTAB);
> -
> -  for (size_t i = 0; i < datasecs.length(); i++)
> -    btf_asm_datasec_type (ctfc, datasecs[i], i, name_offset);
> +  for (size_t i = 0; i < datasecs.length (); i++)
> +    btf_asm_datasec_type (datasecs[i]);
>   }
>   
> -/* Postprocess the CTF debug data post initialization.
> -
> -   During the postprocess pass:
> -
> -   - Prepare the sorted list of BTF types.
> -
> -     The sorted list of BTF types is, firstly, used for lookup (during the BTF
> -     generation process) of CTF/BTF types given a typeID.
> -
> -     Secondly, in the emitted BTF section, BTF Types need to be in the sorted
> -     order of their type IDs.  The BTF types section is viewed as an array,
> -     with type IDs used to index into that array.  It is essential that every
> -     type be placed at the exact index corresponding to its ID, or else
> -     references to that type from other types will no longer be correct.
> -
> -   - References to void types are converted to reference BTF_VOID_TYPEID. In
> -     CTF, a distinct type is used to encode void.
> -
> -   - Bitfield struct/union members are converted to BTF encoding. CTF uses
> -     slices to encode bitfields, but BTF does not have slices and encodes
> -     bitfield information directly in the variable-length btf_member
> -     descriptions following the struct or union type.
> -
> -   - Unrepresentable types are removed. We cannot have any invalid BTF types
> -     appearing in the output so they must be removed, and type ids of other
> -     types and references adjust accordingly. This also involves ensuring that
> -     BTF descriptions of struct members referring to unrepresentable types are
> -     not emitted, as they would be nonsensical.
> -
> -   - Adjust inner- and inter-type references-by-ID to account for removed
> -     types, and construct the types list.  */
> +/* Write out all BTF debug info.  */
>   
>   void
> -btf_init_postprocess (void)
> +btf_output (ctf_container_ref ctfc)
>   {
> -  ctf_container_ref tu_ctfc = ctf_get_tu_ctfc ();
> -
> -  holes.create (0);
> -  voids.create (0);
> +  output_btf_header (ctfc);
> +  output_btf_types (ctfc);
> +  output_btf_vars (ctfc);
> +  output_btf_func_types ();
> +  output_btf_datasec_types ();
> +  output_btf_strs (ctfc);
> +}
>   
> -  num_types_added = 0;
> -  num_types_created = 0;
> +/* Workaround for 'const void' variables.  These variables are sometimes used
> +   in eBPF programs to address kernel symbols.  DWARF does not generate const
> +   qualifier on void type, so we would incorrectly emit these variables
> +   without the const qualifier.  Find any such variables, and update them to
> +   refer to a new 'const' modifier type for void.  */
>   
> -  /* Workaround for 'const void' variables.  These variables are sometimes used
> -     in eBPF programs to address kernel symbols.  DWARF does not generate const
> -     qualifier on void type, so we would incorrectly emit these variables
> -     without the const qualifier.
> -     Unfortunately we need the TREE node to know it was const, and we need
> -     to create the const modifier type (if needed) now, before making the types
> -     list.  So we can't avoid iterating with FOR_EACH_VARIABLE here, and then
> -     again when creating the DATASEC entries.  */
> +static void
> +btf_early_add_const_void (ctf_container_ref ctfc)
> +{
>     ctf_dtdef_ref constvoid_dtd = NULL;
>     varpool_node *var;
>     FOR_EACH_VARIABLE (var)
> @@ -1393,120 +893,389 @@ btf_init_postprocess (void)
>   	  if (die == NULL)
>   	    continue;
>   
> -	  ctf_dvdef_ref dvd = ctf_dvd_lookup (tu_ctfc, die);
> +	  ctf_dvdef_ref dvd = ctf_dvd_lookup (ctfc, die);
>   	  if (dvd == NULL)
>   	    continue;
>   
>   	  /* Create the 'const' modifier type for void.  */
>   	  if (constvoid_dtd == NULL)
> -	    constvoid_dtd = ctf_add_reftype (tu_ctfc, CTF_ADD_ROOT,
> +	    constvoid_dtd = ctf_add_reftype (ctfc, CTF_ADD_ROOT,
>   					     dvd->dvd_type, CTF_K_CONST, NULL);
>   	  dvd->dvd_type = constvoid_dtd;
>   	}
>       }
> +}
>   
> -  size_t i;
> -  size_t num_ctf_types = tu_ctfc->ctfc_types->elements ();
> +/* Functions actually get two type records: a BTF_KIND_FUNC_PROTO, and also a
> +   BTF_KIND_FUNC.  But the CTF container only allocates one type per function,
> +   which matches closely with BTF_KIND_FUNC_PROTO.  For each such function,
> +   construct a BTF_KIND_FUNC entry.  This is done early, because we want FUNC
> +   records even for functions which are later inlined by optimizations.  */
>   
> -  if (num_ctf_types)
> +static void
> +btf_early_add_func_records (ctf_container_ref ctfc)
> +{
> +  cgraph_node *func;
> +  FOR_EACH_FUNCTION (func)
>       {
> -      init_btf_id_map (num_ctf_types + 1);
> -
> -      /* Allocate the types list and traverse all types, placing each type
> -	 at the index according to its ID.  Add 1 because type ID 0 always
> -	 represents VOID.  */
> -      tu_ctfc->ctfc_types_list
> -	= ggc_vec_alloc<ctf_dtdef_ref>(num_ctf_types + 1);
> -      tu_ctfc->ctfc_types->traverse<ctf_container_ref, btf_dtd_postprocess_cb>
> -	(tu_ctfc);
> -
> -      /* Build mapping of CTF type ID -> BTF type ID, and count total number
> -	 of valid BTF types added.  */
> -      for (i = 1; i <= num_ctf_types; i++)
> -	{
> -	  ctf_dtdef_ref dtd = tu_ctfc->ctfc_types_list[i];
> -	  ctf_id_t btfid = btf_adjust_type_id (dtd->dtd_type);
> -	  set_btf_id (dtd->dtd_type, btfid);
> -	  if (btfid < BTF_MAX_TYPE && (btfid != BTF_VOID_TYPEID))
> -	    num_types_added ++;
> -	}
> +      dw_die_ref die = lookup_decl_die (func->decl);
> +      if (die == NULL)
> +	continue;
> +
> +      ctf_dtdef_ref dtd = ctf_dtd_lookup (ctfc, die);
> +      if (dtd == NULL)
> +	continue;
> +
> +      /* Do not add FUNC records for kernel helpers.  */
> +      if (DECL_EXTERNAL (func->decl)
> +	  && (lookup_attribute ("kernel_helper",
> +				DECL_ATTRIBUTES (func->decl))) != NULL_TREE)
> +	continue;
> +
> +      ctf_dtdef_ref func_dtd = ggc_cleared_alloc<ctf_dtdef_t> ();
> +      func_dtd->dtd_data = dtd->dtd_data;
> +      func_dtd->dtd_data.ctti_type = dtd->dtd_type;
> +      func_dtd->ref_type = dtd;
> +      func_dtd->linkage = dtd->linkage;
> +      func_dtd->dtd_name = dtd->dtd_name;
> +      /* Type ID will be assigned just before output.  */
> +
> +      /* Only the BTF_KIND_FUNC type actually references the name.
> +	 The BTF_KIND_FUNC_PROTO is always anonymous.  */
> +      dtd->dtd_data.ctti_name = 0;
> +
> +      /* Mark 'extern' funcs.  */
> +      if (DECL_EXTERNAL (func->decl))
> +	func_dtd->linkage = BTF_FUNC_EXTERN;
> +
> +      /* Buffer newly created FUNC records.  We cannot simply insert them
> +	 into the types map, because types are keyed by their DWARF DIE,
> +	 and we have no unique DIE to use as a key since the FUNC_PROTOs
> +	 are already present in the map.  */
> +      vec_safe_push (funcs, func_dtd);
> +      func_map->put (dtd, func_dtd);
>       }
>   }
>   
> -/* Process and output all BTF data. Entry point of btfout.  */
> +/* Initial entry point of BTF generation, called at early_finish () after
> +   CTF information has possibly been output.  Translate all CTF information
> +   to BTF, and do any processing that must be done early, such as creating
> +   BTF_KIND_FUNC records.  */
>   
>   void
> -btf_output (const char * filename)
> +btf_early_finish (void)
>   {
>     ctf_container_ref tu_ctfc = ctf_get_tu_ctfc ();
>   
> -  init_btf_sections ();
> -
> -  datasecs.create (0);
>     vec_alloc (funcs, 16);
> +  func_map = hash_map<ctf_dtdef_ref, ctf_dtdef_ref>::create_ggc (16);
>   
> -  ctf_add_cuname (tu_ctfc, filename);
> +  btf_early_add_const_void (tu_ctfc);
> +  btf_early_add_func_records (tu_ctfc);
> +}
>   
> -  btf_emit_preprocess (tu_ctfc);
> +/* Push a BTF datasec entry ENTRY into the datasec named SECNAME,
> +   creating the datasec record if it does not already exist.  */
>   
> -  output_btf_header (tu_ctfc);
> -  output_btf_types (tu_ctfc);
> -  output_btf_vars (tu_ctfc);
> -  output_btf_func_types (tu_ctfc);
> -  output_btf_datasec_types (tu_ctfc);
> -  output_btf_strs (tu_ctfc);
> +static void
> +btf_datasec_push_entry (ctf_container_ref ctfc, const char *secname,
> +			struct btf_datasec_entry entry)
> +{
> +  if (secname == NULL)
> +    return;
> +
> +  /* If we already have a datasec record for the appropriate section,
> +     append the new entry to it.  */
> +  for (size_t i = 0; i < datasecs.length (); i++)
> +    if (strcmp (datasecs[i].name, secname) == 0)
> +      {
> +	datasecs[i].entries.safe_push (entry);
> +	return;
> +      }
> +
> +  /* If we don't already have a datasec record for secname, make one.  */
> +  uint32_t str_off;
> +  ctf_add_string (ctfc, secname, &str_off, CTF_AUX_STRTAB);
> +  if (strcmp (secname, ""))
> +    ctfc->ctfc_aux_strlen += strlen (secname) + 1;
> +
> +  /* Note: ID will be assigned just before output.  */
> +  btf_datasec_t ds;
> +  ds.name = secname;
> +  ds.name_offset = str_off;
> +
> +  /* Insert the entry into the new datasec record.  */
> +  ds.entries.create (1);
> +  ds.entries.quick_push (entry);
> +
> +  /* Insert the datasec record itself.  */
> +  datasecs.safe_push (ds);
>   }
>   
> -/* Reset all state for BTF generation so that we can rerun the compiler within
> -   the same process.  */
> +/* Create a datasec entry for a function, and insert it into the datasec
> +   record for the appropriate section.  Create the record if it does not
> +   yet exist.  */
>   
> -void
> -btf_finalize (void)
> +static void
> +btf_datasec_add_func (ctf_container_ref ctfc, cgraph_node *func,
> +		      ctf_dtdef_ref func_dtd)
>   {
> -  btf_info_section = NULL;
> +  const char *section_name = get_section_name (func);
>   
> -  /* Clear preprocessing state.  */
> -  num_vars_added = 0;
> -  num_types_added = 0;
> -  num_types_created = 0;
> +  /* Note: get_section_name () returns NULL for functions in text
> +     section.  This is intentional, since we do not want to generate
> +     DATASEC entries for them.  */
> +  if (section_name == NULL)
> +    return;
>   
> -  holes.release ();
> -  voids.release ();
> -  for (size_t i = 0; i < datasecs.length (); i++)
> -    datasecs[i].entries.release ();
> -  datasecs.release ();
> +  struct btf_datasec_entry entry;
> +  gcc_assert (func_dtd);
> +  entry.dtd = func_dtd;
> +  entry.is_var = false;
>   
> -  funcs = NULL;
> +  /* Size is left as zero at compile time, to be filled in by loaders
> +     such as libbpf.  */
> +  entry.size = 0;
>   
> -  btf_var_ids->empty ();
> -  btf_var_ids = NULL;
> +  btf_datasec_push_entry (ctfc, section_name, entry);
> +}
>   
> -  free (btf_id_map);
> -  btf_id_map = NULL;
> +/* Create a datasec entry for a variable, and insert it into the datasec
> +   record for the appropriate section.  Create the record if it does not
> +   yet exist.  */
>   
> -  ctf_container_ref tu_ctfc = ctf_get_tu_ctfc ();
> -  ctfc_delete_container (tu_ctfc);
> -  tu_ctfc = NULL;
> +static void
> +btf_datasec_add_var (ctf_container_ref ctfc, varpool_node *var,
> +		     ctf_dvdef_ref dvd)
> +{
> +  /* PR112849: avoid assuming a section for extern decls without
> +     an explicit section, which would result in incorrectly
> +     emitting a BTF_KIND_DATASEC entry for them.  */
> +  if (DECL_EXTERNAL (var->decl) && var->get_section () == NULL)
> +    return;
> +
> +  const char *section_name = get_section_name (var);
> +  if (section_name == NULL)
> +    return;
> +
> +  gcc_assert (dvd);
> +  struct btf_datasec_entry entry;
> +  entry.dvd = dvd;
> +  entry.is_var = true;
> +  entry.size = 0;
> +
> +  tree size = DECL_SIZE_UNIT (var->decl);
> +  if (tree_fits_uhwi_p (size))
> +    entry.size = tree_to_uhwi (size);
> +  else if (VOID_TYPE_P (TREE_TYPE (var->decl)))
> +    entry.size = 1;
> +
> +  btf_datasec_push_entry (ctfc, section_name, entry);
>   }
>   
> -/* Initial entry point of BTF generation, called at early_finish () after
> -   CTF information has possibly been output.  Translate all CTF information
> -   to BTF, and do any processing that must be done early, such as creating
> -   BTF_KIND_FUNC records.  */
> +/* Add datasec entries for functions to CTFC.  */
>   
> -void
> -btf_early_finish (void)
> +static void
> +btf_late_add_func_datasec_entries (ctf_container_ref ctfc)
> +{
> +  /* We need to create FUNC records at early_finish, so that we have them
> +     even for functions which are later inlined by optimization passes.
> +     But on the other hand, we do not want datasec entries for such functions,
> +     so only create the datasec entries for them late.  This loop will not
> +     hit functions which have already been inlined.  */
> +  cgraph_node *func;
> +  FOR_EACH_FUNCTION (func)
> +    {
> +      dw_die_ref die = lookup_decl_die (func->decl);
> +      if (die == NULL)
> +	continue;
> +
> +      ctf_dtdef_ref dtd = ctf_dtd_lookup (ctfc, die);
> +      if (dtd == NULL)
> +	continue;
> +
> +      ctf_dtdef_ref *pdtd = func_map->get (dtd);
> +      if (pdtd && DECL_EXTERNAL (func->decl))
> +	btf_datasec_add_func (ctfc, func, *pdtd);
> +    }
> +}
> +
> +/* Helper function used to determine whether or not a BTF_KIND_VAR record
> +   for the variable VAR shall be emitted.  */
> +
> +static bool
> +btf_emit_variable_p (ctf_container_ref ctfc, varpool_node *var,
> +		     ctf_dvdef_ref *pdvd)
> +{
> +  dw_die_ref die = lookup_decl_die (var->decl);
> +  if (die == NULL)
> +    return false;
> +
> +  ctf_dvdef_ref dvd = ctf_dvd_lookup (ctfc, die);
> +  if (dvd == NULL)
> +    return false;
> +
> +  /* If this is an extern variable declaration with a defining declaration
> +     later, skip it so that only the defining declaration is emitted.
> +     This is the same case, fix and reasoning as in CTF; see PR105089.  */
> +  if (ctf_dvd_ignore_lookup (ctfc, dvd->dvd_key))
> +    return false;
> +
> +  /* Skip variables with unrepresentable types.  */
> +  if (!btf_emit_type_p (dvd->dvd_type))
> +    return false;
> +
> +  *pdvd = dvd;
> +  return true;
> +}
> +
> +/* Add BTF_KIND_VAR records for variables.  */
> +
> +static void
> +btf_late_add_vars (ctf_container_ref ctfc)
>   {
> -  btf_init_postprocess ();
> +  size_t num_ctf_vars = ctfc->ctfc_vars->elements ();
> +
> +  ctfc->ctfc_vars_list = ggc_vec_alloc<ctf_dvdef_ref>(num_ctf_vars);
> +
> +  varpool_node *var;
> +  ctf_dvdef_ref dvd;
> +  FOR_EACH_VARIABLE (var)
> +    {
> +      if (!btf_emit_variable_p (ctfc, var, &dvd))
> +	continue;
> +
> +      /* Mark 'extern' variables.  */
> +      if (DECL_EXTERNAL (var->decl))
> +	dvd->dvd_visibility = BTF_VAR_GLOBAL_EXTERN;
> +
> +      /* Add the variable to the vars list.  */
> +      ctfc->ctfc_vars_list[ctfc->ctfc_vars_list_count++] = dvd;
> +
> +      /* Add a BTF_KIND_DATASEC entry for the variable.  */
> +      btf_datasec_add_var (ctfc, var, dvd);
> +    }
> +}
> +
> +/* Callback used by btf_late_assign_type_ids to insert types into their initial
> +   positions in the type list.  */
> +
> +static int
> +btf_type_list_cb (ctf_dtdef_ref *slot, ctf_container_ref ctfc)
> +{
> +  ctf_dtdef_ref dtd = *slot;
> +  ctfc->ctfc_types_list[dtd->dtd_type] = dtd;
> +  return 1;
> +}
> +
> +/* Construct the initial type list and assign BTF IDs for all types translated
> +   from CTF.  */
> +
> +static void
> +btf_late_collect_translated_types (ctf_container_ref ctfc)
> +{
> +  size_t num_ctf_types = ctfc->ctfc_types->elements ();
> +
> +  /* First, place each type at its CTF-assigned index in the list.
> +     The '+1' here and below is to account for the implicit void type with
> +     ID 0.  There is no real type at index 0 in the list.  */
> +  ctfc->ctfc_types_list = ggc_vec_alloc<ctf_dtdef_ref>(num_ctf_types + 1);
> +  ctfc->ctfc_types->traverse<ctf_container_ref, btf_type_list_cb> (ctfc);
> +
> +  /* Now, pass through the list and adjust IDs to account for types which will
> +     not be emitted.  This results in each type that will be emitted in BTF
> +     being assigned an appropriate ID.  Note that types which will not be
> +     emitted remain in the list; they are skipped at output time.  */
> +  unsigned int skip = 0;
> +  for (size_t i = 1; i <= num_ctf_types; i++)
> +    {
> +      ctf_dtdef_ref dtd = ctfc->ctfc_types_list[i];
> +      if (!btf_emit_type_p (dtd))
> +	{
> +	  dtd->dtd_type = BTF_INVALID_TYPEID;
> +	  skip += 1;
> +	  continue;
> +	}
> +
> +      dtd->dtd_type -= skip;
> +      ctfc->ctfc_num_types++;
> +      ctfc->ctfc_num_vlen_bytes += btf_calc_num_vbytes (dtd);
> +    }
> +
> +  max_translated_id = ctfc->ctfc_num_types;
> +  ctfc->ctfc_nextid = ctfc->ctfc_num_types + 1;
> +}
> +
> +/* Assign BTF IDs for FUNC records and account for their size.  */
> +
> +static void
> +btf_late_assign_func_ids (ctf_container_ref ctfc)
> +{
> +  ctf_dtdef_ref dtd;
> +  unsigned int i;
> +  FOR_EACH_VEC_ELT (*funcs, i, dtd)
> +    {
> +      dtd->dtd_type = ctfc->ctfc_nextid++;
> +      ctfc->ctfc_num_types++;
> +    }
> +}
> +
> +/* Assign BTF IDs for variables and account for their size.  */
> +
> +static void
> +btf_late_assign_var_ids (ctf_container_ref ctfc)
> +{
> +  for (size_t i = 0; i < ctfc->ctfc_vars_list_count; i++)
> +    {
> +      ctf_dvdef_ref dvd = ctfc->ctfc_vars_list[i];
> +      ctf_id_t id = ctfc->ctfc_nextid++;
> +      gcc_assert (id <= BTF_MAX_TYPE);
> +      dvd->dvd_id = id;
> +
> +      ctfc->ctfc_num_types++;
> +      ctfc->ctfc_num_vlen_bytes += sizeof (struct btf_var);
> +    }
> +}
> +
> +/* Assign BTF IDs for datasec records and account for their size.  */
> +
> +static void
> +btf_late_assign_datasec_ids (ctf_container_ref ctfc)
> +{
> +  for (size_t i = 0; i < datasecs.length (); i++)
> +    {
> +      datasecs[i].id = ctfc->ctfc_nextid++;
> +      datasecs[i].name_offset += ctfc_get_strtab_len (ctfc, CTF_STRTAB);
> +      ctfc->ctfc_num_types++;
> +      ctfc->ctfc_num_vlen_bytes += (datasecs[i].entries.length ()
> +				    * sizeof (struct btf_var_secinfo));
> +    }
>   }
>   
>   /* Late entry point for BTF generation, called from dwarf2out_finish ().
>      Complete and emit BTF information.  */
>   
>   void
> -btf_finish (const char * filename)
> +btf_finish (void)
>   {
> -  btf_output (filename);
> +  ctf_container_ref tu_ctfc = ctf_get_tu_ctfc ();
> +  init_btf_sections ();
> +
> +  datasecs.create (0);
> +
> +  tu_ctfc->ctfc_num_types = 0;
> +  tu_ctfc->ctfc_num_vlen_bytes = 0;
> +  tu_ctfc->ctfc_vars_list_count = 0;
> +
> +  btf_late_add_vars (tu_ctfc);
> +  btf_late_collect_translated_types (tu_ctfc);
> +  btf_late_add_func_datasec_entries (tu_ctfc);
> +  btf_late_assign_var_ids (tu_ctfc);
> +  btf_late_assign_func_ids (tu_ctfc);
> +  btf_late_assign_datasec_ids (tu_ctfc);
> +

The "late" keyword in the function names is somewhat confusing. 
btf_finish () is also be called from early_finish () (this will happen 
with LTO builds in this patch series).

> +  /* Finally, write out the complete .BTF section.  */
> +  btf_output (tu_ctfc);
>   
>     /* If compiling for BPF with CO-RE info, we cannot deallocate until after
>        CO-RE information is created, which happens very late in BPF backend.
> @@ -1516,6 +1285,27 @@ btf_finish (const char * filename)
>       btf_finalize ();
>   }
>   
> +/* Reset all state for BTF generation so that we can rerun the compiler within
> +   the same process.  */
> +
> +void
> +btf_finalize (void)
> +{
> +  btf_info_section = NULL;
> +  max_translated_id = 0;
> +
> +  for (size_t i = 0; i < datasecs.length (); i++)
> +    datasecs[i].entries.release ();
> +  datasecs.release ();
> +
> +  funcs = NULL;
> +  func_map->empty ();
> +  func_map = NULL;
> +
> +  ctf_container_ref tu_ctfc = ctf_get_tu_ctfc ();
> +  ctfc_delete_container (tu_ctfc);
> +  tu_ctfc = NULL;
> +}
>   
>   /* Traversal function for all BTF_KIND_FUNC type records.  */
>   
> diff --git a/gcc/ctfc.h b/gcc/ctfc.h
> index b2060eaf7e9b..d0b724817a7f 100644
> --- a/gcc/ctfc.h
> +++ b/gcc/ctfc.h
> @@ -164,10 +164,14 @@ struct GTY ((for_user)) ctf_dtdef
>     ctf_id_t dtd_type;	      /* Type identifier for this definition.  */
>     ctf_dtdef_ref ref_type;     /* Type referred to by this type (if any).  */
>     ctf_itype_t dtd_data;	      /* Type node.  */
> -  bool from_global_func; /* Whether this type was added from a global
> -			    function.  */
>     uint32_t linkage;           /* Used in function types.  0=local, 1=global.  */
> -  bool dtd_enum_unsigned;     /* Enum signedness.  */
> +
> +  /* Whether this type was added from a global function.  */
> +  BOOL_BITFIELD from_global_func : 1;
> +  /* Enum signedness.  */
> +  BOOL_BITFIELD dtd_enum_unsigned : 1;
> +  /* Lots of spare bits.  */
> +
>     union GTY ((desc ("ctf_dtu_d_union_selector (&%1)")))
>     {
>       /* struct, union, or enum.  */
> @@ -194,6 +198,7 @@ struct GTY ((for_user)) ctf_dvdef
>     uint32_t dvd_name_offset;	/* Offset of the name in str table.  */
>     unsigned int dvd_visibility;	/* External visibility.  0=static,1=global.  */
>     ctf_dtdef_ref dvd_type;	/* Type of variable.  */
> +  ctf_id_t dvd_id;		/* ID of this variable.  Only used for BTF.  */
>   };
>   
>   typedef struct ctf_dvdef ctf_dvdef_t;
> @@ -388,7 +393,7 @@ extern void ctf_output (const char * filename);
>   extern void ctf_finalize (void);
>   
>   extern void btf_early_finish (void);
> -extern void btf_finish (const char * filename);
> +extern void btf_finish (void);
>   extern void btf_finalize (void);
>   
>   extern ctf_container_ref ctf_get_tu_ctfc (void);
> @@ -443,7 +448,9 @@ extern int ctf_add_variable (ctf_container_ref, const char *, ctf_dtdef_ref,
>   			     dw_die_ref, unsigned int, dw_die_ref);
>   
>   extern ctf_dtdef_ref ctf_lookup_tree_type (ctf_container_ref, const tree);
> -extern ctf_id_t get_btf_id (ctf_id_t);
> +
> +/* Callback and traversal function for BTF_KIND_FUNC records.  Used by BPF
> +   target for BPF CO-RE implementation.  */
>   
>   typedef bool (*funcs_traverse_callback) (ctf_dtdef_ref, void *);
>   bool traverse_btf_func_types (funcs_traverse_callback, void *);
> diff --git a/gcc/dwarf2ctf.cc b/gcc/dwarf2ctf.cc
> index a6c8541ef2b4..910f523f9c5c 100644
> --- a/gcc/dwarf2ctf.cc
> +++ b/gcc/dwarf2ctf.cc
> @@ -976,7 +976,7 @@ ctf_debug_early_finish (const char * filename)
>   
>         /* For LTO builds, also emit BTF now.  */
>         if (flag_lto && !in_lto_p)
> -	btf_finish (filename);
> +	btf_finish ();
>       }
>     else
>       /* Otherwise, done with the CTF container.  */
> @@ -986,12 +986,12 @@ ctf_debug_early_finish (const char * filename)
>   /* Finish CTF/BTF debug info emission.  */
>   
>   void
> -ctf_debug_finish (const char * filename)
> +ctf_debug_finish ()
>   {
>     /* Emit BTF late, unless this is an LTO build in which case it was
>        already done early.  */
>     if (btf_debuginfo_p () && !flag_lto)
> -    btf_finish (filename);
> +    btf_finish ();
>   }
>   
>   #include "gt-dwarf2ctf.h"
> diff --git a/gcc/dwarf2ctf.h b/gcc/dwarf2ctf.h
> index 46184325bae6..f8a181a97625 100644
> --- a/gcc/dwarf2ctf.h
> +++ b/gcc/dwarf2ctf.h
> @@ -32,7 +32,7 @@ extern void ctf_debug_init (void);
>   extern void ctf_debug_init_postprocess (bool);
>   extern bool ctf_do_die (dw_die_ref);
>   extern void ctf_debug_early_finish (const char *);
> -extern void ctf_debug_finish (const char *);
> +extern void ctf_debug_finish (void);
>   
>   /* Wrappers for CTF/BTF to fetch information from GCC DWARF DIE.  Used in
>      ctfc.cc.
> diff --git a/gcc/dwarf2out.cc b/gcc/dwarf2out.cc
> index e406df8673ce..47e73629e3aa 100644
> --- a/gcc/dwarf2out.cc
> +++ b/gcc/dwarf2out.cc
> @@ -32305,7 +32305,7 @@ dwarf2out_finish (const char *filename)
>     /* Generate CTF/BTF debug info.  */
>     if ((ctf_debug_info_level > CTFINFO_LEVEL_NONE
>          || btf_debuginfo_p ()) && lang_GNU_C ())
> -    ctf_debug_finish (filename);
> +    ctf_debug_finish ();
>   
>   #ifdef CODEVIEW_DEBUGGING_INFO
>     if (codeview_debuginfo_p ())