Re: [PATCH 5/7] bpf: BPF CO-RE support

["Jose E. Marchesi" <jose.marchesi@oracle.com>]

Hi David.
This BPF part is OK.

> This commit introduces support for BPF Compile Once - Run
> Everywhere (CO-RE) in GCC.
>
> gcc/ChangeLog:
>
> 	* config/bpf/bpf.c: Adjust includes.
> 	(bpf_handle_preserve_access_index_attribute): New function.
> 	(bpf_attribute_table): Use it here.
> 	(bpf_builtins): Add BPF_BUILTIN_PRESERVE_ACCESS_INDEX.
> 	(bpf_option_override): Handle "-mcore" option.
> 	(bpf_asm_init_sections): New.
> 	(TARGET_ASM_INIT_SECTIONS): Redefine.
> 	(bpf_file_end): New.
> 	(TARGET_ASM_FILE_END): Redefine.
> 	(bpf_init_builtins): Add "__builtin_preserve_access_index".
> 	(bpf_core_compute, bpf_core_get_index): New.
> 	(is_attr_preserve_access): New.
> 	(bpf_expand_builtin): Handle new builtins.
> 	(bpf_core_newdecl, bpf_core_is_maybe_aggregate_access): New.
> 	(bpf_core_walk): New.
> 	(bpf_resolve_overloaded_builtin): New.
> 	(TARGET_RESOLVE_OVERLOADED_BUILTIN): Redefine.
> 	(handle_attr): New.
> 	(pass_bpf_core_attr): New RTL pass.
> 	* config/bpf/bpf-passes.def: New file.
> 	* config/bpf/bpf-protos.h (make_pass_bpf_core_attr): New.
> 	* config/bpf/coreout.c: New file.
> 	* config/bpf/coreout.h: Likewise.
> 	* config/bpf/t-bpf (TM_H): Add $(srcdir)/config/bpf/coreout.h.
> 	(coreout.o): New rule.
> 	(PASSES_EXTRA): Add $(srcdir)/config/bpf/bpf-passes.def.
> 	* config.gcc (bpf): Add coreout.h to extra_headers.
> 	Add coreout.o to extra_objs.
> 	Add $(srcdir)/config/bpf/coreout.c to target_gtfiles.
> ---
>  gcc/config.gcc                |   3 +
>  gcc/config/bpf/bpf-passes.def |  20 ++
>  gcc/config/bpf/bpf-protos.h   |   2 +
>  gcc/config/bpf/bpf.c          | 579 ++++++++++++++++++++++++++++++++++
>  gcc/config/bpf/coreout.c      | 356 +++++++++++++++++++++
>  gcc/config/bpf/coreout.h      | 114 +++++++
>  gcc/config/bpf/t-bpf          |   8 +
>  7 files changed, 1082 insertions(+)
>  create mode 100644 gcc/config/bpf/bpf-passes.def
>  create mode 100644 gcc/config/bpf/coreout.c
>  create mode 100644 gcc/config/bpf/coreout.h
>
> diff --git a/gcc/config.gcc b/gcc/config.gcc
> index 93e2b3219b9..6c790ce1b35 100644
> --- a/gcc/config.gcc
> +++ b/gcc/config.gcc
> @@ -1515,6 +1515,9 @@ bpf-*-*)
>          use_collect2=no
>          extra_headers="bpf-helpers.h"
>          use_gcc_stdint=provide
> +        extra_headers="coreout.h"
> +        extra_objs="coreout.o"
> +        target_gtfiles="$target_gtfiles \$(srcdir)/config/bpf/coreout.c"
>          ;;
>  cr16-*-elf)
>          tm_file="elfos.h ${tm_file} newlib-stdint.h"
> diff --git a/gcc/config/bpf/bpf-passes.def b/gcc/config/bpf/bpf-passes.def
> new file mode 100644
> index 00000000000..3e961659411
> --- /dev/null
> +++ b/gcc/config/bpf/bpf-passes.def
> @@ -0,0 +1,20 @@
> +/* Declaration of target-specific passes for eBPF.
> +   Copyright (C) 2021 Free Software Foundation, Inc.
> +
> +   This file is part of GCC.
> +
> +   GCC 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.
> +
> +   GCC 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 GCC; see the file COPYING3.  If not see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +INSERT_PASS_AFTER (pass_df_initialize_opt, 1, pass_bpf_core_attr);
> diff --git a/gcc/config/bpf/bpf-protos.h b/gcc/config/bpf/bpf-protos.h
> index aeb512665ed..7ce3386ffda 100644
> --- a/gcc/config/bpf/bpf-protos.h
> +++ b/gcc/config/bpf/bpf-protos.h
> @@ -30,4 +30,6 @@ extern void bpf_print_operand_address (FILE *, rtx);
>  extern void bpf_expand_prologue (void);
>  extern void bpf_expand_epilogue (void);
>  
> +rtl_opt_pass * make_pass_bpf_core_attr (gcc::context *);
> +
>  #endif /* ! GCC_BPF_PROTOS_H */
> diff --git a/gcc/config/bpf/bpf.c b/gcc/config/bpf/bpf.c
> index 85f6b76a11f..5edc8cc715a 100644
> --- a/gcc/config/bpf/bpf.c
> +++ b/gcc/config/bpf/bpf.c
> @@ -54,6 +54,25 @@ along with GCC; see the file COPYING3.  If not see
>  #include "builtins.h"
>  #include "predict.h"
>  #include "langhooks.h"
> +#include "flags.h"
> +
> +#include "cfg.h" /* needed for struct control_flow_graph used in BB macros */
> +#include "gimple.h"
> +#include "gimple-iterator.h"
> +#include "gimple-walk.h"
> +#include "tree-pass.h"
> +#include "tree-iterator.h"
> +
> +#include "context.h"
> +#include "pass_manager.h"
> +
> +#include "gimplify.h"
> +#include "gimplify-me.h"
> +
> +#include "ctfc.h"
> +#include "btf.h"
> +
> +#include "coreout.h"
>  
>  /* Per-function machine data.  */
>  struct GTY(()) machine_function
> @@ -104,6 +123,27 @@ bpf_handle_fndecl_attribute (tree *node, tree name,
>    return NULL_TREE;
>  }
>  
> +/* Handle preserve_access_index attribute, which can be applied to structs,
> +   unions and classes. Actually adding the attribute to the TYPE_DECL is
> +   taken care of for us, so just warn for types that aren't supported.  */
> +
> +static tree
> +bpf_handle_preserve_access_index_attribute (tree *node, tree name,
> +					    tree args,
> +					    int flags,
> +					    bool *no_add_attrs)
> +{
> +  if (TREE_CODE (*node) != RECORD_TYPE && TREE_CODE (*node) != UNION_TYPE)
> +    {
> +      warning (OPT_Wattributes,
> +	       "%qE attribute only applies to structure, union and class types",
> +	       name);
> +      *no_add_attrs = true;
> +    }
> +
> +  return NULL_TREE;
> +}
> +
>  /* Target-specific attributes.  */
>  
>  static const struct attribute_spec bpf_attribute_table[] =
> @@ -116,6 +156,11 @@ static const struct attribute_spec bpf_attribute_table[] =
>   { "kernel_helper", 1, 1, true, false, false, false,
>     bpf_handle_fndecl_attribute, NULL },
>  
> + /* CO-RE support: attribute to mark that all accesses to the declared
> +    struct/union/array should be recorded.  */
> + { "preserve_access_index", 0, -1, false, true, false, true,
> +   bpf_handle_preserve_access_index_attribute, NULL },
> +
>   /* The last attribute spec is set to be NULL.  */
>   { NULL,	0,  0, false, false, false, false, NULL, NULL }
>  };
> @@ -136,11 +181,18 @@ enum bpf_builtins
>    BPF_BUILTIN_LOAD_BYTE,
>    BPF_BUILTIN_LOAD_HALF,
>    BPF_BUILTIN_LOAD_WORD,
> +
> +  /* Compile Once - Run Everywhere (CO-RE) support.  */
> +  BPF_BUILTIN_PRESERVE_ACCESS_INDEX,
> +
>    BPF_BUILTIN_MAX,
>  };
>  
>  static GTY (()) tree bpf_builtins[(int) BPF_BUILTIN_MAX];
>  
> +
> +void bpf_register_coreattr_pass (void);
> +
>  /* Initialize the per-function machine status.  */
>  
>  static struct machine_function *
> @@ -173,6 +225,15 @@ bpf_option_override (void)
>  
>    if (flag_lto && TARGET_BPF_CORE)
>      error ("BPF CO-RE does not support LTO");
> +
> +  /* BPF CO-RE support requires BTF debug info generation.  */
> +  if (TARGET_BPF_CORE && !btf_debuginfo_p ())
> +    error ("BPF CO-RE requires BTF debugging information, use %<-gbtf%>");
> +
> +  /* -gbtf implies -mcore when using the BPF backend, unless -mno-core
> +     is specified.  */
> +  if (btf_debuginfo_p () && !(target_flags_explicit & MASK_BPF_CORE))
> +    target_flags |= MASK_BPF_CORE;
>  }
>  
>  #undef TARGET_OPTION_OVERRIDE
> @@ -192,6 +253,30 @@ ctfc_debuginfo_early_finish_p (void)
>  #undef TARGET_CTFC_DEBUGINFO_EARLY_FINISH_P
>  #define TARGET_CTFC_DEBUGINFO_EARLY_FINISH_P ctfc_debuginfo_early_finish_p
>  
> +/* Implement TARGET_ASM_INIT_SECTIONS.  */
> +
> +static void
> +bpf_asm_init_sections (void)
> +{
> +  if (TARGET_BPF_CORE)
> +    btf_ext_init ();
> +}
> +
> +#undef TARGET_ASM_INIT_SECTIONS
> +#define TARGET_ASM_INIT_SECTIONS bpf_asm_init_sections
> +
> +/* Implement TARGET_ASM_FILE_END.  */
> +
> +static void
> +bpf_file_end (void)
> +{
> +  if (TARGET_BPF_CORE)
> +    btf_ext_output ();
> +}
> +
> +#undef TARGET_ASM_FILE_END
> +#define TARGET_ASM_FILE_END bpf_file_end
> +
>  /* Define target-specific CPP macros.  This function in used in the
>     definition of TARGET_CPU_CPP_BUILTINS in bpf.h */
>  
> @@ -841,11 +926,18 @@ bpf_init_builtins (void)
>  	       build_function_type_list (ullt, ullt, 0));
>    def_builtin ("__builtin_bpf_load_word", BPF_BUILTIN_LOAD_WORD,
>  	       build_function_type_list (ullt, ullt, 0));
> +  def_builtin ("__builtin_preserve_access_index",
> +	       BPF_BUILTIN_PRESERVE_ACCESS_INDEX,
> +	       build_function_type_list (ptr_type_node, ptr_type_node, 0));
>  }
>  
>  #undef TARGET_INIT_BUILTINS
>  #define TARGET_INIT_BUILTINS bpf_init_builtins
>  
> +static tree bpf_core_compute (tree, vec<unsigned int> *);
> +static int bpf_core_get_index (const tree);
> +static bool is_attr_preserve_access (tree);
> +
>  /* Expand a call to a BPF-specific built-in function that was set up
>     with bpf_init_builtins.  */
>  
> @@ -896,7 +988,75 @@ bpf_expand_builtin (tree exp, rtx target ATTRIBUTE_UNUSED,
>        /* The result of the load is in R0.  */
>        return gen_rtx_REG (ops[0].mode, BPF_R0);
>      }
> +  else if (code == -1)
> +    {
> +      /* A resolved overloaded builtin, e.g. __bpf_preserve_access_index_si */
> +      tree arg = CALL_EXPR_ARG (exp, 0);
> +
> +      if (arg == NULL_TREE)
> +	return NULL_RTX;
> +
> +      auto_vec<unsigned int, 16> accessors;
> +      tree container;
> +
> +      if (TREE_CODE (arg) == SSA_NAME)
> +	{
> +	  gimple *def_stmt = SSA_NAME_DEF_STMT (arg);
> +
> +	  if (is_gimple_assign (def_stmt))
> +	    arg = gimple_assign_rhs1 (def_stmt);
> +	  else
> +	    return expand_normal (arg);
> +	}
> +
> +      /* Avoid double-recording information if the argument is an access to
> +	 a struct/union marked __attribute__((preserve_access_index)). This
> +	 Will be handled by the attribute handling pass.  */
> +      if (is_attr_preserve_access (arg))
> +	return expand_normal (arg);
> +
> +      container = bpf_core_compute (arg, &accessors);
> +
> +      /* Any valid use of the builtin must have at least one access. Otherwise,
> +	 there is nothing to record and nothing to do. This is primarily a
> +	 guard against optimizations leading to unexpected expressions in the
> +	 argument of the builtin. For example, if the builtin is used to read
> +	 a field of a structure which can be statically determined to hold a
> +	 constant value, the argument to the builtin will be optimized to that
> +	 constant. This is OK, and means the builtin call is superfluous.
> +	 e.g.
> +	   struct S foo;
> +	   foo.a = 5;
> +	   int x = __preserve_access_index (foo.a);
> +	   ... do stuff with x
> +	 'foo.a' in the builtin argument will be optimized to '5' with -01+.
> +	 This sequence does not warrant recording a CO-RE relocation.  */
> +
> +      if (accessors.length () < 1)
> +	return expand_normal (arg);
> +
> +      accessors.reverse ();
> +
> +      container = TREE_TYPE (container);
> +
> +      rtx_code_label *label = gen_label_rtx ();
> +      LABEL_PRESERVE_P (label) = 1;
> +      emit_label (label);
> +
> +      /* Determine what output section this relocation will apply to.
> +	 If this function is associated with a section, use that. Otherwise,
> +	 fall back on '.text'.  */
> +      const char * section_name;
> +      if (current_function_decl && DECL_SECTION_NAME (current_function_decl))
> +	section_name = DECL_SECTION_NAME (current_function_decl);
> +      else
> +	section_name = ".text";
> +
> +      /* Add the CO-RE relocation information to the BTF container.  */
> +      bpf_core_reloc_add (container, section_name, &accessors, label);
>  
> +      return expand_normal (arg);
> +    }
>    gcc_unreachable ();
>  }
>  
> @@ -950,6 +1110,425 @@ bpf_debug_unwind_info ()
>  #undef TARGET_ASM_ALIGNED_DI_OP
>  #define TARGET_ASM_ALIGNED_DI_OP "\t.dword\t"
>  
> +
> +/* BPF Compile Once - Run Everywhere (CO-RE) support routines.
> +
> +   BPF CO-RE is supported in two forms:
> +   - A target builtin, __builtin_preserve_access_index
> +
> +     This builtin accepts a single argument. Any access to an aggregate data
> +     structure (struct, union or array) within the argument will be recorded by
> +     the CO-RE machinery, resulting in a relocation record being placed in the
> +     .BTF.ext section of the output.
> +
> +     It is implemented in bpf_resolve_overloaded_builtin () and
> +     bpf_expand_builtin (), using the supporting routines below.
> +
> +   - An attribute, __attribute__((preserve_access_index))
> +
> +     This attribute can be applied to struct and union types. Any access to a
> +     type with this attribute will be recorded by the CO-RE machinery.
> +
> +     The pass pass_bpf_core_attr, below, implements support for
> +     this attribute.  */
> +
> +/* Traverse the subtree under NODE, which is expected to be some form of
> +   aggregate access the CO-RE machinery cares about (like a read of a member of
> +   a struct or union), collecting access indices for the components and storing
> +   them in the vector referenced by ACCESSORS.
> +
> +   Return the ultimate (top-level) container of the aggregate access. In general,
> +   this will be a VAR_DECL or some kind of REF.
> +
> +   Note that the accessors are computed *in reverse order* of how the BPF
> +   CO-RE machinery defines them. The vector needs to be reversed (or simply
> +   output in reverse order) for the .BTF.ext relocation information.  */
> +
> +static tree
> +bpf_core_compute (tree node, vec<unsigned int> *accessors)
> +{
> +
> +  if (TREE_CODE (node) == ADDR_EXPR)
> +    node = TREE_OPERAND (node, 0);
> +
> +  else if (TREE_CODE (node) == INDIRECT_REF
> +	   || TREE_CODE (node) == POINTER_PLUS_EXPR)
> +    {
> +      accessors->safe_push (0);
> +      return TREE_OPERAND (node, 0);
> +    }
> +
> +  while (1)
> +    {
> +      switch (TREE_CODE (node))
> +	{
> +	case COMPONENT_REF:
> +	  accessors->safe_push (bpf_core_get_index (TREE_OPERAND (node, 1)));
> +	  break;
> +
> +	case ARRAY_REF:
> +	case ARRAY_RANGE_REF:
> +	  accessors->safe_push (bpf_core_get_index (node));
> +	  break;
> +
> +	case MEM_REF:
> +	  accessors->safe_push (bpf_core_get_index (node));
> +	  if (TREE_CODE (TREE_OPERAND (node, 0)) == ADDR_EXPR)
> +	    node = TREE_OPERAND (TREE_OPERAND (node, 0), 0);
> +	  goto done;
> +
> +	default:
> +	  goto done;
> +	}
> +      node = TREE_OPERAND (node, 0);
> +    }
> + done:
> +  return node;
> +
> +}
> +
> +/* Compute the index of the NODE in its immediate container.
> +   NODE should be a FIELD_DECL (i.e. of struct or union), or an ARRAY_REF. */
> +static int
> +bpf_core_get_index (const tree node)
> +{
> +  enum tree_code code = TREE_CODE (node);
> +
> +  if (code == FIELD_DECL)
> +    {
> +      /* Lookup the index from the BTF information.  Some struct/union members
> +	 may not be emitted in BTF; only the BTF container has enough
> +	 information to compute the correct index.  */
> +      int idx = bpf_core_get_sou_member_index (ctf_get_tu_ctfc (), node);
> +      if (idx >= 0)
> +	return idx;
> +    }
> +
> +  else if (code == ARRAY_REF || code == ARRAY_RANGE_REF || code == MEM_REF)
> +    {
> +      /* For array accesses, the index is operand 1.  */
> +      tree index = TREE_OPERAND (node, 1);
> +
> +      /* If the indexing operand is a constant, extracting is trivial.  */
> +      if (TREE_CODE (index) == INTEGER_CST && tree_fits_shwi_p (index))
> +	return tree_to_shwi (index);
> +    }
> +
> +  return -1;
> +}
> +
> +/* Synthesize a new builtin function declaration at LOC with signature TYPE.
> +   Used by bpf_resolve_overloaded_builtin to resolve calls to
> +   __builtin_preserve_access_index.  */
> +
> +static tree
> +bpf_core_newdecl (location_t loc, tree type)
> +{
> +  tree rettype = build_function_type_list (type, type, NULL);
> +  tree newdecl = NULL_TREE;
> +  char name[80];
> +  int len = snprintf (name, sizeof (name), "%s", "__builtin_pai_");
> +
> +  static unsigned long cnt = 0;
> +  len = snprintf (name + len, sizeof (name) - len, "%lu", cnt++);
> +
> +  return add_builtin_function_ext_scope (name, rettype, -1, BUILT_IN_MD, NULL,
> +					 NULL_TREE);
> +}
> +
> +/* Return whether EXPR could access some aggregate data structure that
> +   BPF CO-RE support needs to know about.  */
> +
> +static int
> +bpf_core_is_maybe_aggregate_access (tree expr)
> +{
> +  enum tree_code code = TREE_CODE (expr);
> +  if (code == COMPONENT_REF || code == ARRAY_REF)
> +    return 1;
> +
> +  if (code == ADDR_EXPR)
> +      return bpf_core_is_maybe_aggregate_access (TREE_OPERAND (expr, 0));
> +
> +  return 0;
> +}
> +
> +/* Callback function used with walk_tree from bpf_resolve_overloaded_builtin.  */
> +
> +static tree
> +bpf_core_walk (tree *tp, int *walk_subtrees, void *data)
> +{
> +  location_t loc = *((location_t *) data);
> +
> +  /* If this is a type, don't do anything. */
> +  if (TYPE_P (*tp))
> +    {
> +      *walk_subtrees = 0;
> +      return NULL_TREE;
> +    }
> +
> +  if (bpf_core_is_maybe_aggregate_access (*tp))
> +    {
> +      tree newdecl = bpf_core_newdecl (loc, TREE_TYPE (*tp));
> +      tree newcall = build_call_expr_loc (loc, newdecl, 1, *tp);
> +      *tp = newcall;
> +      *walk_subtrees = 0;
> +    }
> +
> +  return NULL_TREE;
> +}
> +
> +
> +/* Implement TARGET_RESOLVE_OVERLOADED_BUILTIN (see gccint manual section
> +   Target Macros::Misc.).
> +   We use this for the __builtin_preserve_access_index builtin for CO-RE
> +   support.
> +
> +   FNDECL is the declaration of the builtin, and ARGLIST is the list of
> +   arguments passed to it, and is really a vec<tree,_> *.
> +
> +   In this case, the 'operation' implemented by the builtin is a no-op;
> +   the builtin is just a marker. So, the result is simply the argument.  */
> +
> +static tree
> +bpf_resolve_overloaded_builtin (location_t loc, tree fndecl, void *arglist)
> +{
> +  if (DECL_MD_FUNCTION_CODE (fndecl) != BPF_BUILTIN_PRESERVE_ACCESS_INDEX)
> +    return NULL_TREE;
> +
> +  /* We only expect one argument, but it may be an arbitrarily-complicated
> +     statement-expression. */
> +  vec<tree, va_gc> *params = static_cast<vec<tree, va_gc> *> (arglist);
> +  unsigned n_params = params ? params->length() : 0;
> +
> +  if (n_params != 1)
> +    {
> +      error_at (loc, "expected exactly 1 argument");
> +      return NULL_TREE;
> +    }
> +
> +  tree param = (*params)[0];
> +
> +  /* If not generating BPF_CORE information, the builtin does nothing.  */
> +  if (!TARGET_BPF_CORE)
> +    return param;
> +
> +  /* Do remove_c_maybe_const_expr for the arg.
> +     TODO: WHY do we have to do this here? Why doesn't c-typeck take care
> +     of it before or after this hook? */
> +  if (TREE_CODE (param) == C_MAYBE_CONST_EXPR)
> +    param = C_MAYBE_CONST_EXPR_EXPR (param);
> +
> +  /* Construct a new function declaration with the correct type, and return
> +     a call to it.
> +
> +     Calls with statement-expressions, for example:
> +     _(({ foo->a = 1; foo->u[2].b = 2; }))
> +     require special handling.
> +
> +     We rearrange this into a new block scope in which each statement
> +     becomes a unique builtin call:
> +     {
> +       _ ({ foo->a = 1;});
> +       _ ({ foo->u[2].b = 2;});
> +     }
> +
> +     This ensures that all the relevant information remains within the
> +     expression trees the builtin finally gets.  */
> +
> +  walk_tree (&param, bpf_core_walk, (void *) &loc, NULL);
> +
> +  return param;
> +}
> +
> +#undef TARGET_RESOLVE_OVERLOADED_BUILTIN
> +#define TARGET_RESOLVE_OVERLOADED_BUILTIN bpf_resolve_overloaded_builtin
> +
> +
> +/* Handling for __attribute__((preserve_access_index)) for BPF CO-RE support.
> +
> +   This attribute marks a structure/union/array type as "preseve", so that
> +   every access to that type should be recorded and replayed by the BPF loader;
> +   this is just the same functionality as __builtin_preserve_access_index,
> +   but in the form of an attribute for an entire aggregate type.
> +
> +   Note also that nested structs behave as though they all have the attribute.
> +   For example:
> +     struct X { int a; };
> +     struct Y { struct X bar} __attribute__((preserve_access_index));
> +     struct Y foo;
> +     foo.bar.a;
> +   will record access all the way to 'a', even though struct X does not have
> +   the preserve_access_index attribute.
> +
> +   This is to follow LLVM behavior.
> +
> +   This pass finds all accesses to objects of types marked with the attribute,
> +   and wraps them in the same "low-level" builtins used by the builtin version.
> +   All logic afterwards is therefore identical to the builtin version of
> +   preserve_access_index.  */
> +
> +/* True iff tree T accesses any member of a struct/union/class which is marked
> +   with the PRESERVE_ACCESS_INDEX attribute.  */
> +
> +static bool
> +is_attr_preserve_access (tree t)
> +{
> +  if (t == NULL_TREE)
> +    return false;
> +
> +  poly_int64 bitsize, bitpos;
> +  tree var_off;
> +  machine_mode mode;
> +  int sign, reverse, vol;
> +
> +  tree base = get_inner_reference (t, &bitsize, &bitpos, &var_off, &mode,
> +				   &sign, &reverse, &vol);
> +
> +  if (TREE_CODE (base) == MEM_REF)
> +    {
> +      return lookup_attribute ("preserve_access_index",
> +			       TYPE_ATTRIBUTES (TREE_TYPE (base)));
> +    }
> +
> +  if (TREE_CODE (t) == COMPONENT_REF)
> +    {
> +      /* preserve_access_index propegates into nested structures,
> +	 so check whether this is a component of another component
> +	 which in turn is part of such a struct.  */
> +
> +      const tree op = TREE_OPERAND (t, 0);
> +
> +      if (TREE_CODE (op) == COMPONENT_REF)
> +	return is_attr_preserve_access (op);
> +
> +      const tree container = DECL_CONTEXT (TREE_OPERAND (t, 1));
> +
> +      return lookup_attribute ("preserve_access_index",
> +			       TYPE_ATTRIBUTES (container));
> +    }
> +
> +  else if (TREE_CODE (t) == ADDR_EXPR)
> +    return is_attr_preserve_access (TREE_OPERAND (t, 0));
> +
> +  return false;
> +}
> +
> +/* The body of pass_bpf_core_attr. Scan RTL for accesses to structs/unions
> +   marked with __attribute__((preserve_access_index)) and generate a CO-RE
> +   relocation for any such access.  */
> +
> +static void
> +handle_attr_preserve (function *fn)
> +{
> +  basic_block bb;
> +  rtx_insn *insn;
> +  rtx_code_label *label;
> +  FOR_EACH_BB_FN (bb, fn)
> +    {
> +      FOR_BB_INSNS (bb, insn)
> +	{
> +	  if (!NONJUMP_INSN_P (insn))
> +	    continue;
> +	  rtx pat = PATTERN (insn);
> +	  if (GET_CODE (pat) != SET)
> +	    continue;
> +
> +	  start_sequence();
> +
> +	  for (int i = 0; i < 2; i++)
> +	    {
> +	      rtx mem = XEXP (pat, i);
> +	      if (MEM_P (mem))
> +		{
> +		  tree expr = MEM_EXPR (mem);
> +		  if (!expr)
> +		    continue;
> +
> +		  if (TREE_CODE (expr) == MEM_REF
> +		      && TREE_CODE (TREE_OPERAND (expr, 0)) == SSA_NAME)
> +		    {
> +		      gimple *def_stmt = SSA_NAME_DEF_STMT (TREE_OPERAND (expr, 0));
> +		      if (is_gimple_assign (def_stmt))
> +			expr = gimple_assign_rhs1 (def_stmt);
> +		    }
> +
> +		  if (is_attr_preserve_access (expr))
> +		    {
> +		      auto_vec<unsigned int, 16> accessors;
> +		      tree container = bpf_core_compute (expr, &accessors);
> +		      if (accessors.length () < 1)
> +			continue;
> +		      accessors.reverse ();
> +
> +		      container = TREE_TYPE (container);
> +		      const char * section_name;
> +		      if (DECL_SECTION_NAME (fn->decl))
> +			section_name = DECL_SECTION_NAME (fn->decl);
> +		      else
> +			section_name = ".text";
> +
> +		      label = gen_label_rtx ();
> +		      LABEL_PRESERVE_P (label) = 1;
> +		      emit_label (label);
> +
> +		      /* Add the CO-RE relocation information to the BTF container.  */
> +		      bpf_core_reloc_add (container, section_name, &accessors, label);
> +		    }
> +		}
> +	    }
> +	  rtx_insn *seq = get_insns ();
> +	  end_sequence ();
> +	  emit_insn_before (seq, insn);
> +	}
> +    }
> +}
> +
> +
> +/* This pass finds accesses to structures marked with the BPF target attribute
> +   __attribute__((preserve_access_index)). For every such access, a CO-RE
> +   relocation record is generated, to be output in the .BTF.ext section.  */
> +
> +namespace {
> +
> +const pass_data pass_data_bpf_core_attr =
> +{
> +  RTL_PASS, /* type */
> +  "bpf_core_attr", /* name */
> +  OPTGROUP_NONE, /* optinfo_flags */
> +  TV_NONE, /* tv_id */
> +  0, /* properties_required */
> +  0, /* properties_provided */
> +  0, /* properties_destroyed */
> +  0, /* todo_flags_start */
> +  0, /* todo_flags_finish */
> +};
> +
> +class pass_bpf_core_attr : public rtl_opt_pass
> +{
> +public:
> +  pass_bpf_core_attr (gcc::context *ctxt)
> +    : rtl_opt_pass (pass_data_bpf_core_attr, ctxt)
> +  {}
> +
> +  virtual bool gate (function *) { return TARGET_BPF_CORE; }
> +  virtual unsigned int execute (function *);
> +};
> +
> +unsigned int
> +pass_bpf_core_attr::execute (function *fn)
> +{
> +  handle_attr_preserve (fn);
> +  return 0;
> +}
> +
> +} /* Anonymous namespace.  */
> +
> +rtl_opt_pass *
> +make_pass_bpf_core_attr (gcc::context *ctxt)
> +{
> +  return new pass_bpf_core_attr (ctxt);
> +}
> +
>  /* Finally, build the GCC target.  */
>  
>  struct gcc_target targetm = TARGET_INITIALIZER;
> diff --git a/gcc/config/bpf/coreout.c b/gcc/config/bpf/coreout.c
> new file mode 100644
> index 00000000000..d5486b463cf
> --- /dev/null
> +++ b/gcc/config/bpf/coreout.c
> @@ -0,0 +1,356 @@
> +/* BPF Compile Once - Run Everywhere (CO-RE) support.
> +   Copyright (C) 2021 Free Software Foundation, Inc.
> +
> +   This file is part of GCC.
> +
> +   GCC 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.
> +
> +   GCC 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 GCC; see the file COPYING3.  If not see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#define IN_TARGET_CODE 1
> +
> +#include "config.h"
> +#include "system.h"
> +#include "coretypes.h"
> +#include "target.h"
> +#include "memmodel.h"
> +#include "tm_p.h"
> +#include "output.h"
> +#include "dwarf2asm.h"
> +#include "ctfc.h"
> +#include "btf.h"
> +#include "rtl.h"
> +
> +#include "coreout.h"
> +
> +/* This file contains data structures and routines for construction and output
> +   of BPF Compile Once - Run Everywhere (BPF CO-RE) information.
> +
> +   eBPF programs written in C usually include Linux kernel headers, so that
> +   they may interact with kernel data structures in a useful way. This
> +   intrudces two major portability issues:
> +
> +   1. Kernel data structures regularly change, with fields added, moved or
> +      deleted between versions. An eBPF program cannot in general be expected
> +      to run on any systems which does not share an identical kernel version to
> +      the system on which it was compiled.
> +
> +   2. Included kernel headers (and used data structures) may be internal, not
> +      exposed in an userspace API, and therefore target-specific. An eBPF
> +      program compiled on an x86_64 machine will include x86_64 kernel headers.
> +      The resulting program may not run well (or at all) in machines of
> +      another architecture.
> +
> +   BPF CO-RE is designed to solve the first issue by leveraging the BPF loader
> +   to adjust references to kernel data structures made by the program as-needed
> +   according to versions of structures actually present on the host kernel.
> +
> +   To achieve this, additional information is placed in a ".BTF.ext" section.
> +   This information tells the loader which references will require adjusting,
> +   and how to perform each necessary adjustment.
> +
> +   For any access to a data structure which may require load-time adjustment,
> +   the following information is recorded (making up a CO-RE relocation record):
> +   - The BTF type ID of the outermost structure which is accessed.
> +   - An access string encoding the accessed member via a series of member and
> +     array indexes. These indexes are used to look up detailed BTF information
> +     about the member.
> +   - The offset of the appropriate instruction to patch in the BPF program.
> +   - An integer specifying what kind of relocation to perform.
> +
> +   A CO-RE-capable BPF loader reads this information together with the BTF
> +   information of the program, compares it against BTF information of the host
> +   kernel, and determines the appropriate way to patch the specified
> +   instruction.
> +
> +   Once all CO-RE relocations are resolved, the program is loaded and verified
> +   as usual. The process can be summarized with the following diagram:
> +
> +              +------------+
> +              | C compiler |
> +              +-----+------+
> +                    | BPF + BTF + CO-RE relocations
> +                    v
> +              +------------+
> +         +--->| BPF loader |
> +         |    +-----+------+
> +         |          | BPF (adapted)
> +     BTF |          v
> +         |    +------------+
> +         +----+   Kernel   |
> +              +------------+
> +
> +   Note that a single ELF object may contain multiple eBPF programs. As a
> +   result, a single .BTF.ext section can contain CO-RE relocations for multiple
> +   programs in distinct sections.  */
> +
> +/* Internal representation of a BPF CO-RE relocation record.  */
> +
> +typedef struct GTY (()) bpf_core_reloc {
> +  unsigned int bpfcr_type;		/* BTF type ID of container.  */
> +  unsigned int  bpfcr_astr_off;		/* Offset of access string in .BTF
> +					   string table.  */
> +  rtx_code_label * bpfcr_insn_label;	/* RTX label attached to instruction
> +					   to patch.  */
> +  enum btf_core_reloc_kind bpfcr_kind;	/* Kind of relocation to perform.  */
> +} bpf_core_reloc_t;
> +
> +typedef bpf_core_reloc_t * bpf_core_reloc_ref;
> +
> +/* Internal representation of a CO-RE relocation (sub)section of the
> +   .BTF.ext information. One such section is generated for each ELF section
> +   in the output object having relocations that a BPF loader must resolve.  */
> +
> +typedef struct GTY (()) bpf_core_section {
> +  /* Name of ELF section to which these CO-RE relocations apply.  */
> +  const char * name;
> +
> +  /* Offset of section name in .BTF string table.  */
> +  uint32_t name_offset;
> +
> +  /* Relocations in the section.  */
> +  vec <bpf_core_reloc_ref, va_gc> * GTY (()) relocs;
> +} bpf_core_section_t;
> +
> +typedef bpf_core_section_t * bpf_core_section_ref;
> +
> +/* BTF.ext debug info section.  */
> +
> +static GTY (()) section * btf_ext_info_section;
> +
> +static int btf_ext_label_num;
> +
> +#ifndef BTF_EXT_INFO_SECTION_NAME
> +#define BTF_EXT_INFO_SECTION_NAME ".BTF.ext"
> +#endif
> +
> +#define BTF_EXT_INFO_SECTION_FLAGS (SECTION_DEBUG)
> +
> +#define MAX_BTF_EXT_LABEL_BYTES 40
> +
> +static char btf_ext_info_section_label[MAX_BTF_EXT_LABEL_BYTES];
> +
> +#ifndef BTF_EXT_INFO_SECTION_LABEL
> +#define BTF_EXT_INFO_SECTION_LABEL "Lbtfext"
> +#endif
> +
> +static GTY (()) vec<bpf_core_section_ref, va_gc> *bpf_core_sections;
> +
> +
> +/* Create a new BPF CO-RE relocation record, and add it to the appropriate
> +   CO-RE section.  */
> +
> +void
> +bpf_core_reloc_add (const tree type, const char * section_name,
> +		    vec<unsigned int> *accessors, rtx_code_label *label)
> +{
> +  char buf[40];
> +  unsigned int i, n = 0;
> +
> +  /* A valid CO-RE access must have at least one accessor.  */
> +  if (accessors->length () < 1)
> +    return;
> +
> +  for (i = 0; i < accessors->length () - 1; i++)
> +    n += snprintf (buf + n, sizeof (buf) - n, "%u:", (*accessors)[i]);
> +  snprintf (buf + n, sizeof (buf) - n, "%u", (*accessors)[i]);
> +
> +  bpf_core_reloc_ref bpfcr = ggc_cleared_alloc<bpf_core_reloc_t> ();
> +  ctf_container_ref ctfc = ctf_get_tu_ctfc ();
> +
> +  /* Buffer the access string in the auxiliary strtab. Since the two string
> +     tables are concatenated, add the length of the first to the offset.  */
> +  size_t strtab_len = ctfc_get_strtab_len (ctfc, CTF_STRTAB);
> +  ctf_add_string (ctfc, buf, &(bpfcr->bpfcr_astr_off), CTF_AUX_STRTAB);
> +  bpfcr->bpfcr_astr_off += strtab_len;
> +
> +  bpfcr->bpfcr_type = get_btf_id (ctf_lookup_tree_type (ctfc, type));
> +  bpfcr->bpfcr_insn_label = label;
> +  bpfcr->bpfcr_kind = BPF_RELO_FIELD_BYTE_OFFSET;
> +
> +  /* Add the CO-RE reloc to the appropriate section.  */
> +  bpf_core_section_ref sec;
> +  FOR_EACH_VEC_ELT (*bpf_core_sections, i, sec)
> +    if (strcmp (sec->name, section_name) == 0)
> +      {
> +	vec_safe_push (sec->relocs, bpfcr);
> +	return;
> +      }
> +
> +  /* If the CO-RE section does not yet exist, create it.  */
> +  sec = ggc_cleared_alloc<bpf_core_section_t> ();
> +
> +  ctf_add_string (ctfc, section_name, &sec->name_offset, CTF_AUX_STRTAB);
> +  sec->name_offset += strtab_len;
> +  if (strcmp (section_name, ""))
> +    ctfc->ctfc_aux_strlen += strlen (section_name) + 1;
> +
> +  sec->name = section_name;
> +  vec_alloc (sec->relocs, 1);
> +  vec_safe_push (sec->relocs, bpfcr);
> +
> +  vec_safe_push (bpf_core_sections, sec);
> +}
> +
> +/* Return the 0-based index of the field NODE in its containing struct or union
> +   type.  */
> +
> +int
> +bpf_core_get_sou_member_index (ctf_container_ref ctfc, const tree node)
> +{
> +  if (TREE_CODE (node) == FIELD_DECL)
> +    {
> +      const tree container = DECL_CONTEXT (node);
> +      const char * name = IDENTIFIER_POINTER (DECL_NAME (node));
> +
> +      /* Lookup the CTF type info for the containing type.  */
> +      dw_die_ref die = lookup_type_die (container);
> +      if (die == NULL)
> +        return -1;
> +
> +      ctf_dtdef_ref dtd = ctf_dtd_lookup (ctfc, die);
> +      if (dtd == NULL)
> +        return -1;
> +
> +      unsigned int kind = CTF_V2_INFO_KIND (dtd->dtd_data.ctti_info);
> +      if (kind != CTF_K_STRUCT && kind != CTF_K_UNION)
> +        return -1;
> +
> +      int i = 0;
> +      ctf_dmdef_t * dmd;
> +      for (dmd = dtd->dtd_u.dtu_members;
> +           dmd != NULL; dmd = (ctf_dmdef_t *) ctf_dmd_list_next (dmd))
> +        {
> +          if (get_btf_id (dmd->dmd_type) > BTF_MAX_TYPE)
> +            continue;
> +          if (strcmp (dmd->dmd_name, name) == 0)
> +            return i;
> +          i++;
> +        }
> +    }
> +  return -1;
> +}
> +
> +/* Compute and output the header of a .BTF.ext debug info section.  */
> +
> +static void
> +output_btfext_header (void)
> +{
> +  switch_to_section (btf_ext_info_section);
> +  ASM_OUTPUT_LABEL (asm_out_file, btf_ext_info_section_label);
> +
> +  dw2_asm_output_data (2, BTF_MAGIC, "btf_magic");
> +  dw2_asm_output_data (1, BTF_VERSION, "btfext_version");
> +  dw2_asm_output_data (1, 0, "btfext_flags");
> +  dw2_asm_output_data (4, sizeof (struct btf_ext_header), "btfext_hdr_len");
> +
> +  uint32_t func_info_off = 0, func_info_len = 0;
> +  uint32_t line_info_off = 0, line_info_len = 0;
> +  uint32_t core_relo_off = 0, core_relo_len = 0;
> +
> +  /* Header core_relo_len is the sum total length in bytes of all CO-RE
> +     relocation sections.  */
> +  size_t i;
> +  bpf_core_section_ref sec;
> +  core_relo_len += vec_safe_length (bpf_core_sections)
> +    * sizeof (struct btf_ext_section_header);
> +
> +  FOR_EACH_VEC_ELT (*bpf_core_sections, i, sec)
> +    core_relo_len +=
> +      vec_safe_length (sec->relocs) * sizeof (struct btf_ext_reloc);
> +
> +  dw2_asm_output_data (4, func_info_off, "func_info_offset");
> +  dw2_asm_output_data (4, func_info_len, "func_info_len");
> +
> +  dw2_asm_output_data (4, line_info_off, "line_info_offset");
> +  dw2_asm_output_data (4, line_info_len, "line_info_len");
> +
> +  dw2_asm_output_data (4, core_relo_off, "core_relo_offset");
> +  dw2_asm_output_data (4, core_relo_len, "core_relo_len");
> +}
> +
> +/* Output a single CO-RE relocation record.  */
> +
> +static void
> +output_asm_btfext_core_reloc (bpf_core_reloc_ref bpfcr)
> +{
> +  dw2_assemble_integer (4, gen_rtx_LABEL_REF (Pmode, bpfcr->bpfcr_insn_label));
> +  fprintf (asm_out_file, "\t%s bpfcr_insn\n", ASM_COMMENT_START);
> +
> +  dw2_asm_output_data (4, bpfcr->bpfcr_type, "bpfcr_type");
> +  dw2_asm_output_data (4, bpfcr->bpfcr_astr_off, "bpfcr_astr_off");
> +  dw2_asm_output_data (4, bpfcr->bpfcr_kind, "bpfcr_kind");
> +}
> +
> +/* Output all CO-RE relocation records for a section.  */
> +
> +static void
> +output_btfext_core_relocs (bpf_core_section_ref sec)
> +{
> +  size_t i;
> +  bpf_core_reloc_ref bpfcr;
> +  FOR_EACH_VEC_ELT (*(sec->relocs), i, bpfcr)
> +    output_asm_btfext_core_reloc (bpfcr);
> +}
> +
> +/* Output all CO-RE relocation sections.  */
> +
> +static void
> +output_btfext_core_sections (void)
> +{
> +  size_t i;
> +  bpf_core_section_ref sec;
> +  FOR_EACH_VEC_ELT (*bpf_core_sections, i, sec)
> +    {
> +      /* BTF Ext section info. */
> +      dw2_asm_output_data (4, sizeof (struct btf_ext_reloc),
> +			   "btfext_secinfo_rec_size");
> +
> +      /* Section name offset, refers to the offset of a string with the name of
> +	 the section to which these CORE relocations refer, e.g. '.text'.
> +	 The string is buffered in the BTF strings table.  */
> +      dw2_asm_output_data (4, sec->name_offset,  "btfext_secinfo_sec_name_off");
> +      dw2_asm_output_data (4, vec_safe_length (sec->relocs),
> +			   "btfext_secinfo_num_recs");
> +
> +      output_btfext_core_relocs (sec);
> +    }
> +}
> +
> +/* Initialize sections, labels, and data structures for BTF.ext output.  */
> +
> +void
> +btf_ext_init (void)
> +{
> +  btf_ext_info_section = get_section (BTF_EXT_INFO_SECTION_NAME,
> +				      BTF_EXT_INFO_SECTION_FLAGS, NULL);
> +
> +  ASM_GENERATE_INTERNAL_LABEL (btf_ext_info_section_label,
> +			       BTF_EXT_INFO_SECTION_LABEL,
> +			       btf_ext_label_num++);
> +
> +  vec_alloc (bpf_core_sections, 1);
> +}
> +
> +/* Output the entire .BTF.ext section.  */
> +
> +void
> +btf_ext_output (void)
> +{
> +  output_btfext_header ();
> +  output_btfext_core_sections ();
> +
> +  bpf_core_sections = NULL;
> +}
> +
> +#include "gt-coreout.h"
> diff --git a/gcc/config/bpf/coreout.h b/gcc/config/bpf/coreout.h
> new file mode 100644
> index 00000000000..82c203df341
> --- /dev/null
> +++ b/gcc/config/bpf/coreout.h
> @@ -0,0 +1,114 @@
> +/* coreout.h - Declarations and definitions related to
> +   BPF Compile Once - Run Everywhere (CO-RE) support.
> +   Copyright (C) 2021 Free Software Foundation, Inc.
> +
> +   This file is part of GCC.
> +
> +   GCC 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.
> +
> +   GCC 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 GCC; see the file COPYING3.  If not see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +
> +#ifndef __COREOUT_H
> +#define __COREOUT_H
> +
> +#include <stdint.h>
> +
> +#ifdef	__cplusplus
> +extern "C"
> +{
> +#endif
> +
> +/* .BTF.ext information.  */
> +
> +struct btf_ext_section_header
> +{
> +  uint32_t kind;
> +  uint32_t sec_name_off;
> +  uint32_t num_records;
> +};
> +
> +/* A funcinfo record, in the .BTF.ext funcinfo section.  */
> +struct btf_ext_funcinfo
> +{
> +  uint32_t insn_off; /* Offset of the first instruction of the function.  */
> +  uint32_t type;     /* Type ID of a BTF_KIND_FUNC type.  */
> +};
> +
> +/* A lineinfo record, in the .BTF.ext lineinfo section.  */
> +struct btf_ext_lineinfo
> +{
> +  uint32_t insn_off;      /* Offset of the instruction.  */
> +  uint32_t file_name_off; /* Offset of file name in BTF string table.  */
> +  uint32_t line_off;      /* Offset of source line in BTF string table.  */
> +  uint32_t line_col;      /* Line number (bits 31-11) and column (11-0).  */
> +};
> +
> +enum btf_core_reloc_kind
> +{
> +  BPF_RELO_FIELD_BYTE_OFFSET = 0,
> +  BPF_RELO_FIELD_BYTE_SIZE = 1,
> +  BPF_RELO_FIELD_EXISTS = 2,
> +  BPF_RELO_FIELD_SIGNED = 3,
> +  BPF_RELO_FIELD_LSHIFT_U64 = 4,
> +  BPF_RELO_FIELD_RSHIFT_U64 = 5,
> +  BPF_RELO_TYPE_ID_LOCAL = 6,
> +  BPF_RELO_TYPE_ID_TARGET = 7,
> +  BPF_RELO_TYPE_EXISTS = 8,
> +  BPF_RELO_TYPE_SIZE = 9,
> +  BPF_RELO_ENUMVAL_EXISTS = 10,
> +  BPF_RELO_ENUMVAL_VALUE = 11
> +};
> +
> +struct btf_ext_reloc
> +{
> +  uint32_t insn_off;       /* Offset of instruction to be patched. A
> +			      section-relative label at compile time.  */
> +  uint32_t type_id;        /* Type ID of the outermost containing entity, e.g.
> +			      the containing structure.  */
> +  uint32_t access_str_off; /* Offset of CO-RE accessor string in .BTF strings
> +			      section.  */
> +  uint32_t kind;           /* An enum btf_core_reloc_kind. Note that it always
> +			      takes 32 bits.  */
> +};
> +
> +struct btf_ext_header
> +{
> +  uint16_t magic;		/* Magic number (BTF_MAGIC).  */
> +  uint8_t  version;		/* Data format version (BTF_VERSION).  */
> +  uint8_t  flags;		/* Flags. Currently unused.  */
> +  uint32_t hdr_len;		/* Length of this header in bytes.  */
> +
> +  /* Following offsets are relative to the end of this header, in bytes.
> +     Following lengths are in bytes.  */
> +  uint32_t func_info_off;	/* Offset of funcinfo section.  */
> +  uint32_t func_info_len;	/* Length of funcinfo section.  */
> +  uint32_t line_info_off;	/* Offset of lineinfo section.  */
> +  uint32_t line_info_len;	/* Length of lineinfo section.  */
> +
> +  uint32_t core_relo_off;	/* Offset of CO-RE relocation section.  */
> +  uint32_t core_relo_len;	/* Length of CO-RE relocation section.  */
> +};
> +
> +extern void btf_ext_init (void);
> +extern void btf_ext_output (void);
> +
> +extern void bpf_core_reloc_add (const tree, const char *, vec<unsigned int> *,
> +				rtx_code_label *);
> +extern int bpf_core_get_sou_member_index (ctf_container_ref, const tree);
> +
> +#ifdef	__cplusplus
> +}
> +#endif
> +
> +#endif /* __COREOUT_H */
> diff --git a/gcc/config/bpf/t-bpf b/gcc/config/bpf/t-bpf
> index e69de29bb2d..b37bf858d8f 100644
> --- a/gcc/config/bpf/t-bpf
> +++ b/gcc/config/bpf/t-bpf
> @@ -0,0 +1,8 @@
> +
> +TM_H += $(srcdir)/config/bpf/coreout.h
> +
> +coreout.o: $(srcdir)/config/bpf/coreout.c
> +	$(COMPILE) $<
> +	$(POSTCOMPILE)
> +
> +PASSES_EXTRA += $(srcdir)/config/bpf/bpf-passes.def