Re: [PATCH v12] add -fpatchable-function-entry=N,M option

[Torsten Duwe <duwe at suse dot de>]

What is the next step now? Is anybody going to commit that patch?

	Torsten

On Fri, Jul 07, 2017 at 02:57:55PM +0100, Richard Earnshaw (lists) wrote:
> On 06/07/17 15:03, Torsten Duwe wrote:
> +#if TARGET_HAVE_NAMED_SECTIONS

No, this is a hook.  You need to test targetm_common.have_named_sections.

OK with that change.

R.

On Fri, Jul 07, 2017 at 09:30:28PM +0200, Torsten Duwe wrote:
> Change since v11:
> 
> < +#if TARGET_HAVE_NAMED_SECTIONS
> 
> > +  if (record_p && targetm_common.have_named_sections)
> 
> (plus > +#include "common/common-target.h" )
> 
> 	Torsten
> 
> 
> gcc/c-family/ChangeLog
> 2017-07-07  Torsten Duwe  <duwe@suse.de>
> 
> 	* c-attribs.c (c_common_attribute_table): Add entry for
> 	"patchable_function_entry".
> 
> gcc/lto/ChangeLog
> 2017-07-07  Torsten Duwe  <duwe@suse.de>
> 
> 	* lto-lang.c (lto_attribute_table): Add entry for
> 	"patchable_function_entry".
> 
> gcc/ChangeLog
> 2017-07-07  Torsten Duwe  <duwe@suse.de>
> 
> 	* common.opt: Introduce -fpatchable-function-entry
> 	command line option, and its variables function_entry_patch_area_size
> 	and function_entry_patch_area_start.
> 	* opts.c (common_handle_option): Add -fpatchable_function_entry_ case,
> 	including a two-value parser.
> 	* target.def (print_patchable_function_entry): New target hook.
> 	* targhooks.h (default_print_patchable_function_entry): New function.
> 	* targhooks.c (default_print_patchable_function_entry): Likewise.
> 	* toplev.c (process_options): Switch off IPA-RA if
> 	patchable function entries are being generated.
> 	* varasm.c (assemble_start_function): Look at the
> 	patchable-function-entry command line switch and current
> 	function attributes and maybe generate NOP instructions by
> 	calling the print_patchable_function_entry hook.
> 	* doc/extend.texi: Document patchable_function_entry attribute.
> 	* doc/invoke.texi: Document -fpatchable_function_entry
> 	command line option.
> 	* doc/tm.texi.in (TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY):
> 	New target hook.
> 	* doc/tm.texi: Likewise.
> 
> gcc/testsuite/ChangeLog
> 2017-07-07  Torsten Duwe  <duwe@suse.de>
> 
> 	* c-c++-common/patchable_function_entry-default.c: New test.
> 	* c-c++-common/patchable_function_entry-decl.c: Likewise.
> 	* c-c++-common/patchable_function_entry-definition.c: Likewise.
> 
> diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
> index 626ffa1cde7..ecb00c1d5b9 100644
> --- a/gcc/c-family/c-attribs.c
> +++ b/gcc/c-family/c-attribs.c
> @@ -142,6 +142,8 @@ static tree handle_bnd_variable_size_attribute (tree *, tree, tree, int, bool *)
>  static tree handle_bnd_legacy (tree *, tree, tree, int, bool *);
>  static tree handle_bnd_instrument (tree *, tree, tree, int, bool *);
>  static tree handle_fallthrough_attribute (tree *, tree, tree, int, bool *);
> +static tree handle_patchable_function_entry_attribute (tree *, tree, tree,
> +						       int, bool *);
>  
>  /* Table of machine-independent attributes common to all C-like languages.
>  
> @@ -351,6 +353,9 @@ const struct attribute_spec c_common_attribute_table[] =
>  			      handle_bnd_instrument, false },
>    { "fallthrough",	      0, 0, false, false, false,
>  			      handle_fallthrough_attribute, false },
> +  { "patchable_function_entry",	1, 2, true, false, false,
> +			      handle_patchable_function_entry_attribute,
> +			      false },
>    { NULL,                     0, 0, false, false, false, NULL, false }
>  };
>  
> @@ -3260,3 +3265,10 @@ handle_fallthrough_attribute (tree *, tree name, tree, int,
>    *no_add_attrs = true;
>    return NULL_TREE;
>  }
> +
> +static tree
> +handle_patchable_function_entry_attribute (tree *, tree, tree, int, bool *)
> +{
> +  /* Nothing to be done here.  */
> +  return NULL_TREE;
> +}
> diff --git a/gcc/common.opt b/gcc/common.opt
> index e81165c488b..78cfa568a95 100644
> --- a/gcc/common.opt
> +++ b/gcc/common.opt
> @@ -163,6 +163,13 @@ bool flag_stack_usage_info = false
>  Variable
>  int flag_debug_asm
>  
> +; How many NOP insns to place at each function entry by default
> +Variable
> +HOST_WIDE_INT function_entry_patch_area_size
> +
> +; And how far the real asm entry point is into this area
> +Variable
> +HOST_WIDE_INT function_entry_patch_area_start
>  
>  ; Balance between GNAT encodings and standard DWARF to emit.
>  Variable
> @@ -2030,6 +2037,10 @@ fprofile-reorder-functions
>  Common Report Var(flag_profile_reorder_functions)
>  Enable function reordering that improves code placement.
>  
> +fpatchable-function-entry=
> +Common Joined Optimization
> +Insert NOP instructions at each function entry.
> +
>  frandom-seed
>  Common Var(common_deferred_options) Defer
>  
> diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
> index 5cb512fe575..9c171abc121 100644
> --- a/gcc/doc/extend.texi
> +++ b/gcc/doc/extend.texi
> @@ -3105,6 +3105,27 @@ that affect more than one function.
>  This attribute should be used for debugging purposes only.  It is not
>  suitable in production code.
>  
> +@item patchable_function_entry
> +@cindex @code{patchable_function_entry} function attribute
> +@cindex extra NOP instructions at the function entry point
> +In case the target's text segment can be made writable at run time by
> +any means, padding the function entry with a number of NOPs can be
> +used to provide a universal tool for instrumentation.
> +
> +The @code{patchable_function_entry} function attribute can be used to
> +change the number of NOPs to any desired value.  The two-value syntax
> +is the same as for the command-line switch
> +@option{-fpatchable-function-entry=N,M}, generating @var{N} NOPs, with
> +the function entry point before the @var{M}th NOP instruction.
> +@var{M} defaults to 0 if omitted e.g. function entry point is before
> +the first NOP.
> +
> +If patchable function entries are enabled globally using the command-line
> +option @option{-fpatchable-function-entry=N,M}, then you must disable
> +instrumentation on all functions that are part of the instrumentation
> +framework with the attribute @code{patchable_function_entry (0)}
> +to prevent recursion.
> +
>  @item pure
>  @cindex @code{pure} function attribute
>  @cindex functions that have no side effects
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index d0b90503ced..dc93f0ccd50 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -11520,6 +11520,34 @@ of the function name, it is considered to be a match.  For C99 and C++
>  extended identifiers, the function name must be given in UTF-8, not
>  using universal character names.
>  
> +@item -fpatchable-function-entry=@var{N}[,@var{M}]
> +@opindex fpatchable-function-entry
> +Generate @var{N} NOPs right at the beginning
> +of each function, with the function entry point before the @var{M}th NOP.
> +If @var{M} is omitted, it defaults to @code{0} so the
> +function entry points to the address just at the first NOP.
> +The NOP instructions reserve extra space which can be used to patch in
> +any desired instrumentation at run time, provided that the code segment
> +is writable.  The amount of space is controllable indirectly via
> +the number of NOPs; the NOP instruction used corresponds to the instruction
> +emitted by the internal GCC back-end interface @code{gen_nop}.  This behavior
> +is target-specific and may also depend on the architecture variant and/or
> +other compilation options.
> +
> +For run-time identification, the starting addresses of these areas,
> +which correspond to their respective function entries minus @var{M},
> +are additionally collected in the @code{__patchable_function_entries}
> +section of the resulting binary.
> +
> +Note that the value of @code{__attribute__ ((patchable_function_entry
> +(N,M)))} takes precedence over command-line option
> +@option{-fpatchable-function-entry=N,M}.  This can be used to increase
> +the area size or to remove it completely on a single function.
> +If @code{N=0}, no pad location is recorded.
> +
> +The NOP instructions are inserted at---and maybe before, depending on
> +@var{M}---the function entry address, even before the prologue.
> +
>  @end table
>  
>  
> diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
> index 795e49246af..23e85c7afea 100644
> --- a/gcc/doc/tm.texi
> +++ b/gcc/doc/tm.texi
> @@ -4573,6 +4573,15 @@ will select the smallest suitable mode.
>  This section describes the macros that output function entry
>  (@dfn{prologue}) and exit (@dfn{epilogue}) code.
>  
> +@deftypefn {Target Hook} void TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY (FILE *@var{file}, unsigned HOST_WIDE_INT @var{patch_area_size}, bool @var{record_p})
> +Generate a patchable area at the function start, consisting of
> +@var{patch_area_size} NOP instructions.  If the target supports named
> +sections and if @var{record_p} is true, insert a pointer to the current
> +location in the table of patchable functions.  The default implementation
> +of the hook places the table of pointers in the special section named
> +@code{__patchable_function_entries}.
> +@end deftypefn
> +
>  @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size})
>  If defined, a function that outputs the assembler code for entry to a
>  function.  The prologue is responsible for setting up the stack frame,
> diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
> index 98f2e6bce5f..6df08a2c477 100644
> --- a/gcc/doc/tm.texi.in
> +++ b/gcc/doc/tm.texi.in
> @@ -3650,6 +3650,8 @@ will select the smallest suitable mode.
>  This section describes the macros that output function entry
>  (@dfn{prologue}) and exit (@dfn{epilogue}) code.
>  
> +@hook TARGET_ASM_PRINT_PATCHABLE_FUNCTION_ENTRY
> +
>  @hook TARGET_ASM_FUNCTION_PROLOGUE
>  
>  @hook TARGET_ASM_FUNCTION_END_PROLOGUE
> diff --git a/gcc/lto/lto-lang.c b/gcc/lto/lto-lang.c
> index 58935172b2c..6e9a138fa3b 100644
> --- a/gcc/lto/lto-lang.c
> +++ b/gcc/lto/lto-lang.c
> @@ -48,6 +48,8 @@ static tree handle_sentinel_attribute (tree *, tree, tree, int, bool *);
>  static tree handle_type_generic_attribute (tree *, tree, tree, int, bool *);
>  static tree handle_transaction_pure_attribute (tree *, tree, tree, int, bool *);
>  static tree handle_returns_twice_attribute (tree *, tree, tree, int, bool *);
> +static tree handle_patchable_function_entry_attribute (tree *, tree, tree,
> +						       int, bool *);
>  static tree ignore_attribute (tree *, tree, tree, int, bool *);
>  
>  static tree handle_format_attribute (tree *, tree, tree, int, bool *);
> @@ -76,6 +78,9 @@ const struct attribute_spec lto_attribute_table[] =
>  			      handle_nonnull_attribute, false },
>    { "nothrow",                0, 0, true,  false, false,
>  			      handle_nothrow_attribute, false },
> +  { "patchable_function_entry", 1, 2, true, false, false,
> +			      handle_patchable_function_entry_attribute,
> +			      false },
>    { "returns_twice",          0, 0, true,  false, false,
>  			      handle_returns_twice_attribute, false },
>    { "sentinel",               0, 1, false, true, true,
> @@ -473,6 +478,13 @@ handle_returns_twice_attribute (tree *node, tree ARG_UNUSED (name),
>    return NULL_TREE;
>  }
>  
> +static tree
> +handle_patchable_function_entry_attribute (tree *, tree, tree, int, bool *)
> +{
> +  /* Nothing to be done here.  */
> +  return NULL_TREE;
> +}
> +
>  /* Ignore the given attribute.  Used when this attribute may be usefully
>     overridden by the target, but is not used generically.  */
>  
> diff --git a/gcc/opts.c b/gcc/opts.c
> index 7555ed55434..fecf97978fc 100644
> --- a/gcc/opts.c
> +++ b/gcc/opts.c
> @@ -2199,6 +2199,33 @@ common_handle_option (struct gcc_options *opts,
>          opts->x_flag_ipa_reference = false;
>        break;
>  
> +    case OPT_fpatchable_function_entry_:
> +      {
> +	char *patch_area_arg = xstrdup (arg);
> +	char *comma = strchr (patch_area_arg, ',');
> +	if (comma)
> +	  {
> +	    *comma = '\0';
> +	    function_entry_patch_area_size = 
> +	      integral_argument (patch_area_arg);
> +	    function_entry_patch_area_start =
> +	      integral_argument (comma + 1);
> +	  }
> +	else
> +	  {
> +	    function_entry_patch_area_size =
> +	      integral_argument (patch_area_arg);
> +	    function_entry_patch_area_start = 0;
> +	  }
> +	if (function_entry_patch_area_size < 0
> +	    || function_entry_patch_area_start < 0
> +	    || function_entry_patch_area_size 
> +		< function_entry_patch_area_start)
> +	  error ("invalid arguments for %<-fpatchable_function_entry%>");
> +	free (patch_area_arg);
> +      }
> +      break;
> +
>      case OPT_ftree_vectorize:
>        if (!opts_set->x_flag_tree_loop_vectorize)
>          opts->x_flag_tree_loop_vectorize = value;
> diff --git a/gcc/target.def b/gcc/target.def
> index bbd9c015189..6d67b1fe8ba 100644
> --- a/gcc/target.def
> +++ b/gcc/target.def
> @@ -288,6 +288,17 @@ hidden, protected or internal visibility as specified by @var{visibility}.",
>   void, (tree decl, int visibility),
>   default_assemble_visibility)
>  
> +DEFHOOK
> +(print_patchable_function_entry,
> + "Generate a patchable area at the function start, consisting of\n\
> +@var{patch_area_size} NOP instructions.  If the target supports named\n\
> +sections and if @var{record_p} is true, insert a pointer to the current\n\
> +location in the table of patchable functions.  The default implementation\n\
> +of the hook places the table of pointers in the special section named\n\
> +@code{__patchable_function_entries}.",
> + void, (FILE *file, unsigned HOST_WIDE_INT patch_area_size, bool record_p),
> + default_print_patchable_function_entry)
> +
>  /* Output the assembler code for entry to a function.  */
>  DEFHOOK
>  (function_prologue,
> diff --git a/gcc/targhooks.c b/gcc/targhooks.c
> index 940deec67f9..6a8fae656d0 100644
> --- a/gcc/targhooks.c
> +++ b/gcc/targhooks.c
> @@ -73,6 +73,7 @@ along with GCC; see the file COPYING3.  If not see
>  #include "calls.h"
>  #include "expr.h"
>  #include "output.h"
> +#include "common/common-target.h"
>  #include "reload.h"
>  #include "intl.h"
>  #include "opts.h"
> @@ -1610,6 +1611,51 @@ default_compare_by_pieces_branch_ratio (machine_mode)
>    return 1;
>  }
>  
> +/* Write PATCH_AREA_SIZE NOPs into the asm outfile FILE around a function
> +   entry.  If RECORD_P is true and the target supports named sections,
> +   the location of the NOPs will be recorded in a special object section
> +   called "__patchable_function_entries".  This routine may be called
> +   twice per function to put NOPs before and after the function
> +   entry.  */
> +
> +void
> +default_print_patchable_function_entry (FILE *file,
> +					unsigned HOST_WIDE_INT patch_area_size,
> +					bool record_p)
> +{
> +  const char *nop_templ = 0;
> +  int code_num;
> +  rtx_insn *my_nop = make_insn_raw (gen_nop ());
> +
> +  /* We use the template alone, relying on the (currently sane) assumption
> +     that the NOP template does not have variable operands.  */
> +  code_num = recog_memoized (my_nop);
> +  nop_templ = get_insn_template (code_num, my_nop);
> +
> +  if (record_p && targetm_common.have_named_sections)
> +    {
> +      char buf[256];
> +      static int patch_area_number;
> +      section *previous_section = in_section;
> +
> +      patch_area_number++;
> +      ASM_GENERATE_INTERNAL_LABEL (buf, "LPFE", patch_area_number);
> +
> +      switch_to_section (get_section ("__patchable_function_entries",
> +				      0, NULL));
> +      fputs (integer_asm_op (POINTER_SIZE_UNITS, false), file);
> +      assemble_name_raw (file, buf);
> +      fputc ('\n', file);
> +
> +      switch_to_section (previous_section);
> +      ASM_OUTPUT_LABEL (file, buf);
> +    }
> +
> +  unsigned i;
> +  for (i = 0; i < patch_area_size; ++i)
> +    fprintf (file, "\t%s\n", nop_templ);
> +}
> +
>  bool
>  default_profile_before_prologue (void)
>  {
> diff --git a/gcc/targhooks.h b/gcc/targhooks.h
> index 1ddb8891fe4..c73ea0bda20 100644
> --- a/gcc/targhooks.h
> +++ b/gcc/targhooks.h
> @@ -203,6 +203,9 @@ extern bool default_use_by_pieces_infrastructure_p (unsigned HOST_WIDE_INT,
>  						    bool);
>  extern int default_compare_by_pieces_branch_ratio (machine_mode);
>  
> +extern void default_print_patchable_function_entry (FILE *,
> +						    unsigned HOST_WIDE_INT,
> +						    bool);
>  extern bool default_profile_before_prologue (void);
>  extern reg_class_t default_preferred_reload_class (rtx, reg_class_t);
>  extern reg_class_t default_preferred_output_reload_class (rtx, reg_class_t);
> diff --git a/gcc/testsuite/c-c++-common/patchable_function_entry-decl.c b/gcc/testsuite/c-c++-common/patchable_function_entry-decl.c
> new file mode 100644
> index 00000000000..8514b10e820
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/patchable_function_entry-decl.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fpatchable-function-entry=3,1" } */
> +/* { dg-final { scan-assembler-times "nop" 2 } } */
> +
> +extern int a;
> +
> +/* Respect overriding attributes in the declaration.  */
> +int f3 (void) __attribute__((patchable_function_entry(2)));
> +
> +/* F3 should now get 2 NOPs.  */
> +int
> +__attribute__((noinline))
> +f3 (void)
> +{
> +  return 5*a;
> +}
> diff --git a/gcc/testsuite/c-c++-common/patchable_function_entry-default.c b/gcc/testsuite/c-c++-common/patchable_function_entry-default.c
> new file mode 100644
> index 00000000000..0dcf1181dde
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/patchable_function_entry-default.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fpatchable-function-entry=3,1" } */
> +/* { dg-final { scan-assembler-times "nop" 3 } } */
> +
> +extern int a;
> +
> +/* Nothing declared must not mean anything.  */
> +int f3 (void);
> +
> +/* F3 should get a default-sized NOP area.  */
> +int
> +__attribute__((noinline))
> +f3 (void)
> +{
> +  return 5*a;
> +}
> diff --git a/gcc/testsuite/c-c++-common/patchable_function_entry-definition.c b/gcc/testsuite/c-c++-common/patchable_function_entry-definition.c
> new file mode 100644
> index 00000000000..a007867dcb0
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/patchable_function_entry-definition.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fpatchable-function-entry=3,1" } */
> +/* { dg-final { scan-assembler-times "nop" 1 } } */
> +
> +extern int a;
> +
> +int f3 (void);
> +
> +/* F3 should now get 1 NOP.  */
> +int
> +__attribute__((noinline))
> +__attribute__((patchable_function_entry(1)))
> +f3 (void)
> +{
> +  return 5*a;
> +}
> diff --git a/gcc/toplev.c b/gcc/toplev.c
> index e6c69a4ba93..b28f1847c83 100644
> --- a/gcc/toplev.c
> +++ b/gcc/toplev.c
> @@ -1630,8 +1630,10 @@ process_options (void)
>      }
>  
>   /* Do not use IPA optimizations for register allocation if profiler is active
> +    or patchable function entries are inserted for run-time instrumentation
>      or port does not emit prologue and epilogue as RTL.  */
> -  if (profile_flag || !targetm.have_prologue () || !targetm.have_epilogue ())
> +  if (profile_flag || function_entry_patch_area_size
> +      || !targetm.have_prologue () || !targetm.have_epilogue ())
>      flag_ipa_ra = 0;
>  
>    /* Enable -Werror=coverage-mismatch when -Werror and -Wno-error
> diff --git a/gcc/varasm.c b/gcc/varasm.c
> index fbaebc1b5c0..ec1640ea378 100644
> --- a/gcc/varasm.c
> +++ b/gcc/varasm.c
> @@ -1825,6 +1825,46 @@ assemble_start_function (tree decl, const char *fnname)
>    if (DECL_PRESERVE_P (decl))
>      targetm.asm_out.mark_decl_preserved (fnname);
>  
> +  unsigned HOST_WIDE_INT patch_area_size = function_entry_patch_area_size;
> +  unsigned HOST_WIDE_INT patch_area_entry = function_entry_patch_area_start;
> +
> +  tree patchable_function_entry_attr
> +    = lookup_attribute ("patchable_function_entry", DECL_ATTRIBUTES (decl));
> +  if (patchable_function_entry_attr)
> +    {
> +      tree pp_val = TREE_VALUE (patchable_function_entry_attr);
> +      tree patchable_function_entry_value1 = TREE_VALUE (pp_val);
> +
> +      if (tree_fits_uhwi_p (patchable_function_entry_value1))
> +	patch_area_size = tree_to_uhwi (patchable_function_entry_value1);
> +      else
> +	gcc_unreachable ();
> +
> +      patch_area_entry = 0;
> +      if (list_length (pp_val) > 1)
> +	{
> +	  tree patchable_function_entry_value2 =
> +	    TREE_VALUE (TREE_CHAIN (pp_val));
> +
> +	  if (tree_fits_uhwi_p (patchable_function_entry_value2))
> +	    patch_area_entry = tree_to_uhwi (patchable_function_entry_value2);
> +	  else
> +	    gcc_unreachable ();
> +	}
> +    }
> +
> +  if (patch_area_entry > patch_area_size)
> +    {
> +      if (patch_area_size > 0)
> +	warning (OPT_Wattributes, "Patchable function entry > size");
> +      patch_area_entry = 0;
> +    }
> +
> +  /* Emit the patching area before the entry label, if any.  */
> +  if (patch_area_entry > 0)
> +    targetm.asm_out.print_patchable_function_entry (asm_out_file,
> +						    patch_area_entry, true);
> +
>    /* Do any machine/system dependent processing of the function name.  */
>  #ifdef ASM_DECLARE_FUNCTION_NAME
>    ASM_DECLARE_FUNCTION_NAME (asm_out_file, fnname, current_function_decl);
> @@ -1833,6 +1873,12 @@ assemble_start_function (tree decl, const char *fnname)
>    ASM_OUTPUT_FUNCTION_LABEL (asm_out_file, fnname, current_function_decl);
>  #endif /* ASM_DECLARE_FUNCTION_NAME */
>  
> +  /* And the area after the label.  Record it if we haven't done so yet.  */
> +  if (patch_area_size > patch_area_entry)
> +    targetm.asm_out.print_patchable_function_entry (asm_out_file,
> +					     patch_area_size-patch_area_entry,
> +						    patch_area_entry == 0);
> +
>    if (lookup_attribute ("no_split_stack", DECL_ATTRIBUTES (decl)))
>      saw_no_split_stack = true;
>  }