Re: [PATCH v11] add -fpatchable-function-entry=N,M option

[Richard Earnshaw (lists)]

On 06/07/17 15:03, Torsten Duwe wrote:
> Permit A 38
> 
> gcc/c-family/ChangeLog
> 2017-07-06  Torsten Duwe  
> 
>   * c-attribs.c (c_common_attribute_table): Add entry for
>   "patchable_function_entry".
> 
> gcc/lto/ChangeLog
> 2017-07-06  Torsten Duwe  
> 
>   * lto-lang.c (lto_attribute_table): Add entry for
>   "patchable_function_entry".
> 
> gcc/ChangeLog
> 2017-07-06  Torsten Duwe  
> 
>   * 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
> 2017-07-06  Torsten Duwe  
> 
>   * 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 03ba8fc436c..86d567783f7 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 

[PATCH v11] add -fpatchable-function-entry=N,M option

[Torsten Duwe]

Permit A 38

gcc/c-family/ChangeLog
2017-07-06  Torsten Duwe  

* c-attribs.c (c_common_attribute_table): Add entry for
"patchable_function_entry".

gcc/lto/ChangeLog
2017-07-06  Torsten Duwe  

* lto-lang.c (lto_attribute_table): Add entry for
"patchable_function_entry".

gcc/ChangeLog
2017-07-06  Torsten Duwe  

* 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
2017-07-06  Torsten Duwe  

* 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 03ba8fc436c..86d567783f7 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