@@ -365,6 +365,28 @@ decl_attributes (tree *node, tree attributes, int flags)
if (!attributes_initialized)
init_attributes ();
+ /* If we're building NOP pads because of a command line arg, note the size
+ for LTO builds, unless the attribute has already been overridden. */
+ if (TREE_CODE (*node) == FUNCTION_DECL &&
+ prolog_nop_pad_size > 0)
+ {
+ tree pp_attr = lookup_attribute ("prolog_pad", attributes);
+ if (!pp_attr)
+ {
+ tree pp_size = build_int_cstu (integer_type_node, prolog_nop_pad_size);
+ tree pp_entry = build_int_cstu (integer_type_node, prolog_nop_pad_entry);
+
+ attributes = tree_cons (get_identifier ("prolog_pad"),
+ tree_cons (NULL_TREE,
+ pp_size,
+ tree_cons (NULL_TREE,
+ pp_entry,
+ NULL_TREE)
+ ),
+ attributes);
+ }
+ }
+
/* If this is a function and the user used #pragma GCC optimize, add the
options to the attribute((optimize(...))) list. */
if (TREE_CODE (*node) == FUNCTION_DECL && current_optimize_pragma)
@@ -139,6 +139,7 @@ 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_prolog_pad_attribute (tree *, tree, tree, int, bool *);
/* Table of machine-independent attributes common to all C-like languages.
@@ -345,6 +346,8 @@ const struct attribute_spec c_common_attribute_table[] =
handle_bnd_instrument, false },
{ "fallthrough", 0, 0, false, false, false,
handle_fallthrough_attribute, false },
+ { "prolog_pad", 1, 2, true, false, false,
+ handle_prolog_pad_attribute, false },
{ NULL, 0, 0, false, false, false, NULL, false }
};
@@ -3173,3 +3176,10 @@ handle_fallthrough_attribute (tree *, tree name, tree, int,
*no_add_attrs = true;
return NULL_TREE;
}
+
+static tree
+handle_prolog_pad_attribute (tree *, tree, tree, int,
+ bool *)
+{
+ return NULL_TREE;
+}
@@ -2322,6 +2322,34 @@ merge_decls (tree newdecl, tree olddecl, tree newtype, tree oldtype)
TREE_ASM_WRITTEN (olddecl) = 0;
}
+ /* Prolog pad size may be set wrongly by a forward declaration;
+ fix it up by pulling the final value in front.
+ */
+ if (TREE_CODE (newdecl) == FUNCTION_DECL && new_is_definition &&
+ lookup_attribute ("prolog_pad", DECL_ATTRIBUTES (newdecl)) &&
+ lookup_attribute ("prolog_pad", DECL_ATTRIBUTES (olddecl)))
+ {
+ tree last_pp_attr = NULL_TREE;
+ tree *it;
+
+ for (it = &DECL_ATTRIBUTES (newdecl); *it; it = &TREE_CHAIN(*it))
+ {
+ if (IDENTIFIER_LENGTH (get_attribute_name (*it)) !=
+ strlen("prolog_pad"))
+ continue;
+ if (strcmp ("prolog_pad",
+ IDENTIFIER_POINTER (get_attribute_name (*it))))
+ continue;
+
+ last_pp_attr = *it;
+ *it = TREE_CHAIN(last_pp_attr);
+ TREE_CHAIN(last_pp_attr) = NULL_TREE;
+ break;
+ }
+ DECL_ATTRIBUTES (olddecl) = chainon (last_pp_attr,
+ DECL_ATTRIBUTES (olddecl));
+ }
+
DECL_ATTRIBUTES (newdecl)
= targetm.merge_decl_attributes (olddecl, newdecl);
@@ -163,6 +163,13 @@ bool flag_stack_usage_info = false
Variable
int flag_debug_asm
+; If we should generate NOP pads before each function prologue
+Variable
+HOST_WIDE_INT prolog_nop_pad_size
+
+; And how far the asm entry point is into this pad
+Variable
+HOST_WIDE_INT prolog_nop_pad_entry
; Balance between GNAT encodings and standard DWARF to emit.
Variable
@@ -2019,6 +2026,10 @@ fprofile-reorder-functions
Common Report Var(flag_profile_reorder_functions)
Enable function reordering that improves code placement.
+fprolog-pad=
+Common Joined
+Pad NOPs before each function prolog
+
frandom-seed
Common Var(common_deferred_options) Defer
@@ -3072,6 +3072,17 @@ that affect more than one function.
This attribute should be used for debugging purposes only. It is not
suitable in production code.
+@item prolog_pad
+@cindex @code{prolog_pad} function attribute
+@cindex function entry padded with NOPs
+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. Usually,
+prolog padding is enabled globally using the -fprolog-pad= command
+line switch, and disabled by the attribute keyword for functions
+that are part of the actual instrumentation framework, to easily avoid
+an endless recursion.
+
@item pure
@cindex @code{pure} function attribute
@cindex functions that have no side effects
@@ -11207,6 +11207,21 @@ 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 -fprolog-pad=N
+@opindex fprolog-pad
+Generate a pad of N nops right at the beginning
+of each function, which can be used to patch in any desired
+instrumentation at run time, provided that the code segment
+is writeable. For run time identification, the starting addresses
+of these pads, which correspond to their respective functions,
+are additionally collected in the @code{__prolog_pads_loc} section
+of the resulting binary.
+
+Note that value of @code{__attribute__((prolog_pad(N)))} takes
+precedence over command-line option -fprolog_pad=N. This can be used
+to increase the pad size or to remove the pad completely on a single
+function.
+
@end table
@@ -4564,6 +4564,10 @@ 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_PROLOG_PAD (FILE *@var{file}, unsigned HOST_WIDE_INT @var{pad_size}, bool @var{record_p})
+Generate prologue pad
+@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,
@@ -3648,6 +3648,8 @@ 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_PROLOG_PAD
+
@hook TARGET_ASM_FUNCTION_PROLOGUE
@hook TARGET_ASM_FUNCTION_END_PROLOGUE
@@ -50,6 +50,7 @@ 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_prolog_pad_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 *);
@@ -78,6 +79,8 @@ const struct attribute_spec lto_attribute_table[] =
handle_nonnull_attribute, false },
{ "nothrow", 0, 0, true, false, false,
handle_nothrow_attribute, false },
+ { "prolog_pad", 1, 2, false, true, true,
+ handle_prolog_pad_attribute, false },
{ "returns_twice", 0, 0, true, false, false,
handle_returns_twice_attribute, false },
{ "sentinel", 0, 1, false, true, true,
@@ -475,6 +478,14 @@ handle_returns_twice_attribute (tree *node, tree ARG_UNUSED (name),
return NULL_TREE;
}
+static tree
+handle_prolog_pad_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. */
@@ -2080,6 +2080,26 @@ common_handle_option (struct gcc_options *opts,
opts->x_flag_ipa_reference = false;
break;
+ case OPT_fprolog_pad_:
+ {
+ const char *comma = strchr (arg, ',');
+ if (comma)
+ {
+ prolog_nop_pad_size = atoi (arg);
+ prolog_nop_pad_entry = atoi (comma + 1);
+ }
+ else
+ {
+ prolog_nop_pad_size = atoi (arg);
+ prolog_nop_pad_entry = 0;
+ }
+ if (prolog_nop_pad_size < 0 ||
+ prolog_nop_pad_entry < 0 ||
+ prolog_nop_pad_size < prolog_nop_pad_entry)
+ error ("invalid arguments for %<-fprolog_pad%>");
+ }
+ break;
+
case OPT_ftree_vectorize:
if (!opts_set->x_flag_tree_loop_vectorize)
opts->x_flag_tree_loop_vectorize = value;
@@ -288,6 +288,12 @@ hidden, protected or internal visibility as specified by @var{visibility}.",
void, (tree decl, int visibility),
default_assemble_visibility)
+DEFHOOK
+(print_prolog_pad,
+ "Generate prologue pad",
+ void, (FILE *file, unsigned HOST_WIDE_INT pad_size, bool record_p),
+ default_print_prolog_pad)
+
/* Output the assembler code for entry to a function. */
DEFHOOK
(function_prologue,
@@ -1617,6 +1617,25 @@ default_compare_by_pieces_branch_ratio (machine_mode)
return 1;
}
+void
+default_print_prolog_pad (FILE *file, unsigned HOST_WIDE_INT pad_size,
+ bool record_p)
+{
+ if (record_p)
+ fprintf (file, "1:");
+
+ unsigned i;
+ for (i = 0; i < pad_size; ++i)
+ fprintf (file, "\tnop\n");
+
+ if (record_p)
+ {
+ fprintf (file, "\t.section __prolog_pads_loc, \"a\",@progbits\n");
+ fprintf (file, "\t.quad 1b\n");
+ fprintf (file, "\t.previous\n");
+ }
+}
+
bool
default_profile_before_prologue (void)
{
@@ -203,6 +203,7 @@ 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_prolog_pad (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);
@@ -1595,8 +1595,10 @@ process_options (void)
}
/* Do not use IPA optimizations for register allocation if profiler is active
+ or prolog-pads 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 || prolog_nop_pad_size ||
+ !targetm.have_prologue () || !targetm.have_epilogue ())
flag_ipa_ra = 0;
/* Enable -Werror=coverage-mismatch when -Werror and -Wno-error
@@ -1830,6 +1830,40 @@ assemble_start_function (tree decl, const char *fnname)
if (DECL_PRESERVE_P (decl))
targetm.asm_out.mark_decl_preserved (fnname);
+ unsigned HOST_WIDE_INT pad_size = 0;
+ unsigned HOST_WIDE_INT pad_entry = 0;
+
+ tree prolog_pad_attr
+ = lookup_attribute ("prolog_pad", DECL_ATTRIBUTES (decl));
+ if (prolog_pad_attr)
+ {
+ tree pp_val = TREE_VALUE (prolog_pad_attr);
+ tree prolog_pad_value1 = TREE_VALUE (pp_val);
+
+ if (tree_fits_uhwi_p (prolog_pad_value1) )
+ {
+ pad_size = tree_to_uhwi (prolog_pad_value1);
+ }
+ else
+ gcc_unreachable ();
+
+ if (list_length (pp_val) > 1)
+ {
+ tree prolog_pad_value2 = TREE_VALUE (TREE_CHAIN (pp_val));
+
+ if (tree_fits_uhwi_p (prolog_pad_value2))
+ {
+ pad_entry = tree_to_uhwi (prolog_pad_value2);
+ }
+ else
+ gcc_unreachable ();
+ }
+ }
+
+ /* Emit the prolog padding before the entry label, if any */
+ if (pad_entry > 0)
+ targetm.asm_out.print_prolog_pad (asm_out_file, pad_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);
@@ -1838,6 +1872,11 @@ 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 padding after the label. Record it if we haven't done so yet */
+ if (pad_size > pad_entry)
+ targetm.asm_out.print_prolog_pad (asm_out_file, pad_size-pad_entry,
+ (pad_entry == 0));
+
if (lookup_attribute ("no_split_stack", DECL_ATTRIBUTES (decl)))
saw_no_split_stack = true;
}