In case anybody missed it, the Linux kernel side to make use
of this has also been finished meanwhile. Of course it can not
be accepted without compiler support; and this feature patch
is much more versatile than just Linux kernel live patching
on a single architecture.
Changes since the previous version
(which in turn was based on Maxim's suggestion):
* Document the feature in *.texi
* Automatically disable IPA-RA, like normal profiling does.
You never know in advance what the code patched in at run time will do.
Any optimisation here is potentially wrong.
* record a prolog_nop_pad_size value specified on the command line
in each function's attributes, so that it survives an LTO pipe.
Signed-off-by: Torsten Duwe <d...@suse.de>
diff --git a/gcc/attribs.c b/gcc/attribs.c
index 16996e9..a5cf2aa 100644
--- a/gcc/attribs.c
+++ b/gcc/attribs.c
@@ -365,6 +365,21 @@ 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);
+
+ attributes = tree_cons (get_identifier ("prolog_pad"),
+ tree_cons ( NULL_TREE, pp_size, 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)
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index f2846bb..278a99e 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -393,6 +393,7 @@ static tree handle_designated_init_attribute (tree *, tree,
tree, int, bool *);
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_prolog_pad_attribute (tree *, tree, tree, int, bool *);
static void check_nonnull_arg (void *, tree, unsigned HOST_WIDE_INT);
static bool nonnull_check_p (tree, unsigned HOST_WIDE_INT);
@@ -834,6 +835,8 @@ const struct attribute_spec c_common_attribute_table[] =
handle_bnd_legacy, false },
{ "bnd_instrument", 0, 0, true, false, false,
handle_bnd_instrument, false },
+ { "prolog_pad", 1, 1, false, true, true,
+ handle_prolog_pad_attribute, false },
{ NULL, 0, 0, false, false, false, NULL, false }
};
@@ -9687,6 +9690,14 @@ handle_designated_init_attribute (tree *node, tree name,
tree, int,
return NULL_TREE;
}
+static tree
+handle_prolog_pad_attribute (tree *, tree, tree, int,
+ bool *)
+{
+ /* Nothing to be done here. */
+ return NULL_TREE;
+}
+
/* Check for valid arguments being passed to a function with FNTYPE.
There are NARGS arguments in the array ARGARRAY. LOC should be used for
diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
index fec58bc..0220faa 100644
--- a/gcc/c-family/c-opts.c
+++ b/gcc/c-family/c-opts.c
@@ -536,6 +536,10 @@ c_common_handle_option (size_t scode, const char *arg, int
value,
cpp_opts->ext_numeric_literals = value;
break;
+ case OPT_fprolog_pad_:
+ prolog_nop_pad_size = value;
+ break;
+
case OPT_idirafter:
add_path (xstrdup (arg), AFTER, 0, true);
break;
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 88038a0..804c654 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -1427,6 +1427,10 @@ fpreprocessed
C ObjC C++ ObjC++
Treat the input file as already preprocessed.
+fprolog-pad=
+C ObjC C++ ObjC++ RejectNegative Joined UInteger Var(prolog_nop_pad_size)
Init(0)
+Pad NOPs before each function prolog
+
ftrack-macro-expansion
C ObjC C++ ObjC++ JoinedOrMissing RejectNegative UInteger
; converted into ftrack-macro-expansion=
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 2ed9285..463a5a5 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -10387,6 +10387,16 @@ 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.
+
@end table
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 745910f..f6f9d59 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -4553,6 +4553,10 @@ 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,
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index f31c763..b9585da 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -3662,6 +3662,8 @@ 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
diff --git a/gcc/final.c b/gcc/final.c
index 55cf509..94bbf8f 100644
--- a/gcc/final.c
+++ b/gcc/final.c
@@ -1754,6 +1754,7 @@ void
final_start_function (rtx_insn *first, FILE *file,
int optimize_p ATTRIBUTE_UNUSED)
{
+ unsigned HOST_WIDE_INT pad_size = prolog_nop_pad_size;
block_depth = 0;
this_is_asm_operands = 0;
@@ -1766,6 +1767,21 @@ final_start_function (rtx_insn *first, FILE *file,
high_block_linenum = high_function_linenum = last_linenum;
+ tree prolog_pad_attr
+ = lookup_attribute ("prolog_pad", TYPE_ATTRIBUTES (TREE_TYPE
(current_function_decl)));
+ if (prolog_pad_attr)
+ {
+ tree prolog_pad_value = TREE_VALUE (TREE_VALUE (prolog_pad_attr));
+
+ if (tree_fits_uhwi_p (prolog_pad_value))
+ pad_size = tree_to_uhwi (prolog_pad_value);
+ else
+ gcc_unreachable ();
+
+ }
+ if (pad_size > 0)
+ targetm.asm_out.print_prolog_pad (file, pad_size, true);
+
if (flag_sanitize & SANITIZE_ADDRESS)
asan_function_start ();
diff --git a/gcc/target.def b/gcc/target.def
index 20f2b32..e0a4cc4 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -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,
diff --git a/gcc/targhooks.c b/gcc/targhooks.c
index a342277..41e9850 100644
--- a/gcc/targhooks.c
+++ b/gcc/targhooks.c
@@ -1503,6 +1503,22 @@ default_use_by_pieces_infrastructure_p (unsigned
HOST_WIDE_INT size,
return move_by_pieces_ninsns (size, alignment, max_size + 1) < ratio;
}
+void
+default_print_prolog_pad (FILE *file, unsigned HOST_WIDE_INT pad_size,
+ bool record_p)
+{
+ if (record_p)
+ fprintf (file, "1:");
+ for (unsigned 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)
{
diff --git a/gcc/targhooks.h b/gcc/targhooks.h
index 7687c39..6bb41c4 100644
--- a/gcc/targhooks.h
+++ b/gcc/targhooks.h
@@ -200,6 +200,7 @@ extern bool default_use_by_pieces_infrastructure_p
(unsigned HOST_WIDE_INT,
enum by_pieces_operation,
bool);
+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);
diff --git a/gcc/testsuite/c-c++-common/attribute-prolog_pad-1.c
b/gcc/testsuite/c-c++-common/attribute-prolog_pad-1.c
new file mode 100644
index 0000000..7404dc5
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attribute-prolog_pad-1.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+
+void f1(void) __attribute__((prolog_pad(1)));
+void f2(void) __attribute__((prolog_pad(2)));
+
+void
+f1 (void)
+{
+ f2 ();
+}
+
+void f2 (void)
+{
+ f1 ();
+}
diff --git a/gcc/toplev.c b/gcc/toplev.c
index 8979d26..2339ce8 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -1580,8 +1580,10 @@ 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
