Ping? Richard E., this feature will immediately benefit AArch64 backend and Linux kernel. Do you plan to review it?
Thank you. On Wed, May 3, 2017 at 5:48 PM, Torsten Duwe <d...@suse.de> wrote: > On Wed, Mar 01, 2017 at 01:35:52PM +0000, Richard Earnshaw (lists) wrote: >> >> >> >> How about --fpatchable-function-entry=<size-spec>? >> > >> I haven't reviewed it yet. I'm not really planning to spend any more >> time on this until stage1 re-opens. > > So I guess this is about now? Here is version 8, which is functionally > identical > to v6 (v7 tried to guard the gen_nop call, which you wrote isn't neccessary). > The longer names required some reformatting. > > Torsten > > gcc/c-family/ChangeLog > 2017-05-03 Torsten Duwe <d...@suse.de> > > * c-attribs.c (c_common_attribute_table): Add entry for > "patchable_function_entry". > > gcc/lto/ChangeLog > 2017-05-03 Torsten Duwe <d...@suse.de> > > * lto-lang.c (lto_attribute_table): Add entry for > "patchable_function_entry". > > gcc/ChangeLog > 2017-05-03 Torsten Duwe <d...@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 > 2017-05-03 Torsten Duwe <d...@suse.de> > > * c-c++-common/attribute-patchable_function_entry-1.c: New test. > > diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c > index f2a88e147ba..31137ce0433 100644 > --- a/gcc/c-family/c-attribs.c > +++ b/gcc/c-family/c-attribs.c > @@ -139,6 +139,8 @@ 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. > > @@ -345,6 +347,9 @@ 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 } > }; > > @@ -3173,3 +3178,10 @@ 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 b7ece0c73e1..1b698ef4fc5 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 > @@ -2022,6 +2029,10 @@ 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 1255995eb78..d09ccd90c42 100644 > --- a/gcc/doc/extend.texi > +++ b/gcc/doc/extend.texi > @@ -3083,6 +3083,25 @@ 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. Usually, > +patchable function entries are enabled globally using the > +@option{-fpatchable-function-entry=N,M} command-line switch, and > +disabled with attribute @code{patchable_function_entry (0)} for > +functions that are part of the actual instrumentation framework. > +This conveniently avoids an endless recursion. > +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. > + > @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 65308c9d933..6cbb77a8dc4 100644 > --- a/gcc/doc/invoke.texi > +++ b/gcc/doc/invoke.texi > @@ -11382,6 +11382,32 @@ 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 is by default the one created > +by @code{gen_nop ()}. > + > +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 c4f2c893c8e..4a5317d73bb 100644 > --- a/gcc/doc/tm.texi > +++ b/gcc/doc/tm.texi > @@ -4566,6 +4566,10 @@ 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_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 > +@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 1c471d8da35..53696740f48 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 52ab2a8cb81..2312ada48c6 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 ffedb10f18f..f240c01f7d9 100644 > --- a/gcc/opts.c > +++ b/gcc/opts.c > @@ -2155,6 +2155,33 @@ 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 6bebfd5b9d6..53b60f3d276 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_patchable_function_entry, > + "Generate a patchable area at the function start", > + 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 1cdec068ed8..f3d9edafafe 100644 > --- a/gcc/targhooks.c > +++ b/gcc/targhooks.c > @@ -1609,6 +1609,54 @@ 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, 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) > +{ > + static const char *nop_templ = 0; > + > + /* We use the template alone, relying on the (currently sane) assumption > + that the NOP template does not have variable operands. */ > + if (!nop_templ) > + { > + int code_num; > + rtx_insn *my_nop = make_insn_raw (gen_nop ()); > + > + code_num = recog_memoized (my_nop); > + nop_templ = get_insn_template (code_num, my_nop); > + } > + > + if (record_p) > + { > + 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 18070df7839..6206fe20823 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/attribute-patchable_function_entry-1.c > b/gcc/testsuite/c-c++-common/attribute-patchable_function_entry-1.c > new file mode 100644 > index 00000000000..5578759bc36 > --- /dev/null > +++ b/gcc/testsuite/c-c++-common/attribute-patchable_function_entry-1.c > @@ -0,0 +1,36 @@ > +/* { dg-do compile } */ > +/* { dg-options "-fpatchable-function-entry=3,1" } */ > + > +/* Respect overriding attributes in the declaration. */ > +void f1 (void) __attribute__((patchable_function_entry(2,1))); > +void f2 (void) __attribute__((patchable_function_entry(3))); > +/* But nothing declared must not mean anything. */ > +int f3 (void); > + > +void > +f1 (void) > +{ > + f2 (); > +} > + > +void > +f2 (void) > +{ > + f1 (); > +} > + > +/* F3 should never get a NOP area. */ > +int > +__attribute__((patchable_function_entry(0))) > +__attribute__((noinline)) > +f3 (void) > +{ > + return 5; > +} > + > +/* F4 should receive the command line default setting. */ > +int > +f4 (void) > +{ > + return 3*f3 ()+1; > +} > diff --git a/gcc/toplev.c b/gcc/toplev.c > index f1384fc2fda..84969fb8ef4 100644 > --- a/gcc/toplev.c > +++ b/gcc/toplev.c > @@ -1612,8 +1612,10 @@ 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 05e48a5b894..6c3a56419e8 100644 > --- a/gcc/varasm.c > +++ b/gcc/varasm.c > @@ -1830,6 +1830,46 @@ 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); > @@ -1838,6 +1878,12 @@ 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; > } -- Maxim Kuvyrkov