diff --git a/gcc/builtin-types.def b/gcc/builtin-types.def index b01095c..70fae35 100644 --- a/gcc/builtin-types.def +++ b/gcc/builtin-types.def @@ -763,6 +763,12 @@ DEF_FUNCTION_TYPE_VAR_1 (BT_FN_VOID_LONG_VAR, BT_VOID, BT_LONG) DEF_FUNCTION_TYPE_VAR_1 (BT_FN_VOID_ULL_VAR, BT_VOID, BT_ULONGLONG) +DEF_FUNCTION_TYPE_VAR_1 (BT_FN_PTR_PTR_VAR, BT_PTR, BT_PTR) +DEF_FUNCTION_TYPE_VAR_1 (BT_FN_I1_I1_VAR, BT_I1, BT_I1) +DEF_FUNCTION_TYPE_VAR_1 (BT_FN_I2_I2_VAR, BT_I2, BT_I2) +DEF_FUNCTION_TYPE_VAR_1 (BT_FN_I4_I4_VAR, BT_I4, BT_I4) +DEF_FUNCTION_TYPE_VAR_1 (BT_FN_I8_I8_VAR, BT_I8, BT_I8) +DEF_FUNCTION_TYPE_VAR_1 (BT_FN_I16_I16_VAR, BT_I16, BT_I16) DEF_FUNCTION_TYPE_VAR_2 (BT_FN_INT_FILEPTR_CONST_STRING_VAR, BT_INT, BT_FILEPTR, BT_CONST_STRING) diff --git a/gcc/builtins.c b/gcc/builtins.c index 91658e8..9f97ecf 100644 --- a/gcc/builtins.c +++ b/gcc/builtins.c @@ -6716,6 +6716,52 @@ expand_builtin_goacc_parlevel_id_size (tree exp, rtx target, int ignore) return target; } +/* Expand a call to __builtin_speculation_safe_value_. MODE + represents the size of the first argument to that call, or VOIDmode + if the argument is a pointer. IGNORE will be true if the result + isn't used. */ +static rtx +expand_speculation_safe_value (machine_mode mode, tree exp, rtx target, + bool ignore) +{ + rtx val, failsafe; + unsigned nargs = call_expr_nargs (exp); + + tree arg0 = CALL_EXPR_ARG (exp, 0); + + if (mode == VOIDmode) + { + mode = TYPE_MODE (TREE_TYPE (arg0)); + gcc_assert (GET_MODE_CLASS (mode) == MODE_INT); + } + + val = expand_expr (arg0, NULL_RTX, mode, EXPAND_NORMAL); + + /* An optional second argument can be used as a failsafe value on + some machines. If it isn't present, then the failsafe value is + assumed to be 0. */ + if (nargs > 1) + { + tree arg1 = CALL_EXPR_ARG (exp, 1); + failsafe = expand_expr (arg1, NULL_RTX, mode, EXPAND_NORMAL); + } + else + failsafe = const0_rtx; + + /* If the result isn't used, the behavior is undefined. It would be + nice to emit a warning here, but path splitting means this might + happen with legitimate code. So simply drop the builtin + expansion in that case; we've handled any side-effects above. */ + if (ignore) + return const0_rtx; + + /* If we don't have a suitable target, create one to hold the result. */ + if (target == NULL) + target = gen_reg_rtx (mode); + + return targetm.speculation_safe_value (mode, target, val, failsafe); +} + /* Expand an expression EXP that calls a built-in function, with result going to TARGET if that's convenient (and in mode MODE if that's convenient). @@ -7827,6 +7873,17 @@ expand_builtin (tree exp, rtx target, rtx subtarget, machine_mode mode, case BUILT_IN_GOACC_PARLEVEL_SIZE: return expand_builtin_goacc_parlevel_id_size (exp, target, ignore); + case BUILT_IN_SPECULATION_SAFE_VALUE_PTR: + return expand_speculation_safe_value (VOIDmode, exp, target, ignore); + + case BUILT_IN_SPECULATION_SAFE_VALUE_1: + case BUILT_IN_SPECULATION_SAFE_VALUE_2: + case BUILT_IN_SPECULATION_SAFE_VALUE_4: + case BUILT_IN_SPECULATION_SAFE_VALUE_8: + case BUILT_IN_SPECULATION_SAFE_VALUE_16: + mode = get_builtin_sync_mode (fcode - BUILT_IN_SPECULATION_SAFE_VALUE_1); + return expand_speculation_safe_value (mode, exp, target, ignore); + default: /* just do library call, if unknown builtin */ break; } diff --git a/gcc/builtins.def b/gcc/builtins.def index aacbd51..b71d89c 100644 --- a/gcc/builtins.def +++ b/gcc/builtins.def @@ -1003,6 +1003,26 @@ DEF_BUILTIN (BUILT_IN_EMUTLS_REGISTER_COMMON, true, true, true, ATTR_NOTHROW_LEAF_LIST, false, !targetm.have_tls) +/* Suppressing speculation. Users are expected to use the first (N) + variant, which will be translated internally into one of the other + types. */ + +DEF_GCC_BUILTIN (BUILT_IN_SPECULATION_SAFE_VALUE_N, "speculation_safe_value", + BT_FN_VOID_VAR, ATTR_NULL) + +DEF_GCC_BUILTIN (BUILT_IN_SPECULATION_SAFE_VALUE_PTR, + "speculation_safe_value_ptr", BT_FN_PTR_PTR_VAR, ATTR_NULL) +DEF_GCC_BUILTIN (BUILT_IN_SPECULATION_SAFE_VALUE_1, "speculation_safe_value_1", + BT_FN_I1_I1_VAR, ATTR_NULL) +DEF_GCC_BUILTIN (BUILT_IN_SPECULATION_SAFE_VALUE_2, "speculation_safe_value_2", + BT_FN_I2_I2_VAR, ATTR_NULL) +DEF_GCC_BUILTIN (BUILT_IN_SPECULATION_SAFE_VALUE_4, "speculation_safe_value_4", + BT_FN_I4_I4_VAR, ATTR_NULL) +DEF_GCC_BUILTIN (BUILT_IN_SPECULATION_SAFE_VALUE_8, "speculation_safe_value_8", + BT_FN_I8_I8_VAR, ATTR_NULL) +DEF_GCC_BUILTIN (BUILT_IN_SPECULATION_SAFE_VALUE_16, + "speculation_safe_value_16", BT_FN_I16_I16_VAR, ATTR_NULL) + /* Exception support. */ DEF_BUILTIN_STUB (BUILT_IN_UNWIND_RESUME, "__builtin_unwind_resume") DEF_BUILTIN_STUB (BUILT_IN_CXA_END_CLEANUP, "__builtin_cxa_end_cleanup") diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c index f5e1111..32a2de2 100644 --- a/gcc/c-family/c-common.c +++ b/gcc/c-family/c-common.c @@ -6457,6 +6457,121 @@ builtin_type_for_size (int size, bool unsignedp) return type ? type : error_mark_node; } +/* Work out the size of the first argument of a call to + __builtin_speculation_safe_value. Only pointers and integral types + are permitted. Return -1 if the argument type is not supported or + the size is too large; 0 if the argument type is a pointer or the + size if it is integral. */ +static int +speculation_safe_value_resolve_size (tree function, vec *params) +{ + /* Type of the argument. */ + tree type; + int size; + + if (vec_safe_is_empty (params)) + { + error ("too few arguments to function %qE", function); + return -1; + } + + type = TREE_TYPE ((*params)[0]); + if (TREE_CODE (type) == ARRAY_TYPE && c_dialect_cxx ()) + { + /* Force array-to-pointer decay for C++. */ + (*params)[0] = default_conversion ((*params)[0]); + type = TREE_TYPE ((*params)[0]); + } + + if (POINTER_TYPE_P (type)) + return 0; + + if (!INTEGRAL_TYPE_P (type)) + goto incompatible; + + if (!COMPLETE_TYPE_P (type)) + goto incompatible; + + size = tree_to_uhwi (TYPE_SIZE_UNIT (type)); + if (size == 1 || size == 2 || size == 4 || size == 8 || size == 16) + return size; + + incompatible: + /* Issue the diagnostic only if the argument is valid, otherwise + it would be redundant at best and could be misleading. */ + if (type != error_mark_node) + error ("operand type %qT is incompatible with argument %d of %qE", + type, 1, function); + + return -1; +} + +/* Validate and coerce PARAMS, the arguments to ORIG_FUNCTION to fit + the prototype for FUNCTION. The first argument is mandatory, a second + argument, if present, must be type compatible with the first. */ +static bool +speculation_safe_value_resolve_params (location_t loc, tree orig_function, + vec *params) +{ + tree val; + + if (params->length () == 0) + { + error_at (loc, "too few arguments to function %qE", orig_function); + return false; + } + + else if (params->length () > 2) + { + error_at (loc, "too many arguments to function %qE", orig_function); + return false; + } + + val = (*params)[0]; + if (TREE_CODE (TREE_TYPE (val)) == ARRAY_TYPE) + val = default_conversion (val); + if (!(TREE_CODE (TREE_TYPE (val)) == POINTER_TYPE + || TREE_CODE (TREE_TYPE (val)) == INTEGER_TYPE)) + { + error_at (loc, + "expecting argument of type pointer or of type integer " + "for argument 1"); + return false; + } + (*params)[0] = val; + + if (params->length () == 2) + { + tree val2 = (*params)[1]; + if (TREE_CODE (TREE_TYPE (val2)) == ARRAY_TYPE) + val2 = default_conversion (val2); + if (!(TREE_TYPE (val) == TREE_TYPE (val2) + || useless_type_conversion_p (TREE_TYPE (val), TREE_TYPE (val2)))) + { + error_at (loc, "both arguments must be compatible"); + return false; + } + (*params)[1] = val2; + } + + return true; +} + +/* Cast the result of the builtin back to the type of the first argument, + preserving any qualifiers that it might have. */ +static tree +speculation_safe_value_resolve_return (tree first_param, tree result) +{ + tree ptype = TREE_TYPE (first_param); + tree rtype = TREE_TYPE (result); + ptype = TYPE_MAIN_VARIANT (ptype); + + if (tree_int_cst_equal (TYPE_SIZE (ptype), TYPE_SIZE (rtype))) + return convert (ptype, result); + + return result; +} + /* A helper function for resolve_overloaded_builtin in resolving the overloaded __sync_ builtins. Returns a positive power of 2 if the first operand of PARAMS is a pointer to a supported data type. @@ -7111,6 +7226,34 @@ resolve_overloaded_builtin (location_t loc, tree function, /* Handle BUILT_IN_NORMAL here. */ switch (orig_code) { + case BUILT_IN_SPECULATION_SAFE_VALUE_N: + { + int n = speculation_safe_value_resolve_size (function, params); + tree new_function, first_param, result; + enum built_in_function fncode; + + if (n == -1) + return error_mark_node; + else if (n == 0) + fncode = (enum built_in_function)((int)orig_code + 1); + else + fncode + = (enum built_in_function)((int)orig_code + exact_log2 (n) + 2); + + new_function = builtin_decl_explicit (fncode); + first_param = (*params)[0]; + if (!speculation_safe_value_resolve_params (loc, function, params)) + return error_mark_node; + + result = build_function_call_vec (loc, vNULL, new_function, params, + NULL); + + if (result == error_mark_node) + return result; + + return speculation_safe_value_resolve_return (first_param, result); + } + case BUILT_IN_ATOMIC_EXCHANGE: case BUILT_IN_ATOMIC_COMPARE_EXCHANGE: case BUILT_IN_ATOMIC_LOAD: diff --git a/gcc/c-family/c-cppbuiltin.c b/gcc/c-family/c-cppbuiltin.c index bdb5691..0b10e65 100644 --- a/gcc/c-family/c-cppbuiltin.c +++ b/gcc/c-family/c-cppbuiltin.c @@ -1361,7 +1361,10 @@ c_cpp_builtins (cpp_reader *pfile) cpp_define (pfile, "__WCHAR_UNSIGNED__"); cpp_atomic_builtins (pfile); - + + /* Show support for __builtin_speculation_safe_value (). */ + cpp_define (pfile, "__HAVE_SPECULATION_SAFE_VALUE"); + #ifdef DWARF2_UNWIND_INFO if (dwarf2out_do_cfi_asm ()) cpp_define (pfile, "__GCC_HAVE_DWARF2_CFI_ASM"); diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi index 3f7a8fc..efad2c8 100644 --- a/gcc/doc/cpp.texi +++ b/gcc/doc/cpp.texi @@ -2381,6 +2381,10 @@ If GCC cannot determine the current date, it will emit a warning message These macros are defined when the target processor supports atomic compare and swap operations on operands 1, 2, 4, 8 or 16 bytes in length, respectively. +@item __HAVE_SPECULATION_SAFE_VALUE +This macro is defined with the value 1 to show that this version of GCC +supports @code{__builtin_speculation_safe_value}. + @item __GCC_HAVE_DWARF2_CFI_ASM This macro is defined when the compiler is emitting DWARF CFI directives to the assembler. When this is defined, it is possible to emit those same diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi index c7745c4..6eb0c6b 100644 --- a/gcc/doc/extend.texi +++ b/gcc/doc/extend.texi @@ -10935,6 +10935,7 @@ is called and the @var{flag} argument passed to it. @findex __builtin_powi @findex __builtin_powif @findex __builtin_powil +@findex __builtin_speculation_safe_value @findex _Exit @findex _exit @findex abort @@ -11579,6 +11580,34 @@ check its compatibility with @var{size}. @end deftypefn +@deftypefn {Built-in Function} @var{type} __builtin_speculation_safe_value (@var{type} val, @var{type} failval) + +This builtin can be used to help mitigate against unsafe speculative +execution. @var{type} may be any integral type or any pointer type. + +@enumerate +@item +If the CPU is not speculatively executing the code, then @var{val} +is returned. +@item +If the CPU is executing speculatively then either: +@itemize +@item +The function may cause execution to pause until it is known that the +code is no-longer being executed speculatively (in which case +@var{val} can be returned, as above); or +@item +The function may use target-dependent speculation tracking state to cause +@var{failval} to be returned when it is known that speculative +execution has incorrectly predicted a conditional branch operation. +@end itemize +@end enumerate + +The second argument, @var{failval}, is optional and defaults to zero +if omitted. + +@end deftypefn + @deftypefn {Built-in Function} int __builtin_types_compatible_p (@var{type1}, @var{type2}) You can use the built-in function @code{__builtin_types_compatible_p} to diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi index 6d15d99..5de27f6 100644 --- a/gcc/doc/md.texi +++ b/gcc/doc/md.texi @@ -7026,6 +7026,21 @@ should be defined to an instruction that orders both loads and stores before the instruction with respect to loads and stores after the instruction. This pattern has no operands. +@cindex @code{speculation_barrier} instruction pattern +@item @samp{speculation_barrier} +If the target can support speculative execution, then this pattern should +be defined to an instruction that will block subsequent execution until +any prior speculation conditions has been resolved. The pattern must also +ensure that the compiler cannot move memory operations past the barrier, +so it needs to be an UNSPEC_VOLATILE pattern. The pattern has no +operands. + +If this pattern is not defined then the default expansion of +@code{__builtin_speculation_safe_value} will emit a warning. You can +suppress this warning by defining this pattern with a final condition +of @code{0} (zero), which tells the compiler that a speculation +barrier is not needed for this target. + @cindex @code{sync_compare_and_swap@var{mode}} instruction pattern @item @samp{sync_compare_and_swap@var{mode}} This pattern, if defined, emits code for an atomic compare-and-swap diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi index 7e2cdc2..681e53b 100644 --- a/gcc/doc/tm.texi +++ b/gcc/doc/tm.texi @@ -11932,6 +11932,26 @@ maintainer is familiar with. @end defmac +@deftypefn {Target Hook} rtx TARGET_SPECULATION_SAFE_VALUE (machine_mode @var{mode}, rtx @var{result}, rtx @var{val}, rtx @var{failval}) +This target hook can be used to generate a target-specific code + sequence that implements the @code{__builtin_speculation_safe_value} + built-in function. The function must always return @var{val} in + @var{result} in mode @var{mode} when the cpu is not executing + speculatively, but must never return that when speculating until it + is known that the speculation will not be unwound. The hook supports + two primary mechanisms for implementing the requirements. The first + is to emit a speculation barrier which forces the processor to wait + until all prior speculative operations have been resolved; the second + is to use a target-specific mechanism that can track the speculation + state and to return @var{failval} if it can determine that + speculation must be unwound at a later time. + + The default implementation simply copies @var{val} to @var{result} and + emits a @code{speculation_barrier} instruction if that is defined. If + @code{speculation_barrier} is not defined for the target a warning will + be generated. +@end deftypefn + @deftypefn {Target Hook} void TARGET_RUN_TARGET_SELFTESTS (void) If selftests are enabled, run any selftests for this target. @end deftypefn diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in index b7b0e8a..6e20afb 100644 --- a/gcc/doc/tm.texi.in +++ b/gcc/doc/tm.texi.in @@ -8107,4 +8107,6 @@ maintainer is familiar with. @end defmac +@hook TARGET_SPECULATION_SAFE_VALUE + @hook TARGET_RUN_TARGET_SELFTESTS diff --git a/gcc/target.def b/gcc/target.def index 112c772..c8bd7f8 100644 --- a/gcc/target.def +++ b/gcc/target.def @@ -4177,6 +4177,29 @@ DEFHOOK hook_bool_void_true) DEFHOOK +(speculation_safe_value, +"This target hook can be used to generate a target-specific code\n\ + sequence that implements the @code{__builtin_speculation_safe_value}\n\ + built-in function. The function must always return @var{val} in\n\ + @var{result} in mode @var{mode} when the cpu is not executing\n\ + speculatively, but must never return that when speculating until it\n\ + is known that the speculation will not be unwound. The hook supports\n\ + two primary mechanisms for implementing the requirements. The first\n\ + is to emit a speculation barrier which forces the processor to wait\n\ + until all prior speculative operations have been resolved; the second\n\ + is to use a target-specific mechanism that can track the speculation\n\ + state and to return @var{failval} if it can determine that\n\ + speculation must be unwound at a later time.\n\ + \n\ + The default implementation simply copies @var{val} to @var{result} and\n\ + emits a @code{speculation_barrier} instruction if that is defined. If\n\ + @code{speculation_barrier} is not defined for the target a warning will\n\ + be generated.", +rtx, (machine_mode mode, rtx result, rtx val, rtx failval), + default_speculation_safe_value) + + +DEFHOOK (can_use_doloop_p, "Return true if it is possible to use low-overhead loops (@code{doloop_end}\n\ and @code{doloop_begin}) for a particular loop. @var{iterations} gives the\n\ diff --git a/gcc/targhooks.c b/gcc/targhooks.c index 7315f1a..2061f07 100644 --- a/gcc/targhooks.c +++ b/gcc/targhooks.c @@ -2306,4 +2306,31 @@ default_select_early_remat_modes (sbitmap) { } +/* Default implementation of the speculation-safe-load builtin. This + implementation simply copies val to result and generates a + speculation_barrier insn, if such a pattern is defined. If + speculation_barrier is not defined at all, a warning is generated. */ + +rtx +default_speculation_safe_value (machine_mode mode ATTRIBUTE_UNUSED, + rtx result, rtx val, + rtx failval ATTRIBUTE_UNUSED) +{ + emit_move_insn (result, val); +#ifdef HAVE_speculation_barrier + /* Assume the target knows what it is doing: if it defines a + speculation barrier, but it is not enabled, then assume that one + isn't needed. */ + if (HAVE_speculation_barrier) + emit_insn (gen_speculation_barrier ()); + +#else + warning_at (input_location, 0, + "this target does not define a speculation barrier; " + "your program will still execute correctly, but speculation " + "will not be inhibited"); +#endif + return result; +} + #include "gt-targhooks.h" diff --git a/gcc/targhooks.h b/gcc/targhooks.h index 4107e22..80ac283 100644 --- a/gcc/targhooks.h +++ b/gcc/targhooks.h @@ -284,4 +284,6 @@ default_excess_precision (enum excess_precision_type ATTRIBUTE_UNUSED); extern bool default_stack_clash_protection_final_dynamic_probe (rtx); extern void default_select_early_remat_modes (sbitmap); +extern rtx default_speculation_safe_value (machine_mode, rtx, rtx, rtx); + #endif /* GCC_TARGHOOKS_H */ diff --git a/gcc/testsuite/gcc.dg/spec-barrier-1.c b/gcc/testsuite/gcc.dg/spec-barrier-1.c new file mode 100644 index 0000000..106f89a --- /dev/null +++ b/gcc/testsuite/gcc.dg/spec-barrier-1.c @@ -0,0 +1,40 @@ +/* { dg-do run } */ +/* { dg-options "-O" } */ + +/* Test that __builtin_speculation_safe_value returns the correct value. */ +/* This test will cause an unfiltered warning to be emitted on targets + that have not implemented support for speculative execution + barriers. They should fix that rather than disabling this + test. */ +char a = 1; +short b = 2; +int c = 3; +long d = 4; +long long e = 5; +int *f = (int*) &c; +#ifdef __SIZEOF_INT128__ +__int128 g = 9; +#endif + +extern void abort (void); + +int main () +{ + if (__builtin_speculation_safe_value (a) != 1) + abort (); + if (__builtin_speculation_safe_value (b) != 2) + abort (); + if (__builtin_speculation_safe_value (c) != 3) + abort (); + if (__builtin_speculation_safe_value (d) != 4) + abort (); + if (__builtin_speculation_safe_value (e) != 5) + abort (); + if (__builtin_speculation_safe_value (f) != &c) + abort (); +#ifdef __SIZEOF_INT128__ + if (__builtin_speculation_safe_value (g) != 9) + abort (); +#endif + return 0; +} diff --git a/gcc/testsuite/gcc.dg/spec-barrier-2.c b/gcc/testsuite/gcc.dg/spec-barrier-2.c new file mode 100644 index 0000000..7e9c497 --- /dev/null +++ b/gcc/testsuite/gcc.dg/spec-barrier-2.c @@ -0,0 +1,19 @@ +/* { dg-do run } */ + +/* Even on targets that don't need the optional failval parameter, + side-effects on the operand should still be calculated. */ + +int x = 3; +volatile int y = 9; + +extern void abort (void); + +int main () +{ + int z = __builtin_speculation_safe_value (x, y++); + if (z != 3 || y != 10) + abort (); + return 0; +} + +/* { dg-prune-output "this target does not define a speculation barrier;" } */ diff --git a/gcc/testsuite/gcc.dg/spec-barrier-3.c b/gcc/testsuite/gcc.dg/spec-barrier-3.c new file mode 100644 index 0000000..3ed4d39 --- /dev/null +++ b/gcc/testsuite/gcc.dg/spec-barrier-3.c @@ -0,0 +1,13 @@ +/* { dg-do compile } */ +/* { dg-options "-Wpedantic" } */ + +/* __builtin_speculation_safe_value returns a value with the same type + as its first argument. There should be a warning if that isn't + type-compatible with the use. */ +int * +f (int x) +{ + return __builtin_speculation_safe_value (x); /* { dg-warning "returning 'int' from a function with return type 'int \\*' makes pointer from integer without a cast" } */ +} + +/* { dg-prune-output "this target does not define a speculation barrier;" } */