On 08/01/18 02:20, Bill Schmidt wrote:
> Hi Richard,
>
> Unfortunately, I don't see any way that this will be useful for the ppc
> targets. We don't
> have a way to force resolution of a condition prior to continuing
> speculation, so this
> will just introduce another comparison that we would speculate past. For our
> mitigation
> we will have to introduce an instruction that halts all speculation at that
> point, and place
> it in front of all dangerous loads. I wish it were otherwise.
So can't you make the builtin expand to (in pseudo code):
if (bounds_check)
{
__asm ("barrier");
result = *ptr;
}
else
result = failval;
R.
>
> Thanks,
> Bill
>
>> On Jan 4, 2018, at 7:58 AM, Richard Earnshaw <richard.earns...@arm.com>
>> wrote:
>>
>>
>> This patch adds generic support for the new builtin
>> __builtin_load_no_speculate. It provides the overloading of the
>> different access sizes and a default fall-back expansion for targets
>> that do not support a mechanism for inhibiting speculation.
>>
>> * builtin_types.def (BT_FN_I1_CONST_VPTR_CONST_VPTR_CONST_VPTR_VAR):
>> New builtin type signature.
>> (BT_FN_I2_CONST_VPTR_CONST_VPTR_CONST_VPTR_VAR): Likewise.
>> (BT_FN_I4_CONST_VPTR_CONST_VPTR_CONST_VPTR_VAR): Likewise.
>> (BT_FN_I8_CONST_VPTR_CONST_VPTR_CONST_VPTR_VAR): Likewise.
>> (BT_FN_I16_CONST_VPTR_CONST_VPTR_CONST_VPTR_VAR): Likewise.
>> * builtins.def (BUILT_IN_LOAD_NO_SPECULATE_N): New builtin.
>> (BUILT_IN_LOAD_NO_SPECULATE_1): Likewise.
>> (BUILT_IN_LOAD_NO_SPECULATE_2): Likewise.
>> (BUILT_IN_LOAD_NO_SPECULATE_4): Likewise.
>> (BUILT_IN_LOAD_NO_SPECULATE_8): Likewise.
>> (BUILT_IN_LOAD_NO_SPECULATE_16): Likewise.
>> * target.def (inhibit_load_speculation): New hook.
>> * doc/tm.texi.in (TARGET_INHIBIT_LOAD_SPECULATION): Add to
>> documentation.
>> * doc/tm.texi: Regenerated.
>> * doc/cpp.texi: Document __HAVE_LOAD_NO_SPECULATE.
>> * doc/extend.texi: Document __builtin_load_no_speculate.
>> * c-family/c-common.c (load_no_speculate_resolve_size): New function.
>> (load_no_speculate_resolve_params): New function.
>> (load_no_speculate_resolve_return): New function.
>> (resolve_overloaded_builtin): Handle overloading
>> __builtin_load_no_speculate.
>> * builtins.c (expand_load_no_speculate): New function.
>> (expand_builtin): Handle new no-speculation builtins.
>> * targhooks.h (default_inhibit_load_speculation): Declare.
>> * targhooks.c (default_inhibit_load_speculation): New function.
>> ---
>> gcc/builtin-types.def | 16 +++++
>> gcc/builtins.c | 99 ++++++++++++++++++++++++++
>> gcc/builtins.def | 22 ++++++
>> gcc/c-family/c-common.c | 164
>> ++++++++++++++++++++++++++++++++++++++++++++
>> gcc/c-family/c-cppbuiltin.c | 5 +-
>> gcc/doc/cpp.texi | 4 ++
>> gcc/doc/extend.texi | 53 ++++++++++++++
>> gcc/doc/tm.texi | 6 ++
>> gcc/doc/tm.texi.in | 2 +
>> gcc/target.def | 20 ++++++
>> gcc/targhooks.c | 69 +++++++++++++++++++
>> gcc/targhooks.h | 3 +
>> 12 files changed, 462 insertions(+), 1 deletion(-)
>>
>> <0001-builtins-Generic-support-for-__builtin_load_no_specu.patch>
>
