[edk2-devel] [PATCH v2] ArmPkg/CompilerIntrinsicsLib: provide atomics intrinsics
Ard Biesheuvel
ard.biesheuvel at arm.com
Thu May 21 17:02:13 UTC 2020
On 5/21/20 6:59 PM, Philippe Mathieu-Daudé wrote:
> On 5/21/20 6:45 PM, Ard Biesheuvel wrote:
>> On 5/21/20 6:40 PM, Philippe Mathieu-Daudé via groups.io wrote:
>>> On 5/20/20 2:37 PM, Philippe Mathieu-Daudé wrote:
>>>> Hi Ard,
>>>>
>>>> On 5/20/20 1:44 PM, Ard Biesheuvel wrote:
>>>>> Gary reports the GCC 10 will emit calls to atomics intrinsics routines
>>>>> unless -mno-outline-atomics is specified. This means GCC-10 introduces
>>>>> new intrinsics, and even though it would be possible to work around
>>>>> this
>>>>> by specifying the command line option, this would require a new GCC10
>>>>> toolchain profile to be created, which we prefer to avoid.
>>>>>
>>>>> So instead, add the new intrinsics to our library so they are provided
>>>>> when necessary.
>>>>>
>>>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at arm.com>
>>>>> ---
>>>>> v2:
>>>>> - add missing .globl to export the functions from the object file
>>>>> - add function end markers so the size of each is visible in the
>>>>> ELF metadata
>>>>> - add some comments to describe what is going on
>>>>
>>>> Thanks, head hurts a bit less...
>>>>
>>>>>
>>>>> ArmPkg/Library/CompilerIntrinsicsLib/CompilerIntrinsicsLib.inf | 3 +
>>>>> ArmPkg/Library/CompilerIntrinsicsLib/AArch64/Atomics.S |
>>>>> 142 ++++++++++++++++++++
>>>>> 2 files changed, 145 insertions(+)
>>>>>
>>>>> diff --git
>>>>> a/ArmPkg/Library/CompilerIntrinsicsLib/CompilerIntrinsicsLib.inf
>>>>> b/ArmPkg/Library/CompilerIntrinsicsLib/CompilerIntrinsicsLib.inf
>>>>> index d5bad9467758..fcf48c678119 100644
>>>>> --- a/ArmPkg/Library/CompilerIntrinsicsLib/CompilerIntrinsicsLib.inf
>>>>> +++ b/ArmPkg/Library/CompilerIntrinsicsLib/CompilerIntrinsicsLib.inf
>>>>> @@ -79,6 +79,9 @@ [Sources.ARM]
>>>>> Arm/ldivmod.asm | MSFT
>>>>> Arm/llsr.asm | MSFT
>>>>> +[Sources.AARCH64]
>>>>> + AArch64/Atomics.S | GCC
>>>>> +
>>>>> [Packages]
>>>>> MdePkg/MdePkg.dec
>>>>> ArmPkg/ArmPkg.dec
>>>>> diff --git a/ArmPkg/Library/CompilerIntrinsicsLib/AArch64/Atomics.S
>>>>> b/ArmPkg/Library/CompilerIntrinsicsLib/AArch64/Atomics.S
>>>>> new file mode 100644
>>>>> index 000000000000..dc61d6bb8e52
>>>>> --- /dev/null
>>>>> +++ b/ArmPkg/Library/CompilerIntrinsicsLib/AArch64/Atomics.S
>>>>> @@ -0,0 +1,142 @@
>>>>> +#------------------------------------------------------------------------------
>>>>>
>>>>> +#
>>>>> +# Copyright (c) 2020, Arm, Limited. All rights reserved.<BR>
>>>>> +#
>>>>> +# SPDX-License-Identifier: BSD-2-Clause-Patent
>>>>> +#
>>>>> +#------------------------------------------------------------------------------
>>>>>
>>>>> +
>>>>> + /*
>>>>> + * Provide the GCC intrinsics that are required when using GCC
>>>>> 9 or
>>>>> + * later with the -moutline-atomics options (which became the
>>>>> default
>>>>> + * in GCC 10)
>>>>> + */
>>>>> + .arch armv8-a
>>>>> +
>>>>> + .macro reg_alias, pfx, sz
>>>>> + r0_\sz .req \pfx\()0
>>>>> + r1_\sz .req \pfx\()1
>>>>> + tmp0_\sz .req \pfx\()16
>>>>> + tmp1_\sz .req \pfx\()17
>>>>> + .endm
>>>>> +
>>>>> + /*
>>>>> + * Define register aliases of the right type for each size
>>>>> + * (xN for 8 bytes, wN for everything smaller)
>>>>> + */
>>>>> + reg_alias w, 1
>>>>> + reg_alias w, 2
>>>>> + reg_alias w, 4
>>>>> + reg_alias x, 8
>>>>> +
>>>>> + .macro fn_start, name:req
>>>>> + .section .text.\name
>>>>> + .globl \name
>>>>> + .type \name, %function
>>>>> +\name\():
>>>>> + .endm
>>>>> +
>>>>> + .macro fn_end, name:req
>>>>> + .size \name, . - \name
>>>>> + .endm
>>>>> +
>>>>> + /*
>>>>> + * Emit an atomic helper for \model with operands of size \sz,
>>>>> using
>>>>> + * the operation specified by \insn (which is the LSE name),
>>>>> and which
>>>>> + * can be implemented using the generic
>>>>> load-locked/store-conditional
>>>>> + * (LL/SC) sequence below, using the arithmetic operation
>>>>> given by
>>>>> + * \opc.
>>>>> + */
>>>>> + .macro emit_ld_sz, sz:req, insn:req, opc:req,
>>>>> model:req, s, a, l
>>>>> + fn_start __aarch64_\insn\()\sz\()\model
>>>>> + mov tmp0_\sz, r0_\sz
>>>>> +0: ld\a\()xr\s r0_\sz, [x1]
>>>>> + .ifnc \insn, swp
>>>>> + \opc tmp1_\sz, r0_\sz, tmp0_\sz
>>>>> + .else
>>>>> + \opc tmp1_\sz, tmp0_\sz
>>>>> + .endif
>>>>> + st\l\()xr\s w15, tmp1_\sz, [x1]
>>>>> + cbnz w15, 0b
>>>>
>>>> I see at the end \s is in {,b,h} range.
>>>>
>>>> Don't you need to use x15 on 64-bit?
>>>
>>> Ard, I expanded all macros and reviewed this patch, but I am still
>>> having hard time to figure why w15 temp is OK instead of x15. Any hint?
>>>
>>
>> Why do you think it should be x15?
>
> I.e.:
>
> https://developer.arm.com/docs/100076/0100/instruction-set-reference/a64-data-transfer-instructions/ldaxr
>
>
> Syntax
>
> LDAXR Wt, [Xn|SP{,#0}] ; 32-bit
> LDAXR Xt, [Xn|SP{,#0}] ; 64-bit
>
That is the load part, where Wt and Xt map onto r0 in the code above.
https://developer.arm.com/docs/100076/0100/instruction-set-reference/a64-data-transfer-instructions/stlxr
gives the description for the store part, where the w15 register is
actually used.
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