Re: [edk2-devel] [PATCH v2] ArmPkg/CompilerIntrinsicsLib: provide atomics intrinsics

["Laszlo Ersek" <lersek@redhat.com>]

On 05/28/20 17:48, Gao, Liming wrote:
> Leif:
>   BZ 2723 is a tiano feature request. This patch adds support for new GCC10. I agree with Laszlo that this change is like the enhancement instead of the critical bug fix. So, I suggest to delay it after this stable tag. 

In <https://bugzilla.tianocore.org/show_bug.cgi?id=2723#c22> I mentioned
"If there's strong disagreement, we can revert these BZ field changes",
and in another mailing list thread Leif pointed out that the patch only
affects builds that would otherwise fail.

So at the moment I'm neutral on this work; I'm fine either way (merged
or postponed).

Liming: would you consider merging if we delayed the stable tag by a few
days (mid next week)?

Anyway, let me fade into the background on this topic.

Thanks
Laszlo

>> -----Original Message-----
>> From: Leif Lindholm <leif@nuviainc.com>
>> Sent: Thursday, May 28, 2020 5:49 PM
>> To: Gary Lin <glin@suse.com>
>> Cc: devel@edk2.groups.io; ard.biesheuvel@arm.com; lersek@redhat.com; Gao, Liming <liming.gao@intel.com>
>> Subject: Re: [edk2-devel] [PATCH v2] ArmPkg/CompilerIntrinsicsLib: provide atomics intrinsics
>>
>> On Thu, May 28, 2020 at 09:36:33 +0800, Gary Lin wrote:
>>> On Wed, May 20, 2020 at 01:44:48PM +0200, 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@arm.com>
>>> After applying this patch, gcc 10 can build ArmVirtPkg without the
>>> linking error.
>>>
>>> Tested-by: Gary Lin <glin@suse.com>
>>
>> Thanks Gary.
>>
>> Liming, can we consider this patch for stable tag please?
>>
>> With an added link to
>> https://bugzilla.tianocore.org/show_bug.cgi?id=2723 in the commit message:
>> Reviewed-by: Leif Lindholm <leif@nuviainc.com>
>>
>> /
>>     Leif
>>
>>>> ---
>>>> 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
>>>>
>>>>  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
>>>> +	ret
>>>> +	fn_end		__aarch64_\insn\()\sz\()\model
>>>> +	.endm
>>>> +
>>>> +	/*
>>>> +	 * Emit atomic helpers for \model for operand sizes in the
>>>> +	 * set {1, 2, 4, 8}, for the instruction pattern given by
>>>> +	 * \insn. (This is the LSE name, but this implementation uses
>>>> +	 * the generic LL/SC sequence using \opc as the arithmetic
>>>> +	 * operation on the target.)
>>>> +	 */
>>>> +	.macro		emit_ld, insn:req, opc:req, model:req, a, l
>>>> +	emit_ld_sz	1, \insn, \opc, \model, b, \a, \l
>>>> +	emit_ld_sz	2, \insn, \opc, \model, h, \a, \l
>>>> +	emit_ld_sz	4, \insn, \opc, \model,  , \a, \l
>>>> +	emit_ld_sz	8, \insn, \opc, \model,  , \a, \l
>>>> +	.endm
>>>> +
>>>> +	/*
>>>> +	 * Emit the compare and swap helper for \model and size \sz
>>>> +	 * using LL/SC instructions.
>>>> +	 */
>>>> +	.macro 		emit_cas_sz, sz:req, model:req, uxt:req, s, a, l
>>>> +	fn_start	__aarch64_cas\sz\()\model
>>>> +	\uxt		tmp0_\sz, r0_\sz
>>>> +0:	ld\a\()xr\s	r0_\sz, [x2]
>>>> +	cmp		r0_\sz, tmp0_\sz
>>>> +	bne		1f
>>>> +	st\l\()xr\s	w15, r1_\sz, [x2]
>>>> +	cbnz		w15, 0b
>>>> +1:	ret
>>>> +	fn_end		__aarch64_cas\sz\()\model
>>>> +	.endm
>>>> +
>>>> +	/*
>>>> +	 * Emit compare-and-swap helpers for \model for operand sizes in the
>>>> +	 * set {1, 2, 4, 8, 16}.
>>>> +	 */
>>>> +	.macro		emit_cas, model:req, a, l
>>>> +	emit_cas_sz	1, \model, uxtb, b, \a, \l
>>>> +	emit_cas_sz	2, \model, uxth, h, \a, \l
>>>> +	emit_cas_sz	4, \model, mov ,  , \a, \l
>>>> +	emit_cas_sz	8, \model, mov ,  , \a, \l
>>>> +
>>>> +	/*
>>>> +	 * We cannot use the parameterized sequence for 16 byte CAS, so we
>>>> +	 * need to define it explicitly.
>>>> +	 */
>>>> +	fn_start	__aarch64_cas16\model
>>>> +	mov		x16, x0
>>>> +	mov		x17, x1
>>>> +0:	ld\a\()xp	x0, x1, [x4]
>>>> +	cmp		x0, x16
>>>> +	ccmp		x1, x17, #0, eq
>>>> +	bne		1f
>>>> +	st\l\()xp	w15, x16, x17, [x4]
>>>> +	cbnz		w15, 0b
>>>> +1:	ret
>>>> +	fn_end		__aarch64_cas16\model
>>>> +	.endm
>>>> +
>>>> +	/*
>>>> +	 * Emit the set of GCC outline atomic helper functions for
>>>> +	 * the memory ordering model given by \model:
>>>> +	 * - relax	unordered loads and stores
>>>> +	 * - acq	load-acquire, unordered store
>>>> +	 * - rel	unordered load, store-release
>>>> +	 * - acq_rel	load-acquire, store-release
>>>> +	 */
>>>> +	.macro		emit_model, model:req, a, l
>>>> +	emit_ld		ldadd, add, \model, \a, \l
>>>> +	emit_ld		ldclr, bic, \model, \a, \l
>>>> +	emit_ld		ldeor, eor, \model, \a, \l
>>>> +	emit_ld		ldset, orr, \model, \a, \l
>>>> +	emit_ld		swp,   mov, \model, \a, \l
>>>> +	emit_cas	\model, \a, \l
>>>> +	.endm
>>>> +
>>>> +	emit_model	_relax
>>>> +	emit_model	_acq, a
>>>> +	emit_model	_rel,, l
>>>> +	emit_model	_acq_rel, a, l
>>>> --
>>>> 2.17.1
>>>>
>>>>
>>>> 
>>>>
>