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From: Ard Biesheuvel <>
	Ard Biesheuvel <>,
	Dave Martin <>,
	Mark Brown <>,
	Herbert Xu <>,
	Eric Biggers <>, Will Deacon <>,
	Catalin Marinas <>,
	Thomas Gleixner <>,
	Peter Zijlstra <>,
	Sebastian Andrzej Siewior <>,
	Ingo Molnar <>, Andy Lutomirski <>
Subject: [PATCH v2 2/9] arm64: assembler: introduce wxN aliases for wN registers
Date: Tue,  2 Mar 2021 10:01:11 +0100
Message-ID: <> (raw)
In-Reply-To: <>

The AArch64 asm syntax has this slightly tedious property that the names
used in mnemonics to refer to registers depend on whether the opcode in
question targets the entire 64-bits (xN), or only the least significant
8, 16 or 32 bits (wN). When writing parameterized code such as macros,
this can be annoying, as macro arguments don't lend themselves to
indexed lookups, and so generating a reference to wN in a macro that
receives xN as an argument is problematic.

For instance, an upcoming patch that modifies the implementation of the
cond_yield macro to be able to refer to 32-bit registers would need to
modify invocations such as

  cond_yield	3f, x8


  cond_yield	3f, 8

so that the second argument can be token pasted after x or w to emit the
correct register reference. Unfortunately, this interferes with the self
documenting nature of the first example, where the second argument is
obviously a register, whereas in the second example, one would need to
go and look at the code to find out what '8' means.

So let's fix this by defining wxN aliases for all xN registers, which
resolve to the 32-bit alias of each respective 64-bit register. This
allows the macro implementation to paste the xN reference after a w to
obtain the correct register name.

Signed-off-by: Ard Biesheuvel <>
 arch/arm64/include/asm/assembler.h | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index e0fc1d424f9b..7b076ccd1a54 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -23,6 +23,14 @@
 #include <asm/ptrace.h>
 #include <asm/thread_info.h>
+	/*
+	 * Provide a wxN alias for each wN register so what we can paste a xN
+	 * reference after a 'w' to obtain the 32-bit version.
+	 */
+	.irp	n,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30
+	wx\n	.req	w\n
+	.endr
 	.macro save_and_disable_daif, flags
 	mrs	\flags, daif
 	msr	daifset, #0xf

  parent reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-02  9:01 [PATCH v2 0/9] running kernel mode SIMD with softirqs disabled Ard Biesheuvel
2021-03-02  9:01 ` [PATCH v2 1/9] arm64: assembler: remove conditional NEON yield macros Ard Biesheuvel
2021-03-30  9:52   ` Will Deacon
2021-04-12  8:39     ` Ard Biesheuvel
2021-03-02  9:01 ` Ard Biesheuvel [this message]
2021-03-30  9:59   ` [PATCH v2 2/9] arm64: assembler: introduce wxN aliases for wN registers Will Deacon
2021-03-02  9:01 ` [PATCH v2 3/9] arm64: fpsimd: run kernel mode NEON with softirqs disabled Ard Biesheuvel
2021-03-30 10:36   ` Will Deacon
2021-03-02  9:01 ` [PATCH v2 4/9] crypto: aead - disallow en/decrypt for non-task or non-softirq context Ard Biesheuvel
2021-03-02  9:01 ` [PATCH v2 5/9] crypto: skcipher " Ard Biesheuvel
2021-03-02  9:01 ` [PATCH v2 6/9] crypto: arm64/gcm-aes-ce - remove non-SIMD fallback path Ard Biesheuvel
2021-03-02  9:01 ` [PATCH v2 7/9] crypto: arm64/aes-ccm " Ard Biesheuvel
2021-03-02  9:01 ` [PATCH v2 8/9] crypto: arm64/aes-ce - stop using SIMD helper for skciphers Ard Biesheuvel
2021-03-02  9:01 ` [PATCH v2 9/9] crypto: arm64/aes-neonbs " Ard Biesheuvel
2021-04-12 13:11 ` (subset) [PATCH v2 0/9] running kernel mode SIMD with softirqs disabled Catalin Marinas

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